Experimental and theoretical behavior of exterior wood coatings subjected to artificial weathering

Several solvent- and water-borne exterior wood coatings were artificially weathered to study their performance behavior. Penetration and layer thickness were measured on unweathered samples and compared to theoretical estimates by means of measured basic parameters of coating and substrate. Color, surface roughness, gloss, and adhesion were monitored during aging, and the latter two were also calculated and compared to their experimental values. Theoretical values of gloss, and especially those of adhesion, were less successful on an absolute scale, but were in accordance with practical values on a relative scale. The influence of solid content, drying speed, and viscosity on penetration depth manifested itself clearly both in theory and in practice. In general, solvent-borne coatings performed well, but some water-borne coatings also showed good performance. By measuring the characteristics of a coating as described in this article, it is possible to rank the coatings and follow their weatherability. Finally, calculation of theoretical values proved a promising method for initial screening purpose.