Things You'll Need
Trisodium phosphate cleaner
Coarse nylon sponge
Epoxy patching compound
Plastic drywall pan
Plastic stirring stick
Plastic putty knife
Professional painter's tape
Acrylic spray primer
Acrylic enamel or epoxy spray finish
Galvanized metal-etching spray primer
Cast iron sinks are finished with porcelain enamel. Though durable, this coating is not indestructible. Over time, dings and nicks may reveal black patches of bare cast iron. If you need to repair a damaged cast iron sink, accomplish your goal by using a strong, quick-drying epoxy compound. Once the sink is repaired, refinish it with one of two enduring coatings that will resist consistent water exposure.
Wash the cast iron enameled sink with trisodium phosphate using a sponge. Rinse with rags; dry with towels.
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Smooth the damaged portion of the enamel using 60-grit sandpaper.
Scour the entire enameled sink with a finer 120-grit sandpaper. Stop once it feels rough.
Add the two parts of the epoxy compound together inside a plastic drywall pan. Stir the mixture with a plastic stir stick. Never use tools made of metal or wood; the epoxy will bond to these materials.
Apply the wet epoxy patch to the damaged area of the enamel, using a plastic putty knife. Smooth the patch so it conforms with the adjacent enamel. Wipe excess epoxy using a moist rag. Let the patch dry for three hours before beginning the refinishing process.
Mask off all adjacent surfaces to protect them from overspray -- cover them with masking paper and tape.
Roughen the epoxy patch using 180-grit sandpaper.
Spray a coat of acrylic primer onto the enameled sink. Maintain a distance of 8 inches between the existing enameled finish and the spray primer tip. Failure to do so will result in sagging. Let the fresh primer base dry for two hours.
Finish the enameled sink using the same method as when you primed it. For lasting results, use either an acrylic enamel or epoxy spray finish.