Scrape the paint from the grates with a plastic paint scraper. Run the scraper smoothly over the cast iron to chip away as much of the paint as possible.
Scrub the cast-iron grates with a wire brush to further remove the paint. Run the brush back and forth briskly over the surface.
Moisten a clean rag with paint stripper if any paint remains. Dab the paint stripper onto the cast-iron grates.
Tape a piece of plastic wrap over the paint spots so the stripper does not evaporate too quickly. Allow the stripper to remain on the surface for at least 30 minutes.
Take the plastic off and scrape the softened paint with the paint scraper. Wash the cast-iron floor grates with a clean rag and warm, soapy water. Rinse with clean water and dry thoroughly.