Rust is just about any automotive enthusiast's worst nightmare. It's ugly, it spreads, and it can severely put the structural integrity of the car at risk. Leave it long enough, and it can consume practically every bit on metal in its presence, rendering a vehicle unfit to drive.
However, you don't need to freak out if you spot rust on your vehicle. There are ways to completely fix rust issues, but they vary depending on how severe it is. Let's discuss some of the most common rust repair techniques as well as some DIY rust prevention tips.
Why Do Vehicles Rust?
So, why exactly do vehicles rust in the first place? Rust is the result of an electrochemical breakdown in iron-based metals. The iron molecules reacting with the environment's oxygen causes oxidation, which creates a new molecule known as Iron Oxide a.k.a. rust.
Then, of course, you've got the road salt, which can speed up the corrosion process dramatically. These salts and other contaminants dissolve into water, creating an electrolyte that aids in the spread of rust. That's why vehicles in snowy environments, or those near bodies of salt water, are more prone to rust. Automakers spend countless hours of research to figure out ways to prevent this corrosion on new cars, but it can be tough to avoid in certain locations.
If you're looking to stop rust in its tracks, a simple prevention tip is to go to the car wash frequently, and keep the underside clean in particular. It's also important to get into all of those little hidden areas. Many vehicles have drain holes at the bottom of the doors and rocker panels, so be sure to occasionally clean them out so nothing gets trapped inside. There are also different rust-proofing epoxy primers, which can be applied to the undersides of the car, sealing the metal and ensuring no oxidation occurs.
However, if the car rust is already showing, let's go over what you should do to fix it. There are a few different types of rust, and the repair process is different, depending on how bad the metal is.
Fixing Surface Rust
Surface rust is certainly one of the most common types of rust found on modern vehicles. These little rust spots can show up as a result of a nick, scratch, or crack in the body panel. As the name suggests, it sits on the surface, and doesn't actually cause any damage to the structural integrity. Think about when you leave your car parked for a while. If you look at the brake rotors, you'll see a thin layer of rust. This will easily come off after the brake pads make contact a few times.
If this occurs on a painted panel, the process is very similar to a paint repair. First, you'd start sanding the affected area with something around 50-grit sandpaper. Continue sanding until you're through both the paint and the rust, showing you clean, bare metal. Next, even if it was only a small spot of rust, apply a rust treatment with a brush or sponge to the metal area. This helps turn those iron oxide molecules into a chemically stable compound. Add two layers of this, and wait around a day for everything to dry. From here, you can apply your primer, automotive paint, clear coat, and give it a good buff after it dries up. Before you know it, that spot will look good as new.
Fixing Scale Rust
Moving onto something a little bit more severe, we've got scale rust. This could potentially be a result of leaving those surface rust spots untouched. As the rust expands deeper into the metal, it reveals itself with bubbles that start to form in the paint. In most cases, the rust damage causes the outer layer of paint to begin to flake off, exposing even more bare metal, which will soon become corroded as well. Scale means that the surface of the metal has become rough and pitted, but there are still ways to fix it.
Normally, the auto body shop repair process would entail getting through the rust with a wire brush or grinding wheel, before smoothing it out with sandpaper. Once down to bare metal again, apply the rust treatment to the entire area to keep it free from corrosion. Even once all the rust has been sanded off, the surface may still be a bit rough. In this case, applying a bondo or body filler may be required before you can do the paint job. Use a sanding block and once the surface is smooth, move forward with the same steps you would take for surface rust, including primer, paint, and clear coat, followed by a buff.
Fixing Penetrating Rust
Rust removal when you get to the penetrating stage is significantly more difficult. At this point, the metal will begin to show rust holes through it, and the rusting can seriously affect the structure of the car, especially if the frame is a culprit of the corrosion. As tempting as it might be, bondo isn't going to work out very well. Even if it does cover the holes, it won't fix the weakened metal.
Actually, the only real solutions to fix rust at this stage is to either replace the part entirely, or if the affected area is located on a body panel, you could cut the bad section with an angle grinder and replace it with a new piece of sheet metal. This is a challenging task to take on at home, but a reputable body shop should be able to handle the job with no problem. They can shape the metal to fit the curves of the body panel just as it did from the factory, and by the time they weld it in, smooth it, and paint it, you'll never even know the rust was ever there.
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