Rust is cancer for cars, and if left to run riot it can turn any vehicle into scrap. But cars are protected from rust from the factory, and the only reason it sets in later in life is because of use or because damage opens up the door for corrosion.
That's the point at which you’re left to ponder how much a body shop is going to charge to put it right. It's usually a lot.
Don’t panic though. If you’re happy to have a go yourself, the chances are you can stop the rust in its tracks and prolong the life of your beloved motor. There’s really not a lot to it. You just need to be thorough, do the job right and you’ll be onto a winner.
Now, before we get into this, a couple of caveats:
1. We’re talking about surface rust
If you’ve got no floors in your car because they’ve rotted out, you’re going to need a welder, preferably with a professional holding it. The same goes for holes in bodywork, sills, chassis rails etc.
What we’re looking at here is corrosion to the panels that hasn’t eaten through and compromised the structure of the vehicle.
2. Paint
In this guide we’ll take you right up to point of priming the affected area. If you want to have a go at painting the car, then by all means do. Solid colours are going to yield the best results, while metallics will be trickier to get right.
There is no shame in doing the prep work and then asking a body shop to paint it and blend it in. Professional paint spraying equipment is designed for this – the nozzle of an off-the-shelf aerosol isn’t.
How do you fix rust damage on a car?
Vehicles today are much less rust-prone than they were just 20 years ago, but if you live near the ocean or drive in an area that uses salt on the roads, you can still get rust through long before the mechanical parts are worn out.
Minor rust damage on non-structural parts of the car can be easily repaired and with a little practice even made to look like they never happened.
Professionals restoring classic cars usually use a method of cutting out the damage and welding in new material, but for a daily driver fibreglass epoxy and a little body filler makes things much easier.
In past guides we've talked about fixing a scratch in your car's paint, but what if a scratch has progressed to the point of rust through?
Most rust through damage starts out with something as simple as a chip from a piece of flying gravel, or a door ding that cracks the paint, which is why it is so important to give your car a wash and a once over periodically.
A spot of touch-up paint now and then may take a few minutes and save hours of rust repair 10 years from now. Read on for step by step instructions, or check out our video tutorial below.
You’ll need the following tools and materials for this job:
- Angle grinder and flapper wheels
- Wire brush
- Fibreglass epoxy gel
- Body filler
- Various grade sandpaper (80, 400, 600, 1000, 2000)
- Sanding block
- Primer and base coat paint
- 2k clear coat paint (available in aerosol cans)
- Masking materials (paper and tape)
- Rubbing compound
- Mineral spirits
- Rags
- Tack cloth
How to remove and repair rust damage on your car
1) Remove Paint and Rust
Use an angle grinder with flapper wheel to remove the old rust and paint from the surface to be repaired. It is possible to accomplish the same thing by hand with coarse 80 grit sandpaper and a wire brush, but it is much harder to do a thorough job. For an area where you can't reach with the grinder, use the wire brush to remove as much dirt, grime, and rust as you can. You may want to use a rust converter, which goes beyond paint to chemically neutralise rust and leave a protective black coating.
2) Repair with glass fibre
Long strand glass fibre repair gel, unlike body filler, creates a structural repair that is nearly as strong as steel. Mix the gel and hardener, and press into the damaged area from behind. Check with the package, but it typically starts to harden in about 15 minutes and can be sanded in less than an hour.
3) Sand excess glass fibre
Use the angle grinder and flapper wheel to sand off any glass fibre gel that has been pushed out through the rust holes. The surface of the hole should be slightly recessed compared to the metal body panel so that it can be filled with the smoother body filler.
4) Apply body filler
Mix the body filler with the proper amount of hardener. Apply body filler with a flexible, flat spreader, pressing it into the rust holes. The flatter you can get the filler while applying it, the less sanding you will have to do afterward. Be certain to apply enough filler so that there are no low spots, pinholes, or scratches that will have to be filled in with a second coat.
5) Sand it smooth
The most important and most time-consuming part of body work is getting a smooth surface before you start applying paint. Start with 400 or coarser grit sandpaper and sand off any excess body filler; it sands faster if it is not quite fully hard. If sanding a large area, you may need a sanding block to make sure you don't end up with a wavy surface. You are done when the entire area has been sanded smooth to the touch with 400 grade paper.
6) Clean area
Wipe the area you just repaired with a clean rag and mineral spirits to remove any residual dirt or oil from your fingers. The body filler should be so thin you can see metal and paint through it in most places. Let dry, then wipe once again with a tack cloth to remove any lint. Any fingerprint, smudge of oil, or spec of dust will cause spots, fisheyes, or runs in your paint, so cleanliness is crucial from here on out.
7) Apply primer
Spray primer over the repaired area, any bare metal, and at least an inch around it to allow for blending. For best results, spray over the entire area in a thin coat, then go over again a few minutes later with a slightly heavier coat. Let the primer dry the recommended amount of time before sanding.
8) Wet sand and repeat
Wet sand the newly primed area with 400 grit sandpaper until it is smooth and the edges of the repair are feathered into the original paint. Wipe clean, allow to dry and spray another coat of primer. Move to a higher grade of sandpaper, 600, and wet sand and prime again. Two or three coats of primer are typically enough to get a reasonably smooth repair.
9) Spray the base coat
Most cars these days use a base coat (the colour paint) covered with a protective top coat (a thicker clear paint), but many touch-up paints can be applied alone without the clear. Spray two or three thin coats of paint over the primer and repaired area, and up into the original paint. Several thin coats are better than one thick coat because it avoids leaving runs or drips in the paint.
10) Rub out the paint
In order to get the full glossy finish from spray can touch-up paint you need to run it by hand with a rubbing or polishing compound, and if you have any significant mistakes (orange peel, runs, drips), you will need to start with wet sanding. Wet sanding with 1000 and then 2000 grit should allow you to remove runs and orange peel, or you may have to go even coarser, but go too far, and you will have to spray another coat of paint. Polish lightly with rubbing compound, then move up to a finer polishing compound, and you should achieve full gloss. The rubbing will also allow you to blend the new paint of the repair into the original paint around the edges.
11) Spray the clear coat (optional)
A clear coat is optional for most minor repairs, but the advent of 2K clear paint in a spray can has made it a good idea if you plan on keeping the car. The original factory paint uses a two part mixture with paint and an activator or hardener, making the paint like an epoxy that is impervious to weather, UV light, and solvents. Two part, or 2K, spray paint will make your home repair nearly as durable as a professional body shop paint job, and much longer lasting than touch-up paint alone.
We shot a companion rust repair how-to video that quickly and concisely demostrates just how easy repairing rust in this way can be. If you find that video helpful, subscribe to the Haynes YouTube Channel and get more helpful hints, how-tos, and previews of new products.