Natural durability and waterborne preservative treatability of tamarack

Eastern larch or tamarack (Larix laricina (du Roil K. Koch) lumber from New Brunswick was evaluated for heartwood natural durability by laboratory dec ay tests and for preservative treatability with chromated copper arsenate ( CCA-C) and ammoniacal copper arsenate (ACA). The CCA fixation and leaching characteristics of tamarack sapwood and heartwood were also evaluated. The natural durability of tamarack heartwood exposed to two brown-rot fungi, Gl oeophyllum trabeum and Postia placenta, was moderate to low and generally i nferior to that of heartwood of spruce (Picea spp.) and white pine (Pinus s trobus L.) and similar to that of red pine (Pinus resinosa Ait.) sapwood an d heartwood. The decay resistance of tamarack was variable, and not related to extractive content. CCA-C penetration into both sapwood and heartwood w as poor. ACA fully penetrated the sapwood, but penetrated the heartwood onl y marginally better than the CCA-C. The rate of CCA fixation, as defined by rate of reduction of hexavalent chromium varied greatly between sapwood an d heartwood and between different heartwood samples. Heartwood fixed much f aster than sapwood, averaging 2 to 3 days at 21 degrees C and 5 to 6 hours at 50 degrees C as compared to 15 to 20 days and 30 to 35 hours, respective ly, for sapwood. The fixation rate was directly related to the hot water so luble extractive content of the wood. The quality of fixation, as defined b y resistance to leaching of the CCA components, was much lower for the fast er reacting heartwood. The combination of poor penetration and low CCA stab ility in tamarack heartwood suggests that this preservative is not appropri ate for this species.