Summary on present situation regarding Pre-treated Timber

by  Dr C R Coggins

We recently moved from a national system of approvals (Control of Pesticides Regulations – CoPR) via the Biocidal Products Directive (BPD) to, from September this year, the Biocidal Products Regulation (BPR) (which entirely replaces the BPD).

You may be familiar with how CoPR works and be aware there are still a few CoPR products on the market while the BPD/BPR system catches up. The new system involves approval of active ingredients at EU level and subsequent approval of wood preservative formulations at national level with the possibility of mutual recognition of approvals between member states of the EU. A number of wood preservatives have gone through the EU system and are on the UK market.

Copper Chrome Arsenic (CCA) approval ceased in September 2006. Wood already on the market treated with CCA could be sold and used for the permitted uses (not inside buildings for example) but eventually new CCA treated wood disappeared from the supply chain. The BPR introduces controls over treated wood; for example, it is now illegal to import wood treated with CCA into the EU even for those uses that are in theory still approved. Wood treated with CCA can remain in place and second-hand CCA-treated wood could be supplied for the permitted end uses but this rarely happens and eventually CCA-treated wood will disappear as it all comes to the end of its useful life.

In the run-up to September 2006 preservative manufacturers converted many customers to copper- and chromium-based preservatives that could be used in CCA plants without compatibility problems. These included CC, CCB and CCP types. They were used for up to about two years while the change-over to what we call the copper-organic preservatives was completed. Copper-organic preservatives combine copper with organic biocides like propiconazole, tebuconazole and quaternary ammonium compounds, and some have boron added. Boron continues to be approved for wood preservation despite the recent change in classification and we don’t see a change in that situation but you never know.

By about 2008 chromium-based preservatives disappeared from the UK market because chromium was not supported through the BPD process. The UK took the view that chromium was an active ingredient so preservatives containing it had to be withdrawn. Germany and a few other countries allowed chromium-containing preservatives to continue for a while arguing that chromium is a fixative, not an active ingredient but I’m not sure if that is still the case.

About 4 years ago we began to get reports of early failure of treated wood in ground contact, mostly fence posts and these all turned out to due to poor treatment – examples included CCA, the CC types and the newer copper-organic types and this triggered quite a crisis of confidence in the market as you might imagine. The trade press had a field day. The accusation that green wood is just painted with green came partly from this period. The pre-treatment industry – Wood Protection Association (WPA) investigated a number of failures and in all cases it was due to inadequate treatment (poor penetration and low loadings). Now we think that poor practice was common in the CCA era and although the jury is still out on this there is a feeling that CCA was so good it was forgiving of poor practice and even badly-treated posts did reasonably well. With other preservatives, while they do work as has been proved by lab and field tests, it is vital that treatment complies with the requirements for penetration and retention set out in BS 8417. If you get it right, treated wood will deliver the performance expected of it.

To help overcome the crisis of confidence WPA introduced a new scheme – BENCHMARK – where independent auditors check that plants are treating properly. The auditors look at treated wood and areas such as moisture control, solution concentration checking, traceability of treated packs etc. as part of the overall quality check – this goes far beyond what is covered in ISO 9001 audits and is being well received in the industry and the markets. Some companies have started incising their ground contact wood so that the required penetration can be achieved easily and Benchmarked treated spruce is now on the market for the use class 4, 15 year service life category.

For construction use, wood may be treated in pressure plants (vacuum/high pressure) plants and in double-vacuum plants. For many outdoor and all in-ground uses it is all pressure treatment. In both cases it is important that the use class from BS 8417 is specified when treated wood is ordered or purchased. For repair work in buildings, use class 2 (interior, risk of wetting) is probably the best and this will include effectiveness against fungi and insects. Exterior above ground work is use class 3 (coated/uncoated) and in-ground is use class 4. Pretty much all the use class 3 and 4 preservatives provide protection against fungi and insects but PCA members should protect themselves by specifying the use class and state if protection against fungi and insects is required. Buying treated wood with Benchmark certification provides a high level of confidence in performance.

Examples of copper-organic preservatives include Tanalith E, Celcure AC, Wolmanit CX. Examples of low-pressure treatments include Vacsol Aqua and Protim Aqeos.