Dry Rot

Dry Rot Cubiodal crackingDry Rot is the term which refers to wood decay caused by certain species of fungi that digests parts of the wood which give the wood strength and stiffness. It was previously used to describe any decay of cured wood in ships and buildings by a fungus which resulted in a darkly colored deteriorated and cracked condition.

In certain buildings, particularly those with solid 9 inch (or greater) brickwork and those which inherently were built using mortar and lime there is a significant increase in the number of cases of dry rot . Dry rot has been known to travel through and along the wall surface behind plaster and render therefore it is a highly recommended that where dry rot is found, plaster and wall coverings should be stripped back to a metre past the infestation in all directions and the whole area treated. However, given that dry rot attacks only wet timber, common sense should dictate that plaster need not be removed where there is no timber or any timber is dry (outside the zone of wetting that caused the outbreak). Identifying the source of water and allowing the affected timbers to dry will kill dry rot, as it is a fungus and requires water to survive.

Dry Rot Fruiting BodyTypical indications of dry rot include:

  • Wood shrinks, darkens and cracks.
  • A silky grey to mushroom coloured skin frequently tinged with patches of lilac and yellow often develops.
  • White, fluffy 'cottonwool' is normally present.
  • Strands develop in the main fungus and are brittle and when dry and crack when bent.
  • Fruiting bodies are a soft, fleshy pancake with an orange-ochre surface.
  • Rust red coloured spore dust.
  • Where decay is active it produces a musty, damp odour.

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

Wooden beam with Timber can become damp for a number of reasons. Among the most common causes are leaking washing machines, shower trays, baths, and condensation through poor ventilation or clothes drying on radiators. The dampness can also come from outside the building, for example, leaking roofs, rising damp via a ruptured DPC course or penetrating damp through brickwork. Whatever, the source of the dampness, if it is eradicated allowing the timber to completely dry out, this will in turn control the dry rot.

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.