How to Treat Dry Rot in Timber - Armstrong Supplies - Armstrong Cheshire
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How to Treat Dry Rot in Timber

How to Treat Dry Rot in Timber

Sarah Macklin |

When dry rot gets into your timber, it can be difficult to get rid of. However, the good news is it’s treatable, so don’t give up just yet! 

We’ve produced this article that explains exactly what dry rot is, how you can find it and how you can get rid of it, particularly in wooden fence posts. 

What is dry rot?

There are two different types of wood rot - wet and dry. Wet rot is a fungus that develops on surfaces that have a high moisture content of 50 per cent and above. It doesn’t spread through masonry and the wet rot can be treated by figuring out where the moisture is coming from and fixing the problem. 

Dry rot is also a fungus that eats away at and destroys wood. Its full name is Serpula lacrymans and it mainly affects forest timbers as well as timber in ships and buildings. It develops on surfaces that have a relatively low moisture content of 20 per cent and above. 

Wet rot can usually be identified by a damp, musty smell in the building or the cracking of timber that seems discoloured and distorted. For dry rot, there are quite a few signs you can look out for, most of which we’ve outlined below. 

How to detect dry rot

There are various signs that you should look out for to determine if you have a dry rot problem. These include: 

  • Shrunken wood that’s cracked and flaking
  • A grey coloured skin that has grown over the wood
  • Red/orange spore dust that’s covering the floors
  • Cotton wool-like growth on the timber
  • Grey strands hanging from dry rot areas that look like cobwebs
white fungus growing on a rotten wooden beam


Once you’ve identified that you have dry rot, you need to determine what the cause of it is. As previously mentioned, the fungus that causes rot likes damp places. You should check the roof isn’t leaking and that the drainage pipes are drawing the water away properly. You should also check the fixtures and fittings around the sinks, toilet and bathtub to make sure none of these are leaking water.


How to treat dry rot

The first stage of treating dry rot is to fix the cause of the excess moisture so that the wood can dry out. Then, you need to determine how far the dry rot has spread. You should open the affected area by removing any plaster and floorboards to see where the rot ends. 

The area that’s been damaged should be removed, as well as at least 50cm beyond the damage to ensure that all the fungus is cut away. You’ll need to clean away any spore dust and the fungus that’s grown in clumps that looks similar to cotton wool. A bristled brush can be used if needed. 

You can then put new timber in place of the old wood, and make sure it is protected with a dry rot treatment fluid to make sure the fungus doesn’t come back. 

As long as the moisture content of any timber in your home remains under 20 per cent, the dry rot spores become dormant and cannot damage the wood. This means that you can prevent rot in your home by keeping it dry and well ventilated. Open your windows whenever you can, and always use the extractor fans above your cooker and in your bathroom to take away excess moisture. 


How to stop wooden fence posts rotting

Wooden fence posts are prone to wood rot. This is because they’re subject to a lot of rain. The ground around the fence posts can become saturated with water when it rains and, as this water cannot drain away, it is absorbed by the fence posts. Many people find that their wooden posts need replacing after just a couple of years. 

wooden fence posts with a wooden fence and green grass


If you’ve had experience of this in the past, you could invest in fence posts with built in postsavers. The wooden fence posts have a barrier sleeve where the post meets the ground. The sleeve is made from tough polythene that prevents fungi and moisture from getting into the post. A postsaver could allow your fence post to stay in good condition for up to 20 years. 

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