Borate-based wood preservatives are used in industrial pre-treatment as well as remedial treatment of timbers in situ. In both of these areas, understanding the mobile nature of these compounds is important in optimizing the main benefits of borates. Considerable work has been conducted on movement of borates in dip-diffusion treatment of freshly felled wood, as well as focusing on subsequent diffusion following remedial application to dry timber. This paper sets out to review the existing body of data of borate movement in wood, in the context of more recent research findings. Data are presented which show that the movement of borates, up to 6 months after dip treatment of a range of commercially important softwoods, is highly dependent on wood moisture content. Moisture content is of such over-riding importance that the identity of a particular timber species has an insignificant effect on borate movement, provided a minimum moisture content is attained. This observation is despite the fact that species as diverse as Douglas fir, Hem-fir, Southern Yellow Pine, Scots Pine and Norway Spruce were used in this study. It has been suggested that there must be free water in the wood cell wall voids for significant diffusion of borate to occur. However, the precise influence of decreasing moisture content on the rate of borate diffusion is unclear. The data presented in this paper contribute to a more comprehensive understanding of borate movement at moisture contents representative of those seen in timber post-treatment and in-service. In addition, the importance of backing up results from colorimetric spot tests with detailed measurement by analysis is illustrated.

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