Building pathology Flashcards
Can you give me some typical defects for Victorian properties?
- Lintel failure.
- Penetrating damp.
- Spalling brickwork
- Slate roofs (nail sickness).
Can you give me some typical defects for Georgian properties?
- Slate roof issues (nail sickness).
- Penetrating damp.
- Roof spread (low pitch, no trusses).
What are the BRE Digests for dry rot and wet rot?
Dry rot: BRE Digest 299.
Wet rot: BRE Digest 345.
When do the humidity levels begin for dry rot and wet rot?
Dry rot: 20%.
Wet rot: 50%.
What’s the difference between dry rot and wet rot?
- Dry rot: 20%, wet rot 50%.
- Dry rot spreads easier (masonry and plaster).
- Wet rot doesn’t spread easily (timber).
How are you able to determine whether a property had dry rot on site?
- Forms on masonry or timber.
- White fluffy (cotton-like).
- Forms strands.
- Brittle.
How are you able to determine whether a property had wet rot on site?
- Stays within areas of moisture.
- Timber becomes darker and spongey.
- Doesn’t form strands.
What is the risk of dry/wet rot if not dealt with properly?
Weakens timber, health issues.
How would you deal with dry rot/wet rot?
- Find source of moisture.
- Remove rot 500mm past fungus.
- Treat.
What BRE Digest is there for assessing cracks?
BRE Digest 251.
What is the difference between subsidence, heave and settlement?
Subsidence: Soil beneath sinks.
Heave: Upward movement of soil from an increase in moisture levels, which causes clay soils to expand.
Settlement: Downward movement of the ground (caused by weight of the building).
Can you give me some examples of deleterious materials?
Asbestos (1940s-2000).
Lead paint (before 1970s, windows and doors).
Woodwool slabs (1960s, warehouse and soffits - used as permanent formwork in my experience).
HAC (1950s-70s, public sector and industrial buildings).
RAAC (1950s-90s, public sector buildings).
Can you tell me the different types of asbestos?
Chrysotile (white).
Amosite (brown).
Crocidolite (blue) - thin needle like.
What is carbonation?
CO² reaction that makes concrete more acidic.
What is the effect of carbonation?
Rebar begins to expand as it corrodes which casues the concete to spall.
What is the issue with RAAC?
Porous so is susceptible to water damage, deteriorates over time.
What is the issue with HAC?
Loss of strength over time through ‘conversion’, vulnerable to chemical attack.
How do you identify RAAC and HAC?
RAAC: No gravel, bubble appearance internally.
HAC: requires lab testing.
If a property has been suffering from condensation for over a year and the mould is excessive on the surface of the wall and ceiling, how would you know if the subsurface, such as masonry, isn’t damp?
- Calcium carbide test.
- Damp meter [indicative result as salts in masonry reduce accuracy].
What causes rising damp and what are the signs?
Moisture rising though porous materials.
[Identified by tide marks, salt deposits.]
What causes wall tie failure?
How is it identified?
- Corrosion of wall ties.
- Cracking to a course around 5 bricks wide.
Windsor Walk, London - What guidance can you use to assess the severity of cracks?
BRE Digest 251.
What is the relevant guidance note for brickwork repairs?
BRE Good Repair Guide 3.
Can you give me an example of where you have used crack stitching previously?
17 Bowling Green Lane.
Windsor Walk - The helical bars – did you design these?
What was the warranty for this work?
- No I contacted a specialist contractor who undertook the designs and carried out the works.
- 10 year guarantee.
What are some common causes of cracking in brickwork?
- Frost damage.
- Arch failure.
- Settlement.
You mention woodwool slabs – what is the issue with these?
When used as permanent formwork there was poor compaction which created voiding and reduced its structural integrity. [Exposed rebar, combustible].
Where do you typically find woodwool slabs?
I have only seen them in industrial buildings.
You carry out a survey of an industrial building constructed in the 1970’s. What type of defects might you come across?
HAC – 1950s-70s, a process called conversion occurs which weakens the structure, asbestos fibre cement roof sheets.
Bircholt Road, Maidstone - How did you identify composite cladding panels?
Smaller profile to the cladding vs built up system and if you push it its firmer than built up cladding.
What is the Loss Prevention Certification Board (LPCB)?
A third-party organisation that sets standards for fire and security products.
What would you have done if the panels hadn’t been LPCB approved?
Advise the client to discuss this with their insurers to assess the implications of purchasing a building with non-LPCB approved cladding.
Windsor Walk/18-20 Tileyard Road - What flat roof tests did you undertake aside from visual inspections?
Damp meter on timber structure [15-20% indicates moisture is present could lead to issues, over 20% considered high].
What ventilation would you expect to see in a pitched roof?
Eaves ventilation.
Note: Damp meter: WME (Wood Moisture Equivalent); calibrated for timber; foil backed plasterboard can give false readings.
You mention having a knowledge of testing methods, including damp meters. What type of damp meter is calibrated to timber?
Pin type (electrical resistance). Other types? Pinless (electromagnetic waves).
What percentage WME would indicate damp in softwood timber?
Over 20%.
You carry out a survey of an industrial building constructed in the 1970’s. What type of defects might you come across?
- Asbestos – roof sheets, Artex (test samples).
- HAC (lab test of samples), [concrete floor slab cracks].
Record Street, Bermondsey cut edge corrosion – a) what remediation did you recommend?
b) How did you cost it
c) What additional things were there to consider?
a) Clean, prime (corrosion inhibitor), seal (tape), coat (polyurethane waterproofing).
b) I used tendered rates provided by my company.
c) Health and safety – edge protection or mansafe system.
Anchorage House, London – Draw the gutter detail how it should have been.
[Show the membrane to overlap the extension and gutter].
Anchorage House, London – Assuming your hypothesis on the water ingress was correct, how would you rectify this?
Redress the membrane to ensure it lapped the extension and the gutter, giving a continuous layer.
What are the classifications of cracks in BRE Digest 251?
HFERES.
0 - Hairline: <0.1mm.
1 - Fine: up to 1mm.
2 - Easily filled: up to 5mm.
3 - Repairs: 5-15mm.
4 - Extensive: 15-25mm. Break out and replace.
5 - Structural: >25mm. Partial/complete rebuild.
How would cracking form to a brickwork wall if there was subsidence and heave below a building?
- Subsidence: Narrow top, wide bottom.
- Heave: Wide top, narrow bottom.
What directions are the cracks typically for subsidence and heave?
- Subsidence - diagonal.
- Heave - vertical.
[Both related to the direction that pressure is placed on the building.]
Cut edge corrosion: Does alumnium corrode?
No - not a ferrous metal (ferrous metals contain iron). [Magnet does not attract]
Building pathology - Anchorage House, London:
- Details of instruction (service, spec, contract value/claim amount etc)?
- Issues encountered?
- Conditions survey.
- Water ingress - new membrane had been installed which did not overlap the abutment between the new and old buildings or the inside of the gutter.
Building pathology - Windsor Walk, London:
- Details of instruction (service, spec, contract value/claim amount etc)?
- Issues encountered?
- Project.
- £243k.
- New ground floor, windows, brickwork repairs.
- Refurb.
What causes cracking to be wider at the top than at the bottom?
- Subsidence.
- Cracking wider at the bottom for heave.
[Use hands]
