Removing stains from fiberglass tubs and shower enclosures requires the right cleaning solutions and careful application to avoid damaging the finish. Fiberglass bathtubs and showers may develop stains from hard water or mold and may be marred by paint and adhesives. Fiberglass scratches easily; full stain removal with gentle methods may take more than one attempt.
Soap It Away
Apply a mild liquid soap to the stained area of the fiberglass with a sponge or soft cloth. A thick liquid soap such as Castile works well on shower walls.
Leave the soap on the stain for 15 minutes, or up to an hour for a tough stain. When you return, rub the soap over the stain in a circular motion before rinsing.
Rinse the soap away thoroughly with warm water. If any sign of the stain remains, repeat the procedure or try the next method.
Scrub It Away
Mix baking soda with a small amount of water, such as 1 tablespoon of baking soda to 1 teaspoon of water, to create a thick paste.
Dip a moist sponge or soft cloth into the baking soda mixture. Rub this mild abrasive on the stain to remove it without scratching the fiberglass.
Rinse the baking soda off with warm water and wipe the surface with a dry soft cloth.
Bring on the Big Guns
Open the bathroom windows and turn on the fan if there is one. Apply a quarter-size amount of nail polish remover or turpentine to a sponge or soft cloth.
Moisten the stained area with the solvent. Apply more if needed and rub it in well. If the stain includes paint or adhesive, you'll need enough solvent to penetrate the material that's adhering to the fiberglass.
Allow the solvent to soak in for an hour. Scrub the stain with a soft nylon brush. Dip a sponge or soft cloth in hot water and rub the area again if the stain is stubborn. Remove the residue with a clean damp sponge or cloth.