At the M Sora company, the use of certain paints (so-called “Italian paints”) leads to uneven stains on the surface of the treated wood for joinery, which is not acceptable to customers. We discovered that the problem was not in the sanding or paint application technology, but in the wood itself. We took a systematic approach and examined the entire manufacturing process, from gluing to the finished product, comparing different types of wood and colour systems. The results showed that colour stains occur more frequently in fir and spruce wood and when darker colours are used. Light microscope analyses revealed differences in film thickness and the penetration of the pigments into the wood. The hyperspectral camera showed that stains are already present in the raw sanded wood, although they are not visible to the naked eye. Confocal microscope measurements and indirect roughness tests by measuring the contact angles of water on the sanded elements confirmed measurable differences in the roughness of the wood in the areas with stains, which is the cause of their formation on the surface-treated elements. The exact cause of the different roughness on the individual parts of the sanded wooden elements remains unknown and could be the subject of further investigation.
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