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What is treated timber?

It’s a term that is used quite widely, with consideration to both domestic and commercial applications. What we aim to clearly define is commercially treated timber that might be purchased in timber merchants or used in all manner of construction and contract work.

A natural product

Whilst timber is a beautiful and sustainable material to use, both inside and out, it is a completely natural product and without any form of treatment, it will deteriorate over time. For internal timbers such as joists, trusses and framework, that might be deterioration from insects and fungi, whilst for timber that is used externally, damage can come from environmental factors such as the weather and locational specifics such as soil or water.

In all of the above situations (and many more) the service life of the wood can be maximised by choosing treated timber.treated timber

What’s the treatment process

The principle of creating commercially treated timber is generally the same, whatever the specification of treatment. The packs of timber are manoeuvred into large tanks which are then closed and filled with the appropriate preservative chemical and water. 

The treatment process is either described as high pressure or low pressure and which to use is determined by a number of factors. High-pressure timber treatment, such as our TreatWright HP brand, can also be called vacuum pressure timber treatment. The chemical mixture penetrates deep into the wood to provide long-lasting protection.

Commercially treated timber offers a thorough and professional result every time and delivers excellent durability.

When to use low pressure treated timber

Internal timbers tend to be treated with a low-pressure process. In terms of Use Class, this is 1 and 2. WJ Group offers its TreatWright LP brand of low pressure treatment. Typical applications include CLS framing, joinery, trusses and flooring. The treatment protects against inserts and fungi for the lifetime of the building. If the timber is going to be exposed to moisture (such as window frames) then the treated timber will need a coating to help protect it.

Low pressure timber treatment uses less water and so the wood returns to its optimum moisture content and dimensions far more quickly. It also remains a more natural colour, compared to high pressure treated timber.

When to choose high pressure treated timber

If the wood is to be used outside, high pressure timber treatment will be required. In Use Class terms, that’s 3 and 4. Typical end uses include fence posts, cladding, decking and garden furniture. The chemicals need to penetrate more deeply into the wood in order to provide sufficient protection and so a high pressure process is used. The further the chemical penetrates into the wood, the higher the Use Class. Timber to be used in the ground must be treated to Use Class 4. Service life varies from 5 to 30 years dependant on a number of factors such as wood species, level of treatment and end use. WJ Group is able to advise you on the optimum treatment for your specific requirements.

A word about fire retardant treated timber

WJ Group can also undertake fire retardant timber treatment in a similar way, protecting the timber from fire and slowing its burning significantly, should the worst happen. Choose our FireWright brand for this type of treatment.

For further information about treated timber, please contact us on 01482 338950 or email .(JavaScript must be enabled to view this email address). We’ll be happy to help.


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