Wood will need special treatment before paint is applied. Some wood species such as cedars and redwoods contain oils that may stain or prevent the paint from adhering to the surface. Older woods that have a coat of paint on them will need cleaning to remove heavy buildup. This buildup can prevent the fresh coat from bonding to the wood's surface. In all cases, the paint must have a solid connection with the wood or the paint will quickly flake off.
Wood Preparation
Sand the wood surface with a fine grit paper. The higher the number printed on the sand paper, the finer the grit. Lower numbers or heavier grit sand paper works well for removing old paint from surfaces after the wood has been scraped with a metal edge. Paint scrapers and metal wire brushes work well for mechanically removing old paint from wood. The surface of the wood, though, will have raised surfaces. This can prevent the paint from bonding to the surface. The raised edges from sanding are also called mouse whiskers. Remove the mouse whiskers by applying a finer grit paper to remove the small particles. Wipe the wood surface down with a clean rag wetted with mineral spirits. The mineral spirits will remove any surface sawdust which can prevent the paint from adhering. The chemical will quickly evaporate. Exercise caution when using chemicals to remove paint. Many removers may harm the wood and create a caustic situation when used indoors. Follow all manufacturer's directions whenever using chemical-based paint removers and strippers.
Priming
Prime all wood surfaces with an appropriate covering. Latex-based paints will require the use of a latex-based primer. Add some color from the finished paint to the primer. On fresh woods that contain no paint, add one cup of the finished colored paint into a gallon of the primer. The pigment will help cover the fresh wood. This allows for fewer coats of the final color paint. Use an oil-based stain prevention primer such as Kilz brand. The chemical used in this type of stain reducing primer seals any oils from the wood that can leach back onto the surface. Follow the manufacturer's recommended applications as more than one coat may be needed for certain woods that are stained or contain heavy oils.
Brushing, Rolling or Spraying
Choices for applications are yours and may be tied to a budget. Large wood surfaces may be better served by rolling the paint onto the surface after trimming with a brush. Sprayers will may make quick work of small-width clapboards that have a lot of surface area. The smaller clapboards may take a long time to apply the paint with a brush. The multiple raised edges may make rolling a tedious chore.
Apply paint to large, smooth surfaces with a roller. Work the paint onto the surface with overlapping seams. Pay attention as the paint begins to dry as roller edges can be seen on the surface. Roll over the areas to conceal any seams or color differences.
Mask off any areas where paint from a sprayer can cause over-spray onto unwanted surfaces. Cover with paper or plastic sheeting held in place by masking tape. Large canvas sheets can be draped over garden beds and shrubs to protect plants from any paint. Move all vehicles well out of the way from any errant paint or drips. Paint outdoor surfaces with a sprayer on calm, dry days. Wind will carry the colored wet paint for many feet in all directions.
