What do I do about the dark stains in cedar & in redwood known as tannin bleeding?
Tannin is just one type of organic material that occurs naturally in decay-resistant species. While aesthetically displeasing, this discoloration does not harm the timber or the coating. Extractive bleed is not stain failure. When extractive discoloration occurs, tannins are dissolved by moisture and are then drawn to the surface by the sunlight. When extractives do appear, they can often be removed with detergent and water. Stubborn tannin stains can be removed with an oxalic acid-based wood brightener.
