Damp proofing methods for timber structures

Timber structures are highly durable, sustainable and aesthetically pleasing. However, they are susceptible to dampness and fungal decay due to their organic nature. Exposure to moisture and humidity can cause timber to rot and decay, which can compromise the structural integrity of the building. Therefore, it is crucial to protect timber structures from dampness and fungal decay to ensure longevity and reduce Maintenance costs. This article explores the various treatments and coatings available to protect timber structures from these threats and enhance their lifespan.

Understanding Dampness and Fungal Decay

Before delving into treatments and coatings, let’s understand the causes of dampness and fungal decay in timber structures. Timber absorbs moisture easily, and when exposed to a humid environment, it can create conditions that support fungal growth. If left untreated, the fungi can break down the wood’s structure, cause discoloration, weaken the timber and compromise its durability.

There are two types of fungal decay that can occur in timber structures – Brown Rots and White Rots. Brown Rots break down the cellulose and hemicellulose which cause the timber to become brown and crumble, whereas White Rots break down the lignin, causing the timber to whiten and soften.

Dampness can also cause a variety of problems, including promoting the growth of mold and bacteria, causing metal fixings to corrode, and reducing the effectiveness of insulating materials. Therefore, it is crucial to take measures to prevent dampness and fungal decay.

Treatments to Protect Timber Structures from Dampness and Fungal Decay

There are several treatments that can protect timber structures from dampness and fungal decay.

Pressure Treated Timber

Pressure treated timber is a popular choice amongst Contractors, which involves the infusion of preservatives into the timber to protect it from moisture and fungal decay. The treatment involves placing the timber in a pressure treatment vessel and applying a vacuum to remove the air trapped within the timber. Once the vacuum has removed the air, a water-based preservative is pumped into the chamber under pressure, forcing the solution deep into the timber’s fibers. The timber is then left to dry, and the treatment solution sets in, providing long-lasting protection against moisture and fungal decay.

Chemical Treatments

Chemical treatments are another way of preserving timber structures and preventing fungal decay. They include copper-based compounds, Borates and Triadimefon. Copper-based compounds are mainly used in pressure treated timber, whereas Borates and Triadimefon are used in surface treatments.

Borates provide effective protection against fungal decay and insect infestation by penetrating the timber’s fibers, making the timber unpalatable to insects and fungi. Triadimefon, on the other hand, targets the fungal spores, inhibiting their growth, and breaking down the existing fungal infestation. These treatments reduce the need for regular maintenance and extend the lifespan of timber structures.

Wraps and Foils

Wraps and foils are an alternative treatment that can protect timber from fungal decay, although they are less commonly used. The timber is wrapped in a foil or membrane that provides a barrier between the timber and the environment, preventing moisture from entering and creating conditions favorable for fungal growth.

Coatings to Protect Timber Structures from Dampness and Fungal Decay

Apart from treatments, coatings are an excellent way to protect timber structures from dampness and fungal decay. Coatings provide a physical barrier that separates the timber from the environment, preventing moisture from entering the timber’s surface, and reducing the risks of fungal decay.

Paints and Stains

Paints and stains are popular coating options that offer protection from dampness and fungal decay. They form a waterproof barrier that seals the timber’s surface, preventing moisture from penetrating the timber’s interior. Paints and stains come in different finishes, ranging from matt to satin to high gloss, and there are also tinted options that can add color to the timber, enhancing its appearance.

Varnishes and Oils

Varnishes and oils are another great option for coating timber structures. They penetrate the timber’s surface, providing an extra layer of protection against moisture and fungal decay. Varnishes come in many finishes, including matt, satin, and high gloss. They are long-lasting and offer excellent protection against the elements. Oils, on the other hand, provide a natural look to the timber and do not create a barrier between the timber and the environment.


Can I apply coatings to untreated timber?

Yes, you can apply coatings to untreated timber to provide protection against fungal decay and dampness. However, it is recommended that you use a combination of coatings and treatments for long-lasting protection.

How often should I reapply coatings?

The frequency of reapplication depends on the type of coating used and the environment in which the timber structure is situated. It is recommended to reapply coatings every two to five years to maintain the timber’s protection against dampness and fungal decay.


In conclusion, protecting timber structures from dampness and fungal decay is crucial for ensuring longevity and reducing maintenance costs. There are several treatments and coatings available that can provide effective protection against these threats. Pressure treated timber, chemical treatments, wraps and foils, paints and stains, and varnishes and oils are all excellent options to consider. It is recommended to consult a professional contractor and follow the instructions when applying these treatments and coatings for the best results.

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