Unfortunately, your external balustrades are often subjected to corrosion and the accumulation of rust, especially as time passes and exposure to the elements increases. To prevent the metal from degrading further, it is important that you remove the rust and treat the railing so that the substances that cause corrosion are blocked at all times.
Step 1: If possible, remove the balustrade using an electric screwdriver. Make sure that you save any hardware that you remove so that you can reinstall the metal when you're finished.
Step 2: Use a wire brush to scrub away as much of the rust as you can. Then use a medium grit sanding sponge to rough up any remaining paint on the surface and to remove any rust that you missed.
Step 3: Use a tack cloth to carefully clean the balustrade and to remove any paint or rust residue. Lay some newspaper underneath the metal to protect the area, using painter's tape to hold it in place.
Step 4: Coat the external balustrade with a thin layer of a rust resistant metal primer (those in spray cans often have the best finish), applying lightly to avoid drips. Leave the metal to dry completely.
Step 5: Apply a second coat of the primer and leave to dry completely. Do not be afraid to do one side of the balustrade at a time, as this will ensure that the primer is dry before you move on.
Step 6: Coat the railing with a rust resistant metal enamel paint (again, those in spray cans tend to work best). Make sure that you apply two coats and allow for adequate drying time between each.
Step 7: Replace the balustrade using the electric screwdriver. Make sure that you examine each piece of hardware before returning it, as you should replace any screws that appear to be worn.
Even though spray paint tends to work best, as it will easily get into the tiniest gaps where the external balustrade joins together, if you cannot remove the metal you can use a traditional primer and paint. This will prevent the coatings from getting all over your home or garden, although you can use newspaper to help lessen the chances of this occurring.