The decay of timber in contact with dampness is generally due to fungal attack. There are two types of fungal attack found in buildings - dry rot and wet rot. Both require timber moisture content in excess of 20%. Timbers most at risk of dry rot are in the range of 23% moisture content. Dry rot requires more extensive treatment than wet rot so accurate diagnosis is critical. Very often dry rot and wet rot are confused even by experienced surveyors. It is therefore advisable to instruct a CSRT qualified surveyor to diagnose the type of decay and recommend the appropriate remedial treatment.
Dry rot (Serpula lacrymans) is one of the most serious threats a property has. If left unchecked it can lead to extensive damage both to the timbers and masonry, spreading throughout a building.
Dry rot generally establishes itself in areas where there is typically limited ventilation such as in a sub floor and usually results from a plumbing leak or rainwater entering through defective masonry or poorly sited air bricks. Dry rot feeds on the cellulose content of timber leaving it weakened often to the point of structural collapse.
Dry rot has four components: hyphae, mycelium, sporophores and spores.
The hyphae or strands are usually off-white in colour and have the appearance of a root system. Their purpose is to transfer nourishment through the other components of the fungus and to search out new food sources. The mycelium usually takes more of a sheet or skin form but variations occur. It is usually accompanied by a mushroom type smell. The sporophore or fruiting body is the reproductive mechanism of the fungus. It appears either plate or bracket shaped and has a rusty red appearance usually with a pale off-white perimeter. Other colours such as lilac can also be present depending on humidity and other conditions. The sporophore ultimately bursts to release thousands of rusty red spores over the surrounding areas. The spores are individual 'seeds' each with the potential of creating a new outbreak of dry rot.
Dry rot treatment has to be extensive. All traces of the fungus should ideally be removed. Directly affected timbers along with those in contact with affected areas should be replaced and masonry sterilised. Sub floor areas need to be scraped and cleaned to remove any dry rot spores. Timber and mortar used for re-instatement work should also include fungicides. Any new plasterwork should be chemically modified. Ventilation should be improved where necessary and the moisture source removed.
