The protective galvanised coating found on carbon steel fades over time. If the galvanised coating no longer protects the surface of the steel, rust forms on the metal. You need to remove the rust to ensure that the metal does not receive structural damage. Then you need to provide the repaired area with a protective coating to eliminate the possibility of the rust reforming. Standard paints will not adhere to galvanised metal and do not provide protection against further rust damage to the metal.
Put on the safety glasses and work gloves.
Attach the wire wheel to the 4-inch grinder.
Turn on the grinder and run along the rust with long steady strokes. Continue grinding until the shinny surface of the metal returns.
Clean areas inaccessible with the grinder with the wire brush. Clean the metal's surface with the rag to remove the dust created while removing the rust from the surface of the metal.
Read the back of the can of cold galvanising. Shake the can per the manufacturer's instructions to ensure that the paint is thoroughly blended.
Hold the spray can 6 to 8 inches away from the surface of the metal. Spray light fast coats to the surface by depressing the spray button and starting the stroke and then releasing the button at the end of the stroke. Holding the spray button down and moving back and forth will cause the thin paint to run and create an unsightly finish.