Building Pathology

Question 1

What is Regent’s Street Disease?

Answer 1

• The corrosion of the steel frames within masonry clad buildings.
• Its so called because a lot of the buildings on regents street are built around early to mid 1900s and have masonuary packed tightely around their steel frames.
• These leaves no room for expansion, if moisutre gets inside the facade the steelwork can corrode, it then expands massively and causes damage to the stonework such as cracking and spalling and in severe cases falling masonary.
• 1900s to 1950 builders packed masonry tight around the framework, leaving no room for the steel to expand.
• Rain can permeate the porous facade stone or brickwork corrode the steelwork or it can be moist air inside the cavity from inside the building.
• Corroded steel exapands in volume and can cause stonework to spall and leading to falling masonary which is dangerous

Question 2

What remedial works might you suggest for Regent’s Street disease?

Answer 2

1. Temporary resin stitch repairs to tie loose masonary
2. Retained facade, renew steel structure
3. Remove cladding, remove rust from steel and treat with a corrosion inhibitor and repair
4. Cathodic protection.
5. There are temporary solutions such as stitching loose masonry together with resin on fixed stainless-steel bars at the affected area. Other methods may help just delaying the inevitable.

The only way to resolve it permanently, as has been successfully done on many buildings in Regent Street, is to retain the façade but replace the entire steel frame with a new, purpose-built frame, constructed back from the masonry. The masonry is then fixed to the new “web” using stainless steel secondary fixings.

Repairing the façade steelwork is an extensive but effective method – provided it is carried out correctly.This work involves removing the masonry cladding and the surface rust by blasting the existing steel before treating it with a protective coating/paint.

Cathodic protection, a less invasive method, involves reducing the corrosion process by running an electrical current through the corroded steelwork.

Cathodic protection (CP) is a technique used to control the corrosion of a metal surface by making it the cathode of an electrochemical cell. A simple method of protection connects the metal to be protected to a more easily corroded “sacrificial metal” to act as the anode

DC current from the environment into the protected metal surface to reverse the direction of electric currents associated with the corrosion process. It does not make good previous corrosion but suppresses the continuation of the process.

Question 3

Can you name some typical defects you might find in a victorian property?

Answer 3

1. roof spread - poorly supported roofs
2. nail fatigue
3. Structural issues -soil movement shallow foundations make more suceptible
4. Weathered brickwork from pollution acide rian, masonary bees, in appropriate repairs.
5. penetrating damp throguh single skin walls failure of the damp proof course.
6. chimney leaning sulphate attack (products of burning, hydroscopic salts), poor flashing, water ingress missing flanching, weathering. missing pots
7. Defective rainwater goods cast iron
8. Lead paint and lead water supply pipes
9. Water ingress through parapet walls -
10. Bay window differential movement
11. Poor sub floor ventilation - dry rot
12. Dated service installations
13. later additions 1960s back boilers
14. Asbestos likely to have been added later on
15. Water ingress to basements

Question 4

Can you name som concrete defects?

Answer 4

1. Carbonation - phenol phalein test
2. Chloride attack
3. Concrete cancer Alkali-silica Reaction (moisture and high alkali content)
4. High alumina cement
5. Sulphate attack
6. Mundic and Bungaroosh
7. Fire damage
8. Lack of concrete cover and honeycombing (poor concrete mix)
   9.

Question 5

1. Can you tell me about the defects you may encounter in a flat roof?

Answer 5

• Intersitial Condensation
• Missing termination bar
• blisters (liquid applied coating)
• ponding
• solar degradation
• Age related (cracking and crazing) of asphalt
• Woodwall slab roof deck
• Rotten timber deck due to water ingress
• Lack of appropirate falls to drainage
• lack of insulation

Question 6

Why might you specify a retention period of 12 months?

Answer 6

To allow enough time for any defects to show themselves, particularly those which might be due to seasonal variations such as flash flooding, snow etc.

Question 7

What is the difference between dry and wet rot?

Answer 7

• Wet rot is confined to the area of damp timber whereas dry rot can spread and affect timbers some distance away from the source of damp.
• They are cause by different species of fungus
  
  • Wet rot is caused by Coniophora puteana
  • Dry rot is caused by serpula lacrymans
• They prefer different moisure levels
  
  • Wet rot grows at a higher moisurte level 50% +
  • Dry rot 20-30%
• Wet rot you tend to see the wood turn black whereas dry rot you see rusty dust like brownmarks where you can see a fruiting body which contains the spores. Mycelium are white turning grey with age.
• Dry rot grows in a dark humid environement inside the building such as in a roof void or under a timber foor whereas wet rot can be on external timbers.
• Dry rot you might see cuboidal cracking on the skirting boards but this tends to be hidden behind paintwork, timber is crumbley.
• Wet rot the wood turns soft nd spongey with the fibres showing
• Dry rot smells of mushrooms!
• Recognising wood rot and insect damage in buildings. BR 453

Question 8

What are the different types of damp?

Answer 8

1. condensation -
   
   1. warm moist air within a property condenses ona cold surface which is below the dew point forming water droplets on the surface.
   2. Black mould growth on cold surfaces such as outside wall when internal relative humidity is high and there is insufficient ventilation
   3. Interstitial condensation occurs within or between the layers of the building envelope, e.g. water vapour enters the roof void and condensation has occurred to the cold underside of flat roof decking
2. Rising damp
   
   1. damp which rises from ground level and wicks up porous materials by capilliary action
   2. Caused by
      
      1. High water table
      2. failure or bridging of damp proof course
   3. wavy tide mark up to 1 metre high of salts and water staining on internal finishes
3. Penetrating damp
   
   1. rainwater entering the building - defective rainwater goods, poorly fitting windows
   2. Services leaks
      
      1. Infrared thermography can be useful here, because this technique will identify surface temperatures that can be linked to symptoms of dampnes
   3. flooding
   4. Reference BRE

Understanding dampness BR 466

Question 9

Can you tell me three different invasive plant species and how you would identify them and deal with them?

Answer 9

1. Japanese knotweed
   
   1. green, purple-speckled, bamboo-like stems around 3m tall
   2. Grows on volcanos introduced to Uk mid 1800s to stablise railway cuttings
   3. heart- to shield-shaped leaves

alternate leafing pattern along stems

4. completely hollow stems that can be snapped easily.
5. Rhizome fragments are also easily excavated and spread when soil is disturbed
6. Can break up concrete tarmac grow through foundations destabilizing properties.
7. Dies back in winter, canes can be removed.
8. Contaiminated waste 2. Giant Hogweed
1. hollow, purple (or green speckled with purple) and covered in fine hairs.
2. Toothed Leaves.
3. large white umbrella like flowers, dies back in winter
4. sap is an irritant to skin causes sun sensitivity, can cause blindeness, teratogenic and carcinogenic
5. Causes destabilisation, bad for crops
6. Exacavate using equipment and PPE, herbicide remove to licensed refuse. 3. Himalayan Baslam
1. Pink flowers, red stems, grows on riverbanks, spreads by seed
2. Increases flooding risks by blocking water courses.
3. Herbicide, excavate remove, grazing 4. All are controlled waste Environmental Protection Act 1990 - licensend landfil site,

Question 10

Can you tell me different patterns of structural cracking and what they might mean for a building?

Answer 10

1. Horizontal cracking to brick work/stone
   
   1. wall tie failure (cavity walls)
   2. Regents street disease
2. Stepped cracking wider at bottom than the top
   
   1. Heave
3. Stepped cracking wider at the top than the bottom throuhg brick and mortar
   
   1. subsidence
4. Stepped cracking either side above a lintel/brick arch
   
   1. lintel failure
5. Hairline cracking at wall and ceiling joints
   
   1. Shrinkage
   2. Settlement - usually of a new build
6. Large 5mm+ cracks or multiples of 3mm between a house and an extention or a bay window
   
   1. Differential movement.
7. Vertical cracking on a steel framed structure or between two different materials
   
   1. thermal expansion
8. Large scale cracking and sudden damage.
   
   1. sink holes
   2. mines.

Question 11

What is a cold bridge and which approved document refers to them?

Answer 11

A thermal bridge (sometimes referred to as thermal bridging, a cold bridge or thermal bypass) describes a situation in a building where there is a direct connection between the inside and outside through one or more elements that are more thermally conductive than the rest of the building envelope.

As a result, there will be wasteful heat transfer across this element, its internal surface temperature will be different from other, better insulated internal surfaces and there may be condensation where warm, moist internal air comes into contact with the, potentially cold, surface. This condensation can result in mould growth.

Thermal bridges are common in older buildings, which may be poorly constructed, poorly insulated, with single skin construction and single glazing.

In modern buildings, thermal bridging can occur because of poor design, or poor workmanship. This is common where elements of the building penetrate through its insulated fabric, for example around glazing, or where the structure penetrates the building envelope, such as at balconies.

The Approved Documents to Part L of the building regulations (Conservation of fuel and power) state that ‘The building fabric should be constructed so that there are no reasonably avoidable thermal bridges in the insulation layers caused by gaps within the various elements, at the joints between elements and at the edges of elements such as those around window and door openings.’

Question 12

1. Can you explain what is meant by lateral restraint?
2. Can you explain how there can be a failure of lateral restraint in a victorian building and what this might cause?

Answer 12

• Lateral restraint - means litereally sideways support. As a masnonary wall gets taller it needs to be tied in to supports otherwise it would bend and topple outwards.
• In a house the force of the roof pushing out at the top should be balanced by beams at floor and ceiling level which tie the walls into the structure.
• If those same beams go rotten and the wall loses its connection to the floor joists you have a lack of lateral restraint and the wall will start to pull away creating a bulge seen from outside, inside the nearby floors may have excessive movement or spring because of the same lack of support.
• There may also be horizontal cracks appearing and eventually the wall could collapse.
• • A surveyor is more likely to come across this problem when a roof covering is changed from something lightweight, such as slate, to something much heavier. The common example is when heavy concrete tiles are used on a late Victorian terrace’s roof, which would originally been covered with slates: the increased load causes the top of the walls to be pushed out, and because masonry walls do not have much flexibility, horizontal cracks will appear just a few courses down from the eaves.

Question 13

Apart from subsidence, what else might cause diagonal cracking around a window in a masonary building?

Answer 13

Lintel failure

Where a lintel does not have enough bearing; that is, it may not be extended far enough into the surrounding wall.

When this happens, one end of the lintel can often slip where the pressure of the wall above causes a diagonal crack through that wall.

Usually the lintel will stop in a secure position and the cracking will be minor, in category 1 or 2. More severe movement and cracking – category 3 or 4 – can result in sticking doors or windows and repairs will be required.

Question 14

What is subsidence and how might you diagnose it?

Answer 14

Subsidence is when cohesive soils such as clay shrink usually because a tree is drawing up a lot of moisture. This shrinkage then creates voids in the soil which can lead to the downward movement of the foundation.

Visible symtons:

• Diagnoal cracking
• visible both inside and outside the property
• Cracks extending below the damp-proof course
• Sticking doors and windows due to warping.
• BRE has a guide to cracking 5 steps.

Question 15

What is heave

Answer 15

• Heave is when there is suddenly more mositure in the soil and the ground under a building swells and moves upwards
• for example

1. following removal or death of a tree.
2. Change in ground water levels
3. leaking drains

• Normally associated with clay soil.
• Cracking is often vertical
• Doors sticking
• Where ground heave is likely to be a problem, cellular raft foundations may be installed to reduce the upward force of heave from transmitting to the structure above (includes voids to accomodate upward movement).

Question 16

How does water enter buildings?

Answer 16

1. Condensation
2. Penetrating dampness
3. Rising dampness
4. Leaks (e.g. from pipework)
5. Trapped construction water (new builds)

Question 17

Describe the main consequences caused by dampness within buildings.

Answer 17

1. Health hazard
2. Reduce strength of building materials
3. Cause movement in building elements
4. Lead to timber decay (dry and wet rot, insect attack)
5. Cause chemical reactions in building components
6. Reduce effectiveness of insulation
7. Damage decorations

Question 18

How can you record damp in buildings?

Answer 18

1. Oven Drying (Gravimetric Testing)
2. Conductance Meter (aka Protimeter)
3. Carbide Testing (aka Speedy Meter)

Question 19

Explain the process of oven drying to measure damp.

Answer 19

1. Sample is weighed, dried in an oven and then weighed again
2. Moisture content = (wet weight - dry weight x 100) / dry weight

Question 20

Explain how a conductance meter can be used to measure dampness.

Answer 20

1. When materials absorb water, they can conduct electricity
2. Conductance meters have two metal probes (electrodes) which are firmly pressed into the material being tested
3. Electrical resistance between the two probes can then be measured

Question 21

Explain how carbide testing can be used to measure damp.

Answer 21

1. Used for masonry products (e.g. bricks, blocks, mortars etc.)
2. Material is drilled slowly to minimise heating (and thus drying) then weighed and placed in a container
3. Specific amount of calcium carbide is added and container is sealed
4. Container vigorously shaken so two materials mix
5. Moisture in sample reacts with calcium carbide to produce acetylene gas, causing pressure inside the container, which gives a reading on the pressure gauge

Question 22

Explain some of the limitations of oven drying to measure damp.

Answer 22

1. Destructive
2. Little practical use on site

Question 23

Explain some of the limitations of using a conductance meter to measure damp.

Answer 23

1. Calibrated for timber, so not accurate for other materials (only comparative readings)
2. Readings may be higher if timber has been treated with water-based preservatives
3. Electrical conductive surfaces (e.g. aluminium foil-backed wallpaper) may cause inaccurate readings
4. Only surface readings can practically be taken (deep probes with insulated sides needed otherwise)
5. Salts naturally present in walling materials conduct electricity and can be confused with damp problems
6. Hygroscopic salts left by previous dampness may cause high reading, not necessarily ongoing damp problems

Question 24

Explain some of the limitations of carbide testing to measure damp.

Answer 24

1. Knowledge of material being tested is required as different materials will differ in the amount of moisture they can contain and still be regarded as ‘dry’
2. Destructive - requires several readings for accuracy

Question 25

What guidance is available in relation to dampness in buildings?

Answer 25

1. BRE BR 466 - Understanding Dampness
2. BS 5250:2011 - Code of practice for control of condensation in buildings
3. BRE Digest 245 - Rising Dampness in Walls: Diagnosis and Treatment
4. BS 6576:2005 - Code of practice for diagnosis of rising damp in walls of buildings and installation of chemical DPCs

Question 26

What is condensation and how is it caused?

Answer 26

1. Condensation - change of water vapour naturally present in air into liquid water
2. The amount of water vapour the air can hold depends on its temperature (the warmer the air, the more water vapour it can hold)
3. If moist air comes into contact with a cold surface, the air will be cooled and its ability to hold water will reduce
4. Once the air falls to a temperature where it can no longer hold the amount of water vapour present (i.e. it becomes saturated), liquid water will form on the cold surface

Question 27

What is meant by the terms ‘dew point’ and ‘relative humidity’?

Answer 27

• Dew point - the temperature at which the air becomes saturated and will condense
• Relative humidity - moisture content present within the air, referred to as a percentage of the amount of water vapour it can hold at that temperature

Question 28

How does modern living standards affect the occurrence of condensation within buildings?

Answer 28

1. Double-glazed windows can create a more ‘sealed’ building that lacks adequate ventilation
2. Trickle vents in windows (where present) are often kept closed
3. Balanced flue boilers (instead of open fires) reduce natural ventilation
4. Central heating systems are often used intermittently, meaning cold surfaces may coincide with high humidity levels

Question 29

What problems are associated with condensation?

Answer 29

1. Mould growth, particularly where RH remains above 70% for long periods (usually more than 12 hours)
2. Health risks to the elderly, young children, asthmatics and those with weakened immune systems
3. Can encourage timber decay where timbers are sublect to prolonger moisture exposure

Question 30

How would you identify condensation within a building?

Answer 30

1. Wall has a ‘misty’ surface
2. Stains or streaks of water runnin gdown a wall (particularly in bathrooms, kitchens and below windows)
3. Damp patches with no definitive edges
4. Dampness behind wall cupboards or inside wardrobes against external walls (areas where air circulation is restricted)
5. Localised dampness at potential ‘cold bridges’
6. Patches of mould growth
7. Humidity (measured using a hygrometer), insulation and ventilation levels as well as heating and living patterns must also be taken into account

Question 31

What steps would you recommend to eliminate condensation?

Answer 31

• Short term - mould-affected areas can be washed using a fungicidal or bleach solution - do not use water as this will just spread the mould
• Long term - combination of the following:
  
  1. Reduce moisture generation (lids on pans, dry clothes outside, vent tumble dryers externally, do not use paraffin or bottled gas heaters, put cold water in bath before hot)
  2. Increase ventilation to remove moisture-laden air (open trickle vents, open windows, mechanical ventilation)
  3. Increase air temperature by heating - warmer air can hold more water vapour without condensing
  4. Increase surface temperature by thermal insulation (external or internal)

Question 32

What is interstitial condensation and how would you deal with it?

Answer 32

• Interstitial condensation is condensation that occurs within the structure of an element, as opposed to on its surface
• For example inside a flat roof on the roof deck.
• Check factors affecting this- blocked ventilation, lack of vapour barrier
• Check timbers for signs of rot and repalce/treat with preservative as necesary
• Additional insulationad
• unblock ventialtion
• vapour barrier membrane on WARM SIDE of the insulation
• If it occurs in a material such as timber, action will be needed to prevent risk of rot, usually by installing additional wall insulation

1. If internal inuslation is added, a vapour barrier must be provided on the warm side of the insulation to act as a barrier to interstitial condensation

Question 33

What are the health risks associated with the presence of mould in buildings?

Answer 33

1. Moulds produce allergens, irritants and sometimes toxic substances, so inhaling or touching mould spores can cause allergic reactions (e.g. sneezing, runny nose, red eyes, skin rash etc.) and respiratory problems (e.g. asthma attacks)
2. There is contradicting research that certain toxigenic moulds can cause rare health conditions such as bleeding in the lungs - research is ongoing

Question 34

To avoid mould growth, what level should the relative humidity be kept under?

Answer 34

70%

Question 35

What guidance is available in relation to condensation in buildings?

Answer 35

BS 5250:2011 - Code of practice for control of condensation in buildings

Question 36

What is penetrating damp?

Answer 36

Water that ingresses through the structure of a building

Question 37

What are the different mechanisms of water ingress relating to penetrating dampness?

Answer 37

1. Gravity
2. Capillary action
3. Surface tension
4. Kinetic energy (splashing)
5. Wind force
6. Differential air pressure (inside and out)

Question 38

What are the common causes and routes of penetrating dampness?

Answer 38

1. Slipped roof tiles
2. Inadequate chimney/parapet flashing
3. Copings without drips or not bedded on DPCs
4. Leaking gutters (lack of correct support, damaged joints, lack of regular clearing)
5. Overflowing hopper heads
6. Leaking downpipes (broken joints, rusting cast iron downpipes to rear against wall)
7. Continuously running cistern overflows (not discharging water clear of wall)
8. Blocked gulleys (resulting in water splashing against wall)
9. Cracked render or movement cracks in brickwork
10. Defective pointing (recessed joints that could lead to frost action)
11. Cavity ties (upside down so drip ineffective, mortar droppings resting on ties, uneven courses resulting in ties sloping toward inner leaf)
12. Inadequately fixed cavity insulation boards causing bridging of the cavity from outer to inner leafy
13. Poorly fitted windows and doors
14. Sills without drips
15. Poorly designed thresholds
16. Missing vertical DPCs
17. Driving rain on solid walls in particularly exposed situations (on cliff sides/west side of the Pennines)
18. Vegetation growth to damp/shaded brickwork
19. Repointing older buildings with cement mortar - stronger but less breathable than lime mortar, reducing the rate of evaporation. Also not as flexible so more likely to crack through drying shrinkage, thus allowing water ingress
20. Applying strong external renders (for the same reasons as using strong mortars)
21. Walls built in denser materials (e.g. granite or engineering bricks) - lack the ability to absorb water so most water runs down the face, which makes minor cracks more critical in allowing moisture ingress. Evaporation is also restricted

Question 39

What problems are associated with penetrating damp?

Answer 39

1. Lead to outbreaks of dry or wet rot under the right conditions
2. Reduce the strength of building materials, such as chipboard and plasterboard
3. Cause chemical reactions in building components (e.g. sulphate attack)
4. Reduce the effectiveness of insulation
5. Damage decorations

Question 40

How would you identify penetrating damp within a building?

Answer 40

1. Distinct damp patches with well-defined edges
2. Often in localised areas
3. Moisture readings show sharp change from wet to dry
4. Patches of efflorescence (crystallisation of sulphates and carbonates present in building materials)
5. Timber in area of damp has high moisture content
6. External inspection may reveal obvious defects (e.g. cracked render/brickwork, damaged downpipes etc.)
7. Deep wall probes indicate high readings in centre of wall
8. Line of dampness on internal plasterwork corresponding with mortar joints where cement mortar/dense wall materials have been used
9. Measure wall temperature, air temperature and RH to eliminate condensation
10. Salt analysis shows zero level of nitrates and chlorides, eliminating rising damp

Question 41

What steps would you recommend to eliminate penetrating damp?

Answer 41

• Identify the source of penetrating damp and remove or provide a barrier, for example:
  
  • Replace defective rainwater goods
  • Introduce DPCs beneath copings or vertical DPCs around openings
  • Repair cracked render/brickwork
  • Unblock gulleys/rainwater goods
  • Replace poorly installed cavity ties
• Application of a hydrophobic masonry paint (repels water but still allows the wall to breathe) may also be beneficial for solid walls that experience excessive rain penetration

Question 42

What is rising damp and how is it caused?

Answer 42

• Ground water rising by capillary action through pores of the wall or floor material
• Causes:
  
  1. Lack of DPC/DPM
  2. Inadequate lapping of DPC/DPM
  3. Bridging of an existing DPC/DPM (often by external rendered finishes or raised ground levels)
  4. DPC/DPM failure through natural deterioration or damage caused by building movement
  5. Splashing from rain or downpipes where DPC is less than the recommended 150mm above ground (Approved Document C)
  6. Increase in ground water levels (e.g. man-induced changes to the water table, leaking drains, blocked land drainage systems, leaking water mains and springs) - likely if rising damp occurs fairly suddenly

Question 43

What height can rising damp reach and what factors can affect this?

Answer 43

• Rarely higher than 1.5m
• Depends on:
  
  1. Supply of water
  2. Pore structure of materials
  3. Rate of evaporation
  4. Heating within building
  5. Chemicals in ground and walls - efflorescence can block capillaries through which water evaporates, thus driving water further up the wall

Question 44

What problems are associated with rising damp?

