Durable wood linings for outdoor exposure : the consequences using wood with vertical annual rings.

One of the most important parameters affecting 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 of this project is to test the durability under outdoor exposure of wood sawn according to two different sawing patterns. Conventional sawing exposes tangential surfaces, whereas the star-sawing method gives radial surfaces. The development of cracks and changes in appearance have been investigated on radial and tangential surfaces of pine (Pinus sylvestris L.) and spruce (Picea abies Karst.) which have been exposed outdoors for 61 months. The annual ring orientation was the most important factor affecting crack development on weathering. The type of wood and the impregnation treatment had only a marginal effect on the crack development. After 61 months of outdoor exposure, the tangential surfaces of pine had 1.7 – 2.2 times greater total crack length per unit area than the corresponding radial surfaces. In spruce, the total crack length on the tangential surfaces was 2.2 – 2.6 times greater than that on the radial surfaces. Tangential surfaces of both pine and spruce have a lager number of cracks per unit area and wider cracks than are found on the corresponding radial surfaces. Tangential and radial surfaces show the same colour change as a result of weathering