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Car rust repair DIY: How to remove rust from a car

Rust spots not only look unsightly, but get worse if not addressed.

Rust is a scary word as most people think it signals the death of their car but, with basic tools and a little time, you can stop your car rotting away.

This isn’t just for full-blown restoration work on a classic car. Thankfully, you don’t need to completely dismantle your car to fix it, or spend thousands, if you catch the rust early enough.

Identify the issue

The first step to any rust repair DIY job is to identify the problem. Rust will start under the paint of your car hidden out of sight, but eventually bubbles to the surface looking like cauliflower under the paint. Car rust repair begins with a thorough inspection of the area to see if it has spread along a panel or is in one small area.

Rust normally starts where dirt gets trapped in an area over time, traps moisture, and then eats the metal away. When you wash your car, make sure to clean behind the fuel filler, clean around the inside of the boot (trunk) and bonnet (hood), behind the bumpers, around the front and rear windscreens, wipe under the doors, and inside the wheel arches, as these are all common areas to find rust.

Prevention is better than cure, as someone very wise once said!

How to remove rust from metal

You need to clean away the paint and look at the raw metal to see if it is just pitted and dimpled, or if it has been fully eaten away leaving nothing behind. When it comes to fixing rust, cleanliness is next to godliness, and you need to ensure no dirt or rust is left behind to regrow later.

You can clean the paint off using sandpaper or a wire cup on a drill, which allows you to see how much rust is hiding under the paint. For a good car rust repair you need full rust removal; if you don’t remove rust from metal it will just keep eating away.

You should fix rust in a garage with good ventilation as you need to be out of the weather to prevent contamination to the repair, but keep ventilation up when working with paints and chemicals.

How to fix small rust spots on car

If the metal hasn’t eaten a hole in the metal your repair is simple.

Clean the area thoroughly and brush on a good automotive rust convertor to the affected area like Oxytech’s Anti-Ox. This eats the oxidisation, stopping the chemical rusting process.

Mix up a small amount of body filler with the supplied hardener, until it turns light pink. Spread the filler evenly in a thin layer across the section and leave it two hours.

Once dried sand it with 400-grit paper, feathering the edges to blend into your existing paint job. Mask the area around the repair using tape and clear plastic, and spray primer over the top using short, dusty strokes to build the level of primer up gradually.

Lightly sand the dried repair with 400-grit, then lay down two coats of colour. Again, use light, fluid sideways motions to prevent runs.

Fixing large rusty sections

Large sections of rust require a lot more careful work, but untrained hobbyists like myself can still fix them. I had to fix this section of one of my cars to be safe to drive on the road, but managed to do it at home.

Novices should seek out friends experienced in this kind of rust removal bodywork as it is easy to get the job wrong. It took me two full days to do this repair, working slowly and carefully, and much of that time was spent fitting the metal patch panel.

1. I removed the chrome trim and cleaned the rusty area to see how far the rust had spread.

2. I marked out the area to cut out with masking tape, giving me a line to cut through using a basic 125mm angle grinder and thin cut-off wheel bought from Bunnings.

3. Under the panel had surface rust, so I cleaned it with Oxytech Anti-Ox, which neutralises the rust’s oxidisation process.

4. Fabricating a repair starts with a template made out of a manila folder. I made it using multiple sections because the stock panel has complex shapes, meaning it is easier to get a good fit by breaking the template up.

5. Before I welded the patch panel in I painted the inner section with a special rust- proofing paint from KBS Coatings – an Aussie company which specialises in rust- proofing.

6. I bought new sheet metal from a local supplier and cut out the shape I needed from my template, with an extra few millimetres around the edge so I could trim it perfectly on the car.

7. The Pontiac’s body line has a deep V along its length, but also slopes down at the rear. Without proper body-working tools it took me a few goes to bend it far enough on a workbench to fit the car nicely.

8. I used a MIG welder to attach the patch panel to the car, with a series of small tacks every 30mm or so. I then stitched them together gradually so I didn’t put too much heat through the panel. These were then ground down with a flap disc on an angle grinder.

9. Once the welds were ground I put a thin skim coat of body filler, gave them a light sand with 120-grit before laying down two coats of etch primer from a can.

10. The car is going for a full respray later on so I covered the primer with a basic rattle can grey to seal the repair. Primer is porous and the car would have to go into the weather before it goes for its final paint job.

Tools required

You’ll need a fairly basic selection of tools, which you can pick up at any decent auto parts store, like Supercheap Auto, who can also sell you paint in a spray can matched to your car’s particular colour so the repair won’t stick out.

- Black nitrile gloves
- A small tin of wax and grease remover
- Dust mask
- 50mm-wide masking tape
- Masking plastic (or newspaper)
- A couple of cans of etch primer
- Sheets of sandpaper in 40, 120, and 400 grit
- Sanding block
- Wire wheel, or wire cup, or flap disc
- Angle grinder or electric drill
- Auto body filler
- Body filler applicator
- Spray paint matched to your car
- Rust converter

Got any tips on how to remove rust from car surfaces? Tell us in the comments below.

Iain Kelly
Contributing Journalist
A love of classic American and European cars drove Iain Kelly to motoring journalism straight out of high school, via the ownership of a tired 1975 HJ Holden Monaro.  For nearly...
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