Durability of Selected Transparent and Semi-Transparent Coatings on Siberian and European Larch during Artificial Weathering

Comparison of Exterior Coatings Applied to Oak Wood as a Function of Natural and Artificial Weathering Exposure

Artificial weathering can significantly reduce the testing time needed for proving coating durability, nevertheless its reliability is still not thoroughly proven. In this study, eight different transparent and pigmented coating systems, namely oil, acrylate, alkyd and urethane alkyd were evaluated through natural and artificial weathering tests on oak samples by measuring colour, gloss and surface wettability and by macroscopic and microscopic evaluation. The oil coatings performed well in wood colour stability evaluations, while the best gloss and wettability change results were noted for acrylate coatings. Pigmented coatings were characterized by significantly lower colour changes than transparent ones. The gloss and wettability changes were more sensitive to coating disruption than to total colour changes of coated wood associated with chemical changes in wood. The findings in this work showed that values of gloss changes and surface wettability for all types of coatings exposed to artificial and natural weathering resulted in significant differences from each other. The data obtained by artificial weathering method provide basic results of coatings durability and, ideally, natural weathering should be performed at the same time to support the results from laboratory tests by exposing wood under real conditions.

Effectiveness of Two Different Hydrophobic Topcoats for Increasing of Durability of Exterior Coating Systems on Oak Wood

A top hydrophobic layer can increase the durability of exterior coatings applied on wood. Two hydrophobic topcoats - synthetics and waterborne acrylate resin with wax additives, were tested as top layers on twenty-four different coating systems applied on oak wood in this experiment. Artificial accelerated weathering lasted for six weeks. Changes of color, gloss, surface wetting were evaluated, and microscopic analyses of coated surfaces were done during weathering. The results have shown that a top hydrophobic layer increases the durability of tested coating systems in most cases. However, the effectiveness of the two tested hydrophobic topcoats turned out to be different depending on the specific coating systems used.