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Traditions and problems with exterior wood coatings in Germany

: Hora, G.; Böttcher, P.; Heinskill, J.; Pohlandt, K.

Korpilahti, E.:
Caring for the forest. Research in a changing world : Posters, abstracts
Vienna, 1995
ISBN: 951-40-1452-9
IUFRO World Congress <20, 1995, Tampere>
Fraunhofer WKI ()
durability; half-timbered house; transparent stain; UV-stabilization; water-borne dispersions; window

Half-timbered houses mainly made of oak, spruce and pine have a long tradition and are respected as cultural values in Germany. Tendencies to renovate or to rebuild these wooden framework type of buildings lead to a variety of problems concerning the surface finishing. In ancient years half-timbered houses often were treated with water vapour tight oil paints consisting of 3 to 4 layers. In the past the utilization conditions of half-timbered houses have rapidly changed. Due to heating a much higher moisture level is established indoors. Hence, a coating systems is required that allows a good water vapour diffusion to let excess wood moisture easily penetrate to the atmosphere. Water-borne acrylates based on copolymers indicate the lowest water vapour diffusion resistance (m-value) and should be favoured since water-borne paints also comprise economical benefits. Windows are mainly treated with semi-transparent stains in Germany in order to pertain visibility of the wood structure. Def iciencies in constructive wood protection, non-compliance of the necessary renovation intervalls and the lack of a sufficient amount of pigmentation often lead to accelerated deterioration of the stain. Therefore, chemical modification of stains to raise their durability must be one of the major research areas in future. Prelimenary investigations have focused on the effectiveness of UV-stabilizers. By adding UV-stabilizers to solvent-borne alkyde stains, the transmission of light with low wavelength between 200 nm and 380 nm can be reduced to less than 1 %. Additionally, investigations are necessary to secure a sufficient durability of wood coatings. Hence, chemical, physical and microscopic techniques must be combined to evaluate the coatings lifetime expectation at an early aging stage. Key words: Half-timbered houses, windows, water-borne topcoats, durability