The first step to painting over rust is to remove the rust from the metal surface. There are various methods for doing this, depending on what your project is and how much you are willing to spend. For the smaller projects, such as lawn ornaments, I have removed most of the rust with a wire brush and then wiped the surface with a clean dry rag. You can use steel wool or emery cloth to sand it further, but always clean the surface with a dry rag before painting. This will ensure that you will get a smooth finish that is clean of debris.
Next, apply a light coat of Rustoleum evenly over the entire surface. Avoid applying too much paint with one application, as this will cause runs and an uneven coat. It is best to use two or three light coats, rather than one thick coat. The purpose of using Rustoleum is that it is a rust inhibitor, and it serves to seal the metal from exposure to air and moisture, which causes rust.
Finally, paint the metal with two light coats of finish paint. Use good quality exterior enamel paint. It is far better to use better quality paint, as it will last longer. However, do not get fooled by a product that cost more money. Carefully read the label of the paint to find warranty information and in order to ensure that you are using the correct paint for the right application.
There are some other ways to remove the rust, again, depending on your set of circumstances. For small pieces, you may wish to have the piece sandblasted, but this method is not practical for a wrought iron fence. Neither would it be practical to use a wire brush for a project as large as a perimeter wrought iron fence.
Ospho makes a line of rust remover, inhibitor, metal treatment, and primers. With Ospho rust remover, you just apply it to the metal surface and let is set for 24 hours. You will then take a wire brush and brush off the dried product. This is supposed to take the rust off, but I have never used it. As with using any product, make sure that you read the label. Be especially careful when handling any chemicals as some may contain carcinogens.
Whatever product or method you use to remove the rust with, always use a clean dry cloth to remove any residue, as this will have an effect on the finish. Applying paint to a soiled surface may also shorten the expected period of time that your new finish will last.
Finally, when using any method of rust removing and surface finishing, do not forget to wear and use proper safety methods. You should always wear eye protection, as chips and grit can cause you great discomfort and may even cost you a trip to the emergency room or clinic. Some chemicals can cause irreversible damage to your eyes as well. When using these methods of rust removal and painting, you may also need to wear a mask or respirator.
