Tannin wood staining
Wood Staining causes - Tannin escaping moisture and primers that don't black staining. The brownish stains are likely to come from redwood, cedar, mahogany and knots without priming. Severe staining mat require more than one primer coat. Staining is more visible on light colors.
Tannin staining solutions - locate and correct moisture sources. Wash with a commercial grade bleach solution, rinse thoroughly and allow to dry for 48 hours minimum. Severe staining needs 2 coats or more of a stain blocking primer. Cedar and redwood always require a stain blocking primer.
Primers and Exterior finishes - priming is critical. Stain will bleed through multiple top coatss without proper priming. Ask your Muralo dealer for the best Muralo exterior paint for your project, in the color and sheen of your choice.