Finishing of thermally modified wood Czapiewski, Christopher
An exterior wood finish can be an effective way to reduce thermally modified wood’s sensitivity to ultra violet light. But, which finish is the most resistant at preventing premature graying? How do we know that the finish will perform on thermally modified wood the same way as it does on unmodified wood? This study delves into these questions by examining the colour stability of 3 thermally modified, and unmodified, wood species coated with 6 commercially available deck stains subjected to artificial weathering for 1000 hours. A Spectrophotometer was used to measure the colour change of latewood and earlywood in finished and unfinished thermally modified and unmodified wood. Stain #4 outperformed the other 5 stains in terms of its ability to resist lightening and overall colour change of different wood samples. Douglas-fir had the greatest resistance to discolouration and maintained the most uniform colouration of its growth rings. This study also confirms previous findings that thermally modified wood is more colour stable than unmodified wood. While the modified wood samples became lighter after UV exposure, the unmodified wood became darker. The earlywood in thermally modified wood changed colour to a greater extent than latewood, and always became lighter. The latewood in thermally modified wood turned darker on the unstained samples, but turned lighter on the stained samples, and at a faster rate than the earlywood. Therefore, staining a piece of thermally modified wood creates uniformity between the colours of the latewood and earlywood. This study indicates that not all wood species or exterior finishes perform equally and that some finishes are better at resisting discolouration of thermally modified wood products. For that reason, there is merit in performing further studies to find the combination of finish type and thermally modified wood species that is the best at resisting discolouration during weathering.
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