Water damage in buildings and the prospect of timber decay
Should timber decay be expected without question, and what can be done to minimise the risk?
by Dr Matthew Green
A fungus that might appear after several months is the ‘Elf Cap’ (Peziza sp.). This fungus also does not harm timber; instead growing on plaster and debris. Its presence does highlight the need to remove debris from the building as it will prevent the structure from drying and promote the growth of more serious decay fungi. The mycelium is white, although the fruiting bodies are far more obvious. They are fleshy and lobed, often growing on plaster on floor coverings.
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Examples of Peziza sp. (Click on the above images for larger versions)
Among the first fungi to cause damage to timber that might occur in a drying building within the first year is an ink cap fungus Coprinus domesticus. This fungus can cause decay in hardwood laths, a problem in period suspended ceilings. It is also found growing on building debris, particularly where an original ceiling or lining has been covered with a more recent finish. The mycelium is a gingery-red colour and is grows as bristled tufts or a thin sheet. The fruiting body of this fungus is a slender toadstool with a white cap that turns inky black as the spores are released.
Example of Coprinus
sp.
Eventually, evaporation of water from the walls slows down and the
building enters a second stage of drying. Water evaporates from small
pores and moves from deep inside the walls to the surfaces. This stage
of drying may take years to complete and varies dramatically with the
construction of the building.
It is during this protracted stage that an outbreak
of dry rot may become visible. It is not the case that the building
suddenly becomes susceptible to dry rot attack, or indeed that a building
‘dries through’ a phase where dry rot can attack it. A dry
rot spore requires a substantial amount of fresh water (rather than
ground water) in order to germinate and grow. A water-damaged building
is by no means assured to experience a dry rot outbreak indeed; if the
joinery timbers are oak, it is highly unlikely. However, if the building
has a history of dry rot a dormant outbreak may attack with renewed
vigour. It is important to ascertain this before any stripping out or
exposure works are undertaken as it can change the focus of the drying
regime.
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