The crosswise bonding of the layers in laminated solid wood panels results in internal stresses when the humidity varies. The layers hinder one another as a result of the anisotropy of wood. The purpose of this study was to determine the internal stress state in free and constrained swelling. The expansion properties in the three panel directions were measured. Furthermore, the swelling of samples was constrained while the resulting forces were recorded. Hygroscopic warping experiments were carried out inducing a climate gradient within the panels. Afterwards the stresses were calculated from released deformations and non-destructive measurements of the Young's modulus. The materials used were untreated and heattreated beech wood, the latter modified in two levels. In addition to homogenously structured panels, treated top layers were combined with an untreated middle layer. Swelling, swelling pressure, warping and internal stresses considerably decreased from untreated to treated wood. If layers from treated and untreated material were combined, stresses and deformations increased as compared to the variants produced only from treated wood. It was concluded that the lower equilibrium moisture content of heat-treated beech wood improves its dimensional stability, which results in smaller deformation differences between the layers. Hence, the stresses were less distinctive.

Traditional, unconventional wood treatment methods were tested in comparison with commercially available wood protection products on thermically tempered spruce. Unconventional treatment methods were found to be no better regarding vapour resistance, water absorption or outdoor weathering.

The enterprises of the forest- and wood-based industries (saw mills as interface in the wood production-chain as well as the further process levels) belong to the elements of a concept of sustainable development in the sense of the Rio Summit. Products competing within the international market, a purposeful argumentation and propagation of products and education as well as further education are important factors for the realisation of an essential contribution to a sustainable development in this field.

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The tests showed that the unorthodox methods could be an alternative to the common treatments in some fields of application. Tests on the rate of fungal decay showed that some historical methods (boric acid, sodium carbonate,potash) perform quite well in unweathered condition, whereas weathered samples perform significantly worse. This is due to the fact that these preservation agents do not adhere to the wood, or do so only weakly. Weathering clearly shows the susceptibility of traditional methods due to leaching caused by the weather. We found great differences amongst standard products.