Naturally occurring onyx is a semiprecious stone related to agate. Its chemical formula is SiO2, and it has a vitreous finish and bands of color that make it a favorite among gemstone collectors. That sounds like an attractive raw material for decorative shower walls, except for one small problem. Onyx is formed in caves by water dripping from stalagmites and stalactites, and unlike granite, marble and other igneous rocks, onyx stones are too small to cut into countertops or wall panels. Onyx wall panels are a manufactured product and, yes, it's safe to clean them with vinegar.
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Onyx shower walls aren't actually onyx but a solid surface material made with aluminum trihydrate and polyester resin. It's safe to clean them with vinegar.
Onyx Collection Isn't Onyx
The vast majority of onyx shower wall panels, if not all of them, come from a company called Onyx Collection, which also manufactures onyx countertops, tub surrounds and shower pans, among other things. They offer onyx solid surface material in a variety of colors, including black, gray, terracotta, beige and white. The onyx the company uses to make shower walls isn't actually onyx, but a solid surface material made with aluminum trihydrate crystals and polyester resin, according to Grandview Winnelson Company.
Manufactured onyx is more akin to cultured marble or quartz than it is to real stone. It isn't porous and won't lose its luster if you clean it with an acidic cleaner, such as vinegar. In fact, Onyx Collection recommends cleaning its products with vinegar, saying that it's one of the best cleaners for hard water deposits and soap scum and that it kills mildew.
Clean Onyx With Vinegar
Onyx Collection recommends cleaning with a 50-50 solution of vinegar and water. You can wipe this on the surface of the shower wall directly to dissolve soap scum and kill mildew, but if you want to use it to remove hard water deposits, it needs a little more time to work. Put some in a spray bottle and wet down the onyx thoroughly. Wait 10 to 20 minutes and rinse well with plain water.
if you have very hard water and you don't clean your shower walls often, there's a good chance the minerals have formed ugly white streaks, and vinegar will need even more time, perhaps an hour or two, to dissolve these. Because a vinegar and water solution will evaporate too quickly to do the job, make a paste using laundry detergent or borax (not baking soda). Spread it on the streaks and keep it wet by spraying it periodically with the vinegar solution. When you rinse it off after a few hours, the streaks should be gone.
Keep Your Onyx Shiny
It doesn't take long for hard water deposits to turn an onyx shower wall dull, but you can forestall this dulling by following a tip from the company. Wipe down the walls periodically with Gel-Gloss or spray Rain-X, which are both designed to repel water from glass. They create a glossy finish that makes water fall off in sheets rather than forming beads and evaporating slowly.
You can also use the tried-and-true method used by many homeowners to keep their shower doors free of calcium haze: Squeegee the walls every time you use the shower. Keep the squeegee in a prominent place in the shower stall so everyone remembers to use it, and you won't need to clean the walls with vinegar often, if at all.
Chris Deziel is a contractor, builder and general fix-it pro who has been active in the construction trades for 40 years. He has degrees in science and humanities and years of teaching experience. An avid craftsman and musician, Deziel began writing on home improvement topics in 2010. He worked as an expert consultant with eHow Now and Pro Referral -- a Home Depot site. A DIYer by nature, Deziel regularly shares tips and tricks for a better home and garden at Hunker and Family Handyman.