Cast-iron sinks are usually coated with a layer of enamel to provide an attractive finish and protect the iron. If the enamel becomes chipped, the iron may be exposed to water that could cause rust and weaken the sink. If the finish on your cast-iron sink appears worn, painting it with a fresh coat of enamel paint could prevent rust and extend the sink's life.
Sprinkle scouring powder into the cast-iron sink. Add a small amount of water and scrub the sink clean with a scouring pad.
Rinse away the scouring powder with water and dry the sink with a clean towel.
Sand the sink with 220-grit sandpaper if the sink has flaking paint. Wipe away any debris or dust with a rag. If the finish is in good condition, skip this step.
Apply an oil-based enamel paint to the cast-iron sink with a paintbrush. Let the paint dry and apply a second coat.
Wet a piece of 600-grit wet/dry sandpaper under running water and add a few drops of dish soap to the sandpaper. Sand the dry enamel paint with the wet sandpaper to create a smooth and shiny finish. Wipe away the suds created during sanding with a damp cloth when you are finished.