Brownish or tan discoloration on the paint surface due to migration of tannins from the substrate through the paint film. Typically occurs on 'staining timbers,' such as redwood, cedar and mahogany, or over painted knots in certain other timer species.
- 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
Correct any possible sources of excess moisture (see Efflorescence and mottling). After thoroughly cleaning the surface, apply a high quality stain-resistant solvent-based or water-based primer.
Solvent-based stain-resistant primers are the best type to use on severely staining boards. In extreme cases, a second coat of primer can be applied after the first has dried thoroughly.
Finish with a top quality water-based paint. Dulux recommends Dulux 1Step® Oil Based Primer Sealer Undercoat and Dulux Weathershield®.