Thermally modified wood is still a natural, organic material and will fade in color from UV exposure. The brown tint will fade to a silver/gray over a 1 to 2 year period if untreated with a UV protectant. Although the wood is resistant to checking, it is more likely for checking to occur if a UV protectant is not applied. Checking of the wood has no effect on the long term durability or its resistance to rot and decay.
In order to maintain and improve thermo-treated woods performance against checking, and accentuate the natural grain structure, we recommend the use of a semi-transparent UV protectant. PENOFIN® clear is a commercially available UV protectant that works well with thermally modified products.