Cedar and redwood contain water soluble extractives, pitches and oils. These extractives are the most common cause of objectionable discoloration of exterior house paints. (The discoloration, however, does not affect the durability of the paint film.) Moisture causes the extractives to migrate to the surface and bleed through the paint film. The resulting stain is often more visible when the color selected for the house is of light or medium value.
By following these simple guidelines, you will greatly reduce the problems associated with extractive bleeding on cedar or redwood siding.
1. If you are planning to finish your siding with a solid color stain or housepaint, prime all areas first with a quality exterior primer. If discoloration is present after priming a second application of primer may be necessary. For best results Hirshfield's recommends our 100% Acrylic Latex Primer followed by a topcoat of Latex Solid Color Stain or Acrylic Latex Housepaint. Be certain primer is dry before topcoating.
2. You may use an oil based semi-transparent stain. Generally, this type of application will not be problematic. The reddish brown extractives will tend to migrate through the semi-transparent stain and wash off. (NOTE: Light colored semi-transparent stains may show objectionable discoloration during this migration period.) Select a cedar or redwood ìnatural toneî color, or a color darker than the natural wood.
3. Darker colored paints or solid stains do not usually show this discoloration problem. You may be able to get by with a single coat. Two coats are preferable.
The ultimate performance of your paint job depends on the wood, the applicator, and the paint or stain. Follow all label directions and call the experts at Hirshfieldís if you are in doubt about any portion of your job.