Fiberglass showers and tubs can become dull or develop buildup with frequent use. Hard water, which contains magnesium and calcium, is often the culprit and can be difficult to remove. According to the Washington Post, these minerals remain on the fiberglass once the shower water dissolves, creating very stubborn stains.
Be Gentle With Fiberglass
As a rule of thumb, avoid damaging the surface of fiberglass tubs and showers by using only nonabrasive cleaners. Make sure to use a gentle scrubbing tool to clean. The Old Farmer's Almanac advises avoiding steel wool, scouring pads, scrapers and razor blades since these are too abrasive and could cause damage to the fiberglass. Use a light touch when scrubbing.
Start With Household Products
There are a few cleaning options found in your kitchen cabinets. Use dishwashing liquid in your first cleaning attempt since these products are gentle. You can add a few drops of dishwashing liquid to a spray bottle of warm water. This will cause the solution to bubble and foam, which helps remove stains. Try bathroom cleaners and all-purpose cleaners, but read the labels carefully to make sure they're fiberglass-safe.
Bob Vila suggests creating your own cleaner by mixing vinegar with dishwashing liquid. Dish soap is a surfactant that lifts deposits and prevents them from reattaching, and vinegar is an acid, so they make a great team when combined. Allow the mixture to set for 15 minutes before scrubbing. This works well for stubborn soap scum.
You may need to repeat the cleaning process if the stains seem lessened but don't fully come out the first time. You can also leave the cleaner on for up to an hour if staining is significant.
Make a Paste
Try using a paste of baking soda and water. Wet down the shower and tub area first; then apply a layer of the paste. Allow it to settle for a few minutes to activate.
If the hard water stains are especially stubborn, try creating a paste from vinegar and cream of tartar. Cream of tartar is a byproduct of winemaking and grape juice making. Adding it to vinegar intensifies its acid. Scrub with either a scrubbing brush or an old toothbrush.
Try Marine Cleaners
If your hard water stains are particularly resistant to other cleaning methods, consider using a marine cleaner, like Star Brite Ultimate Fiberglass Stain Remover or Davis FSR, that contains oxalic acid, which is safe for fiberglass. While both products are typically used to clean boats, they're also great for fiberglass tubs and showers.
Both products come in a gel formula that clings to the tub or shower. They're nonabrasive, and the oxalic acid is great at dissolving rust, mineral deposits and stains from tannins. Always do a test in a small area at the back of the tub or shower to see how your specific setup reacts. When you're done cleaning, wash the area thoroughly with water to prevent it from being slippery. This will also flush the marine cleaner out of your septic system.
Perhaps the best tip for preventing buildup on fiberglass is to simply dry off the shower and tub after each use with either a towel or squeegee. This will help the shower stay clean and require less cleaning in the long run.
Meg Scanlon earned a Masters from Johns Hopkins University. Her writing can be found on Hunker, Cuteness, Funny or Die, BarkPost, Taste of Home, LoveTV and ALittleBitFunny.com.