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Wet rot a general term used to cover the majority of timber decaying fungi. The two main types are brown rot and white rot.


Wet rot requires moisture to begin, wood being hygroscopic and so will absorb moisture from materials it is in contact ie wet walls, earth and high humidity’s similar to that which aid Aspergillus like moulds.  Bacteria & micro fungi colonise resulting in partial breakdown of the cell structure, the timber then becomes more porous. Timber with moisture sustained above 30% MWE provides perfect rutting for timber to become infected and wet rot to colonises, germinate and lead to decay

Spores land on cellulose material, germinate and produce hyphae growth (this is the starting process and the rooting structure). Each hyphae releases chemicals (enzymes) into the surrounding wood. Decay is caused by the process of these chemicals dissolving nutrients in the wood. The nutrients are then absorbed by the fungal hyphae, enabling further growth.

After time rot becomes stressed from one of the following:-

  1. lack of water (moisture)
  2. air
  3. lack of food (cellulose material like timber)
  4. exposure to light
  5. a disturbance to its habitat

The rot will form a sporophyte, or fruiting body (reproducing spores). This is it reproductive organ, sending out possibly thousands of spores with the hope a spore can land in another suitably wet timber, which is the perfect environment. 

Fungal growth can be rampant in the right conditions and has been known to travel 2m per year and up to 4m  in laboratory conditions. It generally needs severe water ingress to start off, for example a leaking gutter, a cracked down pipe, rising damp etc.


Wood loses its strength/ weight and breaks in to cubical pieces.

Larger sectional timbers can appear sound to the surface. This may only be a 2-5mm veneer where the infection has travelled through the inner core of the timber, so special attention will be required for large sectional timbers which are within contact of this fungus infected materials.  Engineers reports are likely to be required in these circumstances.


Wet rot spores are omnipresent (in the atmosphere all the time) as the spores are air born all cellulose material is susceptible to attack given the right conditions

Wet rot fungi call for special attention. It is important to identify the source or sources of the moisture ingress.

The fungi derives no nutrition from masonry and causes no significant damage to the masonry itself, although the fungi is able to spread over some masonry surfaces. For this reason prompt remedial action is required after the discovery of fungus. Drying of the wall and the associated timber will therefore prevent further spread of and damage by the fungus.

Wet rot doesn't have the same ability to conduct moisture like that of Serpula Lacrymans ‘dry-rot’ allowing the fungus to spread from an attack in damp timber to adjacent, poorly ventilated voids where it is able to introduce additional water to marginally damp timber which might otherwise remain just below the moisture threshold for decay.

Gloss/vinyl paints and other impervious coatings can trap moisture in skirting and joists and these can assist the fungus growth. 

Wet rot requires three elements to sustain growth which are:-

Water, air & food (Timber-Cellulose)

Wood is composed of cellulose and lignin. Wet rot comes in two varieties - brown rot and white rot - each of which attach the wood differently.

Brown Rot

Brown rot can only attack the lignin. It leaves the wood cross cracked and brown similar to that of the dry rot fungi. However the cubidol cracking (timber cracking along and against the grain) is generally smaller in size than the 25mm of  ‘dry-rot’ (Serpula Lacrymans) so you can’t identify the fungus on this alone.

White rot

Wet rot that attacks both the cellulose and lignin is known as ‘White rot’.  It has a bleaching affect on the timber leaving it in a fibrous, straw-like condition often found on external joinery.

Cellar FungUS

One of the most common forms of wet rot is Coniophora Puteana or ‘Cellar fungus’

Many wood boring insects can be associated with rot and decay, like Pentarthrum Huttoni ‘or Wood boring weevils’.  Remedial measures in this instance are to remove the source of moisture, promote rapid drying so the infected/ infested timber will dry and decay so the fungus can no longer colonise, which causes the weevils will leave. No chemical treatment necessary. 

The fungus is relatively restricted to the area of wetting and doesn't have the ability of transporting moisture or growth through the substrate, as does dry rot.  Although wet rot is able to grow over the surface of non–wood material, it rarely grows through masonry material, it doesn't have the same ability to transport moisture and colonise wood that is below the 20% threshold.

Strands may be found growing at the interface between brick and lime sand plaster, the decay takes no nourishment from the masonry and  cannot cause any deterioration of the masonry.

This growth and decay can only take place where timbers are suitably wet.  WME of 22% can aid growth, for a more rapid out break then WME of 30%  or greater is required. Wet rot can grow over the surface of old lime mortars and lime plasters where the alkalinity has become reduced over time. High alkalinity, as found in fresh lime or cement mortar, will normally prevent this, although growth over the surface of new masonry is possible, the decay causes no direct damage to masonry.


Establish the size and significance of the infection as wet rot is limited to the source of moisture. Locate and remove the moisture source. In some basic terms cases, removing the source of moisture will cause the rot to die. Cut out rotten wood. Treatment may differ from property and infections, We highly recommend requesting a specialist survey and investigation to determine remedial action required

Timbers with a WME of 20% or less are not at risk of wet rot infections.

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