Moisture dynamics and fungal susceptibility of plywood

Engineered wood products are widely used in construction and transportation. Plywood has one of the best physical and mechanical properties for application under moist conditions in use class 3, i.e. exterior exposure without ground contact. Yet a profound knowledge of their moisture dynamics and fungal susceptibility is a prerequisite for proper use. In this paper the results of more than two years of continuous recording of the moisture content of different plywood types in exterior exposure is presented. Clear differences concerning moisture dynamics are apparent regarding wood species, glue type, and veneer thickness. X-ray tomography scans literally offer insight into the weathering state of the veneer layers and glue lines. Fungal susceptibility of the samples relates primarily to wood species and glue type. Furthermore, edge-sealing for fungal testing is necessary to represent in-service situations and yields distinct differences compared to non-sealed test results. There seems to be a relationship between the accumulated moisture content and layered structure of the plywood, but an unequivocal link with fungal decay is not straightforward.