Hot rodders have many enemies. The high price of horsepower is always a problem, as is never having enough time. But perhaps a hot rodder's worst enemy is rust. It seems as if Mother Nature schemes to find new and innovative ways to turn your precious metal into a lump of junk. Water, humidity, salt on the roads and just about every other natural phenomenon cooperate to create an ideal environment for rust.
Fighting rust is a never-ending battle, because whether or not you drive your car everyday, rust never stops. In keeping with our paint and body theme this month, we'll focus on ways to deal with body and sheetmetal damage, although many of these plans will also work with any ferrous metal. The ideal way to prevent rust is to never drive your car and keep it in a temperature-controlled, humidity-free bank vault. But since driving cars is so much fun, there are alternatives. Preventing rust from forming is the next best alternative, but that also requires nonstop attention to detail. We'll outline a few ways to prevent rust from starting, keep it from spreading or eliminate it altogether.
PREVENTION
It should be obvious that rust prevention is the best way to keep your sheetmetal in original condition. Start with constant inspection. Watch for tell-tale signs of corrosion in paint: slight bubbles around wheelwells, rocker-panel moldings and other areas where water might be trapped. Stripping the paint around these bubbles would probably reveal small rusty holes that have lifted the paint from the body. Typically, rust damage is far greater than it appears on the surface.
In street cars, rust often forms behind the tires in the lower rocker-molding areas and in the lower quarter-panels. In most cars, corrosion forms behind the front tires because leaves and dirt clog the cowl drains that exit just behind this area. To prevent this, you must clean out the drain so the water does not stagnate behind the sheetmetal. Since salt is an excellent rust accelerator, cars driven where roads are salted in winter must be washed thoroughly to prevent salt buildup, especially in wheelwell areas. If you've ever seen daily driven cars from the Detroit area, you'll know why this part of the country is known as the land of the missing rocker panel.
Floorpan rust is generally due to water that collects in the lowest point of the floorpan. Trunks and passenger-footwell areas are especially prone to this type of damage for several reasons. First, the water can dampen carpets, which hold the water in place for several days. This is especially true of those plastic trunk mats, which can trap water between the mat and the trunk floor for days before evaporating. In addition, trunk floors are generally splatter painted, which is a poor rust-preventative coating. The best prevention is to immediately repair water leaks into the interior and get rid of those plastic trunk mats. Repainting trunk and passenger-area floors with a good rust-resistant primer and a top coat will also keep corrosion from forming.
If the stock splatter-paint look is important, be sure to use a good rust-preventative primer underneath the splatter paint to prevent corrosion from recurring.
LIGHT RUST
Surface rust is the easiest to eliminate, especially in sheetmetal where excessive pitting has not formed. There are a number of rust-removal products, but the simplest is a quick scuffing with some light-grit sandpaper. Duro/ Permatex makes Naval Jelly, a phosphoric acid that neutralizes light surface rust, making removal easier with an abrasive such as a steel wool pad. Naval Jelly is a caustic chemical and should be handled carefully only in well-ventilated areas while using gloves and eye protection.
Once the light surface rust has been removed, you should immediately coat the area with some type of primer to prevent the surface rust from reappearing. For external body panels, the best foundation is a two-part etching primer. These primers create an excellent rust-prevention foundation.
For sheetmetal areas&—such as trunk and passenger-area floors, the inside of doors and undercarriage areas&—a less expensive rust-preventative primer like Rustoleum's Rusty Metal Primer is an excellent choice. Rustoleum will help prevent corrosion and can be applied over rusty metal where removal is difficult. Pete Santini of Santini's Paint and Body Werkes strongly advises against using this type of primer for any external body area, since it is not compatible with most automotive top coats. However, Rustoleum does work well when combined with spray-can semi-gloss top coats.
Another alternative to removing rust is the new generation of rust-conversion chemicals, which convert rust into a hard, paintable surface that according to the manufacturers will keep rust from spreading. Santini does not feel comfortable using these chemical conversions for exterior body rust, but he thinks they work well in more inaccessible areas, such as the inside of door panels and in trunk or floorpan areas where the surface finish is not critical.
Most of these chemicals, including Plasti-Kote's Neutra-Rust and RestoMotives's POR-15, interact with the rusted sheetmetal to create a hard, usually black finish that stops further corrosion. The coating is thin and does not fill in surface imperfections. However, all the manufacturers claim the surface can be smoothed with body filler and painted for a cleaner finish.
Unless rust is chemically treated or physically removed, it will continue to spread. This is why you should avoid the temptation to just smooth a little plastic body filler over a small rust hole to do a quickie repair. This will merely cover further corrosion of the body panel and will create a more difficult job later on.
HEAVY RUST
Hot rodders love old cars. Unfortunately, there are very few old cars that don't suffer from body cancer. It is an inevitable fact of life. The older the sheetmetal, the longer the environment has had a chance to rust it. According to Santini, heavy rust is almost impossible to completely remove. It is also impossible to guarantee that rust will not come back on these types of repairs. Most body shops prefer to replace an entire panel, such as a fender, a door skin, a quarter-panel or a trunk floor, rather than put the effort into a piece of sheetmetal that may begin to rust in another spot at some later date.
If repair is the only option, do-it-yourselfers can improve their chances of success by using a portable sand-blaster, such as those sold by The Eastwood Company, to clean the offending area before beginning repair. Once the area has been thoroughly blasted, what appears to be a 1/4-inch-diameter rust hole will more likely be a 3/4- to 1-inch area that has been weakened and rusted. It's important to use strong parent metal as a solid foundation for the patch. Santini prefers to butt-weld the patch to make the repair as smooth as possible. A MIG welder is an excellent choice for welding because it limits heat buildup and can create a solid weld, even in the hands of an amateur. Once the patch is fully welded, Santini suggests sandblasting the repair to remove any weld flux or carbon inclusions. After the weld has been dressed and smoothed, the base metal should be thoroughly cleaned with one of the popular metalprep finishes. A light coating of body filler should be added to smooth any imperfections.
CORROSIVE CONCLUSIONS
Fighting rust is not an easy job. Typically, shortcut cures and quick fixes only delay the inevitable, larger rust-repair job. Small rust repairs can be easy even for the beginning bodyworker and can provide solid lessons on curing sheetmetal cancer. But short of locking your car up in a temperature-controlled room with no humidity, you're going to face off against rust in almost all of your automotive adventures. To be a hard-core rust buster, you must head into the fight heavily armed.
