Fungus in timber

Fungi are plants and therefore do not really belong in this book. Nevertheless they are often associated with animal pests and are therefore worth considering quite briefly.

There are several different species of fungus which attack timber in houses, but they only do so when the timber is damp. This may happen when timber is used before it has had time to dry out, but more often it is due to water coming in through the roof or from an overflowing drain, or through lack of ventilation.

Such fungi are most active when the timber has a water content of 30-50 per cent. Timber that has been attacked by a fungus is usually dark brown to black when wet. One of the common species is the yellow Coniophora cerebella.

DRY ROT is caused by the fungus Merulius lacrymans which can thrive in timber with a water content as low as 20 per cent, and once an attack has started the fungus can spread to dry timber, because it brings with it the water derived from the break- down of the original damp timber.

Dry rot can spread several metres through cracks and over masonry and cement, which it cannot feed on, in order to reach timber. The fungus is also distributed by its spores, produced in millions, which cover the floor and furniture as a brown dust. The spores are also spread by the wind. Dry rot mainly attacks softwoods, but sometimes also beech and oak.

Many other fungi, known colloquially as moulds or mildew, attack timber through which they spread relatively slowly, without producing any fructification comparable to the familiar mush- rooms and toadstools. It is interesting that quite a number of animal pests, mainly insects will only attack timber that has already been attacked by fungus. Certain dark mildew-like fungi produce a bluish discoloration of the timber. This occurs particularly in new timber with a water content of 50-80 per cent. The timber is not weakened mechanically.

Some moulds only grow as surface films, as for instance on wet timber and sometimes also on the inside of cold external walls where water condenses.