Building Pathology Flashcards
What are the three main types of mould?
- Allergenic, types of moulds which can cause allergic reactions in people who are sensitive
- Pathogenic, can cause health problems in people with underlying medical conditions
- Toxigenic, really dangerous types of mould which can lead to serious or life-threatening health conditions.
Why does mould occur?
Mould only grows when there is sufficient moisture on a surface or humidity in the air. Common causes include:
- Leaky roofs and walls including blocked gutters and downpipes
- Leaky plumbing.
- Condensation from cooking, showering, clothes drying and from breathing in areas with poor air circulation.
How is mould growth remedied?
The most important actions you can take to prevent mould are those that minimise moisture.
- Fix leaking plumbing and roofs and building defects.
- Ensure gutters are clear and maintained.
- Increase air circulation
Mould can be removed from a surface with soap and water.
Name the measuring threshold for the three categories of cracks.
Fine cracks - up to 1.5mm wide
Medium Cracks - from 1.5mm to 10mm wide
Large cracks - over 10mm wide
Draw and describe the identifying factors associated with typical cracking patterns in walls.
What is ‘Dry Rot’?
Known in scientific terms as ‘Serpula Lacrymans’, dry rot is a wood destroying fungus.
Describe the characteristics of ‘Dry Rot’?
- The timber elements shrink, darken and crack in a ‘cuboidal’ manner
- White, fluffy ‘cottonwool’ mycelium develops under humid conditions.
Describe the different stages of the life cycle of ‘Dry Rot’ and ‘Wet Rot’.
Stage 1 - Spores remain inactive until they come in contact with timber and enough moisture to make them active.
Stage 2 - Hypha (long white strands) grow inside and outside the timber element and allow the fungus to spread rapidly.
Stage 3 - Mycelium (group of Hypha) develops.
Stage 4 - Fruiting bodies develop and take on a mushroom like appearance. Fruiting bodies produce spores that emit from the surface to be carried along by air currents.
When does ‘Dry Rot’ occur?
When timber becomes too wet with a moisture content of 20%. Dry rot can spread on other building elements and materials.
What is ‘Wet Rot’?
Wet rot is caused by a fungus that is attracted to very damp wood and feeds off the timber, destroying it in the process. There are many different types of fungus, but ‘Coniophora puteana’, also known as cellar fungus is the most common.
Describe the characteristics of ‘Wet Rot’?
- Cuboidal or linear cracking.
- Brittle texture, timber will begin to breakdown causing a weakened structure and sponge-like texture.
-White strands across the surface of the timber.
When does ‘Wet Rot’ occur?
Wet rot occurs in timber with a moisture content of around 30-50%. Wet rot cannot spread on other materials other than timber due to the material needing a high moisture content for the fungus to develop.
What are the common defects associated with flat roofs?
- Blistering
- Ponding
- Flashings and falls around openings
What is blistering on a flat roof?
Blisters can be caused by water vapour pressure occurring below the roof covering. The blister should be cut and then re-bonded to the underlay allowing the trapped moisture to escape it first. The source of he moisture should also be traced and rectified.
What is ponding on a flat roof?
Where the appropriate fall has not been built in or has been altered by structural movement ‘ponding’ is likely to occur. Where water is allow to sit on the surface of a felt roof for an extended period its lifespan will be drastically reduced. Could also be due to blocked drainage.
