Tannin Staining

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.

Possible Cause:

• Failure to adequately prime and seal the surface before applying the paint.

• Use of a primer that is not sufficiently stain-resistant.

• Excess moisture escaping through the exterior walls, which can carry the stain to the paint surface.

Solution:

Correct any possible sources of excess moisture (see efflorescence/mottling). Choose a high quality stain resistant oil-based or acrylic latex primer. After thoroughly cleaning the surface, apply the primer. Oil-based primers are preferred on severely stained boards. In extreme cases, a second coat of primer can be applied after the first has dried thoroughly. Finish with a high quality latex house paint.