The field performance of CCA-C treated sawn refractory softwoods from North America
M J Richards, W S McNamara
Approximately 15% of the total volume of wood treated in the United States consists of difficult to treat softwoods known as "refractory softwoods". The long term positive performance record of CCA treated sawn material is based upon the testing of yellow pine sapwood stakes with only limited field data available for sawn refractory softwoods. As a result, the existing North American wood preservation standards for sawn refractory softwoods appear not to be based upon field performance data, but are believed to be based upon the depth of incisions which were achievable by conventional incisors. In the mid 1980's, new incising technology emerged which produced uniform envelopes of CCA penetration and a greatly improved surface appearance. In 1986, this new technology was evaluated in a study to determine the treatability and field performance of CCA-C treated sawn refractory softwoods. The treatability results showed that in general, none of the species evaluated met the existing North American wood preservation standards. However, the field test results for these non-conforming refractory softwoods have shown excellent performance during eight years of above ground and ground contact exposure at two sites in North America. These test results, which are the subject of this paper, indicate that a modification of existing wood preservation standards for refractory softwoods is feasible.