In the previous edition of F&LN we reported on how the WPA and TTF had joined forces to help grow demand for treated wood. Market research had highlighted three key areas that had to be addressed for treated wood to achieve its market potential. These were:

  1. a common failure to specify treated wood correctly;
  2. a lack of understanding on how to correctly install and use treated wood and
  3. providing independent quality verification of the treatment process.

In this F&LN we take a look at how wood treaters can comply with the TTF’s move to introduce third-party verification of the pressure impregnation process and the fitness for purpose of a preservative treated wood.

Factors affecting the performance of treated softwood Spruce, pine, Douglas fir and larch are the dominant softwoods available in the UK. It’s a well- known fact that all softwoods lack sufficient natural durability (i.e. resistance to fungal decay) to perform reliably in a wet climate like the UK’s. It’s also important to know that each species has its own biological characteristics that influence how the enhanced durability performance conferred by the pressure impregnation of preservative is achieved. For example, the biological structure of spruce makes it a difficult to treat whereas pine is more readily penetrated. The service life performance of all treated wood products is determined by several factors: the characteristics of the species from which it is made; the ratio of sapwood to heartwood; the conditioning and preparation of the wood prior to treatment as well as making sure the correct treatment process controls have been set accurately.

These controls include ensuring the correct preservative solution strength and the process pressure cycles are used to achieve the penetration and retention necessary for any given end use and service life. This combination of factors is known in the wood preservation industry as the ‘Safe Relationship’. Getting the safe relationship right is essential to ensuring treated wood will meet the requirements of the desired service life specification
in the British Standard for wood preservation, BS8417. This is particularly important for outdoor (use class 4) applications where treated wood is installed in the ground, close to the ground or in a freshwater situation.

Treatment quality verification Until the current TTF move to raise the quality of treated wood the UK has stood alone in the major wood treating markets of the world by resisting third-party verification of treated wood. Quality schemes have existed for many years in the USA, Canada, Scandinavia and other major European markets. And whilst membership of these schemes is not mandatory, the supply chain in each country has come to appreciate that supplying treated wood independently verified as fit- for-purpose is beneficial to both the supply chain and buyers.

The requirements for treaters looking to comply with a UK move to third-party verification of treatment quality will be the same requirements as those of the quality schemes operating in other major markets. It will involve a treater operating, documenting and maintaining a quality management system sufficient to ensure that the treatment specifications received from customers are met in full and that the quality of wood treated to those specifications can be verified by an independent auditor.

In order to do this the treater being audited must be able to provide suitable evidence1 that a consistent relationship exists (the Safe Relationship) between the preservative penetration and retention requirements for a particular species/end use combination and the treatment process, such as preservative concentration and pressure cycle. The key to any quality assurance scheme is the ability of the treater to control these parameters consistently in all treatment activities.

The TTF and WPA say that to join the move to independent verification of the treatment process, treaters need not specifically have ISO 9001 quality management accreditation but they point out that such an accreditation provides a good framework within which to organise and record the evidence above. Whichever QA process a treater chooses to use there will be one universal and mandatory requirement: it must be compliant with WPA Quality Guidance Note QGN2. This is a controlled document available from WPA and was produced to provide specific guidance on how to manage a wood treatment operation in accordance with the principles set down in BS EN ISO 9001.

QAS Compliance Options In driving this move to raise the quality of treated wood on the UK market, the TTF is not being prescriptive about which auditing and accreditation body its treater members use to verify performance levels, providing the principles it has set out in collaboration with WPA are met. Examples of the quality schemes available to treaters are:

1. WPA Benchmark

This Scheme was developed by a committee of UK treatment operators, preservative manufacturers and BRE and is operated by the WPA on a third- party basis. It was introduced in 2011 as the first stage of a WPA strategy to build buyer confidence in good quality, fit for purpose treated wood products.

Under this scheme those treaters operating a warranty and/ or quality scheme supported by their chemical supplier or other third party will already be in a strong position to provide the required evidence, but scheme membership is not restricted to such operations.

2. Nordic NTR Quality Scheme

For companies treating wood in the Nordic region, membership of the NTR scheme will satisfy TTF quality criteria. However, the TTF and WPA is at pains to point out that when material is required to be treated in accordance with BS8417 ‘Preservation of wood – Code of Practice’, this will need to be made clear to NTR treaters.

TTF/WPA has produced helpful guidance for NTR treaters on how to meet BS8417 specifications.

3. Other TTF-Approved National Quality Schemes

There are a number of other national quality schemes for industrial wood treatment, for example CTBB+ in France (see http:// ctbbplus.fr for details). Please check with TTF for advice, depending on the source of your treated wood.

4. Other UK accreditation body

Another UK based audit and accreditation body recognised as having experience in the timber sector, such as TRADA or BRE, can be used provided the quality management system in place at the treatment plant also meets the baseline requirements of WPA QGN2.

The WPA is totally committed to helping TTF and WPA members and treaters in general succeed
in moving to third-party quality verification.

To find out more about what’s involved in joining the WPA Benchmark QA Scheme and the benefits it can bring contact WPA Chief Executive Gordon Ewbank on gordon.ewbank@ wood-protection.org


COVID-19 DigitalCopy


If needed any subscriber and advertiser can request a digital version of the April edition as of Thursday 9th April. Hard copies of the magazine are been mailed out as normal. Email benwalton@fencing-news.com to request a copy.

You have Successfully Subscribed!