People often say that classic cars are made of "real steel." Unfortunately, real steel has a habit of rusting. This happens quite quickly anytime the finish (primer or paint) protecting the outer layer of the steel is exposed to water and salt that's lying on the road or is in the air. Causes of this type of exposure can range from severe paint barrier damage from the car being in a serious collision damage to a tiny scratch caused by rocks that the wheels throw up to hit the body. Wherever paint and primer protecting the metal is removed, rust will start. Also, cars that have been sitting unprotected for a long time can develop surface rust. This is because UV rays from the sun, as well as other environmental contaminants can break down the protective barrier provided by paint.
Rust problems showed all over the floor of Jeff Noll's '67 Camaro after the car was disassembled. Rust can only be properly repaired by stopping its spread, cutting out any rusted-through metal, installing new metal and doing body work.
As we all know from classified ads in hobby magazines, the geographical location of a collector car can have a big effect on its likelihood of being rusty. "California cars" are prized by collectors for their legendary "rust-free" state of condition. When a car spends decade after decade in states like Michigan, Wisconsin and Minnesota, it is typical to find both obvious and hidden rust. Excessive amounts of rain can cause rust, but the worst culprit is winter driving in areas where road salt is used to reduce snow and ice on the highways. Hobbyists often refer to the Northeast, Midwest and Northwest as the "rust belt."
There are several recommended ways for motorists to deal with minor rust in a maintenance sense.
These foam rubber Soft-Sanders from Style-Line Corp. are the latest in sanding block technology. For about $40 you get six 11-inch blocks in three densities plus a hand sanding tips and techniques DVD.
Sanding the car using an air-powered dual-action "jitterbug" sander, such as this Ohio Technical College instructor is using, is a faster way to remove paint and rust or do an initial smoothing of filler or primer.
In the "real world" ongoing paint touch up repairs like these are rarely carried out with any consistency. If they are done at all, they are often done improperly. Usually, the touch-up paint is dabbed on right over the break in the finish, with no real attempt to remove the existing rust. If you're very lucky, you'll find that such do-it-yourself repairs were done enough on your vintage car to at least save the metal from totally rusting through. However, it is much more common to discover old cars with significant amounts of obvious and hidden rust.
Rust is like a cancer, often spreading unseen through a steel car body until it is too late to do anything about it. Once corrosion starts poking through the sheet metal, it can no longer be repaired by simple methods like those listed above. Instead, the corroded metal sections must be entirely cut out. Then, all areas that the rust has affected must be completely cleaned up or replaced. Rust starts in places you can't readily see. When you finally do see it, it's usually much worse than it looks at first. Sometimes it is amazing to scrape away rusty metal and watch a body panel or chassis piece disintegrate before your very eyes.