Opti-Bond can also be used on aluminum siding or steel decking, he said, and may take only one coat to do the job. If your galvanized metal contacts corrosive industrial fumes, you need an epoxy. Some epoxies are designed to go directly on galvanized metal, with additives that make the coating more flexible, said Hart. One of these is Sherwin-Williams' Macropoxy. These coatings are especially designed to maintain their integrity during that change.
Epoxies require less surface preparation than acrylics.
With an acrylic, you need to be cautious that you have a relatively sound substrate. Acrylics are out, since they require a scrubbed substrate, said Insl-X's Daniel Drucker. So you'll probably need to back off the DTM idea, and get a primer. If it's corroded because it's in a harsh environment, you ought to lock into a specific system for that specific use, and not use a universal product. Yet in most states there's still the old-fashioned alkyd, which can get a foothold in rust.