Preservation of wooden boards

The aim of the investigation was to study the prospects for the development of decay and insect resistant plywood and particle boards. The treatment of the boards during manufacture and possibilities of protecting the finished boards were clarified. The investigation comprised phenolic glued birch and spruce plywood and PF- and UMF-particle board. In the decay tests the reference material comprised different species of timber and impregnated A- and B-class pine (SFS 3974). The plywood boards were protected by treatment of wet veneers with water-soluble diffusible compounds, by dipping, immersion or spraying of dry veneers with oil soluble preservatives, or by addition of preservative to the glue. The particle boards were treated by spraying the preservative on the chips before gluing, or by addition of preservative to the glue. The finished boards were protected by impregnation with water or oil soluble agents and by coating and edge sealing. The strength properties, contents of preservatives, decay resistance to Coniophora puteana and Gloephyllum sp., and resistance against termites (Heterotermes judicola) were studied. A greenhouse test was started an the same time which studied the durability of the boards in contact with ground. The impregnation of finished boards proved particularly difficult with regard to plywood. The particle boards were more easy to impregnate, but in both boards the drying was very slow. The treatment of wet veneers with different preservatives gave deviating results. Acidic and oxidacive substances and barium containing substances weakened the strength of the glue joint. Wood-based boards almost corresponding to the A-class impregnated wood in the laboratory tests were obtained with ammoniacal copper compounds. Of the treatments on dry veneers the immersion and spraying proved more efficient against decay than glue protection treatment. TBTO was both in spraying and immersion efficient against Coniophora. The impregnation of the veneers before gluing with CCA-compound weakened glue joint clearly in concentrations required against decay. The preservation of particle boards did not influence the strength properties of the boards. TBTO treatments protected the boards rather effectively against decay. However, they did not prevent moulds. Plywood and particle boards protected by mixing preservations in glue were in the termite tests relatively more resistant than in the decay tests, even though separate treatments with permetrin were more effective in plywood. The edge sealing of the plywood board decreased the leaching of the preservative and even increased the decay resistance of unprotected plywood. Coating with a phenolic film and edge sealing with acrylate paint prevented leaching of the preservative and decay of treated and untreated plywood and PF -particle board.