How to get rid of mildew stains on travertine?

Q. There are black mildew stains around the drain of my travertine sink. I was away when they appeared and had a house guest during that time using the bathroom. I don't know nor does she know how the stains got there. The sink was new. I did follow directions for treating the stone with a sealer specific to travertine before I left. I went back to the store where I bought the sink for ideas from the staff. They showed me a poultice type powder to use on it, and I did according to the directions on the product. I applied the poultice material twice over a period of two days and neither time did the stains go away or even lessen. My plan is to reseal the sink so this doesn't happen again, but I don't like those stains being there. Is there a type of paint that I can dab on carefully that will cover the stain and not hurt the travertine? I've given up on the idea of removing the stains with a cleaner or other compound. I also tried a poultice of baking soda and water to no avail.

A. Black mildew stains on travertine can be difficult to remove because the stone is porous and easily absorbs organic material. It's a good thing you haven't tried bleach or harsh acids, because these can etch and permanently damage travertine. Abrasives can scratch the finish, so avoid these, as well.

Unfortunately, painting over the stains is not recommended. Paint will not adhere evenly to travertine, and over time, it will peel, flake, and chip. This is especially true of a wet area like a sink. Even if the paint would adhere properly, it would diminish the appearance of the stone. Suppose you change your mind. Once paint is applied, it’s difficult to remove without damaging the stone. 

Here’s what you can try instead. Apply a hydrogen peroxide poultice. Use 40-volume hydrogen peroxide (available at beauty supply stores) and a few drops of ammonia along with a dry ingredient, such as diatomaceous earth. This often works better than baking soda or commercial poultices for organic mildew stains. For detailed, step-by-step instructions on how to mix and apply a poultice correctly, check out our free Stain Management App.

If the stains won’t come out, your best option is to consult a professional stone restoration contractor. They have tools and products designed to safely deep-clean and remove the stain if it is not permanently set. Suppose the stains are impossible to remove. An experienced PRO can grind the affected area, apply a stone-safe epoxy or color-matched filler rather than standard paint, if needed, and then hone and polish to restore the finish.

Once the stains are removed, reseal the sink with a high-quality penetrating sealer made for travertine. This can help prevent future staining. A PRO can provide this service for you, as well.

To find a vetted PRO in your area, visit www.surfacecarepros.com and click on Find a PRO.