421 WOOD RESEARCH 59 (3): 2014 421-430 COLOUR STABILITY AND SURFACE DEFECTS OF NATURALLY AGED WOOD TREATED WITH TRANSPARENT PAINTS FOR EXTERIOR CONSTRUCTIONS Miloš Pánek Czech University of Life Sciences Prague, Faculty of Forestry and Wood Sciences Prague, Czech Republic Ladislav Reinprecht Technical University in Zvolen, Faculty of Wood Sciences and Technology Zvolen, Slovak Republic (Received April 2014) ABSTRACT Wooden constructions and their parts in the exterior, e.g. houses, cottages, bowers, bridges, claddings, decking, windows or garden furniture, are degradable by bio-agencies, fire and weathering. Their service life can be increased by well-designed construction systems, by using of more durable wood species and composite materials, and also by convenient biocides and anti- weathering paints. In experiments, the colour changes (valued by CIELab) and surface defects (valued at 10x magnification) in wood samples during their 3-year’s outdoor weathering at 45° were determined in an accordance with the EN 927-3 2000, taking into account these variable factors: 1) two wood species (black locust, Norway spruce); 2) four transparent coating systems (PerlColor, PerlColor + AquaStop, OsmoUV-Protection Oil 420, OsmoUV-Protection Oil 420 + AquaStop); 3) two roughness of wood (grinded with 60 or 120 sandpaper). Generally at natural weathering, the colours of the black locust wood untreated and treated with transparent paints were more stable than of the Norway spruce one. The OsmoUV-Protection Oil 420 ensured good colour stability to the black locust samples, and its combination with the AquaStop also to the Norway spruce ones. The top water repellent paint AquaStop put off degradation of the PerlColor and OsmoUV-Protection Oil 420 paints, with significant colour stability increase of the Norway spruce samples. A higher initial roughness of wood surfaces had usually a negative influence for the colour stability of coated wood and its surface quality. KEYWORDS: Construction wood, paints, weathering, colour stability, surface defects.