Timber Decay and defects Flashcards
How would you identify dry rot?
Wood crumbly
Light in weight
Dark brown colour
No longer has fresh or resinous smell of sound timber
Cuboidal cracking
(note - beware as it can resemble wet rot)
What are the different types of timber decay?
Wet rots and dry rots
What is the difference between brown and white rot?
Brown rots - cause the timber to become darker, and crack along and across the grain. Very decayed timber will crumble and turn to dust. Can be both dry rot and wet rots.
White rots - Cause timber to become light in colour and lint like in texture without cross cracking. All white rots are wet rots
What conditions are necessary for dry rot to develop?
Damp conditions - Grows best in conditions above 30% moisture content, and can’t grown in conditions below 20% moisture content
(internal timber should be c. 9-14% in heated environments, c. 15-19% in unheated or externally)
Dry, still air - where sufficient ventilation is not in place, and heating is inadequate
Sufficient food source - Cellulose is needed. The fungus can also send hyphae across plaster and other non timber food sources for several metres until timber is reached.
Which fungus causes dry rot?
Serpula Lacrymans
What treatments are available for dry rot?
Prevent further moisture entering the building
Drying out the moisture which has already entered
Remote rotted timber
Treat remaining timber with preservatives
Replace remove timber with preservative treated timber
Damp timbers supported on masonry should be separated from the masonry with DPM or joist hangars
Eradicate the fungus:
- Surface application of fungicidal fluid
- Fungicidal renderings
- Preservative plugs or pastes
Where would you commonly find the dry rot fungus?
Beneath floorboards
Behind panelling
Behind plaster walls
Cellars
Where timber is in contact with brickwork
What are the common signs dry rot might be present?
Softening of timber
Mushroom odour
Shrinkage and distortion
Can you name a common wet rot?
Coniophora puteana or Cellar Fungus
Coniophora marmarata
What are the growth characteristics of Dry rot?
Four stages of growth:
Spores
Hyphae - delicate filaments called hyphae
Mycelium - mass of hyphae appearing as white fluffy growths or sheets of pearly grey or white colour
(strands - these form behind the mycelium to conduct food and water - to identify dry rot from wet rot if these are dried overnight they will become brittle)
Fruiting Body - Shaped like pancakes or brackets and tough and fleshy when wet but brittle when dry. Centre covered with shallow pores of folds where spores produced. Can form under floors or other concealed locations.
How can dry rot and wet rots be distunguished?
Fruiting bodies are distinctive and offer a good method of identification
The colour and appearance of mycelium and strands
Form of the decay - brown rot or white rot?
Where can information to identify timber decay be found?
BRE Digest 299 - Dry rot
BRE Digest 345 - Wet rot
What do brown rots and wet rots feed on?
Brown rots - Cellulose
White rots - Lignin
What conditions are necessary for wet rots to develop?
Timber moisture content above 22%
Saturated timbers
Various wet rots have different conditions in which they grow however. Coniophora Puteana for example needs very wet conditions. Coniophora Marmorata generally lives in floors and cellars. Others need higher temperatures, timber in contact with brickwork etc.
What are the common signs wet rot might be present?
Damp earth smell like rotting soil
Soft and spongy timber
Shrinkage
