Got stubborn marks and stains on your shower doors that simply will not budge no matter what you try? You’re not the only one.

I’ve heard from readers who say they’ve tried everything from my magic soap scum cleaner to cleaning vinegar, hydrogen peroxide, oven cleaner, muriatic acid, steel wool, Bar Keepers Friend, Bon Ami and other expensive chemicals to get rid of the horrid, ugly, hard water stains and white haze.

While most of the time the Magic Soap Scum Cleaner takes care of the problem, even it cannot touch a severe situation where the hard water minerals have become so embedded, the surface of the glass has become permanently etched.

Some readers say it took multiple cleanings with the magic stuff to get their glass doors truly clean, while others report they’ve tried everything from magic stuff to 30-percent white cleaning vinegar; hydrogen peroxide, oven cleaner, muriatic acid, steel wool, Bar Keepers Friend, Bon Ami and even razor blades to scrape away the problem, all without success.

I have to admit this has left me in a quandary and about this far from advising new doors to be the only solution.

Then I discovered the solution: Sandpaper.

Yes, you read that right but don’t stop reading yet. This is no ordinary sandpaper.

I’m talking about automotive waterproof sanding wet/dry paper with such a fine grit, it is used in the automotive industry to polish the surface of a car to a mirror finish. You can use the same type of sandpaper to sand away the mineral buildup and return a glass shower door to its original clear, clean, sparkling self.

The best product I know of for this job is Wet/Dry Premium Waterproof Sheets, about $12. This is a 6-sheet assortment of finish sanding paper ranging from #3000 to #7000 grit. The grit on this type of sanding paper is so fine it will not scratch the glass, the way that woodworker’s sandpaper, steel wool or other abrasive products might.

For severe watermark stains, start with a piece of #3000 grit paper (cut it to a size that feels comfortable in your hand as you are going to scrub the glass with it). Wet both the glass surface and the sanding paper with water to provide a lubricant. You do not want to do this completely dry.

Using a circular motion, scrub the entire surface of the glass. You will immediately begin to cut through those stubborn deposits, prepare to be amazed.

Next, move up to #5000 and then to #7000 as needed to remove even the tiniest micro scratches that may have been left behind. At this point, you will be polishing the surface to that mirror finish, with what feels like a piece of paper—that’s how fine #7000 grit is.

Depending on the severity of the problem, this could take five minutes or much longer to finally achieve the level of success you have in mind. But know it will work. Your shower doors will look like new—no fumes or expensive chemicals.

To keep your glass shower doors looking beautiful, get a cheap shower squeegee or use a microfiber cloth to wipe the shower surfaces (walls and doors) to remove all standing water after every use.