In new or exposed woods (untreated): sand in the direction of the grain until a smooth surface is obtained.Then you can apply White Background for Pro Madera Wood if you are going to paint with Enamel, or Madera Stain Lasur, or Pro Madera Varnish.On surfaces that have already been painted: loose or peeled paint layers should be removed, roughened by sanding when the surface is very smooth and repaired properly.In both cases, take into account the general considerations.