Reddish, brown (or sometimes black) stains appearing as blotches or streaks on surface or paint. See also Tannin Staining.
- Steel in contact with air and moisture will rust (e.g., nails, steel railings, damaged galvanized, flashing, etc.).
- Steel nails may develop black discoloration when in contact with damp wood that possesses a high amount of tannic acid.
- Prime bare steel as soon as possible with a rust-inhibiting primer or finish.
- Replace steel nails with galvanized or other non-rusting nails.
- Rusted nails that cannot be removed must be sanded to shiny metal; countersunk; coated with a rust-preventive primer; and then caulked, filled, or patched; and topcoated.