A Destroying Fungus
Wood is a very hard-wearing material and is resistant to most kinds of fungi or biological attack. However, when it’s subject to prolonged damp or wet conditions and the moisture content is raised to above 20%, it can be susceptible to the dry rot fungus. This wood-rotting fungus breaks down the cells in wood and causes it to lose its strength.
Today most homes and buildings are well designed and professionally constructed and if they’re also maintained properly the fungus that is dry rot should not develop in any of the timbers. However, the hidden wooden timbers in a home or building can be subject to prolonged exposure to moisture that we don’t know about and it’s here that serious problems can result.
Prolonged damp conditions
Some of the most common causes of prolonged wet conditions are leaking baths, shower trays or washing machines, where water continually seeps under floorboards and soaks into the timbers. A build-up of moisture can also occur as a result of rising damp that penetrates the walls of homes and allows moisture to build up in the timbers. The good news is that if it’s caught in time, and the timber is allowed to dry out properly, dry rot can be controlled.
Types of wood rots
There are two types of fungal wood rots: brown and white.
- Brown Rot causes the wood to crack across the grain and also darkens the colour of the wood. If the decay has been going on for a protracted period of time, the wood, when dry, will crumble to a fine dust.
- White Rot causes the wood to become lighter in colour and in weight. It also causes the wood to become stringy in texture but there’s no cross cracking.
Dry rot fungus
Brown and white rots are known collectively as wet rots, however, one brown rot is commonly referred to as dry rot. It’s not so important to know the difference between the wet rots, but we should know the difference between the wet rots and the dry rot.
What makes the dry rot fungus special is its incredible ability to travel through building materials other than timber. It can spread behind plaster and through brick walls and this can make effective dry rot treatment much more expensive than wet rots.
The first thing to do is identify whether the wooden timber decay has been caused by dry rot or one of the other wood-destroying fungi such as brown or white rots. Because dry rot can travel through building materials other than timber, it has the potential to spread quickly through a building. This means that over and above the treatment required to deal with other wood-rotting fungi, in the case of dry rot, additional measures such as masonry sterilisation often have to be undertaken.
Dry rot indications
- The affected wood will normally darken, shrink and crack in a cube-like manner
- A mushroom-coloured or grey skin, often tinged with patches of yellow and lilac, will appear on the timber
- A type of fluffy, white, cotton wool develops
- The wet decaying wood will produce a musty odor
- Strands can be seen which are brittle and when dry can crack
- Rust or red-coloured spore dust can often be seen
- In the final stage, the fruiting body, a soft, fleshy pancake with an orange-ochre surface, will pump new microscopic spores out into the surrounding air
Dry rot treatment
As dry rot can cause widespread structural damage, it’s recommend that a professional timber treatment company is called in to carry out a survey and issue a report on the best way forward in terms of treatment.
In the first instance, removing the source of moisture from any timber will form the basis of any dry rot treatment. However, as it’s not always possible to be know if the timbers will remain dry over the long term, it’s vital that other measures are quickly put in place to defend against re-infection.
All affected timbers need to be removed and replaced with pre-treated timber. Any remaining timber that may be at risk of being affected by the dry rot should be treated with an effective fungicide. Where dry rot has spread and passed through masonry, it should be isolated using containment and/or masonry sterilisation.
There are a range of effective fungicides for the treatment of dry rot, which are able to penetrate more deeply into the timber than conventional preservatives. This gives them an added performance advantage, as wood preservatives only start working once they come into contact with the fungi they’re designed to defend against.
Written by Mike James, an independent writer working with a small selection of RICS Chartered Surveyors, including Harrogate based Bradley Mason – who were consulted over the information in this post.