Environmental friendly wood linings for outdoor exposure.

One of the most important parameters for the durability of wood linings for outdoor exposure is the amount of surface checks that are initiated already in the sawing procedure. The main object for this project is to test the durability under outdoor exposure for wood from two different sawing patterns. At conventional sawing pattern tangential surfaces are exposed, while the star-sawing method gives radial surfaces. The development of cracks and changes in appearance has been investigated on radial and tangential surfaces of pine (Pinus sylvestris L.) and spruce (Picea abies Karst.) which have been exposed for outdoor climates for 61 months. The annual ring orientation is the most important factor for crack development on weathering. The type of wood and impregnation treatment has only a marginal effect on the crack development. After 61 months of outdoor exposure, tangential surfaces of pine have 1.7 – 2.2 times more total crack length per unit area than the corresponding radial surfaces. In spruce, the total crack length on the tangential surfaces is 2.2 – 2.6 times greater than on the radial surfaces. Tangential surfaces of both pine and spruce have a greater number of cracks per unit area and wider cracks than the corresponding radial surfaces. Tangential and radial surfaces show the same colour change in the surface as a result of weathering