COLOUR AND DIMENSIONAL MODIFICATIONS OF SOLID WOOD PANELS MADE FROM HEAT-TREATED SPRUCE WOOD AFTER THREE MONTHS OF OUTDOOR EXPOSURE

The paper presents the results of an experimental research performed with spruce wood (Picea abies L.), originating from mature trees and thinnings cut from the same forest parcel from the Stroesti-Arges region in Romania. Solid wood panels were manufactured, both from heat-treated and untreated strips. The panels were open-air exposed for three winter months, in order to evaluate the colour and dimensional modifications which may occur if this material is used under outdoor conditions. The results showed that the panels made from heat-treated wood strips swelled by up to 74% less in case of mature wood and by up to 60% less in the case of juvenile wood. The colour of the heat-treated wood panels got lighter in time, the total colour change after three months ranging up to E*=12, while the panels made from untreated wood strips suffered severe darkening during the period of open-air exposure (L*=-16) and their total colour change ranged up to E*=19. The overall conclusion of this research is that both mature and juvenile spruce wood are suitable for outdoor uses from the viewpoint of dimensional stability, but the severe colour modification (from glossy dark brown to glossy silver) after only three months of open-air exposure must be taken into consideration