Like all exterior wood products as the wood is exposed to the ultraviolet light it begins to breakdown the woods natural color and the wood begins to fade and then grey. All natural species of woods such as Ipe, Western Red Cedar, Pine, Douglas Fir ,including thermally modified wood, will naturally grey over time if there is no accompanying maintenance program such as applying a yearly or semi-yearly coating of wood stain containing a UV inhibitor.
Thermally modified wood seems to grey more quickly due to the process of extracting the woods natural tannin’s during the thermal modification process. Lignin a compound found in wood is easily degraded by natural sunlight. If lignin and other color giving structures could be stabilized during the thermal modification process it could help reduce the seemingly rapid greying effect of the woods surface.
All wood once thermally modified will make the woods appearance darker. Recent studies have shown that applying “In-Organic UV” based coatings will increase the photo-stabilization of wood surfaces by blocking UV radiation from reaching the woods surface by scattering and absorption while remaining transparent to visible light. There is nothing to suggest that the thermally modified wood’s lifetime performance is effected in any way due to the grey appearance of the woods surface.
North American Ash is commonly used in the thermal modification process and often utilized into the wood decking and siding industry here in North America. Many customers appreciate its final patina grey appearance if the wood is left to grey naturally but if you want to maintain the woods natural appearance then here is a list of some reliable coating product manufacturers that customers have applied to our thermally modified wood.