The first co-operative field trial was designed to study the occurrence of soft-rot in CCA treated hardwoods. Generally speaking very similar results were obtained from the different field sites. In the early part of the trial considerable variability was evident with regard to the rate and type of attack which occurred in the untreated material. With the CCA treated timber the type of decay was predominantly soft-rot. It cannot be assumed that with alternative preservatives that the same mode of failure will be as dominant. In such cases the treated timber in different sites may well perform differently. On the other hand, the pattern of failure may be very similar between sites with variation in rates of decay being more evident due to differing distribution of the causal organisms. Tolerant soft-rot fungi tend to be ubiquitious but this is not necessarily the case with other groups. After consideration in the sub-group it was decided to study the variability between sites with regard to the performance of a range of preservatives in a limited number of wood species. A standard CCA preservative would also be included as a point of reference. The overall objective of the trial was very simply summarised as follows: "To identify the number and type of sites required to have confidence in approving a wood preservative". This overall objective has the great attraction that it takes into account all the possible objectives raised in the discussion. It offers the scope to provide data and material to study a whole range of problems and factors of interest to the members, and of international importance when assessing and predicting the performance of wood preservatives.

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