Rust can eat away at your car's fenders, doors, wheel wells and create holes in the floor and trunk unless you tend to it. You can take steps to eliminate rust and protect your car against it in the future.
Survey the car to locate all the rust. Closely examine the lower half of the car. Determine if you have just surface rust below the paint with little metal decay, or if the rust has eaten away the metal itself. You may have to remove the body trim or moldings to do a proper survey.
Bubbles in the paint is a sign that rust is below. Definite rust holes that are obvious can be noted, and check around and below any body trim, emblems or moldings, which are hot spots for rust.
For surface rust that has not eaten through the metal, use your rust scuffer or 60-grit sandpaper to sand clean the entire area surrounding the rust, at least 2 inches out. You want to have nothing but shining metal surrounding the surface rust. Concentrate on the rust spots with your 60-grit paper until it is fairly smooth.
Test the area you just cleaned before you go any further. Poke your scratching awl in and around the rust spot to see if the rust has weakened the metal below the surface. This would mean the rust is active on the underside as well.
If the scratching awl pokes through, use your small grinder and open up the holes completely. Grind or cut away with your snippers until you have solid, clean metal surrounding the opening.
If you have solid metal and no holes after probing with your awl, sand the area smooth with your 120-grit paper, and then treat the with your rust treatment spray or naval jelly, according to the label's instructions. Let the surface dry overnight before applying any top coating. The chemicals within the rust treatment neutralize any remaining rust and also treat the bare metal against future rust.
If you have very serious rust damage that has caused evident holes or rotting, for instance in a rear quarter panel or around a wheel well, remove any trim from the area and cut the entire rusted area out back to solid metal. Then grind and sand clean the edges and the metal to at least 2 inches around the cut out area. Sand with 120-grit and rust treat on both sides of the remaining metal.
Ultimately you will need to replace bad metal sections cut out with new sheet metal.
