Many homes and gardens still have cast-iron fixtures, from fireplaces and radiators to railings and gates. Some of these may have been there for decades or even centuries. They may also have been painted over and started to rust. You can restore these fixtures back to their original metal finish -- or prepare them for repainting -- by stripping the paint and the rust from the iron. This involves using harsh chemicals and plenty of hard work.
Removing paint from cast iron
Sandblast the iron item. Blasting with abrasive grit is the fastest way to remove thick layers of paint. Avoid high pressures and do not use copper-based aggregates, as they may react with the iron. You should also avoid very sharp or hard aggregates; sand or iron slag are the best choices. You can hire a sandblaster from most DIY shops or tool hire centres.
Apply a chemical paint-remover such as methylene chloride or potassium hydroxide. These are strongly alkaline compounds, so wear gloves and goggles when applying them. They are often available in a paste or gel that you can spread over the painted areas; use a putty knife and a brush to work them into cracks and crevices. Let the remover sit on the paint for as long as the instructions on the package dictate.
Wipe the paint and paint remover off of the iron using a rag or a scouring pad. Remove all of the paint remover, as leftover traces will weaken paint you apply later.
Paint the iron item with an anti-corrosive primer immediately after cleaning and drying to prevent the surface from rusting.
Stripping rust from cast iron
Wipe down the rusted surface with white spirit. Dab the spirit on a rag and rub the iron. This will cut through any wax or sealant on top of the rust.
Scrub rusted areas with steel wool or a piece of 400-grit wet-or-dry sandpaper wrapped around a wooden block.
Wipe down the areas you have scrubbed with a clean rag to remove the rust and dirt that the steel wool has loosened.
Dry the areas you scrubbed thoroughly before applying any paint, polish or other products to them. This will avoid trapping water underneath their surfaces, where it will rust the iron again.
Always wear gloves when working with chemical rust and paint removers, as they contain harsh and poisonous chemicals.
Never use chemical cleaners on any surface from which you may eat (like a frying pan). Scrub them with abrasive wool or sandpaper instead.
Before sandblasting, cover the surrounding area with dust sheets to protect it from the grit. Always wear goggles, gloves and a dust mask when using a sandblaster.