Wood products for exterior use are most commonly finished with surface coatings which highlight the decorative properties of wood. However, surface coatings do not provide sufficient protection to wood products that are exposed to weathering. But any pre-treatment of wood, such as impregnation with biocides or modification of wood, may affect the properties of coatings as well as resistance of surface systems against ageing. Therefore, the influence of impregnation and thermal modification of the substrate on water and water-vapour permeability as well as on adhesion was studied. Weathering was simulated on the "substrate-coating" systems with artificially accelerated ageing. It was shown by the results that biocide pre-treatment and thermal modification of wood did not have any important negative influences on the observed properties' some of the properties were even better. During artificially accelerated weathering some defects on the coatings' surfaces appeared which were the lowest in the case of the "thermally modified wood-coating" systems followed by the "impregnated wood-coating" ones.