Slate is a natural stone frequently used for indoor and outdoor flooring. Though slate is durable and lends a classic look to any room, it's porous and has a tendency to absorb stains that are left unattended. Rust stains can occur on your slate surface when a metal or iron object is left on the slate and is exposed to water or moisture. Natural stone, such as slate, must be cared for and cleaned properly to maintain its condition.
Pour 1 cup diatomaceous earth into a bowl. Diatomaceous earth is a fine, powdery, nontoxic substance that comes from the earth and is sold in hardware stores. Add enough liquid commercial rust remover to the diatomaceous earth to make a paste the consistency of thick peanut butter.
Wet the slate at the site of the rust stain with distilled water. Use just enough water to dampen the surface.
With a rubber scraper, apply the diatomaceous earth and rust remover poultice to the rust stain on the slate. Make the poultice about 1 inch thick over the rust stain, and extend it about 1 inch beyond the edges of the rust stain.
Cut a piece of cling film large enough to completely cover the poultice. Tape the cling film over the poultice with masking tape.
Leave the poultice on the rust stain so it can dry completely; this usually takes 24 to 48 hours. Remove the cling film and tape from the poultice after 24 hours to aid the drying process. As the poultice dries, it draws the rust stain out of the slate.
Lift the dry poultice material from the slate with your rubber scraper. Discard the poultice material, then rinse the slate with distilled water. Dry and buff the surface with a clean cloth.
Apply poultice materials twice, if needed, for stubborn rust stains. Consult a natural stone specialist if you're unable to completely remove the stain.
Avoid abrasive cleaners, as they will scratch slate, leaving grooves that collect dirt.