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.

Prevention of fungal attacks

In order to prevent the attacks of fungi it is essential that all timber should be properly dried before it is used. Once it has been installed the next step is to ensure that there is adequate ventilation, particularly of roof spaces and of the space below the floor boards on the ground floor. Ventilation louvres should be installed and these should not be closed in winter.

Damp may also arise from leaking drains and gutters, and from condensation arising on the inside of external walls.

If such constructional measures are not sufficient to prevent fungal growth it may be necessary to resort to chemical treatment, using one of the numerous substances which render the timber unsuitable as a substrate for fungi.

The surface of the timber can be painted or sprayed with the chemical, or the wood can be immersed in it, if this is still possible.

However, this will only protect the surface as the penetration of the chemical will be very limited, depending upon the type of timber, the nature of its surface and the degree to which it has been dried. The most efficient method of protecting timber is to impregnate it with the chemical, preferably under pressure, so that this reaches all parts. The heartwood of some trees cannot be impregnated but generally speaking this is protected naturally, e.g. in oak and pine.

Once the source of the damp has been traced and suitable countermeasures have been taken, it would be advisable to identify the fungus involved. This will usually involve consultation with an expert, al- though in some cases an experienced building craftsman may be able to help.

When dry rot has been identified it is essential that all the infected timber is removed and burnt in order to prevent the dispersal of the spores. In the case of panelling and floor boards it is advisable to remove about half a metre of timber beyond the infected area.

Adjacent brickwork should be carefully cleaned and then scorched with a blowlamp. Newly installed timber must, of course, be completely dry and it should have been impregnated under pressure.

The measures recommended above would apply in cases of serious attacks by other fungi, and here again the advice of professional experts can be sought.