Answer 44

1. Lead to outbreaks of dry or wet rot under the right conditions
2. Reduce the strength of building materials, such as chipboard and plasterboard
3. Reduce the effectiveness of insulation
4. Damage decorations

Question 45

How would you identify rising damp within a building?

Answer 45

1. Visual inspection of possible causes (lack of / bridging of DPC/DPM etc.)
2. Characteristic tide mark that does not extend beyond the lower part of the wall
3. Damp contours can be pinpointed with a moisture meter
4. Damp limited to usually 1m-1.5m above ground and readings above peak will drop quickly
5. High percentage of moisture content in timber skirtings
6. Salt analysis using a calcium carbide meter determines a high level of nitrates and chlorides, which are contained naturally in the subsoil
7. Areas of dampness appear to get wetter in humid conditions due to hygroscopic salts (nitrates and chlorides) brought up from the ground, which attract water in from the atmosphere
8. BRE Digest 245 (Rising Damp in Walls - Diagnosis and Treatment) contains detailed guidance on rising damp identification and remediation

Question 46

What steps would you recommend to eliminate rising damp?

Answer 46

• Identify the source of rising damp and remove or provide a barrier, for example:
  
  • Lower the ground level (where DPC is breached or ground level is not 150mm below DPC)
  • Repair leaking drains/water mains
  • Unblock land drainage systems
  • Replace DPC or provide new where non-existent
• Replace plaster/finishes where hygroscopic salts may still be present
  
  • Renew to height 300mm above level of rising damp
  • Re-plaster with a cement-based plaster (not gypsum plaster as most of these cannot prevent the passage of hygroscopic salts and quickly breakdown in wet conditions), preferably containing a waterproofer or salt inhibitor

Question 47

What different methods of installing/replacing DPCs are available?

Answer 47

Installation of any type of DPC must be by a reputable company and members of the British Wood Preserving and Damp-Proofing Association (BWPDA) offering an insurance backed guarantee for the works:

1. Physical replacement - more expensive, disruptive and can only be laid on horizontal course (not suitable for rubble walls)
2. Chemical injection - cheaper, lines the pores with a water-repellent solution (usually silicone/latex) however effectiveness depends on its successful penetration of the wall and lack of ‘viscous fingering’ (chemical spreads out and does not form a continuous barrier)
3. Electro Osmotic DPC - a titanium wire (anode) is secured around the wall at DPC level and connected to a small power supply, which causes moisture molecules to repel down the wall back into the ground (not supported by the BRE)

Question 48

What guidance is available for rising damp problems?

Answer 48

1. BRE Digest 245 (Rising Damp in Walls - Diagnosis and Treatment) - rising damp identification and remediation
2. BS 6576:2005 - Code of practice for diagnosis of rising damp in walls of buildings and installation of chemical DPCs

Question 49

What methods can be used to minimise dampness within a basement?

Answer 49

1. Dense Monolithic Concrete
2. Cementitious Tanking
3. Mastic Asphalt Tanking
4. Bund Wall System
5. Drained Cavity System

Question 50

How is dense monolithic concrete used to waterproof a basement and what are its main disadvantages?

Answer 50

1. Walls and floor are constructed from high quality dense monolithic concrete to form a watertight barrier
2. May not always be water vapour proof so some form of lining (tanking) may be required
3. Only applies to new-builds

Question 51

What is the difference between cementitious tanking and mastic asphalt tanking?

Answer 51

Cementitious Tanking:

1. Certain additives are added to a cement based medium and applied to the base slab and walls
2. Not very good at withstanding substantial levels of hydrostatic pressure

Mastic Asphalt Tanking:

1. Provides a continuous waterproof membrane applied to the base slab and walls
2. Can be applied internally or externally depending on the circumstances on site (i.e. external may not be possible in existing buildings)
3. Membrane needs additional protection by building an inner skin wall backfilled to keep the membrane adhered to the earth-retaining wall

Question 52

What are the disadvantages of using tanking as a method of waterproofing a basement?

Answer 52

1. Water is not drained, merely pushed to other areas around the structure, which could cause problems elsewhere
2. Only external tanking will protect the structure from aggressive sulphates that may be present in the surrounding soil, which is not always possible

Question 53

What is a bund wall and how can it be used as a method of waterproofing a basement?

Answer 53

1. Construction of an inner non-load bearing wall to form a cavity joined to special triangular tiles laid to falls
2. This enables moisture to collect in the cavity and drain away into a sump, where it can be pumped into the surface water drainage system
3. Cavity should be ventilated

Question 54

What is a drained cavity system and how can it be used as a method of waterproofing a basement?

Answer 54

1. Plastic membrane in an egg-crate type formation applied to the wall and floor with properly bonded overlap joints in one continuous system
2. Allows air and moisture to circulate and drains water into a sump, where it can be pumped into the surface water drainage system

Question 55

What guidance is available for waterproofing basements?

Answer 55

BS 8102:2009 ‘Protection of Below Ground Structures against Water from the Ground’

Question 56

How would you differentiate between rising damp and penetrating damp?

Answer 56

For rising damp:

1. Positive salt analysis (containing nitrates and/or chlorides)
2. Visible tide mark to lower part of wall
3. Limit of dampness usually 1m-1.5m above ground
4. Moisture readings quickly drop above tide mark
5. Areas of dampness appear to get wetter in humid conditions (due to hygroscopic salts drawn up from the ground)
6. External inspection may indicate missing or bridged DPC

Question 57

How would you differentiate between penetrating damp and condensation?

Answer 57

For penetrating damp:

1. Moisture content is usually localised/isolated
2. Moistures readings identify an epicentre of the water entry
3. High moisture content within fabric of element, not just on its surface
4. Evidence of an external defect (e.g. wall cracking, defective downpipe etc.)
5. Measure wall temperature, air temperature and RH to eliminate condensation
6. Mould growth unusual

Question 58

How would you differentiate between rising damp and condensation?

Answer 58

For condensation:

1. Water is usually on the wall face when wiped with hand
2. Negative salt analysis (no nitrates or chlorides)
3. Moisture readings may occur across the full height of a wall (although higher readings at lower levels as warm air rises so less chance of condensation)
4. Moisture content of skirting normal but may contain staining due to water run-off
5. Deep wall probes indicate low readings in centre of wall
6. Mould growth likely
7. Surface temperature is below dew point temperature (established by measuring air temperature and RH)

Question 59

What are hygroscopic salts and are they problematic?

Answer 59

1. Salts that absorb moisture in from the air
2. As they absorb water, they continually re-dissolve, which prevents any crystallisation
3. Often associated with rising damp, as nitrates and chlorides (both of which are hygroscopic) naturally present in sub-soil are drawn up through the wall with water and are left behind on the surface once the water evaporates, causing surfaces to become wetter from moisture in the air as well

Question 60

What is efflorescence and is it problematic?

Answer 60

1. Temporary white powdery substance often seen on the face of new brickwork and in cases of rising damp
2. Caused by sulphates and carbonates naturally present in building materials crystallising as water evaporates, due to their relatively insoluble nature
3. These salts are not hygroscopic and merely indicate that moisture is evaporating from the structure
4. They may only be problematic in cases of rising damp, as the crystals can sometimes block pores in brickwork, thus preventing evaporation and driving damp higher up the wall
5. Can be brushed off if appearance is causing a concern

Question 61

What is cryptoflorescence and is it problematic?

Answer 61

1. Crystallisation of salts (often magnesium) below the surface of the brick
2. Can cause spalling where old, relatively weak bricks are re-used inappropriately, particularly in areas of excessive dampness
3. Can also occur through salts deposited by the run-off from limestone or from air pollution
4. Damage can also occur where bricks are covered by a surface treatment (as salts may crystallise behind it)
5. The effect on the bricks is similar to that caused by frost attack
6. water penetration poorly sealed joints missing gaskets

Question 62

How do you test to establish if service pipes are leaking?

Answer 62

???

Question 63

What is the adverse effect of well-insulated buildings?

Answer 63

???

Question 64

When carrying out a survey of a Victorian house, what potential pathology issues could lead to damp problems in the building?

Answer 64

???

Question 65

What problems are associated with vegetation growth to damp/shaded brickwork?

Answer 65

Can retain moisture and cause pentrating dampness

Question 66

What measures should be adopted to repair a property affected by flooding?

Answer 66

???

Question 67

What would be required from a damp specialist before you recommended them?

Answer 67

Must be by a reputable company and members of the British Wood Preserving and Damp-Proofing Association (BWPDA) offering an insurance backed guarantee for the works

Question 68

What are the main defects typically associated with timber?

Answer 68

1. Wood-rotting fungi
2. Wood-boring insects

Question 69

What is the average moisture content for internal and external timber?

Answer 69

1. Internal timber: 2-16% (depending on level of heating within building)
2. External timber: +20% (depending on weather conditions)

Question 70

What is dry rot and how is it caused?

Answer 70

Type of brown rot that thrives and spreads rapidly in damp buildings and caused by a certain type of fungus present in the air latching onto damp timber to use as a food source under specific conditions, namely:

1. Moisture content is between 20-35%
2. Temperature is between 0-26°C
3. Space is not ventilated

Question 71

What is the Latin name for dry rot and what is its meaning?

Answer 71

Serpula Lacrymans (literal meaning: ‘creeping tears’)

Question 72

What is the life cycle of dry rot?

Answer 72

1. Spores - microscopic fungus spores omnipresent in the air land on timber surfaces
2. Germination - if the timber is damp, the spores germinate (grow)
3. Hyphae - upon germination, the spores begin to grow fine white strands (not unlike cobwebs) known as hyphae. Hyphae reach out in search of moisture and it is through this process that it feeds on the timber and causes decay
4. Mycelium - a mass of hyphae forms, known as mycelium, which continues to feed on the organic matter and is capable of spreading over large distances, including through masonry and plaster
5. Fruiting body - a sporophore within the mycelium develops which thrives on the moisture being brought back to it from the hyphae. The fruiting body releases further spores that travel on air currents to other susceptible areas for the lifecycle to start over

Question 73

What problems are associated with dry rot?

Answer 73

1. Timber becomes dry and crumbly
2. Reduces structural integrity of timber
3. Can spread through an entire building given the right conditions
4. ‘Softened’ timber becomes more easily attacked by wood-boring insects

Question 74

How would you identify dry rot?

Answer 74

1. Decayed wood has dull brown colour with deep cuboidal cracking along and across the grain, light in weight and can crumble between fingers
2. The rot has left no skin of sound wood
3. Hyphal strands are white/grey in colour and 2-8mm thick
4. Silk-white sheets or cotton wool-like mycelium
5. Rusty red coloured spores
6. Reddish brown fruiting body with grey/white edges, usually pancake or bracket-like in shape
7. Conditions (such as lack of ventilation, moisture content of timber etc.) should also be used in identification

Question 75

What steps would you recommend to remediate dry rot?

Answer 75

Set out in BRE 299 (Dry Rot: Recognition and Control):

1. Establish the size and significance of the attack, particularly if structural timbers are affected as measures may be needed to secure structural integrity
2. Locate and eliminate sources of moisture
3. Promote rapid drying of the structure through heating and ventilation
4. Introduce support measures (e.g. ventilation pathways between sound timber and wet brickwork, barriers such as DPMs or joist hangers etc.)
5. Remove all rotted wood and cut away timber 300-450mm beyond last evidence of rot
6. Do not retain timber infected by dry rot without seeking expert advice
7. Strip back affected plaster and contain fungus within wall by applying surface biocides or fungicidal paints/renders
8. Apply localised superficial preservative treatment only to timbers that are likely to remain damp
9. Replace any timbers necessary only with preservative pre-treated timbers

Question 76

What is wet rot and how is it caused?

Answer 76

Type of white or brown rot that thrives in wetter conditions (mainly external joinery) and is caused by a certain type of fungus present in the air latching onto the damp timber to use as a food source

Question 77

What problems are associated with wet rot?

Answer 77

1. Reduces structural integrity of timber
2. ‘Softened’ timber becomes more easily attacked by wood-boring insects

Question 78

How would you identify wet rot?

Answer 78

1. Where species is a white rot, wood becomes lighter (as if bleached) and cracked along the grain
2. Where species is a brown rot, wood becomes darker with cuboidal cracking (but not as severe as that found in dry rot)
3. A thin veneer of sound wood remains
4. Often found where wood is repeatedly wetted (e.g. as a result of faulty plumbing or leaking gutters)
5. Hyphae, mycelium and fruiting bodies differ between species, however typically:

• Hyphae (not always present) is thinner than dry rot and flexible when dry, usually creamy-white in colour
• Mycelium (usually not present in daylight areas) is generally creamy-brown in colour
• Fruiting body is not very common but where present is usually flat and plate-like with a greenish-brown centre and yellow margins

Question 79

What steps would you recommend to remediate wet rot?

Answer 79

Set out in BRE 345 (Wet Rot: Recognition and Control):

1. Establish the size and significance of the attack, particularly if structural timbers are affected as measures may be needed to secure structural integrity
2. Locate and eliminate sources of moisture
3. Promote rapid drying of the structure through heating and ventilation
4. Introduce support measures (e.g. ventilation pathways between sound timber and wet brickwork, barriers such as DPMs or joist hangers etc.)
5. Remove all rotted wood, however there may be occasions when it can be retained (e.g. large beams or where there are conservation considerations)
6. Where retained, deeply penetrating preservative treatments should be applied to rotten areas in conjunction with other repairs (e.g. resin bonding systems)
7. Apply localised superficial preservative treatment only to timbers that are likely to remain damp
8. Replace any timbers necessary only with preservative pre-treated timbers

Question 80

What is the difference between dry and wet rot?

Answer 80

• Location:
  
  • Dry rot - rare outside
  • Wet rot - stays localised to moisture source
• Type:
  
  • Dry rot - a brown rot
  • Wet rot - can either be a white or brown rot
• Hyphae:
  
  • Dry rot - 2-8mm in and brittle when dry
  • Wet rot - thinner and flexible when dry
• Mycelium:
  
  • Dry rot - silky white cotton wool-like sheets
  • Wet rot - brown branching strands
• Decaying wood:
  
  • Dry rot - deep cuboidal cracking with no skin of sound wood
  • Wet rot - smaller cuboidal cracking and a thin veneer of sound wood remains
• Fruiting body:
  
  • Dry rot - reddish brown with grey/white edges
  • Wet rot - not very common but usually greenish-brown centre with yellow margins
• Conditions for growth:
  
  • Dry rot - 20-35% timber moisture content, 0-26°C
  • Wet rot - 45-60% timber moisture content, -30 to +40°C

Question 81

How would you identify whether rot was wet or dry?

Answer 81

1. Location - if outside, likely to be wet rot
2. Conditions - if space is unventilated, could be dry rot
3. Appearance - deep cuboidal cracking, no skin of sound wood, rusty red spores, fruiting body and mycelium would indicate dry rot
4. Smell - mushroom smell would indicate dry rot
5. Moisture content - dry rot would be between 20-35%, wet rot would be 45-60%

Question 82

What is the difference between brown rot and white rot?

Answer 82

1. White rots - cause wood to become lighter in colour and fibrous in texture, without cross-cracking
2. Brown rots - cause wood to become darker in colour and crack along and across the grain, forming cubes in the decaying process. When dry, very decayed wood will crumble to dust

Question 83

Timber decay is often found to suspended timber floors in traditionally constructed buildings. What does the occupier commonly do to the property to lead to this problem?

Answer 83

1. Often block the air bricks
2. Inadequate ventilation will allow the RH of the air below the floor to rise (particularly if the ground is wet), as the air steadily absorbs water
3. At the same time, the moisture content of the floor structure will slowly settle into equilibrium with the damp air, causing its moisture content to rise, thus putting it at risk of decay

Question 84

Is there a potential for wet rot turning to dry rot when drying out?

Answer 84

???

Question 85

How would you treat a rotting timber fence?

Answer 85

???

Question 86

Your client owns a Grade I listed building and has found evidence of extensive dry rot. How might this be dealt with to cause minimum disturbance to the building?

Answer 86

1. Splice repairs - rotten timber is removed and reclaimed timber sections are joined to the existing timber (often incorporating internal reinforcement rods) where required
2. Resin bonding systems - used for localised repairs (e.g. window frames) where the rotten timber is removed and a 2-part epoxy resin is mixed and applied to the timber, effectively ‘filling in’ the voids left by the rotten timber, hardening and sanded to a smooth finish
3. Introducing supplementary structures - allows existing timbers to be left in place whilst new supplementary supports perform its function (e.g. doubling up timber, fixing discrete metal plates etc.)

Question 87

What are wood-boring insects and why are they a problem?

Answer 87

• Wood-boring insects are insects that use wood as a food source, as well as a habitat, and can cause damage to timbers within buildings by eating away at it
• Can get into buildings through open windows, doors, fresh-air vents, gaps in eaves etc.

Question 88

What is the general lifecycle of a wood-boring insect?

Answer 88

1. Larva (worm): 1-5 years
2. Pupa (larva to adult): 6 weeks
3. Adult (beetle): 2-3 weeks

Question 89

Name some of the common wood-boring insects.

Answer 89

1. Common furniture beetle (aka ‘woodworm’)
2. Deathwatch beetle
3. House longhorn beetle
4. Lyctus powderpost beetle
5. Ptilinus beetle

Question 90

What are the two most common wood-boring insects?

Answer 90

1. Common furniture beetle (aka ‘woodworm’)
2. Deathwatch beetle

Question 91

What are the key indicators to identify different wood-boring insects?

Answer 91

BRE Digest 307 (Identifying Damage by Wood-Boring Insects) contains extensive guidance, including:

1. Size of flight holes
2. Bore dust (frass) colour
3. Geographical location
4. Type of wood attacked

Question 92

Where is the Longhorn beetle most known to attack?

Answer 92

Only common in the south-east, particularly Surrey

Question 93

Name some harmless insects to timber.

Answer 93

1. Woodlice
2. Silver fish
3. Ants
4. Earwigs
5. Millipedes

Question 94

What works should be undertaken to eliminate and deal with the effects of wood-boring insects?

Answer 94

1. Depends on the type of insect and the extent of the attack
2. Often down to a specialist company
3. Usually involves treatment with an organic solvent, emulsion or paste (or sometimes smoke for the deathwatch beetle)
4. Sometimes when wood is so wet and rotten, preservative treatment is pointless and timbers require replacing
5. New timbers may need to be placed alongside affected timbers, or completely replaced depending on the extent of the damage

Question 95

What changed within the building regulations to deal with a certain wood-boring insect?

Answer 95

House longhorn beetle - Approved Document A prescribes geographical areas where softwood timber for roof construction must be treated against infestation

Question 96

When must the BRE be notified of attacks from wood-boring insects?

Answer 96

BRE must be notified of every house longhorn beetle attack

Question 97

What are the main defects typically associated with timber?

Answer 97

1. Wood-rotting fungi
2. Wood-boring insects

Question 98

What is the average moisture content for internal and external timber?

Answer 98

1. Internal timber: 2-16% (depending on level of heating within building)
2. External timber: +20% (depending on weather conditions)

Question 99

What is dry rot and how is it caused?

Answer 99

Type of brown rot that thrives and spreads rapidly in damp buildings and caused by a certain type of fungus present in the air latching onto damp timber to use as a food source under specific conditions, namely:

1. Moisture content is between 20-35%
2. Temperature is between 0-26°C
3. Space is not ventilated

Question 100

What is the Latin name for dry rot and what is its meaning?

Answer 100

Serpula Lacrymans (literal meaning: ‘creeping tears’)

Question 101

What is the life cycle of dry rot?

Answer 101

1. Spores - microscopic fungus spores omnipresent in the air land on timber surfaces
2. Germination - if the timber is damp, the spores germinate (grow)
3. Hyphae - upon germination, the spores begin to grow fine white strands (not unlike cobwebs) known as hyphae. Hyphae reach out in search of moisture and it is through this process that it feeds on the timber and causes decay
4. Mycelium - a mass of hyphae forms, known as mycelium, which continues to feed on the organic matter and is capable of spreading over large distances, including through masonry and plaster
5. Fruiting body - a sporophore within the mycelium develops which thrives on the moisture being brought back to it from the hyphae. The fruiting body releases further spores that travel on air currents to other susceptible areas for the lifecycle to start over

Question 102

What problems are associated with dry rot?

Answer 102

1. Timber becomes dry and crumbly
2. Reduces structural integrity of timber
3. Can spread through an entire building given the right conditions
4. ‘Softened’ timber becomes more easily attacked by wood-boring insects

Question 103

How would you identify dry rot?

Answer 103

1. Decayed wood has dull brown colour with deep cuboidal cracking along and across the grain, light in weight and can crumble between fingers
2. The rot has left no skin of sound wood
3. Hyphal strands are white/grey in colour and 2-8mm thick
4. Silk-white sheets or cotton wool-like mycelium
5. Rusty red coloured spores
6. Reddish brown fruiting body with grey/white edges, usually pancake or bracket-like in shape
7. Conditions (such as lack of ventilation, moisture content of timber etc.) should also be used in identification

Question 104

What steps would you recommend to remediate dry rot?

Answer 104

Set out in BRE 299 (Dry Rot: Recognition and Control):

1. Establish the size and significance of the attack, particularly if structural timbers are affected as measures may be needed to secure structural integrity
2. Locate and eliminate sources of moisture
3. Promote rapid drying of the structure through heating and ventilation
4. Introduce support measures (e.g. ventilation pathways between sound timber and wet brickwork, barriers such as DPMs or joist hangers etc.)
5. Remove all rotted wood and cut away timber 300-450mm beyond last evidence of rot
6. Do not retain timber infected by dry rot without seeking expert advice
7. Strip back affected plaster and contain fungus within wall by applying surface biocides or fungicidal paints/renders
8. Apply localised superficial preservative treatment only to timbers that are likely to remain damp
9. Replace any timbers necessary only with preservative pre-treated timbers

Question 105

What is wet rot and how is it caused?

Answer 105

Type of white or brown rot that thrives in wetter conditions (mainly external joinery) and is caused by a certain type of fungus present in the air latching onto the damp timber to use as a food source

Question 106

What problems are associated with wet rot?

Answer 106

1. Reduces structural integrity of timber
2. ‘Softened’ timber becomes more easily attacked by wood-boring insects

Question 107

How would you identify wet rot?

