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Q: My fiberglass shower pan has a stain, presumably from hard water, that I cannot remove. The tile and glass for the shower is new, but the pan is original -- 22 years old. I have tried commercial cleaners, a mixture of vinegar and Dawn detergent, and a Magic Eraser. But these were no help. We have a well and septic. Could you suggest something?
A: Hard water -- meaning well or municipal water laden with dissolved minerals such as calcium and magnesium -- leads to cleaning woes in a shower because the minerals are left behind as the water evaporates. When this happens over and over, the buildup is like caked-on rock. It is difficult to remove with just ordinary cleaning, especially when the underlying surface is easy to scratch, as it is with a fiberglass shower floor. Anything abrasive enough to scrub away the deposits would also damage the surface.
The solution is to do chemical battle with the deposits so they dissolve. The crusty stains are alkaline, so to dissolve them, you apply an acid. Using vinegar mixed with hand dishwashing liquid was a smart approach because vinegar is acidic and dish detergent is a surfactant -- a cleaner that helps lift deposits and keeps them from reattaching to the surface. But since it didn't work, you need something more powerful.
Acids used for stain and mineral removal range from mild to powerful. Vinegar (acetic acid) and lemon juice (citric acid) are at the mild- and low-toxicity end of the scale, which is why they show up so often in recommendations for homemade, eco-friendly cleaning products. In heavy-duty, commercially prepared cleaning products, you're more likely to find more powerful ingredients such as hydrochloric acid, hydrofluoric acid, oxalic acid, sodium hypochlorite and sulfuric acid. These are poisonous and carry scary warning labels. That said, these products can sometimes be used safely when less powerful cleaners don't work. But it's critical to choose an appropriate cleaner and to read and follow the safety information on the label.
Before you resort to cleaners with warning labels and special precautions, you might try boosting the cleaning power of vinegar by mixing it with cream of tartar to make a paste. Cream of tartar is a byproduct of making wine and grape juice. When mixed with a liquid, it makes the liquid more acidic, plus it works as a mild scrubbing agent. Grocery stores sell it in little jars in the spice section, but if yours has a bulk-food section, the price is probably better there. An old toothbrush might work well as a scrubbing tool, because the stains on your shower floor appear to be limited to a small area. A brush probably would reach into the texture better than a scrub pad. Let it sit for a bit before you rinse it away. If the stain lessens, repeat.
If this homemade cleaning paste doesn't lighten the stain, try a marine cleaner that contains oxalic acid and is formulated to work on fiberglass, such as FSR ($10.99 from Davis Products) or Star Brite Ultimate Fiberglass Stain Remover ($14.93 on Amazon). Manufacturers of both products state that these can be used to clean fiberglass showers. These products have several characteristics that make them ideal for that purpose, although boat-cleaning is the primary focus. A gel consistency helps them stick to the sides of boats. This also means they will stick to a floor rather than disappear instantly down the drain. They are formulated to be nonabrasive, so they should not scratch the gel coat on fiberglass boats -- or a shower floor.
The oxalic acid is also particularly effective at eating into mineral deposits, lifting rust and erasing tannin stains. Boat hulls can get stained because lake water contains leaves that leach out tannins. Garden soil rich in compost also contains tannins from decomposing twigs and leaves. So if the stains on your floor consist partly of buildup from dirt that's been tracked in, tannin removal might be what you need, too.
In a concentrated form, oxalic acid is powerful and toxic. But there is less concentration in these cleaners, and you shouldn't need much to treat the stained areas on your shower floor. Diluted with plenty of rinse water, the cleaners shouldn't cause a problem with your septic system.
There is another reason to use plenty of rinse water. Products formulated for use on boat hulls need to cling to the surface while they work. So, if you don't rinse thoroughly, some of the cleaner could be left on the shower floor and make it slippery, according to Star Brite spokesman Derick Cote.
Before you apply a cleaner to the stains, which are at the center of your shower floor, test the product in a small area toward the side of the floor to make sure it doesn't damage the surface or add a stain color of its own.
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• Stop the sun from bleaching upholstery and carpets