How best to specify retentions of preservative treatments: kg/m3 or % (m/m)
J K Carey
When specifying treatments according to the European Standard EN 351-1, retentions in the analytical zone are based on the amount of product found to be effective in biological tests; this is expressed in terms of the retention of the product per unit volume (kg/m3) for penetrating treatments and per unit area (g/m2) for superficial treatments. However, to check whether the retentions have been achieved, chemical analyses are carried out where the results are initially expressed as% (m/m). In converting results from% (m/m) to kg/m3 , a value for the density of the wood must be applied that is closely associated with the sample of wood taken for chemical analysis. This is difficult to achieve and it has been suggested that the results from biological tests and the associated retention values be expressed in% (m/m) to avoid this difficulty.
For treatments applied by penetrating treatment processes, expression of the retention of a wood preservative product as% (m/m) reduces error. The initial dry weight of the test specimens affects the relationship between retentions expressed as kg/m3 and% (m/m) because heavier test specimens take up less treating solution. The change in the method of expressing the retention of a wood preservative product to% (m/m) is unlikely to have any major effect on the results within a wood species. However, the change reduces the difference between the retentions which are effective in Scots pine sapwood and beech against attack by Coriolus versicolor.
Use of% (m/m) instead of g/m2 offers no advantages for superficial treatment processes.
Keywords: BIOLOGICAL TESTS; ANALYSIS OF RESULTS; PRESERVATIVE RETENTION
Conference: 98-06-14/19 Maastricht, The Low Countries