The natural weathering of surface treatments was compared at four sites and on five wood species; beech, spruce, Scots pine (sapwood), Douglas fir and dark red meranti, for 24 months. The surface treatments were: impregnating stain, film forming stain, pigmented acrylic latex paint and pigmented alkyd paint (solvent based). Despite substantial differences between the four locations, the results of the exposure differed only little. Spruce was shown to be a substantially better substrate for surface treatments than beech or Scots pine, though Douglas fir and meranti were best of all. The impregnating stain weathered uniformly, whereas the film forming stain cracked and flaked, leading to growth of blue stain fungi. Both acrylic latex and alkyd paint showed little or no damage after 2 years of weathering. The dampening effect of surface treatments on the natural changes of wood moisture content was initially quite good for the impregnating-and the film-forming stains, but both lost their efficiency after approximately 12 months. The protection conferred by acrylic latex was somewhat better, though possibly not sufficient for external joinery requiring dimensional stability. The highest level of moisture exchange damping efficiency was shown by the alkyd paint.