Coating of larch wood for outdoor use
Thanks to its striking grain, larch wood is popular for windows, exterior doors, and façade cladding. However, many manufacturers have had negative experiences with sagging, and cracking of the coatingfilm during application. There are two main reasons for this: On the one hand, the abrupt change between early and latewood leads to significant differences in density. This can lead to adhesion issues, with the result being a 'rippled' surface with air bubbles, wrinkles or cracks in the paint film.
Another complication is water-soluble, phenolic substances in larchwood. In connection with the low pH value of the wood (about 4) they have a negative effect on the thickener system of the paint, and affect its stability. The paint film can break on vertical surfaces, and sagging occurs.
The only option to tackle such complications reliably is to use a special primer. Teknos offers the aqueous 2K special primer ANTI STAIN AQUA 5300 in its product range. It blocks critical substances in the larchwood, and balances out structural differences in the wood. The primer is applied before the topcoat to ensure a smooth, even surface despite varying wood quality.
New research findings provide interesting approaches for the future. The 'LarchCoat' project by Holzforschung Austria (Austrian Wood Research Institute) has shown that the high concentration of polysaccharide Arabinogalactan in the larch heartwood has a negative effect on film formation. Teknos are using these findings in the development of future water borne 1K larch wood primers. Currently, however, the 2K primer ANTI STAIN AQUA 5300 is the method of choice for coating larch wood reliably in water borne system.