Answer 107

1. Where species is a white rot, wood becomes lighter (as if bleached) and cracked along the grain
2. Where species is a brown rot, wood becomes darker with cuboidal cracking (but not as severe as that found in dry rot)
3. A thin veneer of sound wood remains
4. Often found where wood is repeatedly wetted (e.g. as a result of faulty plumbing or leaking gutters)
5. Hyphae, mycelium and fruiting bodies differ between species, however typically:

• Hyphae (not always present) is thinner than dry rot and flexible when dry, usually creamy-white in colour
• Mycelium (usually not present in daylight areas) is generally creamy-brown in colour
• Fruiting body is not very common but where present is usually flat and plate-like with a greenish-brown centre and yellow margins

Question 108

What steps would you recommend to remediate wet rot?

Answer 108

Set out in BRE 345 (Wet Rot: Recognition and Control):

1. Establish the size and significance of the attack, particularly if structural timbers are affected as measures may be needed to secure structural integrity
2. Locate and eliminate sources of moisture
3. Promote rapid drying of the structure through heating and ventilation
4. Introduce support measures (e.g. ventilation pathways between sound timber and wet brickwork, barriers such as DPMs or joist hangers etc.)
5. Remove all rotted wood, however there may be occasions when it can be retained (e.g. large beams or where there are conservation considerations)
6. Where retained, deeply penetrating preservative treatments should be applied to rotten areas in conjunction with other repairs (e.g. resin bonding systems)
7. Apply localised superficial preservative treatment only to timbers that are likely to remain damp
8. Replace any timbers necessary only with preservative pre-treated timbers

Question 109

What is the difference between dry and wet rot?

Answer 109

• Location:
  
  • Dry rot - rare outside
  • Wet rot - stays localised to moisture source
• Type:
  
  • Dry rot - a brown rot
  • Wet rot - can either be a white or brown rot
• Hyphae:
  
  • Dry rot - 2-8mm in and brittle when dry
  • Wet rot - thinner and flexible when dry
• Mycelium:
  
  • Dry rot - silky white cotton wool-like sheets
  • Wet rot - brown branching strands
• Decaying wood:
  
  • Dry rot - deep cuboidal cracking with no skin of sound wood
  • Wet rot - smaller cuboidal cracking and a thin veneer of sound wood remains
• Fruiting body:
  
  • Dry rot - reddish brown with grey/white edges
  • Wet rot - not very common but usually greenish-brown centre with yellow margins
• Conditions for growth:
  
  • Dry rot - 20-35% timber moisture content, 0-26°C
  • Wet rot - 45-60% timber moisture content, -30 to +40°C

Question 110

How would you identify whether rot was wet or dry?

Answer 110

1. Location - if outside, likely to be wet rot
2. Conditions - if space is unventilated, could be dry rot
3. Appearance - deep cuboidal cracking, no skin of sound wood, rusty red spores, fruiting body and mycelium would indicate dry rot
4. Smell - mushroom smell would indicate dry rot
5. Moisture content - dry rot would be between 20-35%, wet rot would be 45-60%

Question 111

What is the difference between brown rot and white rot?

Answer 111

1. White rots - cause wood to become lighter in colour and fibrous in texture, without cross-cracking
2. Brown rots - cause wood to become darker in colour and crack along and across the grain, forming cubes in the decaying process. When dry, very decayed wood will crumble to dust

Question 112

Timber decay is often found to suspended timber floors in traditionally constructed buildings. What does the occupier commonly do to the property to lead to this problem?

Answer 112

1. Often block the air bricks
2. Inadequate ventilation will allow the RH of the air below the floor to rise (particularly if the ground is wet), as the air steadily absorbs water
3. At the same time, the moisture content of the floor structure will slowly settle into equilibrium with the damp air, causing its moisture content to rise, thus putting it at risk of decay

Question 113

Is there a potential for wet rot turning to dry rot when drying out?

Answer 113

???

Question 114

How would you treat a rotting timber fence?

Answer 114

???

Question 115

When must the BRE be notified of attacks from wood-boring insects?

Answer 115

BRE must be notified of every house longhorn beetle attack

Question 116

What changed within the building regulations to deal with a certain wood-boring insect?

Answer 116

House longhorn beetle - Approved Document A prescribes geographical areas where softwood timber for roof construction must be treated against infestation

Question 117

What works should be undertaken to eliminate and deal with the effects of wood-boring insects?

Answer 117

1. Depends on the type of insect and the extent of the attack
2. Often down to a specialist company
3. Usually involves treatment with an organic solvent, emulsion or paste (or sometimes smoke for the deathwatch beetle)
4. Sometimes when wood is so wet and rotten, preservative treatment is pointless and timbers require replacing
5. New timbers may need to be placed alongside affected timbers, or completely replaced depending on the extent of the damage

Question 118

Name some harmless insects to timber.

Answer 118

1. Woodlice
2. Silver fish
3. Ants
4. Earwigs
5. Millipedes

Question 119

Where is the Longhorn beetle most known to attack?

Answer 119

Only common in the south-east, particularly Surrey

Question 120

What are the key indicators to identify different wood-boring insects?

Answer 120

BRE Digest 307 (Identifying Damage by Wood-Boring Insects) contains extensive guidance, including:

1. Size of flight holes
2. Bore dust (frass) colour
3. Geographical location
4. Type of wood attacked

Question 121

What are the two most common wood-boring insects?

Answer 121

1. Common furniture beetle (aka ‘woodworm’)
2. Deathwatch beetle

Question 122

Name some of the common wood-boring insects.

Answer 122

1. Common furniture beetle (aka ‘woodworm’)
2. Deathwatch beetle
3. House longhorn beetle
4. Lyctus powderpost beetle
5. Ptilinus beetle

Question 123

What is the general lifecycle of a wood-boring insect?

Answer 123

1. Larva (worm): 1-5 years
2. Pupa (larva to adult): 6 weeks
3. Adult (beetle): 2-3 weeks

Question 124

What are wood-boring insects and why are they a problem?

Answer 124

• Wood-boring insects are insects that use wood as a food source, as well as a habitat, and can cause damage to timbers within buildings by eating away at it
• Can get into buildings through open windows, doors, fresh-air vents, gaps in eaves etc.

Question 125

Your client owns a Grade I listed building and has found evidence of extensive dry rot. How might this be dealt with to cause minimum disturbance to the building?

Answer 125

1. Splice repairs - rotten timber is removed and reclaimed timber sections are joined to the existing timber (often incorporating internal reinforcement rods) where required
2. Resin bonding systems - used for localised repairs (e.g. window frames) where the rotten timber is removed and a 2-part epoxy resin is mixed and applied to the timber, effectively ‘filling in’ the voids left by the rotten timber, hardening and sanded to a smooth finish
3. Introducing supplementary structures - allows existing timbers to be left in place whilst new supplementary supports perform its function (e.g. doubling up timber, fixing discrete metal plates etc.)

Question 126

Why do buildings crack?

Answer 126

1. Drying shrinkage (sand-lime bricks, too strong rendering mixes)
2. Thermal movement (lack of vertical movement joints)
3. Frost action (freeze-thaw cycle)
4. Ground movement (settlement, subsidence, heave)
5. Wall tie failure
6. Chemical reactions (carbonation, chloride attack, sulphate attack, ASR)
7. Lack of lateral restraint (‘book-end’ effect)
8. Overloading (roof spread, increase of internal imposed loads)
9. Vibration

Question 127

Why is cracking a problem?

Answer 127

Cracking is problematic as not only can it cause the building to be structurally unsafe, it can also lead to water penetration, leading to damp problems and can also exacerbate the cracking in some cases (frost action, carbonation, wall tie failure)

Question 128

Name some of the causes of stepped cracking in brickwork.

Answer 128

???

Question 129

You see a vertical crack internally to a property’s wall - what may have caused it?

Answer 129

???

Question 130

What would cracking at DPC level indicate?

Answer 130

???

Question 131

How do you monitor cracking and what are the procedures?

Answer 131

1. Three studs/screws method - allows for the precise measurement of the sides of the triangle (ideally with a calliper or crack width gauge), indicating the extent and direction of the movement
2. Proprietary calibrated tell-tale - measurement grid/scale is placed over the crack, however they are not always clear to read and are more easily affected by weather and vandals
3. Glass tell-tale - placed over the crack and breaks if there is movement, therefore the least effective method, as it only indicates movement has happened, nothing else

Question 132

Categorise the severity of cracking.

Answer 132

• BRE Digest 251, Table 1 gives 6 categories of cracks based on size, with 0 being hairline cracks and 5 being cracks over 25mm
• Anything under 5mm (category 2) are not regarded as severe

Question 133

How can cracked, worn or spalling bricks be repaired?

Answer 133

???

Question 134

Your client’s Victorian building has solid brick external walls. There are a number of diagonal cracks in different parts of the building. What action would you take?

Answer 134

???

Question 135

Cracking has been identified to the sides of a bay window to a traditionally constructed property circa 1900s. What are the potential causes and how can the problem be rectified?

Answer 135

???

Question 136

What is subsidence?

Answer 136

Downward movement of a building foundation caused by loss of support beneath

Question 137

What are the common causes of subsidence?

Answer 137

Usually associated with volumetric changes in the subsoil, possibly due to:

1. Influence of trees on shrinkable (cohesive) soils
2. Washing away of non-cohesive soils (e.g. leaking drains, burst water mains or underground streams)
3. Change in ground-water levels (e.g. abstraction or land drainage)
4. Mining
5. Nearby excavations

Question 138

How can trees cause subsidence?

Answer 138

Influence of trees on shrinkable (cohesive) soils:

1. Trees and shrubs in close proximity to the building can cause the soil to become desiccated and lose its cohesion as a result of water being taken up through their roots
2. Worse throughout periods of hot, dry weather (soils can become desiccated even without the presence of trees)
3. As a tree grows it will extract increasingly more water from the ground, which can still cause desiccation even without hot weather
4. Introducing new trees causes more water to be removed from the ground, thus heightening the problem

Question 139

How can subsidence be rectified?

Answer 139

1. Repair/alleviate the cause (e.g. repair/replace leaking drains, reduce height of trees)
2. Consult with an arboriculturalist when removing/gradually reducing the height of trees is concerned
3. Monitor the cracks and if no further movement occurs, repoint/patch/replace as necessary
4. Where movement is excessive and on-going, underpinning may be required
5. Where movement is slight and thought to be seasonal (usually where trees are concerned), it will be necessary to monitor the movement

Question 140

Who usually pays for damage caused by subsidence?

Answer 140

Most insurance policies cover the cost of repairing the loss and damage caused by ground movement, but not necessarily the cost of preventing further movement

Question 141

What is heave?

Answer 141

Upward movement of a building foundation caused by the expansion or swelling of the subsoil

Question 142

What are the common causes of heave?

Answer 142

1. The removal of trees on shrinkable (cohesive) soils
2. The freezing of ground water in frost-susceptible soils

Question 143

How can trees cause heave?

Answer 143

1. The ground slowly regains moisture that was once taken up by the tree roots
2. Can last up to 10 years so care is needed when building on sites soon after trees have been removed

Question 144

How can freezing ground water cause heave?

Answer 144

1. After a period of high rainfall, water fills the voids between the particles and in freezing weather expands as it turns to ice
2. Additional damage can be caused when the ice thaws and the ground settles
3. Worse if ground has a high water table

Question 145

What is settlement?

Answer 145

1. Natural compaction of soil due to the load imposed by the building
2. Happens in all buildings and occurs soon after construction
3. Only problematic if it is differential (i.e. happens in different parts at different times, perhaps due to variations in ground conditions or using old/different foundation depths)

Question 146

Explain the process of diagnosing ground movement cracking.

Answer 146

1. Inspect the cracks - location, size, direction, age
2. Investigate the site - ground profile, soil type, tree proximity, drains testing, mining area
3. Determine the cause of the cracks from steps 1 and 2
4. Begin remedial action - alleviate cause, provide underpinning if necessary
5. Monitor cracks - minimum 18 months
6. Assess action for trees (if necessary) with an arboriculturalist

Question 147

What features of a crack may indicate that it has been caused by ground movement?

Answer 147

1. Extends above and below the DPC
2. Affects both internal and external surfaces
3. Diagonal in direction (stepped along brickwork)
4. Tapered

Question 148

How does the width of a crack help determine which type of ground movement has caused it?

Answer 148

1. Heave - cracks are wider at the top and narrower at the bottom (both the cracks themselves and their location on the building)
2. Subsidence - cracks are narrower at the top and wider at the bottom (both the cracks themselves and their location on the building)
3. Local subsidence - cracks are wider at the top and narrower at the bottom

Question 149

Which tree types extract the most water from the ground?

Answer 149

Not all trees present the same risk, however the species that extract the most water are poplar, willow, oak, elm, horse chestnut and sycamore

Question 150

As a general rule, how far away should trees be from buildings?

Answer 150

1. General rule - tree should be at least its full mature height away from a building and one and a half times when part of a group/row
2. However, this does not necessarily mean they should be removed if closer, especially mature trees

Question 151

What RICS guidance is available in relation to ground movement and what information does it contain?

Answer 151

Subsidence in Relation to Insurance Claims GN:

• Guidance for professionals involved in subsidence claims, including:
  
  • Causes of subsidence, heave and landslip
  • Causes of other building fractures
  • Policy cover details
  • Handling claims
  • Repair techniques
  • Recoveries and contribution
  • Relevant voluntary agreements

Question 152

What is underpinning?

Answer 152

Process of strengthening the foundation of an existing structure by transferring the load carried by the foundation from its existing bearing level to a new level at a lower depth

Question 153

Explain the sequence of work involved in underpinning a strip foundation.

Answer 153

1. The traditional method of underpinning involves the soil beneath the existing foundation being excavated and replaced in phases with foundation material, normally concrete
2. Bays of approximately 1500mm long are excavated in a strategic order so there are never adjacent bays being worked on at the same time

Question 154

Detail some alternative methods of underpinning.

Answer 154

• Jack pile underpinning:
  
  • Used where depth required is too deep for traditional underpinning
  • Precast concrete pile is hydraulically jacked beneath existing foundation
  • Existing foundation must be in good condition as it must rest on the pile caps once the pile has been inserted
• Needle and pile underpinning:
  
  • Used where condition of existing foundation is unsuitable for traditional or jack piling
  • Reinforced concrete beams (aka ‘needles’) are connected to small diameter bored piles which take the load
  • Can be cantilevered where access beneath existing foundation is restricted
• Expanding foam:
  
  • Relatively modern technique where foam is injected into foundations, filling any voids and solidifying
  • No excavation required

Question 155

What guidance is available in relation to underpinning?

Answer 155

BRE Digest 352 (Underpinning) contains further information

Question 156

What is cavity wall tie failure and how is it caused?

Answer 156

Cavity wall tie failure is when the wall ties fail to tie the two leaves together, which can be caused by:

1. Rusting of the metal ties (due to water penetration)
2. Poor quality mortar reducing the bond
3. Not installing the correct number of ties

Question 157

What is black ash mortar and how can it be problematic when used in cavity wall construction?

Answer 157

The use of black ash mortar (a product of coal mining which was sometimes added to mortar to give it a black colour) in Victorian buildings can exacerbate the problem of wall tie failure, as high sulphur content in the black ash produces sulphuric acid when wet for long periods, which can corrode the wall ties

Question 158

What problems are associated with cavity wall tie failure?

Answer 158

1. Cracking where rust has caused the ties to expand, which can in turn lead to damp penetration and further accelerate the rusting process
2. Bowing/bulging walls
3. Damage to the roof as the external leaf increases in height
4. Extensive expansion can cause rotation in the foundation as the loads from the roof can be transferred down the outer leaf
5. In severe cases, collapse of the outer leaf

Question 159

How would you identify cavity wall tie failure?

Answer 159

1. Horizontal cracking usually every 6 courses / 450mm, however less bulky wall ties (e.g. butterfly wire ties) will not generally produce enough expansion to induce cracking, therefore failure may occur without any outwardly visible signs
2. Intrusive inspection using a boroscope may also be used to physically inspect the cavity
3. Brickwork may also be removed to physically inspect cavity

Question 160

What steps would you recommend to remediate cavity wall tie failure?

Answer 160

1. Remove old ties
2. Drill in new ties through the centre of the brickwork
3. Repoint/make good brickwork

Question 161

What different methods of replacing cavity wall ties are available?

Answer 161

1. Resin/grouted - pre-drilled holes are filled with resin before new ties are pushed in, then more resin injected through the tie to fill around the end in the inner leaf (not suitable for porous masonry)
2. Mechanical - features a sleeve that expands when the tie is screwed up (only suitable when masonry is in a good condition)
3. Helical - long corkscrew with a wide thread is drilled trough both leaves

Question 162

What guidance is available for replacing cavity wall ties?

Answer 162

BRE 329 (Inserting Wall Ties in Existing Construction) contains further remedial guidance

Question 163

How were the relevant British Standards changed to address cavity wall tie failure?

Answer 163

1. In 1945, a British Standard was introduced that provided a minimum thickness for the galvanised layer
2. In 1968, the minimum thickness was reduced because it was thought the original thickness was excessive
3. In 1981, the minimum thickness was increased again

Question 164

What is carbonation and how is it caused?

Answer 164

1. Carbonation is the process by which carbon dioxide slowly penetrates concrete and dissolves in water present within its pores, forming a mildly carbolic acidic solution
2. This acidic solution reacts with the alkaline calcium hydroxide (one of the components of concrete) to form calcium carbonate
3. This results in a pH drop, reducing the alkalinity of the concrete (from more than 12.5 to approximately 8.5)
4. This carbonation process progressively moves through the concrete over time

Question 165

What problems are associated with carbonation?

Answer 165

1. The passive layer around reinforcing steel will deteriorate when the pH falls below 10.5
2. Therefore, once carbonation reaches any steel, the concrete is insufficiently alkaline to protect the steel’s passive layer and thus becomes ‘active’ (aka depassivation)
3. Moisture and oxygen ingressing through the porous concrete can now react with the steel, which may begin to rust and corrode
4. If this happens, the steel will expand, which can cause cracking and spalling of the concrete cover, thus compromising its structural integrity
5. This also makes it easier for aggressive agents to ingress towards the steel, thus further increasing the rate of corrosion

Question 166

What factors affect the rate of carbonation?

Answer 166

1. Quality and density of the concrete - good quality, well compacted concrete will carbonate at a much slower rate
2. Exposure of the building to water and carbon dioxide (permanently wet conditions hinder penetration so carbonation will be low)
3. Relative humidity of the atmosphere - carbonation is encouraged where RH is between 25-75% (optimum at 50-75%; anything over 75% usually hinders the rate of carbonation as the excess moisture slows the rate of carbon dioxide entry)
4. Temperature - warmer temperatures increase the rate of carbonation (subject to RH)

Question 167

Is the rate of carbonation greater internally or externally? Why?

Answer 167

The rate of carbonation is usually greater internally due to the higher relative humidity and temperature

Question 168

Is carbonation more likely to cause corrosion in internal or external concrete? Why?

Answer 168

External concrete, due to the increased presence of moisture and oxygen that can penetrate the carbonated concrete

Question 169

Under what circumstances is the risk of corrosion through carbonation particularly high?

Answer 169

If poor compaction and strength (perhaps caused by a too high water/cement ratio) is coupled with reinforcement with little cover

Question 170

How would you identify carbonation?

Answer 170

Visual Appearance:

• Longitudinal cracking along the line of any steel reinforcement (hairline cracking can occur as early as a few months after construction)
• Brown stains as a result of the rusting steel
• Over time, the expansion of rusting steel will result in further cracking and spalling of the surface concrete

Chemical Testing:

• Used to determine depth of carbonation
• Phenolphthalein solution is sprayed onto a fresh sample of the concrete
• Non-carbonated areas will turn pink/purple (alkaline), whereas carbonated areas will remain colourless (neutral pH value due to reduced alkalinity)
• The depth of penetration can then be measured

Question 171

How can carbonated concrete be addressed?

Answer 171

Firstly consider the likely rate of ongoing deterioration and the required life of the structure to assess the cost effectiveness of different protection and repair strategies

Options:

1. Patch Repair
2. Re-alkalisation by Diffusion
3. Electrochemical Re-alkalisation
4. Increase Resistivity

Question 172

What is the process of patch repairing carbonated concrete?

Answer 172

1. Clean surface
2. Remove loose concrete
3. Remove corrosion (e.g. grit blasting)
4. Prime the reinforcement with alkali-based solution
5. Reinstate concrete cover using patch repair mortar, sprayed concrete or conventional concrete (for large areas only)

Question 173

What is the process of remediating carbonated concrete through re-alkalisation by diffusion?

Answer 173

1. For concrete that has only suffered minor carbonation
2. A thickness of fresh alkaline concrete is applied to the surface of the concrete
3. Migration of alkalis from the fresh to the original concrete will allow for gradual re-alkalisation
4. Not advisable to rely on this method alone if the average depth of carbonation exceeds 10mm, as moisture from the fresh concrete can ingress and increase the rate of steel corrosion

Question 174

What is the process of remediating carbonated concrete through electrochemical re-alkalisation?

Answer 174

1. A temporary anode mesh is fitted close to the surface of the concrete and is electrically connected to the steel reinforcement (cathode) and a power supply
2. An electrolyte (usually a sprayed cellulose fibre) is applied around the anode mesh
3. The steel cathode then attracts alkali metal ions towards it, so high alkalinity is restored around the steel
4. Process takes approximately 3-10 days

Question 175

How can you increase the resistivity of carbonated concrete?

Answer 175

1. Surface coatings - designed to restrict the penetration of carbon dioxide (must still allow the concrete to dry out)
2. Hydrophobic impregnants - designed to repel water
3. Sheltering the concrete component - e.g. ventilated external cladding

Question 176

What is chloride attack?

Answer 176

Chloride attack is the process by which chloride ions are introduced into concrete, which reduces its alkalinity

Question 177

How can chloride ions be introduced into concrete?

Answer 177

1. Introduced as an accelerator during the mixing process (calcium chloride)
2. Introduced naturally (e.g. from the use of unwashed marine aggregates)
3. Introduced as a result of external contamination (e.g. de-icing salt, exposure to salt spray etc.)

Question 178

When was it common to introduce chloride ions into concrete as an accelerator?

Answer 178

• Prevalent in the 1950s and 1960s - good for concreting in cold weather as the concrete or mortar would harden quickly, thus developing early resistance to freezing and thawing
• Common until around 1978

Question 179

What method of introducing chloride ions into concrete can cause the most damage?

Answer 179

External contamination as the concentration can be more erratic and the ions are not chemically bound

Question 180

What problems are associated with chloride attack?

