Tannin Staining

Causes

• Failure to adequately prime and seal the surface before painting
• Using a primer that is not tannin-stain-resistant
• Excess humidity or other moisture problems that can cause tannins to rise to the paint surface

Solutions

• Locate and correct any moisture sources.
• Remove all loose paint with a scraper or wire brush.
• Remove the stains with oxalic acid or an oxalic-based solution.
• Rinse with a pressure washer.
• Allow the surface to dry thoroughly for at least 48 hours (depending on the existing weather conditions).
• Prime the stained area with a top-quality, stain-blocking wood primer.
• If severe staining exists, apply two coats of primer. Always prime edges and ends of shingles. If possible, prime the backs of shingles prior to installation.
• Repaint using high-quality paint.

Notes

Tannin bleed is a surface problem, not a paint failure. Tannic acid will prolong the drying of oil-based primers and in some cases you will have to wait three to five days for the primer to fully cure before repainting. If staining occurs during the application of the new coat of paint, sand lightly and re-prime the area before applying the final finish.

In spite of all precautions, a certain amount of bleeding will probably occur within one year after the wood is first painted. It is best to wait one year before repainting. This allows the tannins to surface and weather away normally.