Natural exposure weathering tests were carried out by externally exposing treated wood samples for varying periodes of time up to 36 months. In the laboratory these samples were assayed for residual preservative effeciveness using Coniophora puteana FPRL 11E. The results indicated a loss in efficacy over and above that determined using artificial ageing procedures such as EN73 (evaporative ageing) and EN84 (water leaching). Results for two TBT based preservatives indicated a gradual loss in efficacy. Results for the organic biocide 2-thiocyanomethyl-thio benzothiazole (TCMTB) gave a more rapid loss in effeciveness indicative of the high levels of microbial actifity present in the samples. This test provides an intermediate evaluation of preservative performance and permanence between artificial laboratory ageing procedures and the necessary field evaluation using an L-joint type test.

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