Answer 180

1. Loss of alkalinity of the concrete removes its protective capability to stop any encased steel from oxidising (depassivation)
2. Similar to carbonation, moisture and oxygen can then lead to expansion of the steel and cracking and spalling of the concrete cover, thus compromising its structural integrity
3. Furthermore, as the chloride ions make contact with the steel and the surrounding passive material, hydrochloric acid is formed
4. The hydrochloric acid will then eat away at the steel reinforcement (aka ‘pitting’) and could cause loss of section and serious structural failure
5. Where high levels of chloride are present, corrosion of steel can occur even if the concrete is highly alkaline
6. Where carbonation is also present, chloride attack can increase the rate of oxidisation of the steel reinforcement

Question 181

What is meant by the term ‘pitting’?

Answer 181

Localised corrosion that leads to the creation of small holes in the metal

Question 182

What factors affect the rate of chloride attack?

Answer 182

1. Physical characteristics of the concrete - i.e. calcium chloride used as an additive or introduced naturally
2. Quality and density - denser concrete will be less porous and therefore decrease the rate at which chloride ions can reach the steel
3. Physical condition - e.g. cracks and damage can speed up the transportation of moisture and ions to the steel (freeze thaw cycles can then exacerbate the process further)
4. Location - sea walls, marine structures (sea water is a major source of chloride ions), areas where de-icing salts have been used and remain in-situ

Question 183

How would you identify chloride attack?

Answer 183

Visual Appearance:

• Can induce large cracking or bulging within the concrete of a more localised nature than carbonation
• Black coloured rusting and pitting of the steel where aggressive hydrochloric acid has attacked
• May be more difficult to see as pitting can occur where there is no cracking/spalling of the concrete

Chemical Testing:

• Indicator solution is applied and if the liquid turns brown, significant chlorides are present
• If it turns yellow/white, chlorides may be present and further investigation is required

Laboratory Testing

Question 184

Name some of the different methods of obtaining samples to laboratory test for chloride attack.

Answer 184

1. Lump sample - section is knocked off (ideally about 50g from a depth of at least 25mm) for testing, although corner samples may distort results as they may have been subjected to chloride ingress from two sides
2. Dust drilling - dust is extracted using a rotary percussion drill, although cannot take incremental readings / profile
3. Profile grinding - specialist grinder used to obtain concrete powder at selected, exact depth increments

Question 185

Why is it important to take samples at different depths whilst testing for chloride attack?

Answer 185

To establish the concentration at different levels to determine whether the chloride content is a result of:

• Airborne contamination (concentration highest towards the surface and gradually diminishing into the depth of the concrete)
• Other sources (concentration at a more even distribution)

Question 186

How can chloride attack be remediated?

Answer 186

1. Patch Repair
2. Desalination (Chloride Extraction)
3. Cathodic Protection
4. Corrosion Inhibitors

Question 187

What problems are associated with patch repairing chloride attack?

Answer 187

1. Difficult due to the tendency for new corrosion cells to form at the boundary of the repair (aka incipient anode effect) - this can be minimised by removing where possible all concrete with significant chloride contamination
2. Not sufficient for high levels of chlorides and long term protection

Question 188

What can be introduced to help minimise the problems associated with patch repairing chloride attack?

Answer 188

The introduction of proprietary sacrificial zinc anodes embedded within the patch repair attached to the reinforcement can help reduce incipient anode effect

Question 189

What is the process of remediating chloride attack through chloride extraction?

Answer 189

1. Short-term process where negatively charged chloride ions can be electrochemically repelled from the steel
2. A temporary anode mesh is fitted close to the surface of the concrete and is electrically connected to the steel reinforcement (cathode) and a power supply
3. An electrolyte (usually a sprayed cellulose fibre) is applied around the anode mesh
4. Once a current is applied for a period of time (may be up to 40 days), the chloride ions are transported from the concrete to its surface, where they are then carried out by water or removed with the temporary electrolyte

Question 190

What problems are associated with remediating chloride attack through chloride extraction?

Answer 190

1. Chloride that has penetrated deeper than 20mm can be hard to remove
2. Total extraction is impossible, so risk of reoccurrence is likely
3. Difficult to remove chloride ions bound in the mix at the time of construction (easier when chlorides had been introduced from external sources)
4. Worries that it may generate Alkali Silica Reaction (ASR) - currently being researched
5. Cannot be applied to prestressed concrete because of risk of hydrogen embrittlement (phenomenon where high-strength steel becomes brittle and fractures following exposure to hydrogen)

Question 191

What is the process of remediating chloride attack through cathodic protection?

Answer 191

1. Similar to desalination, however current densities are generally lower and the system is designed for continuous use, not a short period of time
2. The anodes are usually connected to a data-logging system so that current densities and corrosion rates can be monitored and corrected where necessary
3. Tried and tested long-term solution for heavily chloride-contaminated structures (e.g. car parks)

Question 192

What is the process of remediating chloride attack through the use of corrosion inhibitors?

Answer 192

1. Penetrates the concrete and creates a very thin protective layer around the steel
2. Cost-effective alternative to conventional repairs

Question 193

What problems are associated with remediating chloride attack through the use of corrosion inhibitors?

Answer 193

1. Molecules are fairly large so can be slow to penetrate, particularly when the concrete mix is dense
2. Applications in damp conditions may also reduce speed and effectiveness of treatment
3. Considered to be more appropriate when used as part of a treatment system, not on its own

Question 194

What is sulphate attack and how is it caused?

Answer 194

1. Sulphate attack is a chemical reaction where water soluble sulphate salts are transported into cement mortar or concrete
2. They react with the tricalcium aluminate (one of the components of Portland Cement) to form ettringite
3. Ettringite is characterised by the formation of acicular crystals, which generate high expansive forces in the mortar or concrete
4. For sulphate attack to occur, there must be sufficient sulphate and sufficient long-term water

Question 195

Name some common sources of sulphates in construction.

Answer 195

1. Soils containing high sulphate levels
2. Contaminated hardcore (that containing high levels of black ash, burnt colliery shale, blast furnace slag and similar materials)
3. Bricks
4. Air pollution
5. Exhaust gases of slow-burning fuel appliances

Question 196

What problems are associated with sulphate attack?

Answer 196

1. Cracking, expansion and bulging due to loss of bond between cement paste and aggregates
2. Sometimes the face of bricks spall, most commonly around their edges
3. Often accompanied by frost attack due to water saturation

Question 197

What building elements are typically affected by sulphate attack?

Answer 197

1. Chimney stacks
2. Mortar joints
3. Concrete floor slabs
4. Internally where cement and gypsum are in contact (e.g. adding gypsum plaster to a cement/sand mix to accelerate its set) and remain wet for long periods
5. Cement-based undercoat plasters if they contain ash (a sulphurous material) and if they remain wet for long periods

Question 198

Why are chimney stacks particularly at risk from sulphate attack?

Answer 198

1. Very exposed to rain
2. Additional sulphates are provided by exhaust gases from fires
3. Additional moisture is provided by exhaust gases condensing inside the cold upper parts of the chimney

Question 199

How would you identify sulphate attack in chimney stacks?

Answer 199

Leaning due to different wetting and drying cycles between elevations (wetter side suffers most expansion)

Question 200

How would you identify sulphate attack in concrete floor slabs?

Answer 200

1. Because it is restrained, upwards bowing towards centre coupled with map pattern cracking
2. Displacement of brickwork at slab level

Question 201

How would you identify sulphate attack in brickwork?

Answer 201

1. Expansion of brickwork along brick joints both horizontally (distinguishable from wall tie failure as it may occur in every joint) and vertically, particularly in rendered brick
2. Bowing upwards, particularly if restrained

Question 202

What level of sulphate is usually considered harmful to cement/concrete?

Answer 202

Laboratory testing as per BS 1881-124 - anything over 5% sulphate content of cement (assuming cement is 15% of mass of concrete) can be harmful

Question 203

What steps would you recommend to remediate sulphate attack?

Answer 203

1. Keep the concrete dry by installing a DPM to serve as a barrier to moisture to prevent salt migration
2. Reconstruct affected elements (floors, walls, foundations) with sulphate-resisting cement
3. Sulphate-resistant bricks may also be used

Question 204

How can rendering brickwork often exacerbate problems caused by sulphate attack?

Answer 204

1. Dense cement renders often crack and let water in, but restrict it from drying out
2. Soluble sulphates in the bricks themselves can then dissolve out to react with the cement mortar, causing it to expand

Question 205

What is ASR and how is it caused?

Answer 205

ASR is a reaction produced when highly alkaline pore water in concrete mixes with silica molecules in certain rocks and minerals

For ASR to occur, 3 interrelated factors must be present:

1. High alkalinity (either from cement or other external sources)
2. Sufficient moisture
3. Critical silica in the aggregate

Question 206

What problems are associated with ASR?

Answer 206

1. The chemical reaction produces a gel, which absorbs water, expands and can cause the concrete to crack or disrupt
2. Cracks then allow more moisture to enter to fuel the reaction, thus producing greater amounts of gel
3. Durability of the concrete can thus be compromised
4. In extreme cases, the tensile strength of the concrete component can be reduced

Question 207

How would you identify ASR?

Answer 207

Visual appearance:

1. Pattern of map cracking occurs - applies to unreinforced concrete
2. In other occurrences, small ‘pop-outs’ (approx. 30-50mm) form - like concrete with acne
3. Spalling will often reveal a reservoir of sticky gel behind it or gel will be exuding from cracks
4. When carbonated, the gel appears as a whitish opaque coating - like bad efflorescence

Laboratory testing can confirm diagnosis

Question 208

What steps would you recommend to remediate ASR?

Answer 208

1. Existence of ASR is not necessarily fatal to a structure (depends on severity and elements affected)
2. A risk-based analyse is recommended before deciding upon replacement strategies
3. Without completing replacing the affected concrete, there are no full remedies, only mitigation measures

Question 209

What measures can be undertaken to mitigate the affects of ASR?

Answer 209

1. Application of penetrating breathable sealers - cannot be used when structure is permanently wet and must be reapplied every 5 years at most
2. Crack filling with flexible caulking - only benefit is it slows water ingress
3. Apply physical constraint to confine/strengthen structure - may be difficult to achieve and does not stop the process of ASR occurring
4. Over-cladding - may trap moisture and cause difficulty in future inspection

Question 210

What is ACR and how is it caused?

Answer 210

1. Very rare as it only occurs with certain impure forms of dolomitic limestone
2. The aggregate reacts with the dissolved potassium and sodium alkalis within the pore fluid
3. This then alters the crystal structure of the aggregate, causing it to expand

Question 211

What is meant by the term concrete cancer?

Answer 211

• Another name given to Alkali Aggregate Reactions (of which ASR is the most common in the UK)
• This term could be misleading and is therefore best avoided

Question 212

What different types of concrete tests are there?

Answer 212

1. Schmidt Hammer Test (aka rebound hammer test) - used to determine the compressive strength of concrete
2. Chemical testing (e.g. phenolphthalein for Carbonation)
3. Laboratory testing (e.g. profile grinding for Chloride Attack)

Question 213

What guidance is available in relation to concrete repair methods?

Answer 213

• BRE 444-3 (Corrosion of Steel in Concrete) - remedial measures and guidance for appropriate repair methods
• BS EN 1504 - 10 parts covering different concrete repairs
• The Concrete Society - Technical Report 69 ‘Repair of concrete structures with reference to BS EN 1504’ (2009) - explains the concepts provided for in the BS

Question 214

The reinforcement bars on a concrete building are exposed and corroding. What are the causes and remedial works strategies?

Answer 214

• Likely to be either carbonation, chloride attack or both
• Remedial measures depend on the extent of the damage
• Combination of the following may be appropriate:

1. Patch repair
2. Re-alkalisation
3. Desalination
4. Cathodic protection
5. Apply corrosion inhibitor

Question 215

What is carbonation and how is it caused?

Answer 215

1. Carbonation is the process by which carbon dioxide slowly penetrates concrete and dissolves in water present within its pores, forming a mildly carbolic acidic solution
2. This acidic solution reacts with the alkaline calcium hydroxide (one of the components of concrete) to form calcium carbonate
3. This results in a pH drop, reducing the alkalinity of the concrete (from more than 12.5 to approximately 8.5)
4. This carbonation process progressively moves through the concrete over time

Question 216

What problems are associated with carbonation?

Answer 216

1. The passive layer around reinforcing steel will deteriorate when the pH falls below 10.5
2. Therefore, once carbonation reaches any steel, the concrete is insufficiently alkaline to protect the steel’s passive layer and thus becomes ‘active’ (aka depassivation)
3. Moisture and oxygen ingressing through the porous concrete can now react with the steel, which may begin to rust and corrode
4. If this happens, the steel will expand, which can cause cracking and spalling of the concrete cover, thus compromising its structural integrity
5. This also makes it easier for aggressive agents to ingress towards the steel, thus further increasing the rate of corrosion

Question 217

What factors affect the rate of carbonation?

Answer 217

1. Quality and density of the concrete - good quality, well compacted concrete will carbonate at a much slower rate
2. Exposure of the building to water and carbon dioxide (permanently wet conditions hinder penetration so carbonation will be low)
3. Relative humidity of the atmosphere - carbonation is encouraged where RH is between 25-75% (optimum at 50-75%; anything over 75% usually hinders the rate of carbonation as the excess moisture slows the rate of carbon dioxide entry)
4. Temperature - warmer temperatures increase the rate of carbonation (subject to RH)

Question 218

Is the rate of carbonation greater internally or externally? Why?

Answer 218

The rate of carbonation is usually greater internally due to the higher relative humidity and temperature

Question 219

Is carbonation more likely to cause corrosion in internal or external concrete? Why?

Answer 219

External concrete, due to the increased presence of moisture and oxygen that can penetrate the carbonated concrete

Question 220

Under what circumstances is the risk of corrosion through carbonation particularly high?

Answer 220

If poor compaction and strength (perhaps caused by a too high water/cement ratio) is coupled with reinforcement with little cover

Question 221

How would you identify carbonation?

Answer 221

Visual Appearance:

• Longitudinal cracking along the line of any steel reinforcement (hairline cracking can occur as early as a few months after construction)
• Brown stains as a result of the rusting steel
• Over time, the expansion of rusting steel will result in further cracking and spalling of the surface concrete

Chemical Testing:

• Used to determine depth of carbonation
• Phenolphthalein solution is sprayed onto a fresh sample of the concrete
• Non-carbonated areas will turn pink/purple (alkaline), whereas carbonated areas will remain colourless (neutral pH value due to reduced alkalinity)
• The depth of penetration can then be measured

Question 222

How can carbonated concrete be addressed?

Answer 222

Firstly consider the likely rate of ongoing deterioration and the required life of the structure to assess the cost effectiveness of different protection and repair strategies

Options:

1. Patch Repair
2. Re-alkalisation by Diffusion
3. Electrochemical Re-alkalisation
4. Increase Resistivity

Question 223

What is the process of patch repairing carbonated concrete?

Answer 223

1. Clean surface
2. Remove loose concrete
3. Remove corrosion (e.g. grit blasting)
4. Prime the reinforcement with alkali-based solution
5. Reinstate concrete cover using patch repair mortar, sprayed concrete or conventional concrete (for large areas only)

Question 224

What is the process of remediating carbonated concrete through re-alkalisation by diffusion?

Answer 224

1. For concrete that has only suffered minor carbonation
2. A thickness of fresh alkaline concrete is applied to the surface of the concrete
3. Migration of alkalis from the fresh to the original concrete will allow for gradual re-alkalisation
4. Not advisable to rely on this method alone if the average depth of carbonation exceeds 10mm, as moisture from the fresh concrete can ingress and increase the rate of steel corrosion

Question 225

What is the process of remediating carbonated concrete through electrochemical re-alkalisation?

Answer 225

1. A temporary anode mesh is fitted close to the surface of the concrete and is electrically connected to the steel reinforcement (cathode) and a power supply
2. An electrolyte (usually a sprayed cellulose fibre) is applied around the anode mesh
3. The steel cathode then attracts alkali metal ions towards it, so high alkalinity is restored around the steel
4. Process takes approximately 3-10 days

Question 226

How can you increase the resistivity of carbonated concrete?

Answer 226

1. Surface coatings - designed to restrict the penetration of carbon dioxide (must still allow the concrete to dry out)
2. Hydrophobic impregnants - designed to repel water
3. Sheltering the concrete component - e.g. ventilated external cladding

Question 227

What is chloride attack?

Answer 227

Chloride attack is the process by which chloride ions are introduced into concrete, which reduces its alkalinity

Question 228

How can chloride ions be introduced into concrete?

Answer 228

1. Introduced as an accelerator during the mixing process (calcium chloride)
2. Introduced naturally (e.g. from the use of unwashed marine aggregates)
3. Introduced as a result of external contamination (e.g. de-icing salt, exposure to salt spray etc.)

Question 229

When was it common to introduce chloride ions into concrete as an accelerator?

Answer 229

• Prevalent in the 1950s and 1960s - good for concreting in cold weather as the concrete or mortar would harden quickly, thus developing early resistance to freezing and thawing
• Common until around 1978

Question 230

What method of introducing chloride ions into concrete can cause the most damage?

Answer 230

External contamination as the concentration can be more erratic and the ions are not chemically bound

Question 231

What problems are associated with chloride attack?

Answer 231

1. Loss of alkalinity of the concrete removes its protective capability to stop any encased steel from oxidising (depassivation)
2. Similar to carbonation, moisture and oxygen can then lead to expansion of the steel and cracking and spalling of the concrete cover, thus compromising its structural integrity
3. Furthermore, as the chloride ions make contact with the steel and the surrounding passive material, hydrochloric acid is formed
4. The hydrochloric acid will then eat away at the steel reinforcement (aka ‘pitting’) and could cause loss of section and serious structural failure
5. Where high levels of chloride are present, corrosion of steel can occur even if the concrete is highly alkaline
6. Where carbonation is also present, chloride attack can increase the rate of oxidisation of the steel reinforcement

Question 232

What is meant by the term ‘pitting’?

Answer 232

Localised corrosion that leads to the creation of small holes in the metal

Question 233

The reinforcement bars on a concrete building are exposed and corroding. What are the causes and remedial works strategies?

Answer 233

• Likely to be either carbonation, chloride attack or both
• Remedial measures depend on the extent of the damage
• Combination of the following may be appropriate:

1. Patch repair
2. Re-alkalisation
3. Desalination
4. Cathodic protection
5. Apply corrosion inhibitor

Question 234

What guidance is available in relation to concrete repair methods?

Answer 234

• BRE 444-3 (Corrosion of Steel in Concrete) - remedial measures and guidance for appropriate repair methods
• BS EN 1504 - 10 parts covering different concrete repairs
• The Concrete Society - Technical Report 69 ‘Repair of concrete structures with reference to BS EN 1504’ (2009) - explains the concepts provided for in the BS

Question 235

What different types of concrete tests are there?

Answer 235

1. Schmidt Hammer Test (aka rebound hammer test) - used to determine the compressive strength of concrete
2. Chemical testing (e.g. phenolphthalein for Carbonation)
3. Laboratory testing (e.g. profile grinding for Chloride Attack)

Question 236

What is meant by the term concrete cancer?

Answer 236

• Another name given to Alkali Aggregate Reactions (of which ASR is the most common in the UK)
• This term could be misleading and is therefore best avoided

Question 237

What is ACR and how is it caused?

Answer 237

1. Very rare as it only occurs with certain impure forms of dolomitic limestone
2. The aggregate reacts with the dissolved potassium and sodium alkalis within the pore fluid
3. This then alters the crystal structure of the aggregate, causing it to expand

Question 238

What measures can be undertaken to mitigate the affects of ASR?

Answer 238

1. Application of penetrating breathable sealers - cannot be used when structure is permanently wet and must be reapplied every 5 years at most
2. Crack filling with flexible caulking - only benefit is it slows water ingress
3. Apply physical constraint to confine/strengthen structure - may be difficult to achieve and does not stop the process of ASR occurring
4. Over-cladding - may trap moisture and cause difficulty in future inspection

Question 239

What steps would you recommend to remediate ASR?

Answer 239

1. Existence of ASR is not necessarily fatal to a structure (depends on severity and elements affected)
2. A risk-based analyse is recommended before deciding upon replacement strategies
3. Without completing replacing the affected concrete, there are no full remedies, only mitigation measures

Question 240

How would you identify ASR?

Answer 240

Visual appearance:

1. Pattern of map cracking occurs - applies to unreinforced concrete
2. In other occurrences, small ‘pop-outs’ (approx. 30-50mm) form - like concrete with acne
3. Spalling will often reveal a reservoir of sticky gel behind it or gel will be exuding from cracks
4. When carbonated, the gel appears as a whitish opaque coating - like bad efflorescence

Laboratory testing can confirm diagnosis

Question 241

What problems are associated with ASR?

Answer 241

1. The chemical reaction produces a gel, which absorbs water, expands and can cause the concrete to crack or disrupt
2. Cracks then allow more moisture to enter to fuel the reaction, thus producing greater amounts of gel
3. Durability of the concrete can thus be compromised
4. In extreme cases, the tensile strength of the concrete component can be reduced

Question 242

What is ASR and how is it caused?

Answer 242

ASR is a reaction produced when highly alkaline pore water in concrete mixes with silica molecules in certain rocks and minerals

For ASR to occur, 3 interrelated factors must be present:

1. High alkalinity (either from cement or other external sources)
2. Sufficient moisture
3. Critical silica in the aggregate

Question 243

How can rendering brickwork often exacerbate problems caused by sulphate attack?

Answer 243

1. Dense cement renders often crack and let water in, but restrict it from drying out
2. Soluble sulphates in the bricks themselves can then dissolve out to react with the cement mortar, causing it to expand

Question 244

What steps would you recommend to remediate sulphate attack?

Answer 244

1. Keep the concrete dry by installing a DPM to serve as a barrier to moisture to prevent salt migration
2. Reconstruct affected elements (floors, walls, foundations) with sulphate-resisting cement
3. Sulphate-resistant bricks may also be used

Question 245

What level of sulphate is usually considered harmful to cement/concrete?

Answer 245

Laboratory testing as per BS 1881-124 - anything over 5% sulphate content of cement (assuming cement is 15% of mass of concrete) can be harmful

Question 246

How would you identify sulphate attack in brickwork?

Answer 246

1. Expansion of brickwork along brick joints both horizontally (distinguishable from wall tie failure as it may occur in every joint) and vertically, particularly in rendered brick
2. Bowing upwards, particularly if restrained

Question 247

How would you identify sulphate attack in concrete floor slabs?

