Things You'll Need
Liquid dish soap
Fiberglass is a popular material for showers because it is cheap and is relatively simple to install. Fiberglass, however, is vulnerable to scratches from tough abrasive cleaning tools and cleaning solutions. Avoid this by properly cleaning fiberglass and seal it to prevent stains from soaking deep into the fiberglass where you may be unable to remove them.
Add a few drops of liquid dish soap to several cups of lukewarm water. Mix until soapsuds begin to form.
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Dip a sponge into the soapy mixture.
Rub the soapy mixture over the surface of the fiberglass until you remove all of the soap scum, mold and mildew.
Add just enough water to 3 tbsp. baking soda to make a thick paste.
Rub the paste into any shower rings, soap scum or mildew stains that are still visible. The baking soda will act as a very mild abrasive that will remove the stains without damaging the fiberglass surfaces.
Rinse the area with clear water and dry it thoroughly.
Pour clear gelcoat into the tank of a spray gun. The gelcoat layer will help protect the shower.
Depress the trigger and spray the gelcoat over the entire surface of the shower. Spray a thin layer of gelcoat. Do not depress the trigger and hold the spray gun in the same area, as this will apply too much gelcoat and it will drip.
Let the gelcoat dry completely.
Wet a clean cloth with acetone and rub it over the fiberglass to remove the tacky surface of the gelcoat.
Lightly sand the entire surface with 1200-grit ultrafine sandpaper. This will smooth out the gelcoat surface.
Rinse the area with clear water and let it dry completely.