Water repellents have the potential to enhance biocidal activity by reducing leaching and lowering the moisture levels in wood exposed to rains. A range of studies have been performed in order to evaluate the potentials of tall oils as wood protective systems. The general conclusion has been that tall oil can provide some protection but that they cannot compete with the copper and organic biocide based preservatives without adding additional active components. The aim of this study was to compare the performance of different tall oils in three different above ground field tests (mini stakes, block test and horizontal double layer - nine years exposure) and two in ground exposure trials (mini stakes and EN 252 – ten years exposure). The results show that for retentions of tall oils at 200-250 kg/m3 the treatment did to some extent delay the decay compared to control but it did not perform at the same level as the reference copper preservative. However, this study also shows that tall oil can perform well, even in soil contact, given high enough retention.

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