A New Look at the Weathering Performance of Solid-Wood Decking Materials

By Christoph Schauwecker, Alan Preston, Jeffrey J. Morrell

Public awareness of resource scarcity and environmental protection has steadily increased during the past three decades. This awareness has been heightened by the public debate of issues such as global climate change, the impending end of the petroleum era, and the responsible management of old growth/native forest ecosystems. Heightened environmental responsibility has also been driving consumer preferences for building products that present a smaller ecological footprint. One material that has the potential to meet the demand for green building products is plantation-grown timber.

This material is near carbon-neutral, is easily machined, and has aesthetic appeal. However, one of the greatest drawbacks associated with wood is poor resistance to weathering when exposed outdoors. Wood is inherently sensitive to ultraviolet light and wet/dry cycling, and the much higher proportions of juvenile wood in the plantation resource exacerbates these problems.

The chemical and anatomical changes that occur within wood exposed to ultraviolet light have been studied extensively. Models indicate that the destruction of wood polymers is driven primarily by self-sustaining free radical reactions, leading to the preferential depolymerization of lignin, leaving behind a weak, disorganized surface of cellulose fibers, appearing white to gray in color.

Further, it is believed that the destabilization of the wood surface along with moisture cycling leads to the development of checks that mar the surface and create avenues for moisture collection and microbial growth.