The impact of ultraviolet radiation on the colour and wettability of wood used for facades.
The study examined the effect of UV radiation on the colour and wettability of cedar, gaboon, meranti and Scots pine wood. The tested species of exotic wood are mainly used in European countries for facades. For this kind of usage they act as a substitute for pine wood. In the study, the colour parameters were determined using the CIE L*a*b* colour space model. The tests showed that the most significant changes in the lightness of the wood occurred after 20 hours of UV radiation exposure. After that time, the L* value change was linear. The cedar wood turned the darkest and it also showed the greatest total change of colour ΔE. Comparable colour changes ΔE, and thus the greatest colour stability of all the tested wood species, were shown by the gaboon and meranti. In addition, it should be noted that all the tested wood species were characterized by a much smaller susceptibility to colour change under UV radiation than the pine sapwood and heartwood. The results also revealed that UV radiation significantly affects the contact angle, and therefore the surface free energy of the cedar and pine sapwood.