You can repair minor surface defects (smears, dents, stains). If the corten is natural/raw (without Antiwashout), rub down the surface with a piece of steel wool ( like Scotch Brite) on the surface, to eliminate the defect. Then, moisten with water and place the product on the outside, until the part returns to the surface characteristics of the rest of the piece.
If the corten is treated with Anti-washout, repeat the previous step, by first removing the treatment left with steel wool (e.g. Scotch Brite). After the area has re-oxidized after exposure to the environment, re-apply with a brush two coats of Anti-washout treatment (purchased from Metalco). If the Anti-washout degrades over time, due to weather or mechanical agents, it is possible to renew the treatment according to the procedure described above (removing residues – oxidation – applying treatment).
After complete maturation (average 12/18 months), corten is considered stable and you can suspend the application of Anti-washout treatment, unless you want to use it in order to revive the surface, making it more shiny and smooth.