Fiberglass surfaces, like other surfaces, are susceptible to stains. From rust stains to soap scum, fiberglass attracts it all. There are several products you can use to clean fiberglass, including acetone--a chemical that is also used to remove nail polish and other paints. Acetone removes not only dirt and grime from your fiberglass surfaces, but also any set-in stains like rust and pen marks.
Put on a pair of latex gloves to protect your skin from the acetone.
Pour 5 tbsp. of acetone into a bucket.
Dip a white cotton cloth into the acetone. Remove the cloth and wring out excess acetone.
Wipe the fiberglass surface with the acetone-soaked cloth.
Apply light pressure to remove any stains from the fiberglass surface.
Wet a white cotton cloth with warm water from a sink. Wring out excess water.
Wipe the fiberglass surface with the damp cloth to remove acetone residue.