Brownish or tan discoloration on the paint surface due to migration of tannins from the substrate (e.g., the surface that was painted) through the paint film.
Typically occurs on “staining woods,” such as redwood, cedar, and mahogany, or over knots in certain other wood species. Tannin staining can occur with any kind of wood. Most tannins are water-extractive, some are solvent-extractive. Application of latex coatings directly to these woods may develop a stain on the finish coat if the product is not specifically designed to trap these tannins.
If dry paint film is intact and discoloration is occurring at a later date, then internal moisture is usually the cause. The moisture source must be located and corrected. Allow the surface to dry thoroughly. Check to be sure the water has not affected the adhesion of the coating (e.g., primer, paint or stain).
Seal the stains with an alkyd/oil primer or a coating designed to trap these tannins.
Note: Even with proper preparation and recommended products, tannin bleed can still occur, especially on new wood, with either latex or oil topcoats.
To wash off the tannin stain, use DeckScapes&tm Revive® Deck and Siding Brightener. Follow label directions carefully.