Q: When we took up the rubber mat in my son’s fiberglass bathtub, we discovered black stains. Efforts to clean with mold and mildew remover and Soft Scrub with bleach had no effect. The tub was installed in 2005, but we only recently saw the stains. No dye has been used in it. How can we remove the stains?

A: Fiberglass tubs and shower-tub combinations are lightweight, which makes them easy to install, and they are often inexpensive. But the finish is prone to scratching, cracking and staining. And, as you’ve discovered, stains aren’t easy to remove.

Before you give up on trying to scrub away the stains, try the cleaning process Home Depot recommends for tough stains on fiberglass: Smear on a paste of baking soda and water, and cover that with a towel soaked in vinegar. Wait one hour, then rub with a cloth or sponge. Rinse. Wipe again with a clean microfiber cloth.

If the stains remain (and there’s a good chance they will), one option is to have the tub refinished. National Refinishing in Chantilly, Virginia, which specializes in refinishing surfaces in bathrooms and kitchens, has several “before” pictures on its website that show fiberglass tubs with stains even worse than the ones on your tub. The “after” pictures show the gleaming results of a new finish, but, of course, the pictures were taken when the finish was new.

National Refinishing and other tub-refinishing companies make stained fiberglass tubs look new by spraying them with an acrylic epoxy. National Refinishing charges $425 for a tub alone or $995 for a tub and shower surround. If you have tile around the tub, the company can refinish that and the grout lines, too, using the same material.

Having a professional refinish a tub costs about the same as buying a new one — or even more, if you base the price of the new tub on a budget model. At Home Depot, for example, a standard 60-inch-long drop-in tub starts at around $155 if you buy one with a porcelain enamel finish on steel or around $254 if you opt for an acrylic tub.


But when you replace a bathtub, its cost is just part of the equation. Unless you are handy enough to do the work yourself, you will need to hire people to make the switch, including a plumber to do the connections. And it might take some work to get the new tub to fit correctly against the tile or whatever is on the walls around the current tub. Given these costs, installing a new tub probably makes more sense as part of a bathroom remodel than as a stand-alone way to handle stains.

If refinishing makes sense but the cost is too steep, consider using a do-it-yourself tub refinishing kit like Rust-Oleum’s Tub & Tile Refinishing Kit costs, which costs about $25. One kit should be enough for the two recommended coats on a standard bathtub.

But will a DIY finish work? Home Depot’s online listing includes reviews from about 1,300 customers, who gave this finish an average rating of four stars, with about half of the reviewers giving it five stars. But at least 170 people assigned just one star. They complained mostly that the finish bubbled up or didn’t stick well. A Rust-Oleum product-support representative, who gave his name only as Arthur, said that when problems occur, it’s usually because the surface wasn’t cleaned or scuff-sanded thoroughly beforehand, as the instructions specify, or because someone failed to remove all of the residue before applying the new finish. Sometimes people brush back and forth too much or put on a coat that’s too thick, which can also keep the finish from curing properly, he said. The temperature and relative humidity also matter.

Professional refinishers spray on the new finish, which should result in a smooth, even coating if done correctly. Rust-Oleum recommends applying its finish with a brush or a 1/4-inch nap roller, so good painting techniques are needed to achieve a smooth, even coat. The product-support specialist suggested starting at a back corner and working toward the front in small sections, perhaps 2 feet by 2 feet. Bubbles may appear right after the finish goes on, but the finish is self-leveling, so they should disappear as the finish cures. But if the finish separates right after you apply it, something went wrong with the preparation. Stop and figure that out before you coat the whole tub.

The DIY finish should last for at least several years, the Rust-Oleum representative said. At that point, you could redo all of the preparation steps and apply a new coat or two of finish, he said.

If that seems like too much work for the expected life of the finish, or if you don’t want to tackle this job in the first place, there’s something else you can try: Buy a new mat for the tub floor and cover the stains. Out of sight, out of mind — until it’s time to remodel.