How To Fix Major Rust on a Car
Photo by Rachel Claire from Pexels
We all like to think our gleaming new automobile is going to remain pristine than ever. But the elements and Father Time will take their toll. Eventually, you’ll see telltale red-brown spots that bloom into patches when they’re left to their own devices. Soon or later, every driver needs to learn how to fix major rust on a car.
What Causes Cars to Rust?
Rust occurs when oxygen and iron react to form iron oxide — the chemical name for what we call rust. This happens whenever iron is exposed to oxygen, but there are a number of factors that can accelerate the process.
Moisture is the first major factor in accelerating rust. The oxygen in air consists almost entirely of O2, which is a relatively stable molecule consisting of two oxygen atoms. When an O2 molecule bumps up against your car’s iron parts, nothing happens.
Water, on the other hand, consists of two hydrogen atoms and a single oxygen atom. This oxygen atom is easy to break free. When a water molecule touches iron in the presence of a catalyst, the oxygen atom jumps off and attaches to the iron instead, creating rust.
A catalyst is an ionic chemical that aids in the reaction. Normally, rainwater and other water have some amount of other compounds in them that can act as catalysts. Unless you’re using distilled water, water will cause some rust.
Salt is the second major factor in causing rust. Remember how we said that water and iron need a catalyst in order for rust to form? As it turns out, salt makes a fantastic catalyst, which is bad news for those of us who live in cold climates where the roads need to be salted.
As you can see, it matters where and how you drive your car! Jeep Wranglers, for example, get a bad rep for rusting, but look what they’re made for. Of course your car will rust faster if you’re driving off road, plowing through snow, and exposing the metal to all kinds of conditions that create rust.
Similarly, there’s an old mechanic’s saying that says: “When they rest, they rust.” Cars rust when they’re kept in storage, due to condensation, pooling, and moving parts remaining stationary. Even if your car is a show car, it’s a good idea to take it for a spin once a month — weather permitting.
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How to Fix Major Rust on a Car
Now we know how rust happens, it’s time to talk about how to fix major rust on a car. Here’s a succinct guide.
Necessary Supplies
Before you set about fixing your rust, you’ll first need to get together all your tools. Here’s a short list of recommended supplies:
- Masking tape and paper rolls
- Sandpaper, ideally with a sanding block
- An angle grinder with metal grinding wheels
- Bondo or another similar body filler
- Automotive primer
- Automotive touch-up paint
- Gloves, goggles, and a dust mask
Prep the Vehicle
Now, it’s time to prepare your vehicle. First, park in a well-vented garage, or in a clean, dry outdoor space. Depending on your location and living arrangements, this may involve waiting for suitable weather.
With your vehicle in place, mask off any parts that are not rusty. If you’re just treating a single area, such as a wheel well, you can mask off the general vicinity. If you’re dealing with multiple patches across the vehicle, you’ll end up masking most of the exterior.
Avoid using wax paper and other highly-flammable materials. These can catch fire if struck by sparks from an angle grinder.
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Sand and Grind
Preparation is just the first part of how to fix major rust on a car. The next is the actual rust removal itself. First, start with the most heavily-rusted areas. Begin with your coarsest sandpaper, or with an angle grinder if the rust is very deep.
Now, start scrubbing away. It’s essential to remove every last bit of rust. If there’s any left over, it will start rusting again almost immediately — even if the area has been painted over. This will leave you right back where you started: with a horribly rusted car.
Since this process involves a lot of effort, it helps to use a sanding block. This provides a more comfortable grip than holding the paper in your bare hand. It also keeps you from nicking your fingers as easily when you slip.
Fill and Prime
When all the rust has been thoroughly removed, wash and dry your car to ensure there’s no dust left over on the surface. If necessary, apply your filling compound and let it dry. Next, spray any unpainted areas with an automotive primer.
When the primer is dry, sand it with light, 200-grit paper, wash it, dry it, and apply a second coat. Sand this second coat with 400-grit paper, wash and dry again, and you’re good to go.
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Paint
When the primer has been applied, you can paint your car. Provided your car isn’t too old, you should just be able to paint the areas you’ve sanded, and the color should match. Apply a thin coat, let it dry, and sand it with 400-grit paper, removing any thicker spots.
Wash away any dust, let the surface dry, and repeat the process twice more. The last time, wet the sandpaper before you sand to get an even glassier finish.
Apply Clear Coat and Wax
When you’re satisfied with your paint job, it’s time to keep it safe. Apply a clear coat to the whole repainted area. This protects the paint from UV to prevent fading, and absorbs many minor bangs and scratches. It’s also glossy and attractive.
After the clear coat is dry, the last step is to wax your car. Apply the wax in a swirling motion, and use a second cloth to wipe away any excess. Much as your clear coat helps protect your paint, your wax helps protect your clear coat. Wax your car every spring and fall, and you’ll have less rust to worry about in the future.
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