Timber that has been pressure treated should have a desired service life of many years, providing it is only used for the purpose for which it is intended at the time of purchase. The pressure treating process should provide a long term protection from decay and insect attack, using chemicals with a minimum risk to health and a low impact on the environment.
The preservative qualities should remain in the timber for many years, although the colour pigment is not UV resistant. Over time, the timber will discolour to a natural wood shade.
We must point out that over the past 10 years the laws with regards to chemical specification have changed considerably. The CCA product which was the industry’s standard for the 30 years prior to July 2004, proved extremely successful. However, the governing body of the EU outlawed it, placing many restrictions on the end uses of the product. They considered that certain elements in the specification may have had an adverse impact on the environment and forced the hands of our industry to accept a revised product to meet their criteria.
The treatment manufacturers assure us that the revised product should perform as well as the original CCA. However, in our experience we have found that the current product (ACQ based) does not come up to the expectations or service life of the old reliable CCA and many people within the industry concur with our opinion on this matter.
We therefore regrettably are unable to offer an anti-rot guarantee of any kind, in the use of pressure treatment timber.
To prolong the life of pressure treated posts or sleepers that are installed below ground level, we always recommend a layer of gravel underneath the post/sleeper to allow for drainage.
Finally, timber is a natural product with inherent defects and characteristics. Its moisture content will vary considerably depending on the time of year, leading to the timber moving, splitting and twisting in situ. Splits are particularly prevalent and should be expected during the warmer months, as the timber dries out and shrinks after absorbing a considerable amount of moisture following a wet winter period. This is not a defect and is to be expected, British Standards 1722, allows for an excessive amount of movement before a product fails their test.