How can I remove a water stain on a stone or slate tabletop?

Q. A water stain was caused by a plant pot overflowing, and the overflow stood for 24 hours, leaving an outline. I tried to clean the outline with steel wool and made a worse mark. What can I do? I am not sure if the table is stone or slate.

A. Just checking—could the stone still be wet? Some stones soak up moisture, and that can make them look darker. In humid conditions, it might take a few days for the appearance to even out as the stone dries.

Assuming the discoloration is not moisture, the first thing you'll need to do is clean the mark with a stone-safe, pH-neutral cleaner. This will help remove contaminants on the surface so you can get a better look.

Next, identify the material. Determining whether the tabletop is slate or another type of stone like marble or granite can help you choose the right cleaning and repair method. Each material reacts differently to moisture, abrasives, and polishing products. Using the wrong approach could make the damage worse. 

Slate usually has a matte, slightly rough surface with a layered or flaky texture and comes in gray, green, black, or warm rust tones. Marble or limestone is often polished and may have veining patterns. Granite and quartzite look grainy or crystalline. You can also look at the edge of the stone to determine stone type. Slate edges often shows thin natural layers, while marble and granite are solid throughout. 

For slate, rub in a small amount of mineral oil using a soft white cloth. Let it soak for a few minutes, then buff off the excess. This treatment can even out color and hide light scratches. You mentioned that when you used steel wool, it made the mark worse. If the scratches from the steel wool are still apparent, you can try lightly sanding the area with 220-400 grit sandpaper. Clean the area with a stone-safe, pH-neutral cleaner and then reapply the mineral oil. 

For other types of stone, clean with a heavy duty soap film remover.