The preservative treatment provides the wood with added durability. However, it’s a mistake to assume that all pressure-treated wood is the same. Whilst one piece of treated wood may look very much like any other, the level of preservative protection could be very different. That’s because national technical standards for wood preservation require that the loading and penetration of preservatives, impregnated into the wood, is tailored to the desired end-use.
Please Visit: https://www.thewpa.org.uk/make-sure-it-s-4
Understanding the different User Classes is more complicated than it sounds. They all look the same from the outside when treated. they all look the same when treated.
For User Class 1 where the timber is permanently dry, you are only treating for insect attack and therefore it is more of a coating to stop the insects burrowing into the wood. http://bf8c2415-5c4f-43c7-aacf-b51b0662a4d4.filesusr.com/ugd/65ba63_d3a8435991094e92802429d42b3da6dc.pdf?index=true
For User Class 2 and above the amount of penetration required increases in-depth as the risk of moisture increases to ground contact materials where permanent wetting can be an issue. http://bf8c2415-5c4f-43c7-aacf-b51b0662a4d4.filesusr.com/ugd/65ba63_d3a8435991094e92802429d42b3da6dc.pdf?index=true
Unfortunately, due to lack of knowledge, a high percentage of posts, sleepers, path edgings, gravel boards, etc sold have not been treated for ground contact.
This year the Wood Protection Association has teamed up with other organizations to promote the correct treatment for the end purpose but there are still large quantities of these items being sold for the wrong end purpose.
As we import the Kiln Dried Radiata Pine, treat it on-site and sell it to both the supplier and the end-user we may still be cheaper for the correct product rather than other companies selling the wrong product.
Descriptions such as “treated for longevity” or “pressure treated for deep penetration” does not tell you what end purpose and use class they have been treated to.
Just because it is treated green does not mean it is suitable for use outside.
Timber treated under pressure adds to the durability of the end product. Unfortunately timber, after treatment will look the same on the outside even when the depth of penetration is 2mm or 20mm. BS 8417 has different loadings and penetration requirements.
The amount of the chemical used when we treat our Radiata Pine to UC4 30 year desires service life compared to treating spruce to UC2 can be as much as 8 times which gives the penetration we believe ground contact timbers require.
Certain species (redwood pines) need to be kiln-dried to below 28% moisture content so that the timber accepts a better penetration of the sapwood.
We import a Kiln Dried European Radiata Pine, a species that accepts very high levels of treatment when treated on the correct cycle. We pressure treat on a specific cycle at a higher chemical concentration to reach User Class 4 with a 30 year desired service life for full sapwood penetration. Find out more:
Since 2017 The Timber Trade Federation (TTF) and the WPA have been working together to grow demand for preservative treated timber. They identified three priority areas for action, which have since been adopted as TTF policy:
- To address the common failure to specify treated wood correctly;
- To address the lack of understanding on how to correctly install and use treated wood;
- To ensure independent verification of the treatment process.
At the TTF AGM on 17 November 2020, members unanimously voted to implement this Preservative Treatment Action Plan into the TTF Code of Conduct. As a result, Members must adhere to the guidance provided in BS8417 (2014) and the 2021 WPA Code of Practice: Industrial Wood Preservation for the choice, use, and application of wood preservatives.