Impregnated and covered birch plywood performance during external exposure

We evaluated the performance of covered and impregnated birch plywood (BP) in the outdoor environment. Fungal growth, crack formation, and surface hydrophobicity were regularly assessed over 36 months. After 2 months, uncovered BP was severely colonised by disfiguring fungi. During the test period, the surface of plywood with better coatings (solvent- or water-based) was not overgrown or was overgrown slightly with fungi, no cracks were formed, and the surface hydrophobicity was stable. Similar results were observed for laminates with phenol and melamine film. Plywood impregnated with copper and organic biocides, with retention conforming to Use Class 3 (EN 335:2013), did not protect the plywood from crack formation within several months and the severe growth of disfiguring fungi within a year. The blue stain fungus Aureobasidium pullulans was identified for all overgrown test variants. No rot fungi were detected after a 36-month exposure.