Most industry observers anticipate a change from copper-based preservatives to metal-free combinations of organics for residential treated wood products in North America within the next one to five years. While the chromium copper provide considerable protection against UV, metal-free formulations will need UV protection in the form of additives or coatings. While transparent coatings can be made reasonably resistant to UV, by necessity clear coatings are transparent to visible light. Visible light can also cause damage over the long term thus the underlying wood needs additional protection. Four novel UV protection systems were tested as pre-treatments on uncoated wood and under three coatings, a water-based film forming coating, a water-based acrylic varnish and a solvent based water repellent. Samples were exposed to natural weathering facing South at 45o at a test site in Saucier, Mississippi, in collaboration with the USDA Forest Products Laboratory. The test material was inspected every six months for discolouration, mold and stain, coating water repellency, flaking, erosion and cracking and substrate condition. After 24 months exposure, coatings over the combination of UV absorber and lignin stabilizer identified by Stephen Ayer and that recommended by Ciba and were both performing substantially better than controls with no pre-treatment. Projection of fitted curves beyond the data appears to indicate that pre-treatment may double the life expectancy of the coating. There was no consistent effect of the synergists on either combination at this time.

Download document (1.1 Mb)
free for the members of IRG. Available if purchased.

Purchase this document