Mold growth on dried Norway spruce and Scots pine sapwood boards was investigated in an accelerated outdoor field test for 96 days. The boards were dried using three different methods of stacking: single stacking, double stacking with the sapwood sides in each pair facing toward each other, and double stacking with sapwood sides facing outward. Drying was performed at three temperatures: 25°C, corresponding to air drying, and kiln drying at 70°C and 110°C. The degree of mold growth was visually assessed on both sides of each board. On average, pine boards showed a higher level of mold growth than the spruce boards. The highest average level of mold growth was found on the boards kiln dried at 70°C, whereas the air-dried boards and the boards kiln dried at 110°C showed considerably less mold growth. Stacking the boards during drying had a large impact on mold susceptibility of the sapwood. This study confirmed that, during the drying process, it is possible to direct the migration of nutrients in sapwood toward one chosen side of each board by double stacking; the opposite side leaches out, which has a great impact on surface mold growth. Chemical analyses of monosaccharide sugar gradients beneath the boards' surfaces confirmed the results.
The authors are, respectively, Assistant Professor and Assistant Professor, Div. of Wood Physics, Dept. of Engineering Sci. and Mathematics, Luleå Univ. of Technol., LTU Skellefteå, Sweden (Margot.Sehlstedt-Persson@ltu.se, Olov.Karlsson@ltu.se); Researcher, SP Trätek Technical Research Inst. of Sweden, Skellefteå, Sweden (Thomas.Wamming@sp.se); and Professor, Div. of Wood Physics, Dept. of Engineering Sci. and Mathematics, Luleå Univ. of Technol., LTU Skellefteå, Sweden (Tom.Moren@ltu.se). This paper was received for publication in March 2011. Article no. 11-00035.