Use of through-boring to improve CCA or ACZA treatment of refractory Douglas-fir and grand fir

Large quantities of smaller diameter materials are available in the overstocked forests of eastern Oregon and Washington, but the costs of removing these materials and the long distances from markets sharply reduce the potential of this resource. Failure to thin these forests will sharply increase the likelihood of catastrophic wildfires. One potential use for these materials is as treated fence posts. Unfortunately, the wood of many of the species in this region (inland Oregon and Washington) is highly resistant to conventional pressure treatment. In this report, we describe tests to improve treatment using combinations of ammoniacal-based preservatives and through-boring. Through- boring had little overall effect on treatment results, while the use of an ammoniacal-based system markedly improved treatment