Decay and leaching resistance of spruce and larch woods treated with preservatives following different incising pretreatments

The objective of this study was to determine the extent to which different incising pretreatments can increase decay and leaching resistance of Picea orientalis (oriental spruce) and Larix decidua (european larch) woods. To this purpose, mechanical, biological, and laser incision treatments were applied to sapwood samples of these refractory wood species to enhance permeability. After the incision treatments, cross sections of the samples were sealed with a polyurethane-based paint commonly used in marine applications to minimize excessive uptake of impregnation chemicals. Subsequently, the treated samples were impregnated using a vacuum method with an alkaline copper quat (ACQ) solution (Celcure C4), a copper (Cu)-based preservative. The impregnated spruce and larch samples with and without different incision treatments were then subjected to leaching. Non-pretreated and non-impregnated samples, pretreated and non-impregnated samples, non-pretreated and impregnated samples (leached and non-leached), and pretreated and impregnated samples (leached and non-leached) spruce and larch were exposed to brown rot (Tyromyces palustris) and white rot (Trametes versicolor) fungi for 16 weeks. The highest Cu content (ppm) in spruce before and after leaching was generally observed in samples treated with laser incision; in larch, the highest values were obtained with biological incision. Moreover, incising treatments did not increase Cu leaching in larch, while only biological incision increased leaching in spruce. Decay resistance against both fungal species generally improved in blocks impregnated with Cu compounds following mechanical and laser incising treatments, both before and after leaching. In addition, leaching reduced decay resistance in the control and in laser incised samples exposed to brown rot fungus.