What is extractive bleeding and how does one clean it off?
Extractive bleeding is characterized by the tannins in the wood being dissolved in moisture and migrating to the surface of the product. Rain will sometimes wash these stains away; however if left to weather, the sun can cause polymerization, thus requiring the addition of a tannin blocker and new top coat finish (ensure proper surface preparation before applying new top coat) once the moisture problem has been solved. Compounds containing oxalic acid appear to be the most effective at removing extractive bleeding stains: ensure you use proper safety precautions and follow the oxalic acid compound manufacturer's application directions. Extractive bleeding does not signify failure of the applied finish, but instead is found in applications where a source of moisture is present. Extractive bleeding is not a manufacturing defect nor is it a finish defect; it is a natural phenomenon that occurs in applications. Tannin blocking products help, however, the CSSB does not provide any finish warranty. Check with your sidewall product manufacturer, finish manufacturer, Member Contractor/Installer or professional contractor for more assistance.