Answer 247

1. Because it is restrained, upwards bowing towards centre coupled with map pattern cracking
2. Displacement of brickwork at slab level

Question 248

How would you identify sulphate attack in chimney stacks?

Answer 248

Leaning due to different wetting and drying cycles between elevations (wetter side suffers most expansion)

Question 249

Why are chimney stacks particularly at risk from sulphate attack?

Answer 249

1. Very exposed to rain
2. Additional sulphates are provided by exhaust gases from fires
3. Additional moisture is provided by exhaust gases condensing inside the cold upper parts of the chimney

Question 250

What building elements are typically affected by sulphate attack?

Answer 250

1. Chimney stacks
2. Mortar joints
3. Concrete floor slabs
4. Internally where cement and gypsum are in contact (e.g. adding gypsum plaster to a cement/sand mix to accelerate its set) and remain wet for long periods
5. Cement-based undercoat plasters if they contain ash (a sulphurous material) and if they remain wet for long periods

Question 251

What problems are associated with sulphate attack?

Answer 251

1. Cracking, expansion and bulging due to loss of bond between cement paste and aggregates
2. Sometimes the face of bricks spall, most commonly around their edges
3. Often accompanied by frost attack due to water saturation

Question 252

Name some common sources of sulphates in construction.

Answer 252

1. Soils containing high sulphate levels
2. Contaminated hardcore (that containing high levels of black ash, burnt colliery shale, blast furnace slag and similar materials)
3. Bricks
4. Air pollution
5. Exhaust gases of slow-burning fuel appliances

Question 253

What is sulphate attack and how is it caused?

Answer 253

1. Sulphate attack is a chemical reaction where water soluble sulphate salts are transported into cement mortar or concrete
2. They react with the tricalcium aluminate (one of the components of Portland Cement) to form ettringite
3. Ettringite is characterised by the formation of acicular crystals, which generate high expansive forces in the mortar or concrete
4. For sulphate attack to occur, there must be sufficient sulphate and sufficient long-term water

Question 254

What problems are associated with remediating chloride attack through the use of corrosion inhibitors?

Answer 254

1. Molecules are fairly large so can be slow to penetrate, particularly when the concrete mix is dense
2. Applications in damp conditions may also reduce speed and effectiveness of treatment
3. Considered to be more appropriate when used as part of a treatment system, not on its own

Question 255

What is the process of remediating chloride attack through the use of corrosion inhibitors?

Answer 255

1. Penetrates the concrete and creates a very thin protective layer around the steel
2. Cost-effective alternative to conventional repairs

Question 256

What is the process of remediating chloride attack through cathodic protection?

Answer 256

1. Similar to desalination, however current densities are generally lower and the system is designed for continuous use, not a short period of time
2. The anodes are usually connected to a data-logging system so that current densities and corrosion rates can be monitored and corrected where necessary
3. Tried and tested long-term solution for heavily chloride-contaminated structures (e.g. car parks)

Question 257

What problems are associated with remediating chloride attack through chloride extraction?

Answer 257

1. Chloride that has penetrated deeper than 20mm can be hard to remove
2. Total extraction is impossible, so risk of reoccurrence is likely
3. Difficult to remove chloride ions bound in the mix at the time of construction (easier when chlorides had been introduced from external sources)
4. Worries that it may generate Alkali Silica Reaction (ASR) - currently being researched
5. Cannot be applied to prestressed concrete because of risk of hydrogen embrittlement (phenomenon where high-strength steel becomes brittle and fractures following exposure to hydrogen)

Question 258

What is the process of remediating chloride attack through chloride extraction?

Answer 258

1. Short-term process where negatively charged chloride ions can be electrochemically repelled from the steel
2. A temporary anode mesh is fitted close to the surface of the concrete and is electrically connected to the steel reinforcement (cathode) and a power supply
3. An electrolyte (usually a sprayed cellulose fibre) is applied around the anode mesh
4. Once a current is applied for a period of time (may be up to 40 days), the chloride ions are transported from the concrete to its surface, where they are then carried out by water or removed with the temporary electrolyte

Question 259

What can be introduced to help minimise the problems associated with patch repairing chloride attack?

Answer 259

The introduction of proprietary sacrificial zinc anodes embedded within the patch repair attached to the reinforcement can help reduce incipient anode effect

Question 260

What problems are associated with patch repairing chloride attack?

Answer 260

1. Difficult due to the tendency for new corrosion cells to form at the boundary of the repair (aka incipient anode effect) - this can be minimised by removing where possible all concrete with significant chloride contamination
2. Not sufficient for high levels of chlorides and long term protection

Question 261

How can chloride attack be remediated?

Answer 261

1. Patch Repair
2. Desalination (Chloride Extraction)
3. Cathodic Protection
4. Corrosion Inhibitors

Question 262

Why is it important to take samples at different depths whilst testing for chloride attack?

Answer 262

To establish the concentration at different levels to determine whether the chloride content is a result of:

• Airborne contamination (concentration highest towards the surface and gradually diminishing into the depth of the concrete)
• Other sources (concentration at a more even distribution)

Question 263

Name some of the different methods of obtaining samples to laboratory test for chloride attack.

Answer 263

1. Lump sample - section is knocked off (ideally about 50g from a depth of at least 25mm) for testing, although corner samples may distort results as they may have been subjected to chloride ingress from two sides
2. Dust drilling - dust is extracted using a rotary percussion drill, although cannot take incremental readings / profile
3. Profile grinding - specialist grinder used to obtain concrete powder at selected, exact depth increments

Question 264

How would you identify chloride attack?

Answer 264

Visual Appearance:

• Can induce large cracking or bulging within the concrete of a more localised nature than carbonation
• Black coloured rusting and pitting of the steel where aggressive hydrochloric acid has attacked
• May be more difficult to see as pitting can occur where there is no cracking/spalling of the concrete

Chemical Testing:

• Indicator solution is applied and if the liquid turns brown, significant chlorides are present
• If it turns yellow/white, chlorides may be present and further investigation is required

Laboratory Testing

Question 265

What factors affect the rate of chloride attack?

Answer 265

1. Physical characteristics of the concrete - i.e. calcium chloride used as an additive or introduced naturally
2. Quality and density - denser concrete will be less porous and therefore decrease the rate at which chloride ions can reach the steel
3. Physical condition - e.g. cracks and damage can speed up the transportation of moisture and ions to the steel (freeze thaw cycles can then exacerbate the process further)
4. Location - sea walls, marine structures (sea water is a major source of chloride ions), areas where de-icing salts have been used and remain in-situ

Question 266

What are the common defects associated with poor design and construction of pitched roofs?

Answer 266

1. Untreated timbers
2. Inadequately sized timbers
3. Omitted/removed roof members
4. Eaves/verge overhang too small
5. Sarking felt improperly installed
6. Inadequate flashings/soakers at abutments
7. Inadequate ventilation
8. Inadequate pitch
9. Nail sickness
10. Delamination of tiles
11. Bitumastic over-sealing

Question 267

What is roof spread and how does it usually occur?

Answer 267

An outwards movement of the roof ususally caused by:

1. Collars placed too high or removed completely to facilitate a habitable space within the roof
2. Ceiling joists inadequately connected to rafters

Question 268

Why is the roof’s pitch important?

Answer 268

1. If coverings are laid at too low a pitch, rain and snow may penetrate
2. Laying coverings on steeper pitches (up to the vertical) is not normally a problem, however all tiles must be nailed, as sole reliance on any nibs may be insufficient

Question 269

What are the problems associated with roof covering laps?

Answer 269

1. If the gauge is extended, thus reducing the lap, it will increase the likelihood of weather penetration
2. If the gauge is reduced, thus increasing the lap, it will provide greater weather resistance but may result in an excessive load on the structure

Question 270

What is nail sickness and why is it problematic?

Answer 270

Nail sickness is the term for when ferrous nails used to secure slates/tiles inevitably rust in the presence of the moisture present between the roof covering and sarking felt, causing slipped or missing slates/tiles that can lead to damp penetration

Question 271

How can nail sickness be remediated?

Answer 271

1. Slipped slates can be re-secured using ‘S’ shaped lead/copper clips (aka ‘tingles’), however this can be unsightly
2. In replacement work, non-ferrous fixings (e.g. copper, aluminium) should always be used - AVOID galvanised steel

Question 272

What are the common defects associated with slate roof coverings?

Answer 272

1. Delamination
2. Torching and bedding
3. Split slates along the line of nail holes
4. Nail sickness
5. Broken head-nailed slates caused by wind uplift
6. Wide joints between slates causing water penetration
7. Well-laid slates lying close to each other causing water seepage due to capillary action
8. Verge failure (half slates used at verges instead of slate-and-a-half, the former of which are difficult to secure properly against wind uplift)
9. Inadequate overhang at verges (water cannot drip away from the face of the wall beneath)
10. Bitumastic over-sealing (impedes ventilation)

Question 273

What is torching and bedding and how may it be problematic?

Answer 273

1. Traditional process of filling the gaps between slates and battens with mortar (commonly lime mortar and animal hair) to prevent rain or snow penetration where no boarding or felt was present
2. Tends to shrink and fall out, leading to water penetration
3. Also leads to inadequate ventilation to the underside of the slate

Question 274

What factors would lead you to recommend re-covering a slate pitched roof rather than patch repairing it?

Answer 274

The extent of the problem and the condition of the battens beneath

Question 275

What are the common defects associated with clay tile roof coverings?

Answer 275

1. Delamination
2. Cambered/non-cambered tiles - cambered tiles (i.e. concave profile across width) more liable to driving rain or snow penetration, non-cambered tiles increase the likelihood of capillary action
3. Slipped tiles - insufficent nailing (should normally be every fourth or fifth course and around all verges, hips and ridges) or nail sickness
4. Torching and bedding
5. Efflorescence
6. Verge failure (half slates used at verges instead of slate-and-a-half, the former of which are difficult to secure properly against wind uplift)
7. Inadequate overhang at verges (water cannot drip away from the face of the wall beneath)
8. Ridges and hips - lime mortar traditionally used to bed ridge and hip tiles loses its ability to bond with age, leading to loose or missing ridge/hip tiles

Question 276

What defects can occur in a concrete tiled roof?

Answer 276

1. Overloading - extra weight of concrete tiles may cause bowing/buckling of the roof structure where a previous slate/clay tile covering has been replaced
2. Loss of surface/colour - originally, the finish of concrete tiles was only surface deep, so once weathered or damaged, the concrete beneath is revealed which is unsightly but does not impair performance
3. Efflorescence
4. Delamination
5. Slipped tiles - insufficent nailing (should normally be every fourth or fifth course and around all verges, hips and ridges) or nail sickness

Question 277

What problems are associated with replacing slated roof coverings with new concrete tiles?

Answer 277

Overloading - extra weight of concrete tiles may cause bowing/buckling of the roof structure where a previous slate/clay tile covering has been replaced

Question 278

Regarding sagging of the roof, what defects would you look for in the roof space?

Answer 278

???

Question 279

What are the common defects associated with metal roofs?

Answer 279

???

Question 280

What are the potential problems with a roof structure incorporating trussed rafters?

Answer 280

1. Roof trusses inappropriately stored or mishandled (physical damage, distortion, water saturation) leading to inadequate structural performance, water saturation and risk of rot
2. Inadequate bracing of roof trusses - trussed roof likely to move or tilt sideways as a unit

Question 281

How do the Building Regulations address the problems associated with trussed rafter roof construction?

Answer 281

???

Question 282

What are the problems associated with a butterfly roof?

Answer 282

???

Question 283

Why do flat roofs fail?

Answer 283

1. Physical failure - thermal movement, building movement, poor workmanship, poor materials
2. Constructional moisture - water trapped by the waterproofing layers (e.g. poured concrete slabs, wet screeds laid to falls etc.)
3. Condensation - lack of ventilation causing interstitial condensation
4. Water penetration form other sources - parapets, copings, DPCs, rooflights, openings, gutters, service pipes in roof voids, uninsulated refrigerant pipework etc.

Question 284

What methods would you use to find flat roof faults?

Answer 284

1. Visual inspection
2. Dye
3. Electronic Leak Detection (ELD)
4. Infra-Red Thermography
5. Endoscopes

Question 285

What would you look for when visually inspecting a leaking flat roof?

Answer 285

1. Obvious signs of water ingress externally
2. Measurement from internal signs of moisture to find the external source (although source of ingress may not be directly above internal signs of moisture - water can run between layers or in voids beneath the covering)
3. Detailing (cappings, drips, upstands etc.)
4. Poor falls leading to ponding
5. Visible signs of movement in the roof / deflection of roof members
6. Leaking services (water tanks, pipework etc.)

Question 286

Explain how electronic leak detection (ELD) might be used to detect a leak.

Answer 286

1. A weak electrical field is created on the dampened surface
2. Any current that ‘earths’ into the building changes the nature of the field locally, pinpointing the penetration (or showing when water penetration is not caused by a roof leak)

Question 287

Explain how thermography might be used to detect a leak.

Answer 287

1. Shows the overall thermal continuity of the roof, highlighting areas of heat loss from poor insulation (possibly as a result of being wet) and cold bridging
2. Useful when source of ingress may not correspond to signs of moisture internally

Question 288

What is ponding and why is it problematic?

Answer 288

Collection of water on a flat roof, which can cause:

1. Stress on the roof covering - water will absorb heat , increasing the surface temperature of the covering which can lead to cracking (especially of built-up felt) - continual freeze/thaw process could also have a detrimental effect
2. Water can attract insects and larvae which in turn may attract birds whose pecking can damage fabric-based coverings
3. Any leak in the ‘pond’ area will result in a greater amount of water penetration than just normal rain
4. Severe cases may affect the structural integrity of the roof

Question 289

What type of common defects with felt flat roofs are you aware of?

Answer 289

1. Ponding
2. Splits, tears and cracks
3. Blistering
4. Lifting of lap joints
5. Failure of solar reflective paint
6. Water ingress where pipes/vents pass through roof
7. Falling away skirting upstands at abutments

Question 290

What type of common defects with asphalt flat roofs are you aware of?

Answer 290

1. Ponding
2. Superficial crazing
3. Distortion (rippling, creeping, sagging)
4. Cracking that penetrates thickness
5. Blistering
6. Chemical damage

Question 291

What are the common defects associated with sheet lead coverings?

Answer 291

1. Ponding
2. Splits and cracks
3. Dents, punctures and rips
4. Lifting around edges
5. Corrosion shown by white streaks
6. Pitting and corrosion of surface
7. Pitting and corrosion of underside

Question 292

How would you advise your client on remediation for the failure of a flat roof?

Answer 292

1. Patch repair / re-cover depending on extent of damage
2. Rebond lifting laps using hot bitumen
3. Provide expansion joints where thermal/structural movement of substrate is involved
4. Clean / prime surface and reapply solar reflective paint if failed
5. Install layer of 10mm light-coloured stone chippings to reduce solar damage
6. Remake inadequate skirtings to minimum height of 150mm above finished roof level
7. Eradicate condensation (insulation, vapour barrier, ventilation etc.)

Question 293

What guidance is available in relation to flat roof coverings?

Answer 293

RICS Information Paper ‘Flat Roof Coverings’ (2011) contains guidance in the common defects associated with different flat roof coverings and how to remediate them

Question 294

Name five deleterious materials

Answer 294

• Asbestos and Asbestos Containing Materials - Woodwool - Lead and lead paints - High Alumia Cement - Silica dust

Question 295

Define what is meant by deleterious materials?

Answer 295

Deleterious materials are materials that are harmful, either harmful to health or that cause failure within buildings. All materials could be deleterious in the wrong circumstance

Question 296

What is nickel sulphide reaction?

Answer 296

Nickel sulphide reaction is a spontaneous fracture of toughened glass as a result of impurities in the molten glass. The fracture is caused by nickel expansion. It can be combated by heat soak testing the glass prior to installations

Question 297

What is urea formaldehyde foam?

Answer 297

Urea formaldehyde foam is a foam product that was used for cavity wall insulation in the 70s and 80s. There is evidence that it can be carcinogenic, it is banned as a toxic substance

Question 298

What is the risk associated with lead in construction, and where would you expect to find it?

Answer 298

Lead can be poisonous if ingested. It was used for pipework and solder joints, and would contaminate water. It was also used in paint, and care should be taken as it can be inhaled when rubbing down. Paint can be tested for lead content

Question 299

What is calcium silicate brickwork?

Answer 299

Calcium silicate brick are made from a combination of lime, sand and crushed flint. Due to their make up they have a tendency to shrink after construction and are susceptible to movement when wetting (often diagonal cracking). Sufficient movements joints - every 7-9 meters are required for construction with calcium silicate brickwork

Question 300

What is sick building syndrome?

Answer 300

Sick building syndrome is a condition where building occupants experience symptoms similar to that of a cold - headache, lethargy, scratchy throat - while in a building, but that disappear after leaving. Cause is unconfirmed, but it thought to be linked to light level, air conditioning, fresh air etc.

Question 301

What is a woodwool slab, and when would its use be considered dangerous?

Answer 301

Woodwool slabs are bonded softwood shavings are cement, compressed to create boards. They are commonly used as permanent formwork, and also as insulation. When used as formwork, the materials can create void within the concrete, creating honeycombing to concrete, therefore reducing the fire and structural properties

Question 302

What is high alumia cement?

Answer 302

HAC is an concrete additive that was used in the 50s and 60s, and was banned in the 1970s. It caused concrete that hardened faster, however it was found that over time is looses strength, particularly in wet environments. Can be suspected in pre-cast concrete members from the right time

Question 303

What is silica dust?

Answer 303

Silica dust is produced when working with a number of materials, including stone and clay when cutting. It can be dangerous to health if inhaled, and therefore measures should be taken to prevent dust (wetting/breathing apparatus)

Question 304

Name five deleterious materials

Answer 304

• Asbestos and Asbestos Containing Materials - Woodwool - Lead and lead paints - High Alumia Cement - Silica dust

Question 305

Define what is meant by deleterious materials?

Answer 305

Deleterious materials are materials that are harmful, either harmful to health or that cause failure within buildings. All materials could be deleterious in the wrong circumstance

Question 306

What is nickel sulphide reaction?

Answer 306

Nickel sulphide reaction is a spontaneous fracture of toughened glass as a result of impurities in the molten glass. The fracture is caused by nickel expansion. It can be combated by heat soak testing the glass prior to installations

Question 307

What is urea formaldehyde foam?

Answer 307

Urea formaldehyde foam is a foam product that was used for cavity wall insulation in the 70s and 80s. There is evidence that it can be carcinogenic, it is banned as a toxic substance

Question 308

What is the risk associated with lead in construction, and where would you expect to find it?

Answer 308

Lead can be poisonous if ingested. It was used for pipework and solder joints, and would contaminate water. It was also used in paint, and care should be taken as it can be inhaled when rubbing down. Paint can be tested for lead content

Question 309

What is calcium silicate brickwork?

Answer 309

Calcium silicate brick are made from a combination of lime, sand and crushed flint. Due to their make up they have a tendency to shrink after construction and are susceptible to movement when wetting (often diagonal cracking). Sufficient movements joints - every 7-9 meters are required for construction with calcium silicate brickwork

Question 310

What is sick building syndrome?

Answer 310

Sick building syndrome is a condition where building occupants experience symptoms similar to that of a cold - headache, lethargy, scratchy throat - while in a building, but that disappear after leaving. Cause is unconfirmed, but it thought to be linked to light level, air conditioning, fresh air etc.

Question 311

What is a woodwool slab, and when would its use be considered dangerous?

Answer 311

Woodwool slabs are bonded softwood shavings are cement, compressed to create boards. They are commonly used as permanent formwork, and also as insulation. When used as formwork, the materials can create void within the concrete, creating honeycombing to concrete, therefore reducing the fire and structural properties

Question 312

What is high alumia cement?

Answer 312

HAC is an concrete additive that was used in the 50s and 60s, and was banned in the 1970s. It caused concrete that hardened faster, however it was found that over time is looses strength, particularly in wet environments. Can be suspected in pre-cast concrete members from the right time

Question 313

What is silica dust?

Answer 313

Silica dust is produced when working with a number of materials, including stone and clay when cutting. It can be dangerous to health if inhaled, and therefore measures should be taken to prevent dust (wetting/breathing apparatus)

Question 314

What is Radon?

Answer 314

1. A colourless, odourless naturalyl occuring radioactive gas formed by the radioactive decay of the small amounts of uranium that occur naturally in all rocks and soils.
2. When radon gas enters the body, it exposes the lungs to small amounts of radiation. In small quantities, experts say this is harmless. However, in persistent exposures or larger quantities, radon can damage the cells of the lining of the lungs, increasing a person’s chance of developing lung cancer

Question 315

How would you reduce radon risk

Answer 315

1. Check radon maps
2. Measure over a period of time
3. Ventilation
4. Special gas proof membrane
5. Seek advice from a specialist

Question 316

Name 10 defects you would commonly find in a Georgian building.

Answer 316

1. Leaning chimneys
2. Overloading of roof due to change of materials (e.g. concrete tiles)
3. Removal of chimney breasts but not the stack
4. Blocked internal gutters
5. Brick walls prone to distortion due to lack of restraint at each floor level
6. Damp penetration through solid walls
7. Rotting timber joists that are built into external wall
8. Dry rot caused by poor cross-ventilation in narrow, long terraces
9. Shallow foundations causing dropping of central spine wall
10. Damp basements

Question 317

Name 10 defects you would commonly find in a Victorian building.

Answer 317

1. Leaning chimneys
2. Overloading of roof due to change of materials (e.g. concrete tiles)
3. Removal of chimney breasts but not the stack
4. Damp penetration through solid walls
5. Rotting timber joists that are built into external wall
6. Wall tie failure (if a cavity wall, particularly in black ash mortar)
7. Differential settlement of bay windows (little to no foundations)
8. Rising damp caused by lack, failure or bridging of DPC
9. Blocked air vents to ground floors, causing dry rot
10. Lead water pipes

Question 318

What defects would you expect to see in properties built between 1945-1970?

Answer 318

???

Question 319

Name 10 defects you would commonly find in a 1960s high-rise office block.

Answer 319

1. Flat roof problems
2. Parapet walls (loose copings)
3. Poor workmanship (inadequate re-bar cover)
4. Concrete defects - carbonation/chloride attack
5. Deleterious material - asbestos/HAC/brick slips
6. Cold bridges
7. Overloading of floors (filing cabinets)
8. Poor access and egress - narrow staircases, change in levels
9. Brittle metal windows
10. Corrosion of steel fixings

Question 320

A 1960s building has misaligned concrete panels - what are the possible causes and what investigates would you undertake?

Answer 320

???

