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What's the difference between Wet and Dry Rot?

We will be right to think that rot involves moisture as most cases of damage from rot is thanks to dampness. You'll also be right in thinking that rot comes about thanks to fungi.

Both wet rot and dry rot will effect timber in different ways yet all negatively.

The main difference between wet rot and dry rot is the moisture content needed in order for each to exist.

  • Wet Rot: Requires a moisture content of around 50%.

  • Dry Rot: Requires a moisture content of 20 to 30% in order to germinate.

If you suspect rot then the first thing you need to do is to identify what rot you have in order to deal with the problem. Both dry and wet rot do have some similarities in that both require moisture, both are a fungus, both can cause significant damage to wood.

There are though more important things to realise and that are the differences:

  • Wet rot is the more frequent of the two.

  • Wet rot is occurs usually at the location of dampness on timber.

  • Wet rot can cause discolouration of timber.

  • Dry Rot is only caused by the fungi Serpula Lacrymans.

  • Dry Rot is notorious for spreading (on untreated timber of above 20% moisture).

  • Dry Rot timber can feel soft and spongy to the touch.

  • Dry Rot offers a damp and musty smell.

In order to deal with dry or wet rot you first need to realise they are present (not all rot is clearly visible in that in occurs in roof spaces and under floors. Once identified you will need to located the source of dampness such as faulty plumbing, external water penetration such as via defective rendering.

Treatment of Wet Rot: Areas where rot occurs can be not in view such as roof areas, under floors. If upon spotting rot it may pay to investigate the immediate area especially if dampness has effected a wider area to where the wet rot was discovered. You will need to of course stop the source of water / dampness!

Damaged timber needs to be replaced or structural timber repaired. Treatment will be required on remaining timbers and new timbers will have to be pre treated.

Treatment of Dry Rot: You will need specialists in order to rid of dry rot, check your local list of professionals to see who offers this service. It would be advisable for a larger survey to be completed should you have dry rot to make sure there is no other effected timber.

The effected timber will need to be removed, the immediate area treated (masonry with biocide) and replacement (treated with fungicide) timber installed. Large timber members (structural) can sometimes be repaired and treated on site.

Title image: Pixabay

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