Building Pathology Flashcards
Name some common flat roof defects and why they occur?
Crazing = Lack of adequate UV protection
Ponding = Where appropriate falls or structural movement causes water to sit on the roof
Blistering = Water vapour or air pressure below the covering
Name some methods of assessing flat roofs defects.
Electronic leak detection
- Uses a low voltage electrical current to find the source of a leak. The current flows towards the leak.
Thermographic imaging
- Uses infrared to measure surface temperatures. Extra water or moisture will show up as a cooler area.
What is damp?
Visible moisture ingress through discolouration or staining and causes defects such as mould growth and frost damage.
How can you test for damp?
Moisture meter
- measures the electrical resistance between the nodes. Usually used for timber. 0-15% is normal, Over 25% reading is high.
Speedy carbide meter
- Intrusive test. Measures moisture in masonry by putting brick dust into a container with calcium carbide which releases a gas in proportion to the amount of moisture present.
What are the negatives of using a moisture meter?
Metal or salts hidden within a wall can increase the reading as they are conductive.
Surface level condensation may give a higher reading.
What is a cold bridge?
When poorly insulated materials come into contact and allow heat to pass through.
What is condensation?
Formed when hot air hits a cold surface and loses some of its moisture as condensation.
Name some types of cracks in buildings and their characteristics.
Subsidence - downward movement of the ground. Cracks usually larger at the top and thinner at the bottom.
Heave - upwards movement of the ground. Cracks larger at the bottom and thinner at the top.
Settlement - movement down due to increased building load
What is dry rot?
A fungal timber decay that digests the parts of wood that give it strength and stiffness. Caused when spores come into contact with damp timber that has a moisture content of 20% - 30%.
What are the stages of dry rot?
Spore - Hyphae - Mycelium - Fruiting body
What are some common concrete defects?
Sulphate attack = chemical process where sulphate in the environment or concrete react with the hydrated cement compounds and form crystals.
Carbonation = reaction of carbon dioxide in the environment with calcium hydroxide in the cement paste. Most common cause of steel corrosion.
Honeycombing = inadequate compacting, use of excessively large aggregate.
What are the remedial measures for dry rot?
Cut out and replace affected timber including 450mm past the affected areas to allow for possible further contamination. Treat with a chemical biocide.
What does Japanese knotweed look like?
Hollow stems with raises nodes. Leaves are broad oval. New shoots appear as red/purple asparagus spears.
How long should a wall be left to dry out?
Depends on the saturation and time of year but could be anywhere between between 6 weeks and 3 months.