Question 321

Name some common defects in a 1970s building.

Answer 321

???

Question 322

In a steel frame brick wall 1950s building, what particular defects would you be looking for?

Answer 322

???

Question 323

What defects would you commonly find in a CLASP building?

Answer 323

1. Penetrating damp through failed joints
2. Poor gaskets around windows
3. Pitched fibre drainage deformed, collapsed or become blocked
4. Cold bridges
5. Excessive solar gain to some elevations
6. Poor U-values of the building fabric
7. Asbestos - boarding around steel members/ceiling tiles/pipe lagging/floor coverings etc
8. Rotting of timber floors and roofs in earlier Marks

Question 324

What is cold bridging?

Answer 324

• Cold bridging occurs in localised spots where the nature of the construction allows heat to escape through the structure at a higher rate than normal
• This creates situations where there may be quite low internal surface temperatures which can encourage patches of local condensation

Question 325

Where would you expect to find cold bridging?

Answer 325

1. Concrete lintels crossing cavity walls
2. Uninsulated box-section lintels
3. Jambs and sills with returned blockwork inner leaf
4. Floor slabs lacking insulated upstands

Question 326

What is radon and why is it a problem?

Answer 326

1. Natural radioactive gas that cannot be seen, smelt, heard or felt
2. Emanates from minute amounts of uranium that occur naturally in all rocks and soils
3. Most radon disperses harmlessly into the air outside but some will collect in spaces under or within buildings
4. Exposure to high levels of radon can increase the risk of developing lung cancer

Question 327

In which areas of the UK are you most likely to come across radon?

Answer 327

Some parts of the country (e.g. the West Country, Derbyshire and Northamptonshire) have higher levels than elsewhere

Question 328

Other than radon, what other ground gases are problematic and why?

Answer 328

1. Methane - explosive in air at concentrations between 5-15%, generated by the anaerobic (absence of oxygen) degradation of organic material
2. Carbon dioxide - dlassed as highly toxic - can result in headaches and shortness of breath

Question 329

Name some legislation that detail requirements when considering ground gases.

Answer 329

1. Town and Country Planning Act 1990 - potential for contamination and risk from landfill and ground gases must be considered during development
2. Environmental Protection Act 1990 - where potential for significant harm exists to a development (either existing or proposed), the local authority can enforce appropriate remediation or mitigation
3. Building Regulations Approved Document C - where there is a potential risk, further investigation is required to determine whether gas measures are required and what level of protection is necessary

Question 330

How would you find out whether radon gas was a problem in a particular area?

Answer 330

1. Desk-based study of the history and geology of the area and any additional information such as mining or landfill activities
2. Public Health England (formerly the Health Protection Agency) and the British Geological Survey publishes maps of radon affected areas across and sets threshold levels for both commercial and residential properties
3. Maps can also be found in BRE Report BR 211 (Radon)

Question 331

What steps would you need to take if your client wanted to build in an area where radon gas was present?

Answer 331

Passive (basic protection):

• Usually achieved by increasing the airtightness of the DPM and extending it across the external leaf of brickwork
• Can also improve ventilation under suspended timber and concrete floors by installing airbricks

Active:

• Used where risks are higher
• Sump pumps connected to a fan in order to extract
• May be required if protective membrane is damaged

Alarm Systems:

• Designed to trigger when gas concentration reach a certain level

Question 332

What is Japanese Knotweed and when was it introduced?

Answer 332

• A hardy bamboo-like plant that grows quickly and strongly
• Introduced to the UK in the mid-19th Century

Question 333

What legislative controls exist for Japanese Knotweed?

Answer 333

1. Banned in the Wildlife and Countryside Act 1981, making it an offence to plant or cause the growth of Japanese Knotweed
2. The Environmental Protection Act 1990 also contains a number of legal provisions, designating contaminated soil as controlled waste, meaning only properly licensed organisations can remove it

Question 334

What problems are associated with Japanese Knotweed?

Answer 334

• Japanese Knotweed is extremely invasive and can cause serious damage to:
  
  • Drains and buried services - can exploit cracks and gaps in pipework
  • Patios, paths and drives - can grow between joints
  • Boundary and retaining walls - can undermine walls with shallow foundations
  • Outbuildings - can overwhelm lightweight structures (sheds, garages etc.)
• There are claims that damage to building foundations can also occur, however this is rare
• The plant can remain dormant, so eradication may be difficult to guarantee

Question 335

How would you identify Japanese Knotweed?

Answer 335

RICS Information Paper ‘Japanese Knotweed’ - Appendix C contains an identification chart throughout the seasons, namely:

1. Hollow stems within distinct raised nodes (like bamboo) which develop purple speckles
2. Can reach heights up to 3-4m in its growing season (summer) and grow in dense clumps (aka ‘stands’)
3. Leaves are lush green and flat heart/shield shaped, approx. 70-140mm long and 50-120mm wide
4. Flowers are small, creamy white spikes of length approx. 60-150mm

Question 336

How would you remediate the problems caused by Japanese Knotweed?

Answer 336

Specialist contractor required, who may specify:

1. Excavation/removal of plant and roots - can extend 3m down and 7m across
2. Biological control - use of ‘pests’ that attack and control the plant
3. Chemical control - use of specialist herbicides (can take up to 3 years to completely eradicate)
4. On-site burial - may require a specialist root barrier membrane

Question 337

What is Giant Hogweed and when was it introduced?

Answer 337

Introduced as an ornamental plant in the 1890s

Question 338

What legislative controls exist for Giant Hogweed?

Answer 338

Banned in the Wildlife and Countryside Act 1981, making it an offence to plant or cause the growth of Giant Hogweed

Question 339

What are the problems with Giant Hogweed?

Answer 339

1. Contact with its sap (present inside the stem and on the hairs that cover the leaves and stem) makes skin highly sensitive to ultra-violet light
2. No discomfort is experienced until around 15-20 hours after exposure, where burns develop that quickly turn into large watery blisters, which recede and leave scars that remain highly photosensitive for years or even life
3. Can cause blindness if contact is made with the eyes
4. Suggestion that toxins within the sap are carcinogenic and could cause cancer or result in malformations of unborn foetuses in pregnant women

Question 340

How would you identify Giant Hogweed?

Answer 340

1. Often grows between 3-5m over four years
2. Stems - hollow, purple (or green speckled with purple) and covered in fine hairs
3. Leaves - dark green, coarsely toothed, hairy like stems, measuring up to 2m across
4. Flowers - numerous small and white flowers, emerge in mid to late summer on top of the stems in umbrella-like clusters

Question 341

How would you remediate the problems caused by Giant Hogweed?

Answer 341

Specialist contractor required, who may specify:

1. Herbicidal treatment - effective, but must be undertaken regularly over several years (seeds can remain dormant for up to 7 years)
2. Dig up and dispose as controlled waste (may need to excavate up to 4m around plants due to seed spread)
3. Combination of both

Question 342

What should you do if you come into contact with Giant Hogweed?

Answer 342

1. Wash immediately with soapy water any area of skin that comes into contact
2. If contact is made with the eyes, flush immediately with water
3. Cover affected areas and keep out of sunlight for at least 48 hours
4. Seek medical advice

Question 343

What is Regent Street Disease and how is it caused?

Answer 343

1. Also known as steel frame corrosion
2. Affects buildings constructed circa 1905 onwards (i.e. when steel became a popular construction material)
3. Load-bearing frames of steel were clad with stone, brickwork or terracotta (notched around the steel frame) with the voids between the two filled with low grade mortar
4. Mortar compaction was poor and often contained lumps of brick or stone, which increased the number of voids
5. Inevitable shrinkage cracks meant that water and oxygen could penetrate the fabric, facilitating corrosion of the steel

Question 344

What problems are associated with Regent Street Disease?

Answer 344

1. Corroded steel expands at least four times its original volume
2. Due to the infilled voids around the steel, expansion inevitably results in cracking of façade, allowing more water to penetrate
3. In extreme cases, loss of support can result from horizontal cracking, causing collapse of pieces of stone or brick

Question 345

How would you identify Regent Street Disease?

Answer 345

1. Vertical or horizontal cracking reflecting the location of the steel frame
2. Physically opening up the façade is an option, although disruptive and may require consent if listed
3. NDT (non-destructive testing) systems are also available to determine the extent of the corrosion or prognosis for future deterioration

Question 346

What steps would you recommend to remediate Regent Street Disease?

Answer 346

1. Expose, clean and protect the steel - expensive and disruptive
2. Provide a corrosion barrier to the steel and then create a void around it so if further corrosion does occur, it will not result in cracking
3. Cathodic Protection Systems

Question 347

Give an example of an interesting pathology issue you have had to deal with?

Answer 347

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Question 348

What are the common causes of spalled brickwork?

Answer 348

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Question 349

What is frost action?

Answer 349

1. Caused by a combination of excessive wet brickwork and freezing temperatures
2. When water turns to ice, it expands
3. The repeated freeze-thaw cycle produces stresses on the brick causing it to spall (the face flaking/crumbling off)

Question 350

Why may the use of strong mortars exacerbate the problem of frost action?

Answer 350

Strong mortar tends to suffer from shrinkage cracks which will allow water to penetrate, and because strong mortars are not as ‘breathable’, it will be difficult for the water to evaporate

Question 351

A white powdery substance has appeared on the surface of some new brickwork. What might it be and what can you do about it?

Answer 351

Efflorescence:

• May only be problematic in cases of rising damp, as the crystals can sometimes block pores in brickwork, thus preventing evaporation and driving damp higher up the wall
• Can be brushed off if appearance is causing a concern

Question 352

You notice the gable wall of an end terrace property is bowing - what could be the reason for this?

Answer 352

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Question 353

What is ‘bookend effect’ and how is it caused?

Answer 353

1. Bulging of a flank wall due to lack of lateral restraint, often due to floor joists running parallel with the wall and/or lack of buttresses
2. Common in buildings built before the mid-1980s however can occur later if alteration are undertaken (e.g. removing a chimney breast that was previously acting as a buttress, removing an internal perpendicular wall or even creating an opening in such a wall)
3. Problem often accentuated by the presence of the staircase adjacent to the flank wall

Question 354

How can ‘bookend effect’ be remediated?

Answer 354

Remedial works involves mechanical insertion of metal tie rods along the length of wall

Question 355

What problems are likely to be associated by rendering over external brickwork?

Answer 355

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Question 356

What issues may there be with a partial fill cavity wall in respect of workmanship?

Answer 356

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Question 357

What is snapped header defect and how is it caused?

Answer 357

1. Often used to save money (facing bricks were much more expensive than commons and therefore ‘snapping’ the brick in two could provide two facing brick heads)
2. Header bricks were traditionally used to tie solid walls together
3. Snapped headers cause defects as there is a lack of tying-in between the inner and outer face

Question 358

How can you tell when timber structural members are deflected or bowed?

Answer 358

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Question 359

A hall floor is re-laid but the screed fails - what are the possible reasons for this?

Answer 359

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Question 360

How can stonework be repaired?

Answer 360

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Question 361

What causes rainwater goods to become defective?

Answer 361

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Question 362

How would you determine if a drainage run was free from and breaks or blockages?

Answer 362

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Question 363

What action might be necessary to free up sliding sash windows that are sticking?

Answer 363

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Question 364

What defects would you associate with portal framed warehouse units?

Answer 364

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Question 365

What is cut edge corrosion?

Answer 365

Occurs when the protective coating on metal sheeting peels back at lap joints (usually where it has been cut), exposing the base metal to risk of corrosion, which can cause section loss

Question 366

How do you repair cut edge corrosion?

Answer 366

1. Remedial work involves cleaning the effective area, removing the defective coating (e.g. by chemical stripping) and treating the sheet lap with a silicone based paint
2. Current guidance states cut edges should be painted before installation, however this is often neglected

Question 367

What problems can arise from using two different metals next to each other?

Answer 367

1. Galvanic corrosion occurs when two different metals are in contact in a corrosive environment: one of the metals experiences an accelerated corrosion rate.
2. The contacting metals form a bimetallic couple because of their different affinities (or attraction) for electrons.

Question 368

According to BRE, what buildings are at risk of cavity wall tie failure?

Answer 368

Building cavity ties built before 1981, when the standards on cavity wall ties increased. Also, until 1970s wall ties were a twisted butterfly type

Question 369

What factors will affect wall tie corrosion?

Answer 369

• Humidity (interstitial condensation) - Rain fall (penetrating damp) - Chlorides - Sulphar dioxide - Changes in PH (carbonation, carbonic acid)

Question 370

What equipment would you use to detect the location of wall ties?

Answer 370

• Wall tie detectors - hand held metal detectors - Borescope (to see within the cavity)

Question 371

What is the typical correct spacing for wall ties within a cavity wall?

Answer 371

• Every 6th course - 900mm centres horizontally - 300mm away from windows/ openings

Question 372

What are the symptoms of cavity wall tie failure?

Answer 372

• Bowed or cracked brickwork - Cracking that follows lines of wall ties (every 450mm horizontally) - Random bulges - Rust staining

Question 373

How can wall tie failure be rectified?

Answer 373

Removal of old ties, then replace with new using resin grout and mechanically fixed wall ties (polyurethane foam can be injected into the cavity to form a bond between the two leafs), and then repairs to the external walls

Question 374

What common defects are found in curtain walling?

Answer 374

• Rarely ever watertight, therefore a mechanism for draining water is required for when wind driven rain gets through seals - Fixings need to be accessible to regularly inspected - Fixings need to be able to accommodate movement - Sealants and gaskets fail for a number of reasons; adhesion failure (poor preparation), cohesive failure (poor joint design), delamination, reversion (turns back to a fluid)

Question 375

What consideration must be given to stone cladding panels in their design?

Answer 375

Support! They need to be supported by gravity where lower panels bear the wight of the upper one, or they need to be individually fixed with appropriate mechanical restraint

Question 376

What issue would you expect with marble cladding?

Answer 376

Thin marble sections can expand in any direction, which is very difficult to accommodate in design. The only available remedy is to remove and clad with a different material

Question 377

What issue would you expect with limestone cladding?

Answer 377

Limestone is durable, but it is damaged by chemical reactions with the atmosphere. Sulphur deposits on the surface form a crust, which can fall

Question 378

What defect is an issue with metal framed cladding systems?

Answer 378

Condensation can cause corrosion to the frame. To avoid this, the metal frame should be kept at a higher temperature (above the dew point) to the glazing, so that any condensation forms on the glass not the frame

Question 379

What issues would you expect to find with low level pressure plates on cladding?

Answer 379

Low level pressure plates can be easily dislodged by a vandal. Repeated renewal of can lead to weakening of the fixings. It may be necessary to re-drill and re-secure a plate to give sufficient pressure

Question 380

What issues would you expect with gaskets?

Answer 380

The lip of a gasket must exert pressure on the glass to remain firmly fixed in place. Gaskets are normally made of elastomeric materials (like butyl rubber) and they can degrade over time, including shrinking or becoming brittle

Question 381

What issues would you expect with gaskets?

Answer 381

The lip of a gasket must exert pressure on the glass to remain firmly fixed in place. Gaskets are normally made of elastomeric materials (like butyl rubber) and they can degrade over time, including shrinking or becoming brittle

Question 382

What issues would you expect to find with low level pressure plates on cladding?

Answer 382

Low level pressure plates can be easily dislodged by a vandal. Repeated renewal of can lead to weakening of the fixings. It may be necessary to re-drill and re-secure a plate to give sufficient pressure

Question 383

What defect is an issue with metal framed cladding systems?

Answer 383

Condensation can cause corrosion to the frame. To avoid this, the metal frame should be kept at a higher temperature (above the dew point) to the glazing, so that any condensation forms on the glass not the frame

Question 384

What issue would you expect with limestone cladding?

Answer 384

Limestone is durable, but it is damaged by chemical reactions with the atmosphere. Sulphur deposits on the surface form a crust, which can fall

Question 385

What issue would you expect with marble cladding?

Answer 385

Thin marble sections can expand in any direction, which is very difficult to accommodate in design. The only available remedy is to remove and clad with a different material

Question 386

What consideration must be given to stone cladding panels in their design?

Answer 386

Support! They need to be supported by gravity where lower panels bear the wight of the upper one, or they need to be individually fixed with appropriate mechanical restraint

Question 387

What common defects are found in curtain walling?

Answer 387

• Rarely ever watertight, therefore a mechanism for draining water is required for when wind driven rain gets through seals - Fixings need to be accessible to regularly inspected - Fixings need to be able to accommodate movement - Sealants and gaskets fail for a number of reasons; adhesion failure (poor preparation), cohesive failure (poor joint design), delamination, reversion (turns back to a fluid)

Question 388

What is a deleterious material?

Answer 388

Deleterious materials are those that are either dangerous to health, commonly cause failures in buildings or are environmentally damaging

Question 389

Name 10 deleterious materials.

Answer 389

1. Asbestos
2. HAC Concrete
3. Calcium Silicate Bricks
4. Lead
5. Woodwool Slabs
6. Hollow Clay Pot Floors
7. Brick Slips
8. Clinker Concrete
9. Chlorofluorocarbons
10. Machine Made Mineral Fibre

Question 390

What deleterious materials might you find in a 1960s office block?

Answer 390

1. Asbestos
2. HAC Concrete
3. Woodwool slabs
4. Brick slips

Question 391

What is asbestos?

Answer 391

• Asbestos is the generic term for several mineral silicates occurring naturally in fibrous form
• It was extensively used as a building material in the UK from the 1950s through to the mid-1980s

Question 392

What guidance is available in relation to asbestos?

Answer 392

1. RICS GN ‘Asbestos and its implications for surveyors and their clients’ (3rd ed. 2011)
2. HSE website
3. HSE Approved Code of Practice - Managing and Working with Asbestos

Question 393

Why is asbestos dangerous?

Answer 393

When asbestos fibres are inhaled, they can cause serious diseases, which often take a long time to develop but once diagnosed it is usually too late to do anything:

1. Asbestosis - permanent scaring of lung tissue (fibrosis), causes lungs to shrink, stiffen and lose elasticity
2. Lung cancer
3. Mesothelioma - cancer of the lining of the lung or, in rare cases, the abdominal cavity (crocidolite only)
4. Pleural thickening - lining of the lung (pleura) thickens and swells, causing shortness of breath and discomfort in the chest

Question 394

What are the different types of asbestos?

Answer 394

1. Chrysotile (white) - accounts for 90% used commercially
2. Crocidolite (blue) - accounts for 6% used commercially
3. Amosite (brown) - accounts for 3% used commercially

Question 395

Which is considered the worst type of asbestos?

Answer 395

Crocidolite (blue)

Question 396

When was asbestos banned?

Answer 396

1. 1970 - voluntary ban of crocidolite
2. 1985 - crocidolite and amosite banned by law
3. 1999 - chrysotile banned
4. 2000 - everything else and most second-hand supply (except for very high performance materials) banned

Question 397

Where might you find asbestos in buildings?

Answer 397

1. Sprayed coatings (e.g. ceilings, walls, beams, columns)
2. Asbestos cement water tank
3. Loose fill insulation
4. Lagging on boilers and pipes
5. AIB (Asbestos Insulating Board) ceiling tiles, partition walls, panels in fire doors, around boilers, behind fuse board, bath panel, behind fire, interior/exterior window panels
6. Toilet seat and cistern
7. Rope seals, gaskets and paper
8. Vinyl floor tiles
9. Textiles (e.g. fire blankets)
10. Textured decorating coatings (e.g. artex)
11. Asbestos cement panels (e.g. roof covering, wall cladding)
12. Asbestos cement gutters, downpipes, soffits, flues
13. Roofing felt

Question 398

Where might you find white asbestos?

Answer 398

1. Cement tiles
2. Floor tiles
3. Gaskets

Question 399

Where might you find blue asbestos?

Answer 399

1. Sprayed coatings (limpet)
2. Insulation
3. Old textiles

Question 400

Where might you find brown asbestos?

Answer 400

1. Wall panels
2. Ceiling tiles
3. Pipe insulation

Question 401

What legislative controls govern asbestos?

Answer 401

• Health and Safety at Work etc. Act 1974:
  
  • Enabling act for asbestos legislation
  • Failure to comply is a criminal offence
• Control of Asbestos Regulations (CAR) 2012

Question 402

What are the requirements of the current asbestos regulations?

Answer 402

Places a duty on the owner or person/organisation that has responsibility for the maintenance or repair of non-domestic premises (i.e. those in control of the premises):

1. If existing ACMs are in a good condition and not likely to be damaged, they may remain in place, their condition monitored and managed to ensure they are not disturbed
2. Duty holders have a ‘duty to manage’ asbestos and protect anyone within the building from the risks of exposure
3. If any building or maintenance works are to be done, duty holders must ensure asbestos is identified, its condition and risks assessed and manage and control these risks
4. Certain work with asbestos is to be carried out by licensed contractors
5. Certain work with asbestos can be carried out by non-licensed contractors, but must still have effective controls
6. The control limit is 0.1 fibres per cubic centimeter (averaged over 4 hours)
7. Training is mandatory for anyone liable to be exposed to asbestos fibres at work

Question 403

What changes have been made to the asbestos regulations in 2012?

Answer 403

1. Some non-licensed work needs to be notified to the relevant enforcing authority
2. By April 2015, ensure notifiable non-licensed workers have a medical examination at least once every 3 years
3. Keep a record of notifiable non-licensed work, e.g. the type and duration of work done with asbestos along with copies of all medical records, for 40 years

Question 404

What is the significance of the asbestos control limit?

Answer 404

• This is the trigger for which regulation 18(2) ‘Designated Areas’ applies, where ‘respirator zones’ must be established, to which access is restricted to ‘competent’ persons and suitable respirators must be worn at all times
• If the control limit is not likely to be exceeded, then it is one of a number of circumstances set out in regulation 3(2) for which specific regulatory requirements may not necessarily apply

Question 405

Explain to your client what his responsibilities are as a duty holder of premises with regards to asbestos under the current regulations?

Answer 405

Duty to manage:

1. Take reasonable steps to determine the location of likely ACMs
2. Presume materials contain asbestos unless strong evidence otherwise
3. Make ACM location and condition record and keep up-to-date
4. Risk assess the likelihood of anyone being exposed to fibres
5. Prepare a plan setting out how risks are to be managed
6. Take necessary steps to put the plan into action
7. Review and monitor the plan periodically
8. Provide awareness training to anyone working on ACMs

Question 406

Name the types of asbestos survey and when they are required.

