Wet Rot or Dry Rot? Wet Rot only affects timbers that are very wet, i.e. where they have a moisture content of over 24%, and Dry Rot prefers a slightly lower moisture content of between 18% and 22%. This dampness may be caused by inadequate ventilation to sub-floor areas, the proximity of the timber to wet or damp walls, rising or penetrating dampness, and water leaks such as from sinks and baths, poorly maintained roofs, and general unwanted water ingress. The spores for all types of timber fungi are in the air, in the same way as are pollen, mould and viruses, and, in the same way, they are harmless until they land on a sensitive host.
There are several different types of Wet Rot, each having its own characteristic growths, strands and fruiting body. Damage to the timber causes it to become very weak and can even be broken up by hand once the attack has developed. The strands, coloured depending on the type of Wet Rot, can grow on to adjacent brickwork or plaster, but cannot damage this. Wet Rot can be a brown rot or a white rot; the white or brown does not refer to the colour of the fungal growth. The brown rot causes the wood to darken and break in to smallish cuboidal cracks, whereas white rot causes a lightening of the timber, and damage is manifested along the grain.
Wet Rot Treatment
All types of Wet Rot require the same treatment. Find the cause of the moisture, remove the source, make sure the surroundings dry out quickly, and remove or repair damaged timber. Damaged parts of the timber will need to be cut out as they will no longer be strong enough to do their job. If the rot is seen in an enclosed area, you’ll need to increase the ventilation to ensure the area dries out quickly.
Dry Rot is different in as much as it can travel through masonry. It will affect timber that has been made damp in the same way as for Wet Rot. When Dry Rot spores land on something suitable they develop into a soft cotton-wool like form, from which white strands are produced, extending along the timber or masonry. Eventually a part of the rot area thickens and darkens, and produces reddish dust. This is called the ‘fruiting body’, and this dust is the new spores.
The Dry Rot eats all of the nutrients in the timber, causing large cracks as it is emptied of its strength and fibres. When the initial food source is exhausted the strands travel through masonry and between plaster and brickwork, in search of the next host.
Dry Rot needs to be stopped as it can travel throughout a property, taking its own moisture supply with via these strands. It can cause severe damage if allowed to get a hold on wall plates and other structural timbers.
Dry Rot Treatment
Dry Rot treatment requires that the extent of the outbreak is identified. Floorboards may need to be lifted, panelling removed, etc. It is better for this to be done at the outset, rather than a half-treatment undertaken. Again, you will need to determine the source of moisture, and halt this. All affected timbers will need to be cut out to ensure that any signs of growth within are gone to approximately half a metre beyond the last signs, and the area needs to be dried as quickly as possible.
Any masonry in contact with any strands etc., and this includes the soil below ground floor timbers, needs to be thoroughly cleaned, and treated with a masonry steriliser, or biocide. Thicker walls require drilling so that this biocide can be injected in, as well as surface sprayed.
All surrounding timbers that can remain need to be sprayed with a biocide to ensure that any strands or spores are killed. Many types of woodworm are associated with partly decayed wood, and it is recommended, and preferred by contractors who may have to insure this work, to use a combined Dry Rot treatment and Insecticide at this point.