Wet rot is a general name for the damage caused by any of several fungi, the most common of which are Conio-phora cerebella and Fibroporia vail-lanti.

The paint film on this window sill has cracked, allowing water to penetrate and wet rot spores to enter.

The end grain of this timber clearly shows evidence of decay due to wet rot. The timber has swollen and cracked.

These fungi require more moisture than dry rot fungus and develop where timber is in direct contact with wet or damp surroundings. Exterior joinery, where the paint film has cracked allowing water to penetrate, is a typical starting point for wet rot. The remaining paint film prevents any water drying out by evaporation, so the wood swells, joints open and wet rot spores enter the cracks.

To detect the first signs of wet rot, inspect any cracked paint on window sills or door frames. A thin veneer of surface wood may conceal a soft, dark mass of rotted wood dust beneath. The fungal strands of wet rot fungus are thinner than those of dry rot and are dark brown in colour. When growing over wood, these strands often develop a fern-like shape.

How to Treat Wet Rot

Outbreaks of wet rot are much more frequent than those of dry rot but are seldom as difficult to treat. The fungus stays around the original site of damp wood in which it germinated, making it easier to isolate.

The treatment itself is less drastic than that required for dry rot. If the cause of dampness is rectified and the timber is allowed to dry out, there should be no further growth. Therefore, it is necessary only to cut out affected wood, which has been seriously weakened by the rot.

However, it is essential to make sure that timbers around affected areas are treated with fungicide. As the timber dries out the moisture content falls until conditions are just right for dry rot to occur.

To check the extent of damage in decaying wood, prod all timbers in the affected area with a strong, pointed tool such as a bradawl. If the bradawl sinks right into the wood, then it is badly decayed.

Cut out and burn all timber that has suffered breakdown and remove all dust, dirt and debris. Select thoroughly dry, well-seasoned timber for replacement, cut it to size and treat it as for dry rot. Also treat the surfaces of adjacent timbers and brick, block and concrete areas with fungicide before installing the replacement wood section.