The effect of outdoor weathering of thermally modified spruce and pine woods on their surface properties

Products from thermally modified wood used outdoors should be stable against sun, rain, wind, and biological agents. The effect of 1-to 24-month outdoor weathering of the Norway spruce (Picea abies) and Scots pine (Pinus sylvestris) thermally modified woods "Thermo- D produced in Oy Lunawood Ltd Finland" (TWs) on their selected surface properties - colour, gloss, roughness, and mould resistance is analysed in the paper. With prolonged weathering, the surfaces of both Thermo-D wood samples lost their original yellow-red shadow. They continuously turned greyer - in the CIE L*a*b* colour system, they obtained greener and bluer colours, together with the logarithmic increase in the total colour difference & UDelta;??????*????????????. Surfaces of both Thermo-D wood samples within the first four months of outdoor weathering turned much lighter with a higher gloss. However, they got darker and matter due to adsorbing soot and dirt. Similar changes, i.e., as in the lightness and gloss, occurred in the roughness of weathered Thermo-D woods, which firstly decreased and subsequently increased with further prolongation of weathering. Moulds Aspergillus niger and Penicillium brevicompactum, in all cases, intensively attacked spruce and pine wood - natural wood, Thermo-D wood, weathered natural wood, weathered Thermo-D wood.