Influence of tannin containing coatings on weathering resistance of wood: Water based transparent and opaque coatings

The aim of this study was to improve weathering resistance of Scots pine wood by treating the surfaces with water based transparent and opaque wood coatings containing valex, mimosa and pine tannins. Samples coated with tannin containing coatings with various concentrations were exposed to artificial weathering for 1512 h. Color, gloss, surface roughness and macroscopic changes were evaluated periodically during the test, and the results of coated samples were compared with controls. Visible surface degradations such as erosion, cracks and checks occurred on control samples while no crack formations were recorded for coated samples. Color measurement data showed that high concentration levels were needed for the least color change on the surfaces however concentration increase of tannins in the transparent coating affected surface gloss and roughness of samples negatively. The most promising tannin types in transparent coatings against the surface degradations were determined as valex and pine tannins. Opaque coating alone was found to be resistant against weathering factors, and the measurements clearly showed that there is no need to corporate any UV absorbers to this coating.