Heat-Treated Wood as a Substrate for Coatings, Weathering of Heat-Treated Wood, and Coating Performance on Heat-Treated Wood

Heat treatment is a method of wood modification with increasing market acceptance in Europe. The major patented European commercial heat treatment processes have trade names ThermoWood, Platowood, Retiwood, Le Bois Perdure, and Oil-Heat-Treated Wood (OHT). To what extent modification of wood affects the resistance of wood to weathering is also an important aspect for wood applications, especially where appearance is important. Unfortunately, heat-treated wood has poor resistance to weathering, and surface treatment with coatings is required for both protection and aesthetic reasons. As a substrate for coating, heat-treated wood has altered characteristics such as lower hygroscopicity and liquid water uptake and changed acidity, wettability, surface free energy, and anatomical microstructure. Various wood species, heat treatment method, treatment intensity, and treatment conditions exhibited a different extent of changes in wood properties. These altered properties could affect coating performance on heat-treated wood. The reported changes in acidity and in surface energy due to heat treatments are inconsistent with one another depending on wood species and temperature of the treatments. This paper gives an overview of the research results with regards to properties of heat-treated wood that can affect coating performance and weathering of uncoated and coated heat-treated wood.