- Rust forms when metal is exposed to water or water vapor. Before painting a car, rust must be completely removed or it will come back, which will then cause the paint the bubble. A rust-free foundation allows a smooth finish to the paint job.
Rust can be removed in several ways. If the rust covers a small area, you can remove the patch of rust and replace it by welding in patches. If the rusting is more severe, the whole panel may need to be replaced. Areas that are not rusted through can be chemically treated with liquid rust inhibitors, which come in liquid or gel forms. These inhibitors chemically stop the oxidation process by converting iron oxide (rust) into iron phosphate. The panels have to be primed and sandblasted after being welded to ensure the area won't rust in the future. - Straighten and fill warped panels. Straightening the panels can be done with a hammer and dolly but often requires a quality, long-lasting body filler to get the body just right. The body filler then has to be sanded down until the panel is straight. Sanding is what will take most of the straightening time, but a power sander, random orbital units, and air files can help speed up the process. However, to distribute the hand's pressure evenly across the panel, block-sanding by hand using 180-grit and then progressively finer sandpaper is always the final process to make the panels look straight. Do not rush the sanding process, and spend as much time as you can sanding, because your car will appear straighter once it's been painted.
- Before painting a car, it must first be primed with quality, two-part or catalyzed primer. Primer allows for a smooth, consistent finish once the paint is applied. The filler, primer and metal usually have different colors, so adding a primer prevents color variations when the paint is applied.
- Once the primer has been added, the car must be taped off using masking tape and paper or plastic such as trash bags. Plastic is the best, as it won't absorb the paint and allow it to bleed through as paper can. Make sure that every part you do not want painted is covered, such as the windows, bumpers and wheels and tires. The next step is to wipe the car down with a cleaner to eliminate any oils or foreign materials from the surface. The final step is to wipe the car with a tack cloth to remove any dust or debris that may get trapped underneath the paint and cause an uneven finish.