How to remove vinegar stains on flagstone?

Q. My pickling vinegar bottle (7 percent acidic) leaked on my flagstone floor. I made a paste of baking soda and applied it after washing the floor with stone floor cleaner. I let the paste sit for the afternoon to no avail. I would appreciate any help to restore my floor. Thank you.

A. The first thing to figure out is what kind of stone your flagstone is. If it’s a calcium-based stone, like marble or limestone, vinegar will chemically react with the calcium in the stone. This reaction changes both the appearance and sometimes the texture of the surface. That type of damage is called etching. Etching isn’t like a stain—it’s a physical change in the stone itself, and cleaning won’t remove it. 

If your stone is sandstone, the situation is different. Sandstone is mostly made of silica, which doesn’t react with vinegar in the same way. You won’t usually see etching, but because sandstone is very porous, liquids like vinegar can soak in and leave behind discoloration. That would be a true stain rather than surface damage. Stains can often be treated or pulled back out.

With vinegar spills, marble and limestone almost always show etching. If the vinegar was darker, like apple cider or balsamic, staining from pigments is also possible, but etching is usually the main concern. On sandstone, the issue is more likely to be staining from the vinegar soaking in than etching.

In short, knowing whether your flagstone is marble, limestone, or sandstone is the key to figuring out what happened and how to fix it. Acid-sensitive stones like marble and limestone will need polishing or restoration to address etching, while sandstone may respond better to poultices or other stain-removal methods. Identifying the stone type will guide you toward the right solution.

So what can you do? If it is marble or limestone and the etch is light, you might try using a high-quality marble polishing compound to remove the etch damage. Most of the time, flagstone has a honed or matte finish. Keep in mind that this area may have more reflectivity than the surrounding area after using a marble polishing compound. If it’s a deeper etch, you’d probably need a stone professional to come hone and polish the area.

If the discoloration is just a stain and not an etch, which would be likely if your flagstone is sandstone, you could try using a poultice to pull the staining agents the vinegar left behind out of the stone. A poultice draws the stain out of the stone over time. You may need to leave a poultice in place for 24 hours or more to completely dry out, and you may need to reapply the poultice multiple times. For detailed, step-by-step instructions on how to mix and apply a poultice correctly, check out our free Stain Management App.