Wood products that are applied in use class III (e.g. cladding, noise barriers, carports, garden furniture and fences) are subject to degradation. Certain ranges of moisture content of wood products used in outside applications can create a convenient environment for wood-destroying insects and fungi. Moulds and sap-stains further influence the wood surface via discolouration. Attack by different kinds of decay fungi can lead to a wide range of wood damage forms and produce a great loss in strength. UV- radiation degrades lignin and leads during weathering to greying of the surface of wood products.
This investigation deals with the advancement and optimisation of process parameters of a combined impregnation procedure using a copper-based chromium-free wood preservative in combination with a subsequent drying process within modified linseed oil. The process parameters, as well as the physical properties, leaching of wood preservative, and biological durability of the treated products were investigated.
The treated samples showed a long-lasting weathering performance during outside weathering, in which water repellence, reduction of crack development and reduction of surface degradations was improved.
A decrease in durability of treated samples was not observed following three years of exposure close to ground and in ground contact.
In addition, an overview of alternative water repellents i.e. paraffin and other modified linseed oils is given and the applicability of this process onto other wood species is described.
Keywords: Wood degradation in use class III, Combined impregnation process, Improved weathering performance
Authors
Andreas Treu
Dept. of Wood Technology, Norwegian Forest and Landscape Institute
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