Laboratory blue stain testing of low VOC paints: Fid-Bau Portal

Laboratory blue stain testing of low VOC paints

Acker, J. van / Stevens, M. / Brauwers, C. / Rijckaert, V. / Mol, E.

The EN 152 method designed for the evaluation of resistance against blue strain in service of brush or dip applied preservatives on wood shows some shortcomings when assessing paint formulations. Based on additional assessment criteria as well as an alternative reverse exposure test several low VOC primers were tested. Both the typology of the primer and the presence of anti-blue fungicides were investigated on their impact on the colonisation of blue stain fungi on the coating surface and in the underlying wood substrate. In a first test paints and wood stains were evaluated on their blue stain resistance using both EN 152 method and its reverse exposure variant. The typology of the exterior coatings tested varied from standard and high solid solvent-borne coatings to different types to water-borne coatings. For all water-borne acrylic, the alkyd based and the hybrid resin coatings a range of synthetic resins was used. Some were applied as opaque primer paints and as decorative wood stains as well. Though some components like dryers or bactericides are present in a number of formulations examined, a clear tendency of dependence of blue stain resistance on the typology of the coating seems obvious when evaluating blue stain development in an early stage. Longer exposures to test fungi fade away the effect of resin emphasising the role of a chemical protection of the coating. In a second test the addition of fungicides to the formulation was evaluated. Results obtained with the reverse exposure method indicate distinct differences in development of blue stain.