Fungal resistance and physical–mechanical properties of beech plywood having durable veneers or fungicides in surfaces

Improvement of insufficient fungal resistance of beech plywood for wet conditions was examined by: (1) incorporation of durable oak (Quercus robur) or black locust (Robinia pseudoacacia) surface veneers instead of beech (Fagus sylvatica) ones; (2) primordial treatment of beech surface veneers with 0.5, 1, 1.5 and 3 % solutions of fungicides DDAC, IPBC, Propiconazole and Tebuconazole; (3) additional treatment of beech plywood with the same fungicides. The anti-fungal efficiency of these three methods, applied to five-layer plywood boards glued with phenolic resin, was assessed either by decay test with two brown rot fungi (Coniophora puteana and Serpula lacrymans) and one white rot fungus (Trametes versicolor) using edge protected specimens according to modified ENV 12038, or by mould test with two microscopic fungi (Aspergillus niger and Penicillium brevi-compactum) according to modified EN 15457. The durability of beech plywood significantly increased after incorporation of black locust veneers into the surface layers, and also thanks to organic fungicides (0.5 % IPBC, Propiconazole or Tebuconazole, and 1.5 % DDAC) present in the surfaces. Other selected properties of beech plywood were sometimes influenced positively (e.g., soaking due to less permeable black locust and oak surface veneers) or negatively (e.g., shear strength due to fungicides).