Color changes of wood and wood-based materials due to natural and artificial weathering

Abstract

Color changes of unpainted wood surfaces caused by weathering are an aesthetic problem and the understanding of the underlying processes is a complex task. This study investigates color changes of wooden boards both outdoors on a test house and in the laboratory. The CIE L*a*b* color system is used to compare exposure directions outdoors, laboratory weathering, and materials used in this study. Results indicate that there is a common pattern for color changes. Solar radiation and wind-driven rain are assumed to be the main driving forces behind color changes, together with graying caused by mold growth. However, no quantitative correlation between color changes and the two main climatic strains could be found. Laboratory weathering is a useful tool when it comes to recreate similar exposure conditions. The present study indicates that results from laboratory weathering can hardly be compared to results from outdoor weathering. Though, how close they are to actual exposure conditions is a widely discussed question. However, color measurement is a useful tool to objectively document changes in appearance.