Hydrophobic chemical modification can be regarded as an alternative approach to conventional wood preservation using biocides in order to protect wood in hazard class 3 according the European Standard EN 335-1. A formulation containing fatty acid modified N-methylol/paraffin and an aluminium salt catalyst was used to change the material properties of wood in order to protect wood from fungal decay and deterioration through weathering. Beech wood (Fagus sylvatica) treated to weight percent gains (WPG) of 10-14% resulted in significant decrease in water uptake in a submersion test of 40-50% when compared to that of untreated wood. The treatment slightly reduced the equilibrium moisture content at 60% and 90% relative humidity by 2% compared to untreated wood. An anti-swell efficient (ASE) of 26.6% was achieved at a WPG of 15.7% and indicated a moderate dimensional stabilisation. Strength properties of treated wood were not reduced by the treatment. In addition to the improvement of water related properties, the durability towards basidiomycetes was highly increased (tested according to EN113); the weight loss at 15% WPG was lower than 3%. Infection by the blue stain fungus Aureobasidium pullulans was significantly reduced in a laboratory test due to the treatment. Outside exposure over 1 year revealed less cracking and blue stain compared to untreated wood. The results of this study show that wood modified with a formulation of fatty acid modified N methylol/ paraffin was able to protect wood applied in hazard class 3 according to the European standard EN 335-1 over a long time period without the application of conventional biocidal products.

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