How to remove stains from marble shower tile

Q: The marble threshold for my shower has reddish marks. How can I remove them?

Annapolis, Md.

A: Marble can develop reddish marks for a variety of reasons, such as spilled red wine, bacteria or moisture that interacts with the iron in the stone.

In a shower, you can probably rule out wine or other spills. But bacterial growth is definitely one of the prime suspects. Serratia marcescens forms colonies that look pink or red on surfaces that are left damp for long periods — and bathrooms make an ideal habitat. If it is allowed to spread, it can cause illness in humans and pets.

A pink ring around the waterline in a toilet, pink grout lines on a tiled shower wall, or red slime on the rim where the shower walls meet the shower pan all can be from this bacteria.

It’s usually possible to just scrub these colonies away with soapy water and a bristled brush. An old toothbrush works well in crevices. But when natural stone, especially relatively porous marble, has been etched with acidic cleaners or is not topped with a sealer, the bacterial growth can extend into the pores of the stone and be impossible to scrub away.

John Forguson, general manager of My Stone Care in Santa Ana, Calif., which sells stone-care products through mystonecare.com, looked at the pictures you sent and said he thinks embedded bacteria could be a big part of your problem. Rust stains caused by water reacting with iron in the marble could also be a factor, he said.

Forguson recommends starting by mixing a solution that is half chlorine bleach and half water. Wear gloves, goggles and old clothes you don’t mind getting spotted from bleach, and open a window. Dampen the marble with the solution, and set a timer for five minutes. At that point, wipe off the bleach solution, rinse several times with plenty of water and towel dry. If the stains have faded but are still visible, repeat the process until there’s no more improvement.

If you start to see orange or brown stains as the red fades, rust could be a factor. As a natural stone, marble often contains traces of various elements. Rust can form when iron is in the stone and moisture penetrates.

To remove the rust, you need a rust remover — but you can’t use most of the ones on the market, because they are very acidic, and acidic solutions eat away at marble. Forguson recommends using ConfiAd’s rust remover gel ($37.95 a liter at mystonecare.com). Lithofin’s Rust-EX nonacidic rust stain remover, which the company also sells ($19.95 a bottle), is another safe option for marble, but it isn’t as powerful and isn’t as easy to use, because it’s a liquid, he said. The gel “stays where you put it.”

With either product, you will see purple stains almost immediately if iron is present. That’s a sign the remover is working. After five to 10 minutes — never longer — wipe away the residue and rinse thoroughly. Over the next couple of days, assuming iron is in the stone, the stains should continue to lighten. If they are still visible, repeat the process until there’s no more improvement. Wait several days between treatments.

If you don’t see rust stains after finishing the initial treatment with a bleach solution, or if you try one of the rust removers but nothing turns purple, it’s possible you’re dealing only with bacterial staining and the growth is too deep to get out by using a liquid cleaner. In that case, Forguson recommends applying a broad-spectrum poultice. He recommends using StonePro’s wet poultice stain remover ($31.95 for one pound at mystonecare.com).

A YouTube video made by StonePro says to spread the poultice one-quarter-inch thick over the stains and about one-quarter-inch beyond, then to cover the paste with plastic and either tape down the edges of the plastic or embed the plastic in the edges of the poultice paste, so you create a seal.

Forguson said he has found it helpful to first mix hydrogen peroxide into the paste, using a ratio of 20 drops of hydrogen peroxide per tablespoon of paste. Wait 18 to 24 hours, then carefully pull back the plastic without removing the paste, and let it dry until the paste becomes a powder you can sweep away. The video says this will happen in 24 hours; Forguson said that it will take closer to 48 hours.

Wait for the stone to completely dry, which might take 18 hours more. If the stains look lighter but aren’t gone, repeat the poultice procedure.

Once the stains are gone, apply a penetrating stone sealer. After the sealer goes on, you won’t be able to try any more stain-removal options — apart from hiring a pro to hone the stone.

Besides that, though, you have two other options: Replace the marble, or decide to live with the stains. If this is your only shower, you might choose to live with it, unless you can come up with a strategy for showering elsewhere during the many days the multistep replacement process could take.

Have a problem in your home? Send questions to localliving@washpost.com. Put “How To” in the subject line, tell us where you live and try to include a photo.

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