How to combat fungal decay in timber

Published Sunday 28th June 2015

Timber is a much-loved material across all types of construction, renowned for lasting a lifetime. However, it has an ancient adversary, honed by evolution to exploit the very conditions that make timber such a favoured construction staple – fungal decay.

Rot can be a crucial setback in any construction project. That’s why we’ve put together this guide on what to look out for and the steps you can take to ensure your timber retains its strength and longevity.

Fungal Decay

There are two main types of fungal decay – dry rot and wet rot. While both thrive in damp conditions, one is more detrimental to timber than the other. We’ll take you through the different characteristics of these types of rot and the ways you can combat them, but first, here’s a bit of background on how infestations occur:                                                                                                                                                                                             

Many organisms have evolved to use timber as a food source – maliciously eating away at the wood, which results in a loss of weight and completely saps the strength of it.

While wood-rotting fungi differ in their optimum temperature for breeding, the majority will thrive in temperatures between 20-30 degrees celsius and the fungus is rapidly killed above 40 degrees. Wet rot fungi usually occur in persistently damp conditions needing an optimum moisture content of 50-60 per cent, while dry-rot optimum growth occurs at just 30-40 per cent. Removing these conditions will stop the rot from growing.

So now you have an overview of the way fungal infestations work, let’s delve into the differences between dry rot and wet rot and the ways you can tackle them.

fungal decayDry rot

Often described as the ‘cancer of buildings’ dry-rot fungus (or ‘Serpula Lacrymans’) will destroy everything in its path - from structural timbers and skirting boards, to door frames and flooring. The fungus thrives in damp, unventilated conditions and while damp timber is the first area to be affected, the infection will then spread wildly to other dry parts.

Commonly affected areas in a property are typically those overlooked, hidden areas, such as floor voids, or behind timber panelling. But don’t worry, we’ll take you through what to look out for, so you can seek out and destroy the rot before any extensive damage occurs.

How to spot it: In its early stages, the fungus appears an off-white colour, with a cotton-wool like texture. If left untreated, it can develop into thicker, fungal strands and if exposed to sunlight, the colour can change to a yellowish tinge. You’ll also notice a distinct, unpleasant smell.

You’ll be able to tell if your timber is entirely dry-rot decayed as it will crumble between your fingers. The fungus leaves deep cracks running across the grain as well as off-white sheets of the fungus on the wood.

How to treat it: The first step to take is to identify the source of the damp – and eliminate it. Damp could be caused by a number of culprits, such as a leaky drain-pipe, condensation, a missing roof-tile or blocked air brick.

Once you’ve dealt with the culprit, you’ll need to thoroughly ventilate the area. The best way to do this is to use dehumidifiers, while keeping the heat on low – this will remove the moisture it thrives upon and ultimately reduce the chance of the fungus continuing to spread.

Then the affected area of the wood should be removed – this involves getting rid of, not only the visible signs of fungus, but also removing 60cm either side of the infection just to be sure. Whilst it might seem brutal, being vigilant at this stage is vital to remove those nasty fungi.

Any timber adjacent to the affected area can also be treated with extensive chemical fungicide treatments to ensure the rot doesn’t spread any further.

fungal decayWet Rot

Wet rot is caused by a fungus called ‘Coniophora puteana’ – also known as the ‘cellar fungus’. While both types of rot are lovers of all things damp - this type of fungus is more common and is only attracted to very damp wood or plaster and will just be confined to the wet area, unlike dry rot. As such, wet rot is generally considered less destructive, but can still prove hazardous if left untreated.

How to spot it: Not only will the timber be damp to touch, it will have spongy feel and often look darker than the surrounding healthy wood. However if the wood is painted this will not be as noticeable and what may appear quite healthy can be rotting behind a mask. The way to discover affected wood in this case, is by poking it with a screwdriver – if it bounces slightly, you have a problem!

How to treat it: In the same way we discussed treating dry rot, you firstly have to eliminate the source of water damage before removing and replacing the affected timbers.

As you can imagine, because the fungus only remains on the damp area of the wood, it is easier to notice the affected area that needs removing. However, we still recommend a 60cm allowance either side.

The green approach

A greener approach to tackle timber rot is to use environmental controls – which simply involve controlling the surrounding environment, ensuring a well-ventilated area. We touched on how to do this briefly above, such as using dehumidifiers to reduce the moisture content of timber. 

Ideally, the moisture content of all timber should be below 16-18 per cent. The timber needs to be isolated from damp masonry by air space or damp proof membrane, allowing free air movement. And finally, all other sources of water should also be eliminated, like leaking plumbing or rising damp.

These environmental controls are designed to avoid the use of potentially hazardous and environmentally damaging chemical pesticides where possible, which will ensure the future health of the building or product. It will also reduce the need to expose and cut out the infected material and minimise the damage to the fabric and the finishes of a building, which will be cost effective too.

Anything else?

We hope we’ve provided you with some clear instructions on how to prevent timber and rot and what to look out for, but if you’ve had any problems with fungal decay you’d like to share, or want to know more about any of the topics discussed above, then feel free to contact us via Twitter.

And be sure to check out our range of treated timbers that boast high rot resistance, or simply get in touch to find out more today.