Modified timber in various above ground exposures - durability and moisture performance

Differently modified timber products have entered the European market in recent years. Although they are nowadays also used for parquet flooring and furniture, the original intention was to improve dimensional stability and durability of wood to allow applications in outdoor environment without using additional biocides. The protective mechanism of modified timber is based on its hydrophobic character and increased moisture performance. Through keeping the wood moisture content below conditions favourable for decay organisms, products made from modified timber are sufficiently durable for many outdoor applications. However, problems occur, when modified timber becomes constantly wet, e.g. when exposed in ground contact. Various standard tests, which had been designed for testing the efficiency of wood preservatives, do therefore not adequately consider the peculiarities of modified timber products, when applying ‘torture conditions’ to the material. Within the research program ‘WoodBuild’ a comprehensive set of laboratory and field test methods has been applied on a variety of different wood materials. Extensive comparative studies have been undertaken with differently modified timbers. The important role of wood moisture content has been considered through automated long-term moisture recording within above-ground test set ups, e.g. lap-joint trials, sandwich tests, and double layer tests. The material climate in terms of wood moisture content and temperature has been determined and compared between different thermally modified, furfurylated, and acetylated timbers, as well as with various reference materials. Results clearly showed that the advantageous moisture performance of modified timber contributes significantly to its enhanced durability.