The first trials using the small L-joint, later adopted for use in BS EN 330 and AWPA Standard E9-97 were exposed at BRE in 1975 but all were assessed destructively during the early stages of exposure. The longest running trial which included replicates for long-term exposure will have been exposed for 20 years in July 2002. This paper provides an overview of the results of testing during that period. Data are presented which show the variation in the rates of decay found in both untreated and treated replicates. In all cases, there is a period of protection before visible decay is present, followed by a decay period during which decay develops until the point of failure is reached. In preservative treated L-joints, the length of the decay period depends on the type of active ingredient, the concentration of active ingredient and the formulation. Different products also exhibit different modes of failure. For all these reasons, it is clear that there is no simple relationship in field trials between long-term performance and the length of the period of protection prior to visible decay.

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