In comparison to inorganic wood preservatives, organic biocides in transient carriers are considerably less effective when the treated wood is exposed to soil contact. Various oils are used in some formulations with pentachlorophenol to improve the efficacy. However, use of these oils imparts unacceptable properties to products used in residential applications. Consequently, there is a need to develop additives other than heavy oils that improve the performance of organic biocides as wood preservatives. In this study the possibility of using the benign antioxidant BHT as a non-biocidal additive to improve the performance of wood treated with isothiazolone and azoles was investigated. The treated wood with and without BHT was exposed to unsterile soil and monitored for decay by dynamic MOE. It was found that the efficacy of both preservative systems was enhanced when BHT was added to the formulations. The use of Dynamic MOE to evaluate the progression of wood decay appears to be far superior to visual ratings.

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