- 1). Pour one cup water and one squirt of liquid dish detergent into a spray bottle.
- 2). Spray over the fiberglass stain and scrub with a nylon scrub brush. This often removes light stains on your fiberglass surface.
- 3). Mix baking soda into a paste form by pouring enough baking soda into a bowl to cover the stain. Stir in hot water slowly until you form a thick paste.
- 4). Spread a layer of the paste over the stain on your fiberglass surface and let sit until dry. This will often take two to three hours.
- 5). Scrub the baking soda paste away with a wet nylon scrub brush, and scrub the stain residue as well. All residue should be lifted. Repeat the paste application if any stain is still present.
Source...