Fiberglass sinks are often painted to enhance a room, or hide ugly stains. Polyester, polyurathane or epoxy works best on fiberglass. Choose a marine grade, or boat paint, for a finish that will hold up well. Marine-grade paints are more expensive, but provide a lasting finish. For proper adherence, the humidity level should be below 60 percent, and the temperature should be from 65 to 90 degrees Fahrenheit, or 19 to 35 degrees Celcius.
Wash the entire interior and exterior of the fiberglass sink with hot soapy water. Dry the sink completely.
Wipe down all surfaces with denatured alcohol to remove oils. Oil will prevent the paint from adhering to the fiberglass, so wear gloves whenever touching the sink after this point.
Cover all plumbing fixtures with tape. Cover all areas surrounding the sink with paper, plastic or a drop cloth.
Apply a coat of primer with a paint brush. Allow the primer to dry completely. Wash the paint brush thoroughly.
Apply two thin coats of paint to the fiberglass sink. Allow the first coat to dry before applying more paint.