Concrete is vulnerable to stains from such things as lemon juice, wine, or vinegar, no matter what kind of sealer or wax you apply. These and other acidic liquids will eat into the surface of the concrete and etch it away. It is possible to remove individual stains without having to refinish the entire piece.
Step 1 – Wet Surface and Polish with 1500 Hand Pad
Polishing the stain out too aggressively will cause a dramatic change in the appearance in that spot. Wet the surface and begin polishing lightly with the a high grit pad, like a 1500.
Move down to an 800-grit pad if the stain isn’t being removed.
Continue polishing until the water gets cloudy. Sponge it off to see how the stain looks. If the stain is removed, dry, re-seal, and wax.
Step 2 – Continue Sanding if Necessary
If the stain is still there, try the 800-grit pad. Work aggressively on the stain, and gradually work out in larger circles. Wipe it clean and check often. There’s a danger that grinding too aggressively with the 800-grit pad could expose some of the fine sand aggregate, which will change the look of the surface slightly.
Step 3 – Re-Seal and Wax
After the 800-grit pad, go over the stain again with the 1200-, 1500-, and 3000-grit pads (the latter will give the surface a shine). Let the surface dry, apply sealer, then wax.