Effect of Species, Precompression, and Seasoning on Heartwood Preservative Treatability of Six Western Conifers

Heartwood boards of the following species were selected for treatment: coastal Douglas-fir [Pseudotsuga menziesii var. menziesii (Mirb.) Franco], interior Douglas-fir [Pseudotsuga menziesii var. glauca (Beissn.) Franco], white spruce [Picea glauca (Moench) Voss], lodgepole pine [Pinus contorta Dougl.], amabilis fir [Abies amabilis (Dougl.) Forb.] and western hemlock [Tsuga heterophylla (Raf.) Sarg.]. They were passed between 6-inch rollers at 50 fpm and compressed to 90 percent of their original thickness. Boards to be treated with CCA (Type C) preservative were kiln-dried to 10 percent MC prior to commercial treatment by a full-cell process. Samples to be creosote treated were either 1) kiln-dried, 2) boiled under vacuum, or 3) both, before full-cell treatment. No general trend of greater retention or penetration due to a particular drying method was noted. The 10 percent pre-compression level generally improved face penetration and retention, but differences were statistically significant in only certain instances and not of practical consequence. Attempts to improve creosote treatability of the refractory species (lodgepole pine, white spruce, and interior Douglas-fir) by increasing precompression to 15 percent and employing a more severe schedule significantly increased face penetration of white spruce and interior Douglas-fir, but the magnitude of the improvement again was not practically important. Excessive collapse of lodgepole pine and white spruce marred this latter treatment. Amabilis fir received the heaviest treatment of any species tested, a feature which warrants its increased utilization for preservative-treated commodities. Each species displayed a characteristic treating pattern; for example, western hemlock received a generally heavy and uni- form treatment, amabilis fir a more erratic treatment with preferential earlywood penetration, while Douglas-fir and lodgepole pine displayed a better treatment within latewood bands.

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