Observations on the Influence of Wood Density on Preservative Retention Calculations, Performance in AWPA Field Tests and the Significance of Retention Variability in Commercial Production

摘要

Currently a number of AWPA field testing standards require the use of test samples in narrow density ranges for each treatment grouping, but allow density to vary between treatment groups. These results are often used to support the setting of minimumretentions for commercial lumber that exhibits a wide range of wood density. This study investigated whether selection of test samples with narrow density ranges is necessary, or even desirable. Field test samples treated with amine copper based preservative systems were selected to include a wide range of wood densities within each test group that was consistent between test groups. These were monitored for the influence of wood density on the calculated retentions of individual samples, as well as their performance in field exposures. Results support that density differences between samples impact calculated retentions as well as performance, and could bias results in field exposure tests when conducted as currently listed in AWPA Standards. When treated with the same preservative solution concentrations, high density samples performed at least as well, and often better, than low density samples, even though the low density samples had higher calculated retentions. Allowing field test procedures touse of treatment groups containing samples with a wide range of wood densities, but consistent between treatment groups, should be an equally valid, if not a better way to test systems for decay performance. Also provided is specific data on the influence of sample density on the variability of individual sample retentions when calculated by different methods, as well as how this variability would be expected to influence composite sample analyses.