For the surface protection of wood, intended for outdoor use, stain coatings with water-based acrylic binders have been established. During the use, so products as well as a coating system are exposed to weathering% ageing. The effects of ageing on a surface system can be determined with natural as well as with a significantly faster artificial accelerated ageing. To determine the effects of ageing on characteristics of coatings and to compare the natural and artificial accelerated ageing, we subjected nine various acrylic stain systems to both ageing procedures. The coating systems differed in hue, the number of layers of coating films, application technique, and content of various UV absorber types. Before, during and after ageing we therefore examined gloss, colour, defect occurrence, adhesion of a coating determined using the pull-off test method, and wet adhesion determined using the cross-cut test method. We also determined the permeability of a coating system, i.e. water absorption through a film into the coated test pieces. The results showed that both ageing procedures have similar effects on the tested surface systems, which is especially true for colour and gloss. Colour stability and small changes in gloss during ageing can be achieved with the right choice of an UV absorber. Additionally, the thickness of a coating system has been shown to have a significant effect on its adhesion and liquid water permeability. The links between the occurrence of defects on a coating system in the artificial accelerated and natural ageing were not confirmed, probably due to a too-short weathering period during the natural ageing procedure.
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