A two-part screening test has been developed to evaluate additives for wood coatings. First, an additive is tested in the microbial laboratory and evaluated based on its inhibitory properties against selected test organisms, directly on agar plates. A microbial growth analysis is prepared and evaluated. If the additive is considered effective, it will be tested in a standard top coating (acrylic or alkyd) and applied onto wooden panels for exposure in a growth chamber developed for this exact purpose. In the growth chamber there is a “24-7-365 constant” humidity and temperature as well as a constant spore pressure throughout the chamber. All test panels are evaluated every week for a total of 6-10 weeks. Every panel gets two evaluations. Respectively, based on the amount of mould attack and based on a qualitative overall visual appearance. It is possible to age the panels and coatings before the exposure in the mold chamber, either by QUV or in a state-of-the-art Weathering Machine, which also includes frost periods in between the UV and the rain, which is important for evaluation of coatings used in geographical areas with cold winters. With this two-part test, an additive can be screened within few weeks (plus any aging process) for its properties as antimicrobial additive in a wood coating.

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