Over time, the cast iron grates on your stove, grill or fireplace can accumulate buildup from food, ash and rust. In extreme cases, such as when rust has substantially eaten into the iron, it's best to replace the grates with new ones. In most cases, though, refinishing cast iron is possible and relatively simple to do. Even with normal use, an occasional refinishing keeps your grates in top condition.
Remove the grates from the stove, grill or fireplace. The grates should be completely cool when you remove them.
Scrub the grates thoroughly with a wire brush to remove as much of the rust, soot and food debris as possible.
Rub the grates with a steel wool pad then wipe them down with a moist microfiber cloth. Repeat until the surface is smooth.
Make a paste of equal parts coarse salt and vegetable oil. Heat the paste in the microwave for 30 seconds.
Scrub the grates with the warm salt and oil mixture applied with a clean, dry sponge.
Wash the grates in hot soapy water then rinse and dry them.
Coat the cast iron with a layer of plain vegetable oil. Replace the grates. For a stove or gas grill, heat the oiled grates for several minutes, before use, to create a seasoned surface that resists sticking.