Tannin Staining
 

Description:
Brownish or tan discoloration on the paint surface due to migration of tannins from the substrate through the paint film. Typically occurs on "staining woods," such as redwood, cedar and mahogany, or over painted knots in certain other wood species. However, tannin staining can occur with any kind of wood.

Possible Cause:
• All woods, but especially 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 b o a rd 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 oil primer that will function as a barrier coat, preventing staining of the topcoat.

Note: Even with proper preparation and recommended products, tannin bleed can still occur (especially on new woods) with both latex and oil topcoats.

Recommended System:
Primer
1 Coat of FLEX BON #169 Series Exterior Alkyd Primer
Topcoat
2 Coats of Top Quality FLEX BON Exterior Latex Paint