Cause Red-colored woods contain a water soluble dye called tannin. Tannin is not soluble in most solvents. Application of latex topcoats directly to these red-colored woods may develop a red-colored stain on the finish coat. If the dry film is intact and discoloration occurs at a later date, then staining is being caused by water moisture within the board wall. This moisture will migrate and eventually carry staining substances from within the wood to the surface of the paint film. Some cedar woods contain colored dyes such as tannin which is water soluble, and other colored extracts which are soluble in mineral spirits. In these instances, a primer that has discolored should be spot tested with a second coat of primer or a latex topcoat to determine which will successfully block future discoloration.
Solution If dry film is intact and discoloration is occurring at a later date, then internal moisture is the culprit. The moisture source must be located and corrected. Remove stains by washing with a solution of equal parts alcohol and water. Allow to dry thoroughly. New red-colored woods must be sealed with an undercoater that will function as a barrier coat, preventing staining of the topcoat. This undercoater can be either a solvent or latex primer, depending on severity of available tannin dyes in the wood. Although the latex primer contains water, the product chemistry is designed to minimize surface discoloration by tannin bleed. Extreme cases of tannin bleed may require one or two coats of alkyd primer to prevent discoloration.
