Finishing the edges of the panels
The edges require special treatment before painting. Before applying any coatings, all edges of the panels indoors should be sanded with sandpaper to a rounding radius of approx. 1 mm. The boards intended for outdoor panels require different sanding. In these boards, the edges should be ground to a rounding radius of 2-4 mm. When the varnish is applied to the surface, a coating of a certain thickness is created (drawing).
Drawing. Edge rounding before varnishing to a radius of 2-4 mm: a) rounded edge, b) the thickness of the varnish coat "a" is the same on the curve and on the plane.
In the liquid state, the varnish on the sharp edge is not able to produce a coating of the same thickness. The lacquer layer is thinner at this point (drawing).
Drawing. A layer of varnish coat applied to a sharp edge: a) on the sharp edge the coating thickness is 1/3 coating thickness on the plane, b) at the edge, the coating breaks and water penetrates.
Moreover, in these places the varnished coating is most often damaged. The small gap then allows water to penetrate into the wood, but prevents it from evaporating, because there is practically no evaporation surface. The local moisture of the wood causes bluing and peeling of the coating layer. Repair is problematic, because sanding the damaged area and re-painting does not remove the cause, i.e.. moisture. On a damp substrate, the varnish peels off quickly again and the wood continues to darken. Therefore, it is necessary to round the edges more.