Building Pathology L1 Flashcards
How does water enter a building? Explain each issue?
Condensation - Water vapour into liquid at dew point when hitting a cold surface. Usually above 70% RH.
Penetrating Damp - Where water enters through poor construction details, porous walls/mortar or disrepair.
Rising Damp - Tide mark of stains approximately 1m high, salts and crumbling plaster and rotten timber.
Leaks or Trapped water
What are the consequences of damp?
Health issues Staining Timber decay Chemical reactions to the structure Movement (drying out)
How can you survey damp using equipment? Explain how this is done and the limitations?
- Gravimetric (Oven drying = Taking samples, weighing before and after been in an oven. Destructive, masonry only and time consuming)
- Conductance meter (Protimeter = Electric resistance using probes. Only for timber, false readings could be due to foil backed plaster board or salts present.)
- Carbide Testing (Speedy carbide = Drilled and weighed, then add in calcium carbide within to cause chemical reaction and release of gases. Destructive, masonry only and time consuming)
How would you check if damp was present after recordings taken?
Use BRE Digest to understand moisture content.
What causes condensation and how would you manage to remove it?
Lack of ventilation and heat change between the property (poor insulation).
You can introduce ventilation to the property both mechanical or natural, also insulating property so walls are not as cold.
What is interstitial condensation and how would you treat it?
Dew point is within the structure.
I would install a vapour barrier on the warm side of the insulation, and further insulation if required.
How can you resolve penetrative damp?
Identify and repair the source. Use of damp repelling paint in render may be useful for porous bricks or repointing.
How can you resolve rising damp?
- Installing a DPC (chemical or physical)
- Tanking (Cementious slurry or tanking membrane)
What is salt efflorescence and how does it occur?
Salts from brickwork washed through onto the surface causing staining and bumps. Typically found 36 months after construction.
Removal can be through time and a wire brush.
What are the main defects related to timber?
Rotting (dry or wet)
Insect attack
What is timber typical moisture content, compared to wet and dry rot timber?
- Internally 2-16% MC
- Externally 20%+ MC
- Dry Rot 20-32% MC
- Wet Rot 30-60% MC
How do you tell difference between wet and dry rot?
- Dry rot is white mycelium in long white strands and rusty coloured fruiting bodies. Cuboidal cracks and both crumbly and lightweight
- Wet rot is dark brown, cracked along grain, mycelium soft and thicker, typically no fruiting bodies.
How do you manage dealing with dry rot?
- Eliminate cause
- Establish effected area
- Dry and ventilate area
- Remove dry rot affected area plus 450mm
- Replace timbers accordingly.
How do you manage dealing with wet rot?
- Eliminate cause
- Identify if structurally sound still
- Dry and ventilate area
- Remove rot or treat with protective coating if listed.
What beetle species are there and how would you deal with them?
- Identify the species of insect attack through hole size, frass, timber and location (common furniture, death watch, powder post, wood boring weevil)
- Remove the structurally damaged timbers.
- Provide a timber coating to prevent further attacks
- Inject holes with gel to seal them.
- Monitor.
