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Wet Rot

Wet rot thrives on wet timber and causes damage to property. Just like dry rot, it is caused by a fungus although the infection is less prone to spreading.

There are different types of wet rot, the most common being coniophora puteana (cellar fungus), followed by poria vaillantii (pore/mine fungus) and phellinus contiguus, the latter most often responsible for the rotten wood around damp window joinery.

For any of these fungi to germinate, they need both water and a food source (the wood). The fruiting body begins by sending down a tube (or hypha) into the timber, which then extends and branches out to become mycelium (hyphal threads). These break down the wood, causing either darkening and cuboid cracking (brown rot) or a bleached, fibrous appearance (white rot).

The brown wet rots (especially pore fungus) is often mistaken for dry rot by the untrained eye so a specialist should be sought to confirm the type. Wet rot isn’t as tenacious as dry rot so its diagnosis should lead to some relief for the homeowner. Unlike dry rot, wet rots are unable to grow across or through masonry unless there is a lot of damp on walls adjacent to the rotten wood.

Searching for signs of damp

The first step in defeating wet rot is to locate the entrance point of the moisture, sort out the initial problem and quickly and thoroughly dry the area.

As with dry rot, a rigorous inspection of the home or business is usually needed, both outside and in, to locate the ingress. The following should all be checked:

Outside Roof

  • Broken or absent tiles/slates
  • Damaged or blocked gutters and rainwater goods
  • Damaged surface to flat roofs
  • Defective flashing around chimney

Outside Walls

  • Blocked air bricks
  • Absent or defective damp-proofing
  • Mortar deterioration in brickwork
  • Window sill flashing
  • Cracked water or waste pipes
  • Bridging of damp-course
  • Damage by tree roots or ivy
  • Water tank or cistern overflows

Inside

  • Excessive condensation
  • Bad quality or absent impervious membrane under concrete or stone floors
  • Leaking disused toilet (via a damaged union or pan)
  • Window joinery
  • Under laminate or vinyl laid on insufficiently ventilated wooden floors
  • Flood water between timber and hard floor

Treating wet rot

Once the initial ingress has been found and the situation remedied, the treatment of the fungus can start. Wet rot treatment should be used as the dry rot chemicals are overly powerful and may breach COSSH rulings.

As wet rot is confined to significant areas of damp in buildings, it is easier to find and eliminate the whole fungus than it is with dry rot.

Any badly damaged timber should be cut out and replaced by treated timber or restored with resin or alternative reinforcement systems. In areas prone to damp on walls, for example cellars, any replacement timber should be pre-treated and, ideally, steel joist hangers used to keep the new wood away from the walls.

Unlike with dry rot, it is rarely necessary to sterilise masonry.