As previously discussed, rust isn’t easy to prevent. But how much rust is too much rust? How do you know if it’s too late for car rust repair? And if you’re shopping for a used car, should rust be considered a deal breaker?
Rust generally falls into one of two categories: surface rust or scale rust.
- Surface rust is superficial. It affects the metal surface on a microscopic scale, going only a few microns (µm) deep. One example of when surface rust can form is after a paint chip or scratch has left the metal exposed for a short period of time. How fast surface rust progresses to scale rust depends on temperature, humidity, and precipitation.
- Scale rust is a natural progression of surface rust. As oxidation works its way deeper, it accelerates, flaking off bits of the converted metal. At first, this will cause pitting, and then paint will eventually start to bubble and flake off. Over time, scale rust eats holes through body panels, frame rails, and chassis components.
How to repair rust on a car
Car rust repair depends greatly on the type of rust you’re tackling. Minor surface rust is easiest to deal with, and eliminating it is the best way to prevent major problems down the road. Sanding and repainting, as well as rust recovery, make for a nice novice-to-advanced DIY job, but body work and frame repairs may take more time, skill, and money than many DIY auto repair guys and gals can afford.
- Fixing surface rust requires sandpaper, primer, paint, and clearcoat. Sandpaper restores the vehicle’s clean metal surface, primer treats it, paint colours it, and clearcoat protects it. Check out this in-depth write-up on repairing scratches and painting.
- Repairing surfaces damaged by scale rust requires more effort. Minor pitting is treated as surface rust: body filler can be used to restore a smooth surface for priming and painting.
- Dealing with scale rust depends on skill, time, and the right tools and budget. For minor damage, scrape off as much scale as possible with a wire brush. Use a rust-specific primer, like Rust Check Rust Converter, to thoroughly soak all exposed rusty metal. Let it dry, and then apply a couple coats of spray paint, plus an undercoating spray, if possible.
- Major scale rust damage usually requires replacement. Some parts are easily replaced, such as subframes and control arms. Other parts are more complicated, such as full frames and body panels. These tasks will likely require using a vehicle lift, working with metal sheeting, welding, and other skills.
Of course, pet projects and restorations are an entirely different story. When you’re working on an old vehicle, learning how to remove, restore, and replace major components is a fulfilling experience.
Car rust repair summary
Surface rust can be sanded out and repainted, and possibly body-filled, but rust holes will require welding or new body panels. Surface rust on the frame rails can be repainted and undercoated, but flaking rust can seriously weaken the structure of a vehicle. This type of issue once led Toyota to recall nearly a million trucks. On any kind of vehicle, body panels are integral to the safety cell, and any weakness can jeopardize your safety in a crash.
While car rust repair is a valuable skill, car rust prevention is undeniably more cost-efficient. Be sure to check out our previous post on how to keep rust at bay.