Effect of angle of exposure on the weathering of wood surfaces

Abstract

The effect of angle of exposure on the degree of weathering of wood has not before been assessed. Historically, during weathering trials specimens have been exposed at an angle of 45° facing the equator. Recently, experiments on polymeric materials which, like wood, weather primarily through photo-oxidative mechanisms, have suggested that an exposure angle of 0° (horizontal) may be preferable since this angle maximises levels of received ultraviolet radiation. In this paper the degradation of Pine ( Pinus radiata D. Don) during weathering was assessed at five angles of exposure (0°, 45°, 60°, 70°, 90°) over 50 days by measuring changes in weight and chemical composition of thin wood strips. Both weight loss and chemical data indicate that degradation of Pine during weathering was negatively correlated ( p<0·001) with increasing angle of exposure. The implications of these findings for the conduct of weathering trials are discussed.