Answer 406

Management Survey:

1. Required to manage ACMs during the normal occupation and use of premises
2. Locates ACMs that could be disturbed by normal activities, maintenance or installing new equipment
3. Involves minor intrusions to make a Materials Assessment, which shows the ability of the ACM to release fibres if disturbed
4. Guides the client in prioritising any remedial work

Refurbishment / Demolition Survey

1. Required where the premises, or part of it, is being refurbished or demolished
2. Locates all ACMs before works begin
3. Does not need to record ACM condition
4. Involves destructive inspection (areas surveyed must be vacated and ‘fit for reoccupation’ after survey)

Question 407

Does asbestos have to be removed from a building and why?

Answer 407

Asbestos should not be removed unnecessarily as doing so could be more dangerous than leaving it in place and managing it

Question 408

What remedial works can be undertaken where materials cannot be removed in their entirety?

Answer 408

Asbestos can be encapsulated, e.g. work to enclose or seal ACMs in good condition

Question 409

What are the statutory requirements for the removal of materials containing asbestos?

Answer 409

1. If existing ACMs are in a good condition and not likely to be damaged, they may remain in place, their condition monitored and managed to ensure they are not disturbed
2. If ACMs are likely to be disturbed, then depending on the type, condition and extent of works being carried out to the ACM will depend on the category of work required

Question 410

What are the different asbestos works categories?

Answer 410

1. Licensed
2. Non-licensed
3. Notifiable non-licensed

Question 411

If you needed to remove asbestos, how would you determine which works category the work would fall under?

Answer 411

The HSE has produced a decision flowchart and illustrative diagram to help determine which category the work falls under

Question 412

What are the general requirements for licensed asbestos removal works?

Answer 412

1. Requires a licensed contractor to undertake the works
2. Higher-risk work
3. All licensable work must be notified to the appropriate enforcing authority at least 14 days before works start

Question 413

What are the general requirements for non-licensed asbestos removal works?

Answer 413

1. Must meet certain requirements within CAR 2012 to be exempt from being licensable
2. Generally involves work that is sporadic and of low intensity
3. Does not require a licensed contractor to undertake the works but work must still be:

• Risk assessed
• Carried out with appropriate controls in place (provided for by the various HSE equipment and method sheets)
• Undertaken by those carrying the correct level of information, instruction and training

Question 414

What are the general requirements for notifiable non-licensed asbestos removal works?

Answer 414

Requires employers to:

1. Notify the relevant enforcing authority of the works
2. Designate areas where the work is being done (marked with suitable warning notices, restricted to those carrying out the work, no food or drink within designated areas)
3. Ensure medical examinations are carried out at least every 3 years whilst continuing to undertake such work
4. Maintain registers of work (health records), including nature and duration of works and dates of medical examinations (must be kept for at least 40 years)
5. Still requires a risk assessment, appropriate controls and the correct level of information, instruction and training as per non-licensed work

Question 415

Give an example of work that may be included under each asbestos work category.

Answer 415

1. Licensed - removing sprayed coatings, disturbance of pipe lagging or work on asbestos insulation board (AIB) where the risk assessment indicates it will not be of short duration
2. Non-licensed - work involving asbestos cement products (e.g. roof sheeting, tiles and rainwater goods), short duration work to AIB or encapsulation of ACMs in good condition
3. Notifiable non-licensed - asbestos cement products that have been/will be substantially broken up

Question 416

Define what asbestos works of a ‘short duration’ means.

Answer 416

Defined as no more than 2 hours in any 7 day period and no one person works for more than one hour in that 2 hour period

Question 417

Do licensed contractors still need to notify asbestos works classed as notifiable non-licensed work?

Answer 417

Yes

Question 418

Is the asbestos content of AIB and asbestos cement sheet similar?

Answer 418

No, AIB is considered to be a higher risk material than asbestos cement sheet

Question 419

If asbestos is identified during a refurbishment project, what actions would you take as Contract Administrator?

Answer 419

1. Stop work immediately
2. Isolate anyone significantly exposed
3. All put on RPE (Respiratory Protective Equipment)
4. Keep everyone out of the area
5. Put up warning signs
6. Engage with an approved contractor to clear the area and decontaminate anyone exposed
7. Wipe down any dust on clothes with damp rags
8. Dispose of rags and contaminated clothes as asbestos waste
9. Keep a record of the event

Question 420

What is HAC concrete?

Answer 420

High Alumina Cement Concrete:

1. UK manufacture began in 1925 to provide concrete that would resist chemical attack, particularly in marine applications
2. The cement developed high early strength, although its relatively high cost prevented extensive use

Question 421

Where would you find HAC concrete?

Answer 421

During the late 1950s and 1960s, the main use of HAC was for the manufacture of precast, prestressed components (‘X’ and ‘I’ beams for floor or roof decks) that could be manufactured quickly to offset the high cost

Question 422

Why is HAC concrete problematic?

Answer 422

1. HAC undergoes a mineralogical change known as conversion, where the concrete increases in porosity, thus resulting in a loss of strength and a reduction in resistance to chemical attack
2. The higher the temperature during the casting of the concrete, the quicker conversion takes place
3. Highly converted HAC concrete is vulnerable to acid, alkaline and sulphate attack, which requires water as well as the chemicals to be present persistently over a long period of time at normal temperatures
4. Like ordinary concrete products, HAC is also affected by carbonation

Question 423

What type of environment does HAC concrete not like particularly?

Answer 423

In a warm and moist environment, a serious reaction known as alkaline hydrolosis may occur (resulting in a severe loss of strength and integrity), where high alkali levels may be present from the use of certain types of aggregate or where alkalis may have ingressed from plasters, screeds or woodwool slabs

Question 424

When was HAC concrete banned in the UK?

Answer 424

Banned from structural use in 1976 following the collapse of a swimming pool roof and several school roofs in the early 1970s, although new uses are now becoming established under the name Calcium Aluminate Cement (CAC)

Question 425

Why may it be contentious to label HAC concrete as a deleterious material?

Answer 425

• On no occasion has weakening of the concrete due to conversion been the sole cause of failure - in the case of the original historic failures, manufacturing faults were eventually discovered (e.g. high water content during mixing and high temperatures during curing)
• There has been no recorded instances of a failure of a floor in this country

Question 426

How would you identify HAC concrete?

Answer 426

• Visual inspection:
  
  • Chemical attack is usually very localised and the concrete typically degenerates to a chocolate brown colour and becomes very friable, often due to sulphate attack
  • Alkaline hydrolosis is characterised by white powdery deposits and a severe loss of strength and integrity
• Rapid chemical testing - usually sufficient to distinguish HAC from other elements, but can give misleading results if not used with care (e.g. carbonated concrete or a sample with gypsum plaster can give a false indication that HAC was used)
• Laboratory analysis - used for conclusive testing
• Examination of construction drawings - a full list of HAC component suppliers is found in the BRAC (Building Regulations Advisory Committee) guidance

Question 427

Your client’s building is known to have been built using HAC concrete. Is this a problem and what would you recommend he does about it?

Answer 427

1. Carry out a strength and durability assessment in line with the Building Regulations Advisory Committee (BRAC) guidance (now published by the BRE)
2. Removal - where necessary, the removal of the HAC elements altogether
3. Replacement - removing or replacing part of the HAC element’s original load-bearing function by adding a secondary support may be satisfactory
4. Carbon plate bonding - an increasingly common method that is likely to be far less disruptive than other, more conventional systems

Question 428

What are the advantages of using calcium silicate bricks?

Answer 428

1. Resistant to frost attack
2. Virtually free from soluble sulphates, making them resistant to sulphate attack

Question 429

What problems are associated with calcium silicate bricks?

Answer 429

1. Shrinkage is the most commonly perceived fault
2. Thermal movement is likely to be about 1.5 times that of clay brickwork
3. Unlike clay, they usually undergo an initial irreversible shrinkage on laying (clay brickwork tends to expand), which can cause cracking

Question 430

Why may it be contentious to label calcium silicate bricks as a deleterious material?

Answer 430

Can perform satisfactorily provided the correct precautions are taken in the design of walls (e.g. incorporating sufficient movement joints)

Question 431

How can calcium silicate bricks be identified?

Answer 431

1. Fine, natural cream colour
2. Small particles of flint up to about 3mm are often visible
3. Manufactured with coarser aggregates, so the edges of the bricks are less well defined
4. Concrete bricks tend to have small pieces of stone aggregate visible and have a fairly coarse surface
5. Not fired in the manner of clay bricks, so no tell-tale kiss marks, wire marks or fine splits in the surface
6. On older bricks, scraping the surface of the brick will reveal that they are easily marked or cut, while concrete bricks can be a good deal harder
7. Laboratory testing through the use of x-ray diffraction could also be used

Question 432

How can you tell when cracking to a wall has been caused by the improper use of calcium silicate bricks?

Answer 432

1. Identify the bricks as calcium silicate bricks
2. Lack of adequate movement joints
3. Cracks of constant width (as opposed to tapering cracks)
4. Shrinkage cracks so generally no displacement evident (brickwork sliding off a damp-proof course, cracking at corners or evident disruption)

Question 433

What steps would you recommend when specifying the installation of calcium silicate bricks?

Answer 433

1. Vertical movement joints should be provided at intervals of between 7.5-9m (BS 5628-3), with the first joint from a return normally half that distance
2. To minimise the effects of movement, the ratio of length to height of masonry panels should not exceed 3:1
3. Below damp-proof course level, the moisture content of the brickwork will be fairly stable and so movement joints are not required
4. Should not be wetted during laying - if suction is too great, additional water can be added to the mortar (within reason) or very light wetting undertaken
5. Should not be used in solid walls with clay facings or backings because of the propensity of the bricks to shrink in contrast with the expansion of clay brickwork

Question 434

Why is lead considered a deleterious material?

Answer 434

1. Lead is toxic and inhalation/ingestion can cause health problems, particularly in children and pregnant women
2. Interferes with the development of the nervous system, causing potentially permanent learning and behaviours disorders
3. Higher doses can lead to renal damage, severe colic, abdominal pain, headaches, confusion and seizures leading to death
4. Uncertainty over whether or not lead poisoning can lead to cancer

Question 435

What is the HSE requirement under the Control of Lead at Work Regulation 2002 for lead used in construction?

Answer 435

???

Question 436

Why is lead banned from use as a construction material for some products, but not for others?

Answer 436

Mere handling of lead will not cause poisoning, so lead in roofing is not perceived to be dangerous

Question 437

Where may you find lead in buildings?

Answer 437

1. Water pipes
2. Paint
3. Roofing (e.g. flashing)

Question 438

When was the use of lead water pipes banned in the UK?

Answer 438

Banned for this use in 1969

Question 439

When was the use of lead based paint banned in the UK?

Answer 439

Environmental Protection (Controls on Injurious Substances) Regulations 1992

• Prohibits the retail sale of all lead paints to the public
• Restricts use of lead paint to special circumstances (e.g. redecoration of listed historic buildings)

Question 440

What procedures should be undertaken when removing lead paint?

Answer 440

1. Wear disposable overalls and a FFP3 mask
2. Only strip back old paint if it is flaking, chipping or a risk to children
3. If paint is in poor condition, remove using a combination of chemical paint stripper, wet abrasive paper and on-tool extraction
4. If paint is in good condition use wet abrasive paper to make a key for the new coat of paint
5. Remove any debris with a damp cloth
6. Place any debris, cloths, abrasive paper in a plastic bag for disposal
7. Wash hands and forearms before eating or drinking

Question 441

What are VOCs and why are they problematic?

Answer 441

• VOCs are solvents that are commonly used in paint to keep it in liquid form, which get released into the atmosphere when the paint dries
• VOCs can cause headaches, nausea and dizziness when released and some (particularly benzene) are known carcinogens
  
  • Water-based paints are now used as a substitute as a result

Question 442

What are the advantages of using paints and glues containing VOCs?

Answer 442

The advantage of using VOCs in paint is it evaporates quickly when applied to a surface, which leaves behind more pigment and therefore requires fewer applications

Question 443

What is woodwool slab?

Answer 443

1. Made from long-fibre wood shavings compressed and bound together with cement
2. Used mainly through the 1950s-1970s as roof decking or permanent shuttering for in-situ concrete
3. Fire resistant, has good insulating properties and is more environmentally friendly than thermoplastics and resin-bonded material

Question 444

How can the use of woodwool slab become problematic?

Answer 444

1. Only problematic when used as permanent shuttering to reinforced concrete
2. Due to the compressive nature of woodwool slabs, compaction of the concrete may be inadequate as the woodwool slab absorbs some of the energy
3. This lack of compaction can result in voids and honeycombing to the underside of the concrete, sometimes leaving no cover for the reinforcing steel
4. This problem is exacerbated if the woodwool slabs are ribbed, as it makes compaction within the narrow ribs very difficult
5. As the woodwool slabs remain in place, such defects can remain undetected

Question 445

What remedial work should be considered where woodwool slab has been identified?

Answer 445

1. Discovery of woodwool slabs does not automatically mean a problem exists, as the concrete may been properly placed and compacted
2. Physical opening up and assessing the concrete soffit is the most reliability means of problem detection
3. Repairs using hand-placed mortars or sprayed concrete may be necessary if defects are found

Question 446

What are clay hollow pot floors and why are they problematic?

Answer 446

1. Hollow clay pots (tiles) were first used early in the 20th Century as a means of constructing fire-proof floors and reducing some of the dead loads of solid construction
2. The pots were separated with a clay spacer, and steel reinforcement bars were placed within the gap this formed, with a concrete structural topping being laid over the top of the pots and filling the gaps between
3. Poor compaction (similar to the problem with woodwool slab) between the pots can lead to voiding and a lack of cover around the reinforcement, reducing the floor’s fire resistance, durability and strength

Question 447

What is mundic concrete and why is it problematic?

Answer 447

• Concrete blocks and concrete manufactured from waste products from Cornwall/Devon’s mining industry, which contained unstable sulphides (pyrite being the main culprit)
• In damp conditions, pyrite oxidises and produces sulphuric acid, which reacts with the cement binder and deteriorates the concrete blocks, causing a loss of integrity

Question 448

What guidance is available in relation to mundic concrete?

Answer 448

RICS guidance note ‘The Mundic Problem’ provides extensive guidance into identification and testing

Question 449

What remedial work should be considered where mundic concrete has been identified?

Answer 449

There are no current remedial measures for properties that have already suffered deterioration of mundic concrete other than removal and reconstruction, however any unaffected mundic blockwork should be kept dry

Question 450

What are brick slips and why are they problematic?

Answer 450

• Popular in the 1960s and 1970s, brick slips were used as a method of concealing the exposed edges of a concrete frame
• Lack of soft joints between the brick slip and structure meant that movement in the concrete (shrinkage) and brick slips (expansion) causes poor adhesion resulting in risks to health and safety as they are forced off the building

Question 451

How do modern brick slips ensure problems typically associated with brick slips are addressed?

Answer 451

Modern brick slips rely on flexible adhesives that give the bond an element of elasticity (a premixed workable mortar can then be applied in a process similar to cake icing)

Question 452

What is clinker concrete and why is it problematic?

Answer 452

• Typically used in the late 19th and early 20th Century for fire resisting floor with steel joists
• In damp conditions, it produces sulphuric acid from combustion products and unburnt coal in the clinker
• The acid then has a corrosive effect on the steel joists, leading to loss of section

Question 453

What are CFCs and why are they problematic?

Answer 453

• First produced in the 1930s as a substitute for hazardous gases used in refrigerators
• Discarded CFC gases from fridges, cooling equipment, aerosols and building materials were found to collect in the stratosphere and catalyse the destruction of the ozone layer
• CFCs used as refrigerants are denoted by codes (such as R-12, R-113 and R-22) depending on the gas type

Question 454

What are the main problems associated with composite panels?

Answer 454

• Composite panels are a sandwich construction of which two outer layers of steel or aluminium sheet enclose an inner core of an adhesive-bonded lightweight material, e.g. polyurethane foam (PUR), polyisocyanurate foam (PIR), expanded polystyrene (EPS)
• These materials can burn fiercely, give off thick black smoke and produce burning droplets that can fall on whatever lies beneath, making them very difficult to deal with

Question 455

What is the key difference between PIR foam and PUR foam used in composite panels?

Answer 455

The fire resistance is significantly lower in PUR (degrades at 250°C) than in PIR (degrades at 400°C)

Question 456

What is GRC and why is it problematic?

Answer 456

GRC (Glass Reinforced Concrete):

1. Commonly used in external cladding panels, glass fibres are added into the concrete mix to increase tensile strength without the need for reinforcement (making the material lighter)
2. Over time, the alkalinity of the concrete degrades the glass fibres, resulting in a loss of strength and can cause bowing of the panels
3. Alkaline-resistant fibres are now used which offer a much better life-expectancy

Question 457

What is MMMF and why is it problematic?

Answer 457

1. Generic term for fibrous material typically used in insulation wool
2. Evidence suggests that MMMF is carcinogenic (however not proven)

Question 458

What are PCBs and why are they problematic?

Answer 458

• Chemical produced from about 1929 until mid-1970s for use within transformers, capacitors, hydraulic oils, adhesives and paints
• PCBs are toxic and are harmful to the environment (as they are very hard to break-down), and they can cause cancer in humans

Question 459

What is RAAC and why is it problematic?

Answer 459

• From the late 1950s until 1982, RAAC planks were commonly used as roof decks, floors, internal partitions and vertical cladding panels as a lightweight alternative to standard concrete
• Investigations by the BRE concluded that RAAC planks had a life expectancy of 30 years and would crack and deflect as a result of the reinforcement ‘slipping’ within its cover over time

Question 460

What is tesserae and why is it problematic?

Answer 460

• Small ceramic, stone, marble or glass tiles bonded to a rendered backing used as an external finish in buildings between the 1960s and 1970s
• Over time, adhesion failure of the background render can cause large heavy ‘plates’ of material to become loose and fall from the building

Question 461

What is UF foam and why is it problematic?

Answer 461

• Mainly used in cavity wall insulation
• Evidence suggests that UF Foam is carcinogenic (however not proven)
• Also, when poorly installed it can cause the passage of water from the external to the internal leaf

Question 462

How can hair plaster be harmful within buildings?

Answer 462

• The use of animal hair to reinforce plaster was a common technique in older buildings
• Hair products imported into the UK pre-1919 could have been taken from animals infected with anthrax, which can be passed onto humans through inhalation or contact with a skin wound

Question 463

How can toughened glass be harmful within buildings?

Answer 463

• Nickel sulphides present during the manufacture of glass can expand and cause glass panels to spontaneously fracture when toughened (or tempered) due to the heat treatment it receives
• Toughened glass should therefore be avoided in sloped overhead applications (not usually a problem in vertical applications as the expansion of the glass holds it within its frame)

Question 464

How can problems with toughened glass be mitigated?

Answer 464

• Using laminated toughened glass or applying safety film to existing panels should be considered
• ‘Heat soaking’ (subjecting the glass to accelerated elevated temperatures) can be used during the manufacturing of glass to initiate immediate failure before it is installed (has an approximate 90% success rate)

Question 465

What is the difference between wet & dry rot?

Answer 465

Wet rot is a number of different types of rot. Dry rot is one specific type of rot - Serpula Lacrymans. Wet rot thrives in wetter environments than dry rot. Wet rot is generally relatively easily treated, dry rot can take extensive treatment. Wet rot can only survive while it has a food source, dry rot can survive dormant for long periods of time and can grow through masonry and plaster.

Question 466

What are the characteristics of wet rot?

Answer 466

Wet rot can have different characteristics. Brown rots can cause cuboidal cracking, and in some cases their fruiting bodies can have a purple hue (very rarely seen). The wood itself if damp and friable.

Question 467

What are the characteristics of dry rot?

Answer 467

Dry rot causes cuboidal cracking to wood, and will make a hollow sound when affect timbers are tapped. The mycelium are cotton wool like white strands, the fruiting bodies are like creamy pancakes with darker edges, and can weep in some cases. The fruiting bodies produce a rust coloured dust that can settle on horizontal surfaces in bad outbreaks. There is also a distinctive mushroom like smell.

Question 468

How do you treat wet rot?

Answer 468

To treat wet rot you must first remove the cause of the water. After that you need to remove all affected timber, ideally by a margin of 300mm past the first signs of affected timber. Any retained timber should be treated with a pesticide and removed timbers replaced with new.

Question 469

What is the difference between wet & dry rot?

Answer 469

Wet rot is a number of different types of rot. Dry rot is one specific type of rot - Serpula Lacrymans. Wet rot thrives in wetter environments than dry rot. Wet rot is generally relatively easily treated, dry rot can take extensive treatment. Wet rot can only survive while it has a food source, dry rot can survive dormant for long periods of time and can grow through masonry and plaster.

Question 470

What are the characteristics of wet rot?

Answer 470

Wet rot can have different characteristics. Brown rots can cause cuboidal cracking, and in some cases their fruiting bodies can have a purple hue (very rarely seen). The wood itself if damp and friable.

Question 471

What are the characteristics of dry rot?

Answer 471

Dry rot causes cuboidal cracking to wood, and will make a hollow sound when affect timbers are tapped. The mycelium are cotton wool like white strands, the fruiting bodies are like creamy pancakes with darker edges, and can weep in some cases. The fruiting bodies produce a rust coloured dust that can settle on horizontal surfaces in bad outbreaks. There is also a distinctive mushroom like smell.

Question 472

How do you treat wet rot?

Answer 472

To treat wet rot you must first remove the cause of the water. After that you need to remove all affected timber, ideally by a margin of 300mm past the first signs of affected timber. Any retained timber should be treated with a pesticide and removed timbers replaced with new.

Question 473

How do you treat dry rot?

Answer 473

To treat dry rot you must first remove the cause of the water. After that, as full inspection is required to establish the extent of the infestation. All affected timber should be removed, and 500mm past last sign of infestation. Surrounding plaster should be removed, and 1m past last sign of infestation. Removed timber should be burnt of site to ensure that wood is not reused. Surrounding timber should be treated, and it may be necessary to irrigate masonry walls etc. All removed timbers should be replaced with new.

Question 474

What is the optimal temperature of dry rot?

Answer 474

20 degrees C

Question 475

What is the optimal temperature for wet rot?

Answer 475

23 degrees C (can grow from -30 - +40)

Question 476

What is the optimal moisture content for wet rot?

Answer 476

Over 43%

Question 477

What is the optimal moisture content for dry rot?

Answer 477

20-30%

Question 478

Name three types of insect that attacks wood?

Answer 478

Common furniture beetle, deathwatch beetle, woodboring weevils

Question 479

What is the rot cycle for dry rot?

Answer 479

Spore on timber, spreads strands of mycelium, once established produces fruiting bodies, fruiting bodies produce spores (repeat)

Question 480

What times of year would you expect to find common furniture beetle?

