Timber treatment manufacturers are confident that the BS 8417 15- or 30-year desired service life categories can be achieved for Use Class 4, but only if the treatment conforms to the combination of penetration and retention of preservative the standard requires.
The WPA has checked the penetration and loading of posts said to have failed prematurely and, in all cases, the retention has not conformed to the requirement of standards. The lack of penetration has been particularly obvious: in one case, the sapwood of a pine sample was found to be at 120% moisture content. It was not a surprise, therefore, that the penetration was almost non-existent.
In each case, it isn’t clear what instructions were passed down the supply chain to the treatment company, but we certainly want to see more and better specification.
Suppliers of treated timber must accept responsibility as experts in their field to provide product that is fit for purpose, but the customer has obligations, too. Basic good practice must be followed, including avoiding cutting, boring or notching on site, or, if these operations are unavoidable, then exposed surfaces must be retreated with a preservative recommended by the manufacturer – and uncut ends should not be placed in the ground. Without these measures, no fitness for purpose obligations on the part of the supplier can ensure an adequate service life.
Minimum standard
Market prices will affect what the customer can expect for their money, but fitness for purpose obligations provide a minimum standard below which it is dangerous to go whatever the price – the viability of companies in the supply chain and even the future of wood as a fencing material could be at risk.
The WPA has published a fact file with recommendations on treatment and good installation practice, available on request. Tel: 01332 225104 or e-mail: info@wood-protection.org.
