Cast iron sinks are chosen by homeowners primarily because they are durable and traditional looking. Typically, they are made of cast iron and coated with enamel. The downside to these sinks is that the enamel chips easily and is often prone to stains. (see reference 1) Especially in dealing with antique sinks, you should use caution to preserve its authenticity and begin by trying to remove stains before completely refinishing the cast iron sink.
Things You'll Need
Cast iron cleaner
Smooth finish roller or paintbrush
Clean the sink using a product intended for removing stains from cast iron. You will want a nonabrasive cleanser. Kohler makes one specifically for cast iron, but SoftScrub or another nonabrasive formula will work. If necessary, allow the cleaner to sit overnight. If stains will not come out or your have chips, proceed to refinishing.
Sand the entire surface area of the sink using fine-grit sandpaper. The sanding will roughen the finish of the enamel over the cast iron and give the epoxy coating the ability to bond to the sink.
Apply the epoxy primer with a roller or brush in light, even strokes, making sure there are no brush marks or raised edges. Using multiple thin coats will provide better results. Apply two to three coats, allowing each to dry completely before applying another.
Brush or roll on acrylic topcoat. Acrylic topcoat will create a strong and durable finish. This coating should also be applied using a thin coat of paint. Paint in one direction and avoid feathering at the end of your brushstroke for a smooth surface.
Do not use your sink for two days to allow it to dry completely. For regular cleanings use a mild, nonabrasive cleanser.
Make sure the room that you are working in has proper ventilation while working with these types of chemicals.