Answer 480

May to September, you would expect to find frass and flight holes

Question 481

What are the treatment options for insect attack?

Answer 481

Fumigation- Liquid treatment - Paste treatment - Gas fumigation - Smoke treatment - Heat sterilisation

Question 482

What is involved in liquid treatment for insect attack?

Answer 482

• Kills larvae in zone of penetration, and leave a zone of persistence layer to kill emerging adults and future infestations - Either organic solvent based or emulsion based (water) - Option to penetrate to deeper greater depth - Emulsion is only suitable for common furniture beetle

Question 483

What is involved in the paste treatment for insect attack?

Answer 483

• Same as liquid applied, but gelatinous emulsion paste - It provides greater penetration, but is a lengthier process - Can stain/bleach the timber

Question 484

What is involved in gas fumigation as a treatment for insect attack?

Answer 484

Must enclose the timber completely, therefore is only suitable for moveables like furniture

Question 485

What is involved in smoke treatment for insect attack?

Answer 485

• Can be good for hard to reach places - Requires repeat treatment - Cannot be highly controlled, so effects not just the timbers

Question 486

What is involved in heat sterilisation as a treatment for insect attack?

Answer 486

A temperature of 52-55’c for 20-60 minutes can be effective. Difficult to achieve, and like smoke treatment effects everything unless done in a controlled situations with moveables

Question 487

How do you treat dry rot?

Answer 487

To treat dry rot you must first remove the cause of the water. After that, as full inspection is required to establish the extent of the infestation. All affected timber should be removed, and 500mm past last sign of infestation. Surrounding plaster should be removed, and 1m past last sign of infestation. Removed timber should be burnt of site to ensure that wood is not reused. Surrounding timber should be treated, and it may be necessary to irrigate masonry walls etc. All removed timbers should be replaced with new.

Question 488

What is involved in heat sterilisation as a treatment for insect attack?

Answer 488

A temperature of 52-55’c for 20-60 minutes can be effective. Difficult to achieve, and like smoke treatment effects everything unless done in a controlled situations with moveables

Question 489

What is involved in smoke treatment for insect attack?

Answer 489

• Can be good for hard to reach places - Requires repeat treatment - Cannot be highly controlled, so effects not just the timbers

Question 490

What is involved in gas fumigation as a treatment for insect attack?

Answer 490

Must enclose the timber completely, therefore is only suitable for moveables like furniture

Question 491

What is involved in the paste treatment for insect attack?

Answer 491

• Same as liquid applied, but gelatinous emulsion paste - It provides greater penetration, but is a lengthier process - Can stain/bleach the timber

Question 492

What is involved in liquid treatment for insect attack?

Answer 492

• Kills larvae in zone of penetration, and leave a zone of persistence layer to kill emerging adults and future infestations - Either organic solvent based or emulsion based (water) - Option to penetrate to deeper greater depth - Emulsion is only suitable for common furniture beetle

Question 493

What are the treatment options for insect attack?

Answer 493

• Liquid treatment - Paste treatment - Gas fumigation - Smoke treatment - Heat sterilisation

Question 494

What times of year would you expect to find common furniture beetle?

Answer 494

May to September, you would expect to find frass and flight holes

Question 495

What is the rot cycle for dry rot?

Answer 495

Spore on timber, spreads strands of mycelium, once established produces fruiting bodies, fruiting bodies produce spores (repeat)

Question 496

Name three types of insect that attacks wood?

Answer 496

Common furniture beetle, deathwatch beetle, woodboring weevils

Question 497

What is the optimal moisture content for dry rot?

Answer 497

20-30%

Question 498

What is the optimal moisture content for wet rot?

Answer 498

Over 43%

Question 499

What is the optimal temperature for wet rot?

Answer 499

23 degrees C (can grow from -30 - +40)

Question 500

What is the optimal temperature of dry rot?

Answer 500

20 degrees C

Question 501

What are the common reasons for cracking?

Answer 501

a) Drying/shrinking, like with calicum silicate bricks, or with a too strong render mix
b) Thermal movement, are there sufficient expansion joints?
c) Frost action
d) Ground movement, such as settlement and subsidence
e) Wall tie failure
f) Chemical attack, such as suphate attack, or carbonation
g) Lack of lateral restraints
h) Overloading - lintel failure or roof spread
i) Vibration
j) Poor qualit materials fire cracks in bricks

Question 502

Why is cracking a problem?

Answer 502

Cracking is a problem as it can cause buildings to become structurally unsound. Additionally, cracks can allow water ingress, which can cause other problems separate from the cracking itself

Question 503

Name the causes of stepped cracking in brickwork

Answer 503

Stepped cracking to brickwork would generally be expected to be caused by movement in the foundations, such as cause by subsidence or settlement

Question 504

What are the procedures for monitoring cracking?

Answer 504

a) Three stud screws - this method allows for precise measurement, using calipers, of the three sides of a triangle; monitoring the direction and size of the crack. b) Proprietary calibrated tell-tales - this method involves a measurement grid being placed over the crack. These can be difficult to read, and are susceptible to damage from both weather and vandals c) Glass tell-tale - this method results in the glass breaking is there is movement. This does not allow for quantifying the movement

Question 505

How do you categorise the severity of a crack?

Answer 505

The BRE Digest 251 lays out classifications of cracking:

Question 506

What are signs of ground movement?

Answer 506

a) Crackings showing internally and externally that correlate, may in some cases go through a DPC to foundations
b) Cracks with tapering that is consistent with differntial foundation movement (see picture)
c) Floor slope, wall tilt, window/door opening distortion

Question 507

What is subsidence?

Answer 507

Subsidence occurs when the soil beneath a building becomes unstable or shrinks

Question 508

What are the common causes of subsidence?

Answer 508

a) It almost always is related to a loss of moisture in the soil
b) Trees - their roots absorp the water from the soil
c) Collapse - such as caused by drains/mines
d) Buried organic matter with decomposes and destabalises the foundations
e) Improperly compacted gound
f) Burst water mains - washing soluble matter away

Question 509

How can trees cause subsidence?

Answer 509

Trees generally only have major influence on shrinkable (cohesive) soils.

Trees require water to grow, and they take this water from the soil around them via their roots. This can cause the surrounding soil to be desiccated due to a lack of water. This effect is exacerbated by periods of hot and/or dry weather. When this desiccation effect takes place in close proximity to a building it can result in the building becoming destablised.

Question 510

How do you treat subsidence?

Answer 510

As with treatments for anything, the most effective treatment will depend of the cause and severity of the problem:

a) Minor cracking that is not progressive may be able to be monitored and simply re-pointed or decorated
b) A burst water main that has been washing soluble soils away can be repaired, and the problem will not worsen
c) Trees causing subsidence can be pruned, or removed. Alternatively, if it’s protected trees implementing root barrier system might be possible. If this were the issue, I would look to seek advice from an arboliculturalist (tree specialist) before making final recommendaitons
d) If severe and progressing subsidence, it may be necessary to take more drastic action, such as underpinning

Question 511

Who usually pays for damage cuases by susidence?

Answer 511

Most building insurance policies will cover rectification of damage caused by subsidence, but in some cases they may not cover the cost of preventing further subsidence

Question 512

What is heave?

Answer 512

Upward movement of soil caused by swelling or expansion of subsoil, common in clay soils when wet

Question 513

What are common causes of heave?

Answer 513

a) Trees are the most common cause. When they are removed or when the die. The roots stop drawing water from the subsoil, so water accumolates and causes swelling
b) “Stress Relief” - when soil is removed and the pressure is release, such as when excavating for a basement
c) A change in the water table
d) Broken drains that effect the ground drainage
e) Swelling of subsoils with seasonal changes
f) Water expanding as it freezes. Silty and sandy clays are particularly susceptible to this

Question 515

What is Alkali Silica Reaction and how would you diagnose it?

Answer 515

• Alkali Silica Reaction is when alkalines in cement (hydroxides) react with silica in aggregates to form a silica gel which expands with contact with water, causing cracking
• It is also known as concrete cancer.
• ASR is best detected by examining concrete in thin sections using a microscope, as the gel may be present in cracks and within aggregate particles

Question 516

How much cover of concrete is required to steel reinforcement?

Answer 516

Minimum of 20-70mm of cover, depending on it’s function. If insufficient cover, steel reinforcement can corrode

Question 517

What are available remedial actions for Alkali Silica Reaction and how can it be avoided in future?

Answer 517

• Remedial actions are limited.
• It is important to monitor the reaction, and recommended to take core samples to test for silica gel.
• Minimising the ability to absorb water will stop the gel from expanding further.
• Badly effected areas will require strengthening or replacement.

Techniques that can be adopted to try and reduce the likelihood of ASR include:

1. the use of low-alkali Portland cement
2. introduction of pozzolans to the concrete mix. The addition of pozzolans reduces the alkalinity of the pore fluid as the amount of cement in the mix is lowered and help to stabilize and prevent formation of silica gel

Question 518

What is Concrete Carbonation and how would you test for it?

Answer 518

• Concrete Carbonation is the reaction of carbon dioxide in the atmosphere, water and cement to form a carbonic acid.
• This acid then reduces the alkaline nature of the concrete
• breaks down the passive layer surrounding the steel reinforcement, and causes corrosion.
• Phenolphalein test turns pink in normal concrete pH (alkaline) but clear in acidic solution
• Note carbonation only takes place in soluion so if the source of moisture can be removed this can help resolve.

Question 519

What is Chloride Attack in concrete?

Answer 519

• Chloride attack in concrete is when chloride ions affect the natural passive protective film to steel reinforcement and cause corrosion.
• Calcium chloride additive in concrete have been banned since 1977.
• Can be introduced from de-icing salts or from sea spray.

Question 520

What are the available remedial actions for Concrete Carbonation?

Answer 520

• Firstly, remove the water source.
• As carbonation can only occur in a solution, removing the water will not only prevent the corrosion of the steel work but also the carbonation.
• To treat the effects, wish brush corroded areas and apply a corrosion inhibitor.
• It may be beneficial to coat the finished concrete to prevent further carbonation.

Question 521

What is Honeycombing to concrete?

Answer 521

• Honeycombing is where there are small voids within the concrete.
• This can be cause by number of things, including insufficient vibration when poured, and poor formwork, including the use of wood wool slabs as formwork.

Question 522

Why is Honeycombing to concrete an issue?

Answer 522

If concrete is honeycombed it becomes more vulnerable to corrosion to the steel reinforcement, to fire, and to the effects of the freeze-thaw cycle due to all of the voids.

Question 523

What remedial actions are available for treating chloride attack in concrete?

Answer 523

• Cut out the affected areas, wire brush corroded reinforcement, apply a corrosion inhibitor and reinstate the concrete.
• Monitoring over time will be required

Question 524

What advice would you give a client if you identified Concrete Carbonation within their property?

Answer 524

If I suspected that Concrete Carbonation was present I would like to confirm that definitely, therefore I would recommend that my client engage concrete specialist to carry out testing to confirm my diagnosis. Following that I would recommend that the water source be reduced as much as possible. Thereafter I would recommend treatment including wire brushing the areas, applying a corrosion inhibitor and possible coating the area to prevent further carbonation.

Question 525

What advice would you give a client if you identified Alkali Silica Reaction within their property?

Answer 525

• If I suspected Alkali Silica Reaction within a property or structure, I would advice the client to engage with a concrete specialist to confirm the diagnosis.
• Sample of the concrete can be taken, and examination/pH test carried out to identify the silica gel or the level of alkaline content in the aggregate.
• If possible, I would advise the client to carry out works that reduced the water ingress to the area.
• Depending on the severity of the issue, it may be necessary to recommend some are of replacement of the concrete.

Question 526

What are the indicators of chloride attack in concrete?

Answer 526

The location may be an indicator, such as a car park where the use of de-icing salts are used, or by the sea. Corrosion of the steel reinforcement, and additionally the concrete will show signs of cracking and crazing. Chloride attack reduces structural strength over time, and is displayed by spalling and pitting of concrete.

Question 527

What are the indicators for Concrete Carbonation?

Answer 527

Corrosion of the steel reinforcement, which expands and causes cracking and damage to concrete surrounding. ACTUAL INDICATOR - Phenolphthalein indicator can be used to assess if the concrete is acidic, and therefore carbonated. It will turn pick if no acidic content, and will remain colourless if carbonation is present.

Question 528

What are the indicators for Alkali Silica Reaction?

Answer 528

Alkali Silica Reaction is uncommon in the UK. It is most easily identified by map like cracking across the surface of the concrete. In some extreme case the silica gel can be seen on the surface of the concrete

Question 529

What is the treatment for Honeycombing of concrete?

Answer 529

Affected areas of concrete should be broken out and replaced

Question 530

How much cover of concrete is required to steel reinforcement?

Answer 530

Minimum of 20-70mm of cover, depending on it’s function. If insufficient cover, steel reinforcement can corrode

Question 531

What are available remedial actions for Alkali Silica Reaction?

Answer 531

Remedial actions are limited. It is important to monitor the reaction, and recommended to take core samples to test for silica gel. Minimising the ability to absorb water will stop the gel from expanding further. Badly effected areas will require strengthening or replacement.

Question 532

What is Concrete Carbonation?

Answer 532

Concrete Carbonation is the reaction of carbon dioxide in the atmosphere, water and cement to form a carbonic acid. This acid then reduces the alkaline nature of the concrete, breaks down the passive layer surrounding the steel reinforcement, and causes corrosion.

Question 533

What is Chloride Attack in concrete?

Answer 533

Chloride attack in concrete is when chloride ions affect the natural passive protective film to steel reinforcement and cause corrosion. Calcium chloride additive in concrete have been banned since 1977. Can be introduced from de-icing salts or from sea spray.

Question 534

What are the available remedial actions for Concrete Carbonation?

Answer 534

Firstly, remove the water source. As carbonation can only occur in a solution, removing the water will not only prevent the corrosion of the steel work but also the carbonation. To treat the effects, wish brush corroded areas and apply a corrosion inhibitor. It may be beneficial to coat the finished concrete to prevent further carbonation.

Question 535

What is Alkali Silica Reaction?

Answer 535

Alkali Silica Reaction is when alkalines in cement react with silica in aggregates to form a silica gel which expands with contact with water, causing cracking

Question 536

What is Honeycombing to concrete?

Answer 536

Honeycombing is where there are small voids within the concrete. This can be cause by number of things, including insufficient vibration when poured, and poor formwork, including the use of wood wool slabs as formwork.

Question 537

Why is Honeycombing to concrete an issue?

Answer 537

If concrete is honeycombed it becomes more vulnerable to corrosion to the steel reinforcement, to fire, and to the effects of the freeze-thaw cycle due to all of the voids.

Question 538

What remedial actions are available for treating chloride attack in concrete?

Answer 538

Cut out the affected areas, wire brush corroded reinforcement, apply a corrosion inhibitor and reinstate the concrete. Monitoring over time will be required

Question 539

What advice would you give a client if you identified Concrete Carbonation within their property?

Answer 539

If I suspected that Concrete Carbonation was present I would like to confirm that definitely, therefore I would recommend that my client engage concrete specialist to carry out testing to confirm my diagnosis. Following that I would recommend that the water source be reduced as much as possible. Thereafter I would recommend treatment including wire brushing the areas, applying a corrosion inhibitor and possible coating the area to prevent further carbonation.

Question 540

What advice would you give a client if you identified Alkali Silica Reaction within their property?

Answer 540

If I suspected Alkali Silica Reaction within a property or structure, I would advice the client to engage with a concrete specialist to confirm the diagnosis. Sample of the concrete can be taken, and examination/pH test carried out to identify the silica gel or the level of alkaline content in the aggregate. If possible, I would advise the client to carry out works that reduced the water ingress to the area. Depending on the severity of the issue, it may be necessary to recommend some are of replacement of the concrete.

Question 541

What are the indicators of chloride attack in concrete?

Answer 541

The location may be an indicator, such as a car park where the use of de-icing salts are used, or by the sea. Corrosion of the steel reinforcement, and additionally the concrete will show signs of cracking and crazing. Chloride attack reduces structural strength over time, and is displayed by spalling and pitting of concrete.

Question 542

What are the indicators for Concrete Carbonation?

Answer 542

Corrosion of the steel reinforcement, which expands and causes cracking and damage to concrete surrounding. ACTUAL INDICATOR - Phenolphthalein indicator can be used to assess if the concrete is acidic, and therefore carbonated. It will turn pick if no acidic content, and will remain colourless if carbonation is present.

Question 543

What are the indicators for Alkali Silica Reaction?

Answer 543

Alkali Silica Reaction is uncommon in the UK. It is most easily identified by map like cracking across the surface of the concrete. In some extreme case the silica gel can be seen on the surface of the concrete

Question 544

What is the treatment for Honeycombing of concrete?

Answer 544

Affected areas of concrete should be broken out and replaced

Question 545

What different types of dampness are there?

Answer 545

• Penetrating damp - Rising damp - Condensation

Question 546

What is the definition of rising damp?

Answer 546

Upward movement of water through a porous material due to capillary action

Question 547

How do you identify rising damp?

Answer 547

BRE Digest 245 set out diagnosis method: - Water approx. 1m high - Salt deposits will be visible where water have evaporated and leave a tide mark - Peeling of wall finishes - Musty smell, rotting timbers (skirting) - Usually where there is no DPC or where the DPC has been bridged

Question 548

What causes rising damp?

Answer 548

• Lack of a DPC - only a requirement after 1875 - Damaged DPC - brittle slate, or penetration through a membrane - Bridged DPC - external landscaping/ground level raising

Question 549

Where should a DPC be located?

Answer 549

Should be 150mm above ground level

Question 550

What materials would you expect a DPC to be constructed from?

Answer 550

• Pre 1900 - slate - 1900s onwards - bitumen - Modern - polymer materials

Question 551

What are the treatment options for rising damp?

Answer 551

• Insert a DPC - either physically or chemically injected - Hack off all blown plaster and replace with breathable/waterproof plaster or render

Question 552

What is the process with physically retro-fitting a DPC?

Answer 552

• Cut out the brickwork and insert (access required from both sides) - Can cause issues with services within wall - Very costly and very disruptive

Question 553

What is the process with chemically injecting a DPC?

Answer 553

• Holes are drilled in brickwork at 120mm centre - Chemical cream is injected at low pressure - External holes should then be plugged - Must be allow to dry before plastering - Can be difficult to ascertain the quality, best to ensure a guarantee for the work is provided

Question 554

What is the definition of penetrating damp?

Answer 554

Penetrating damp is caused by moisture passing through a building fabric

Question 555

What is the cause of penetrating damp?

Answer 555

There are a number of possible causes, often due to construction, design or material failure: - failed rain water goods - failed roof coverings - fixing penetrations in building fabric - installation of services - defective cavity tray - burst water pipe

Question 556

How would you identify penetrating damp?

Answer 556

If the profile of the dampness is consistent with whatever the suspected cause is. Thorough inspection required, and should be aware that moisture can track within buildings

Question 557

What tests are available for penetrating damp?

Answer 557

A die test, when water with a die in it is applied to a suspected ingress point, and if the die comes through to where the damp is manifesting you can link the two

Question 558

What is condensation?

Answer 558

Condensation is when moist air comes into contact with a surface with a lower temperature than the due point

Question 559

What is the cause of condensation?

Answer 559

Condensation is caused by moisture in the air, from normal activities and cold surfaces

Question 560

How would you identify condensation?

Answer 560

Condensation forms on cold surfaces, like windows and insulated areas - it will be visible on the surface

Question 561

What are the consequences of condensation in a building?

Answer 561

Condensation can increase the moisture content of timber, which can in turn lead to rot/infestation Condensation occurring on plaster walls can allow mould growth, with can be detrimental to health

Question 562

What treatment is available for condensation?

Answer 562

• Increase natural ventilation (trickle vents, open windows) - Install mechanical ventilation (extract in toilets and kitchens) - Avoid drying clothes indoors - Improve insulation and double glazing - Ensure adequate heating (Essentially, warm the surfaces to stop them achieving the dew point, and reduce the moisture content in the air)

Question 563

What is interstitial condensation?

Answer 563

Interstitial condensation is condensation that occurs within a void or cavity where there is insufficient

1. ventilation
2. insulation
3. or absence of a vapour control layer

Question 564

What is thermal bridging?

Answer 564

• Thermal bridging, often known as cold bridging, is caused where there is direct contact between internal and external faces of a building due to thermal properties of the fabric being poorer than that around the area.
• wasteful heat transfer across this element - heat loss as the heat conducts from warm to cold area.
• Often viewed with a thermographic camera
• Will often cause localised condensation and therefore mould growth
• Insulation is a thermal break which stops heat transfer
• Thermal bridges can be categorised as ‘repeating’ for example where wall ties regularly bridge the cavity, or ‘non-repeating’ such as a wall junction or lintel.
• The Approved Documents to Part L of the building regulations (Conservation of fuel and power) state that ‘The building fabric should be constructed so that there are no reasonably avoidable thermal bridges in the insulation layers caused by gaps within the various elements, at the joints between elements and at the edges of elements such as those around window and door openings.’

Question 565

What tools would you sure to detect moisture?

Answer 565

• Speedy carbide meter - Thermographic imaging - Electrical resistance meter - Capacitance meter

Question 566

What is a Speedy Carbide Meter?

Answer 566

It’s used to test samples of material extracted, to establish the moisture content. It provides an accurate reading of the moisture content, but can require destructive testing and will most likely need to be sent away or brought back to the office etc. for definitive results

Question 567

How is thermographic imaging used to detect moisture?

Answer 567

Moist areas will generally be a lower temperature. Can be used to detect cold bridging as well

Question 568

What is an electrical resistance meter?

Answer 568

It measures moisture with a current that passes between two prongs. It is only calibrated for timber, though can be used as a comparison in other materials. Easy to use and causes minimal damage, can also react to salts so should be used with caution

Question 569

What is a capacitance meter?

Answer 569

It uses sensors to measure fringe capacitance, which varies with moisture content. Can be used on a number of different surfaces and materials

Question 571

Typical defects within cladding?

Answer 571

• blocked cavity in rainscreen cladding preventing water draining away
• nickel sulphide inclusions in planar glazing
• poor or failed fixings.
• Mechanical Impact damage from crades
• ccracking from thermal expansion brise soleil baguettes GRC
• Movement of the structural frame.
• Aluminium composite materials - combustible insulation
• Corrosion - galvanic, filiform corrosion
• Lack of ashesion tesserae soandrel panels
• Erosion and staining - lime stone panels, pollution