Concrete is an incredibly durable surface that can withstand a great deal. Some however are left unsealed, and can be vulnerable to stains. If the seal on your concrete countertop has been improperly maintained, or non-existent and if the countertop has come into contact with an acidic substance (lemon juice, for example), you could end up with a stain that you're not able to get out simply by cleaning the countertop. So, in order to restore the countertop, you'll have a bit of work to do.

You'll need water, a sponge, mild detergent, a dry towel, fine sandpaper, paste wax and concrete sealer.

To remove the stain, first wipe the counter clean using the sponge and water. If there are oily spots, or grease spots on the counter, first clean them using a solution of water and mild detergent. Wipe the countertop using the towel, and allow it to dry completely. Next, gently sand the stained area with a fine wet sandpaper. You should be able to remove most stains this way, but if they're deeper than the surface, this could be beyond a DIY job - you might need professional assistance. You might also need a pro if your countertop has a mirrored or polished finish.

Once the stain is removed, remove any dust using a damp cloth. Again, allow the countertop to dry completely before moving on to the next step, which is applying the sealer. Simply follow the package directions. Allow it to dry, and then finish off with a coat of paste wax (buff after applying) to protect the countertop from any future damage.

Depending on the countertop, and the quality of the sealer that you've used, you might find that you have to occasionally repeat the process in order to keep the finish looking good. If the countertops are showing signs of wear, its time to re-do them. If you suspect that your countertop isn't properly sealed, or you think that the seal could have become weakened or compromised, you should avoid allowing anything fatty or acidic to come into contact with it. This is because oils and fats leave dark stains, and acidic compounds will cause etching.

To prevent stains in the future, don't use harsh cleansers on your concrete countertop. Cleansers that contain bleach or ammonia have the effect of weakening the seal, and they make the countertop more susceptible to staining.