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Dry Rot

Introduction

Dry rot (Serpula lacrymans) is a wood-destroying fungus that is found in most parts of the world. Although it affects forest timbers, dry rot is best known for its ability to destroy timbers in ships and buildings.

Identification of Dry Rot

It is important to identify whether timber decay has been caused by dry rot or another wood-destroying fungus such as one of the wet rots. This is because dry rot has the ability to travel through building materials other than timber, giving outbreaks the potential to spread quickly through a building. For this reason additional measures often have to be taken when treating dry rot outbreaks over and above those necessary when dealing with outbreaks of other wood-rotting fungi.

Typical indications of dry rot include:

• Wood shrinks, darkens and cracks in a ‘cuboidal’ manner
• A silky grey to mushroom coloured skin frequently tinged with patches of lilac and yellow often develops under less humid conditions. This ‘skin’ can be peeled like a mushroom.
• White, fluffy ‘cottonwool’ mycelium develops under humid conditions. ‘Teardrops’ may develop on the growth.
• Strands develop in the mycelium; these are brittle and dry and crack when bent.
• Fruiting bodies are a soft, fleshy pancake or bracket with an orange-ochre surface. The surface has wide pores.
• Rust red coloured spore dust frequently seen around fruiting bodies.
• Active decay produces a musty, damp odour.

Important Note: Dry rot can cause widespread structural damage. We recommend that a professional timber treatment company is used to carry out a survey if dry rot is suspected. If you suspect dry rot contact our technical department and we will be happy to arrange for an experienced timber treatment surveyor to contact you.

Dry Rot Control and Treatment

Dry rot will only affect timber that is damp, typically affecting timber with a moisture content in excess of 20%. For this reason, removing the source of moisture should form the core of any dry rot eradication strategy.

Timber can become damp for a number of reasons. Among the most common causes are leaking washing machines, shower trays, baths, condensation etc… The dampness can also come from outside the building, for example, leaking roofs, rising dampness, or dampness penetrating through walls. Whatever, the source of the dampness, if it is rectified and the timber allowed to properly dry out, the dry rot will eventually be controlled.

However, it is not always possible or practical to be sure that the timbers will remain dry in the long term. Therefore, it is important that secondary measures are taken to defend against re-infection. Any affected timbers should be removed and replaced with pre-treated timber. Any remaining timbers at risk of being affected by the dry rot should be treated with an effective fungicide. Where the dry rot has passed through the masonry, it should be isolated using physical containment and/or masonry sterilisation.