Building Pathology Flashcards
How would you advise a client if they were experiencing water ingress through a 10 year old single-ply flat roof covering?
- Check if the works are still covered by the guarantee.
- Electronic leak detection
- Thermographic Survey
- Can become contaminated through contact with bitumen below as plasticiser is lost and it become brittle. Normally an isolating membrane is used.
- Puncture damage - e.g. foot traffic
- Failure of welded seams due to poor workmanship.
How would you identify Dry Rot, and reduce risk of it occuring in future?
- Life Cycle: spore, hyphae, mycelium, fruiting body
- Cuboidal cracking
- Spore Dust
- Lower moisture content
- TREATMENT: Heat and Ventilate, Remove area + 450mm, Presevative, Masonry sterilisation.
- PREVENTION: Ventilation, Treated Timber, Waterproofing
How would advise a client if their timber sash windows were in poor condition?
- Heritage/conservation considerations
- Repair (resin) vs like-for-like replacement
- Replacement with better performing alternative?
- EPC considerations
What are the limitations with thermographic surveys and moisture meters?
- Moisture meters generally calibrated to wood moisture content - are not accurate at determining moisture content in other materials - plaster, brick etc. But they do show a pattern.
- Moisture meters just test resistance so may pick up causes other than damp e.g. hygroscopic moisture.
- Thermographic surveys - not suitable for metal or glass that tend to reflect temperatures of surrounding buildings/objects.
- Thermographic surveys - need correct weather and temperature variance between internal and external.
What is freeze thaw action?
When water fills voids of rigid porous material and then freezes and expands, causing material to crack and spall. The damage allows greater volumes of water to enter the material and the damage can become progressively worse.
What types of stone are more susceptible to freeze thaw action?
- Those with a higher porosity e.g. limestone and sandstone, although those with particulalry large pore structure can allow water to evaporate more easily.
- Engineering bricks are less porous than common or facing bricks.
Regent St - How did you determine freeze thaw was the cause of cracking rather than other types of movement?
- Cracks same size at either end.
- No rotational movement
- Walls plumb
- No evidence of other structural failure below.
- No evidence of thermal expansion or contraction at a junction or differential movement between materials.
Is there any guidance that can be referred to for assessing cracks in low-rise buildings?
- BRE Digest 251 - categorised cracks into 6:
- 0 - negligible - up to 0.1mm
- 1 - fine cracks - up to 1mm
- 2 - easily filled cracks - up to 5mm
- 3 - cracks requiring some opening up - 5-15mm
- 4 - extensive damage requiring breaking out and replacement - 15-25mm
- 5 - structural damage - major rebuilding - greater than 25mm
What is Carbonation?
- Reaction of Carbon Dioxide, Water and Calcium Hydroxide in Cement to create calcium carbonate.
- pH lowers and passive layer around reinforcement is broken down, and re-bar corrodes and expands.
What specialist tests are there for identification of carbonation?
- Phenolphthalein - an alkalinity test.
- Pink result - pH is 13-14 = Good
- Clear result - pH 9 = Bad
How would you specify repairs to concrete affected by carbonation?
- Hammer test
- Hack off all loose
- Grit-blast reinforcement to remove all corrosion
- Apply zinc-based primer to reinforcement
- Patch repair concrete
- Apply an anti-carbonation coating
Can you give me 2 other concrete defects you might encounter on a 1960s concrete framed office building?
- Chloride Attack - calcium chlorides used as an accelerator (also de-icing salts or exposure to marine env.) Effect same as Carbonation.
- Sulphate Attack - dissolved salts penetrate into concrete from soil, groundwater etc and destroy with expansive effect. Remedy - install anodes with DC current. Cathodic protection with sacrificial zinc anodes.
- High Alumia Cement - particularly with pre-cast beams. Widespread Use in 50s-70s. Banned in 1976 because it undergoes a transformation where it increases its porosity and loses strength. Can result in collapse.
What are the 3 types of structural waterproofing protection for underground structures?
- Type A - Barrier Protection (tanking) - internal, external or sandwich. Liquid applied, cemetitious or bonded sheet.
- Type B - Structurally Integral e.g. Watertight Concrete
- Type C - Drained Systems - e.g. cavity or through egg-box membrane directing water away.
What advice would you give for a basement car-park suffering water ingress from ground water for a repair strategy?
- A combination of a Type A and a Type C system so there is a back-up system in place.
How would you identify and treat Woodworm / Furniture Beetle?
- Woodworm is the larvae of the the wood-boring beetle
- It creates 1-2mm circular holes with bore dust (frass) left by holes
- Found typically in floorboards, furniture, joists, beams, rafters
- Fairly damp conditions e.g. greater than 15% moisture content (wood boring weevil prefered even damper conditions)
- Treatment - requires Permethrin-based treatment, heating and drying area, cutting out and replacing affected sections.
