Test methods for a reliable assessment of water-borne paints for exterior wood protection

Water-borne paint systems, which are applied in a relatively wet season, may cause an accumulation of water in the wooden substrate. This is exacerbated by an increase in moisture-barrier properties due to the leaching of water-soluble components, and is further promoted by the increasing barrier properties under relatively dry external conditions. Recent tests with four commercially available paint systems show an increase in μ-value with a factor 2.4 to 3.8, after a leaching period of only two weeks. Existing test methods and standards do not take sufficient consideration of the effects of leaching on the moisture barrier properties. The reliable assessment of the quality of water-borne paint systems for exterior wood protection needs new or modified test methods and standards. Mathematical models have to be developed to translate laboratory test results in to different practical conditions, climates and timber dimensions.