When corrosion occurs on the metal of your vehicle, rust will begin to form. It will appear as an orange or brown colour on the metal's surface. When rust begins to form under the paint, it will appear as bubbles on the surface. These bubbles, if left alone, will slowly begin to eat away at the metal until there is a hole. You can fix this problem by removing the rust bubble on the metal.
Use the putty knife or metal scraper to scrape off the paint that has bubbled up from the rust. This will expose a small area of rust and remove any loose paint.
Rub the sandpaper over the rust area in a circular motion. Repeat this process until you have removed the layer of rust, or have reached bare metal.
Blow away the dust, then dampen a clean cloth with White Spirit. Wipe the area to remove any of the dust and dirt that remains. Wait 5 to 10 minutes for the White Spirit to dry.
Apply primer to the exposed metal with the paint brush. The primer should extend beyond the rust area by about ¼ of an inch.
Mix a small amount of body filler until it is the consistency of peanut butter. Apply the body filler to the depression with the putty knife. Wait for the body filler to harden.
Sand the body filler with the sandpaper until it is smooth and even with the surrounding metal.
Wipe the area with White Spirit, using a clean cloth. Apply touch-up paint to the area so it blends with the existing paint.
Polish and wax the new paint for a bright finish. Test the colour match paint on a scrap piece of metal to verify that it is the correct colour.