Layer Thickness Effects on the Ageing Performance and Mould Resistance of Polyurethane-Coated Beech Wood.

The paper deals with the optical stability and biological resistance of solvent-based polyurethane and water-based polyurethane-acrylate finishes intended for interior use, applied on beech wood with mature wood and false heartwood. Optical stability was assessed through colour and gloss measurements. The surface finishes were applied in one (I), two (II), and three (III) layers. Natural ageing was carried out under indoor conditions with exposure to natural daylight behind a glass window. Colour and gloss measurements were performed after 30, 150, and 300 days of exposure. The development of mould growth activity (GAM) during 21-day exposure was assessed on untreated and coated beech wood with different coating thicknesses. A significant colour difference in the solvent-based polyurethane finish on both mature wood and false heartwood occurred after 30 days of natural ageing. The colour difference in the water-based polyurethane-acrylate finish on both mature wood and false heartwood increased with exposure time. The solvent-based polyurethane finish with three layers applied to false heartwood showed reduced colour difference (by 62.5%). Natural ageing under interior conditions did not significantly affect the gloss of the matte surface for either finish on both mature wood and false heartwood. The degree of mould growth decreased with an increasing number of coating layers for both polyurethane and polyurethane-acrylate finishes.