Influence of Coating System Composition on Moisture Dynamic Performance of Coated Wood

By Jan Ekstedt

Model coatings with known composition were assessed for liquid water permeability both as single coat systems and combined as primers and topcoats to form regularly used coating systems—in total 38 different systems. The water permeability of the coatings, expressed as water absorption value, was measured by a method similar to the method that now is proposed as a European standard for the assessment of liquid water permeability.

During artificial weathering, the samples were measured for a water absorption value, thus showing the change in water permeability as a function of weathering. The study has shown that an excess of surfactants in the alkyd emulsions has a negative effect on the coating’s ability to exclude water from the test samples

. A waterborne acrylic paint based on a dispersion of larger particle size (0.4 µm) showed a poor ability to exclude water compared to a similar paint based on smaller dispersion particles (0.1 µm). The alkyd emulsion paints, as single coats, showed high water absorption values compared to solventborne paints and acrylic paints.