Coating systems are essential for the protection of wood, as they extend its durability, maintain colour stability, and shield it against UV radiation and biological attacks. One key property of such systems is their knot staining resistance. The SIST EN 927-7:2020 standard describes a method for determining knot staining resistance using xenon light exposure, but this approach requires 20 samples, which is time-consuming and costly. The aim of our research was to assess the knot staining resistance of six coating systems according to the standard method and compare these results with those obtained with preliminary methods, such as UV exposure and thermal loading in an oven, as well as evaluate the water permeability of the dry coating films. The results showed that despite the higher permeability of the dry coating film, solvent-borne coating systems were more resistant to staining by knots in the wood than water-borne ones. When comparing the results of exposure to xenon light and the oven, the colour differences on knots were smaller in the case of the oven method, which also caused a slight increase in the yellowness of the coatings. The results from the UV light method were closer to those obtained by the standard method, though the values were higher. Despite the use of alternative methods, the standard procedure in the artificial aging chamber with xenon light remains the most effective, but the UV exposure method could be a more cost-effective alternative, although not entirely equivalent to the standard procedure.
|
