Slate is a beautiful and popular medium for fireplaces and patios, but it is highly susceptible to stains from water and hard, calcified deposited stains under pots and other items. If your slate is looking a little worse for wear, do not be alarmed. These stains (usually white but sometimes brown or black) can be removed without too much time or trouble. Even spilled paint and other residues can be removed using a natural process.
Sweep the area clear. You are going to be scrubbing the stains, and if you have dirt or grime in the area, then you may just make "clean" mud that will make it difficult to determine if you are actually making progress on the stains.
Mix up your cleaning solution. Combine half a cup of vinegar, half a cup of lemon juice and half a cup of baking soda in the bowl. This should form a paste. If necessary, add a little water or more baking soda to make the paste thick but manageable.
Apply the paste to the stains. Layer on a thick coating of the paste; then lay a damp, warm cloth over the entire treatment. You can leave it there for up to 20 minutes.
Scrub the stains. Using a damp scrub brush, use firm, circular motions to remove the stains. Rinse regularly, since the paste may get in the way when it comes to determining how effective your efforts are.
Tackle tough spots with the steel wool. Use gentle pressure and circular motions to remove any really tough stains with the steel wool.
Rinse the area thoroughly. If you are cleaning a slate patio, use plenty of water so that you do not hurt surrounding plants with the vinegar runoff. Once the patio dries, you can start enjoying your new, stain-free slate.