Clean a stained fiberglass tub using a professional-grade mildew, calcium and rust cleaner, such as CLR, or using household items like dish or laundry detergent, baking soda and vinegar. Use a soft-bristled scrubbing brush to rub the cleaning solution on the tub’s surface. After the tub is fully scrubbed down, rinse off with warm water.
Apply the cleaning solution evenly to the surface of the tub. Apply more cleaning solution to tougher stains. Allow the tub to soak for at least 10 minutes before scrubbing down the tub with a soft-bristled brush. Avoid using brushes with metal bristles or stiff bristles that can mar the tub’s paint. Brushes with longer handles are ideal for this job. Rinse away the grime and tub cleaner with warm water, and repeat the process until the tub is free of stains.
A cost-effective way to clean a stained fiberglass tub is to use dish or laundry detergent, baking soda and vinegar. Create a paste with the dish detergent and baking soda. Apply this paste to the stained areas on the tub, and leave until dry. Pour vinegar over the dried paste until bubbles form. When the bubbling stops, scrub the paste until the stains chip away. Avoid scrubbing too hard. Wash away the paste with warm water, and repeat the process until the tub is clean.