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How to Use Bondo Body Filler: Step-by-Step Car Dent Repair
Oct 19th 2026
Bondo body filler is the quickest way to fix dents, dings and small rust spots on a car before paint. The steps are simple: sand to bare metal, mix the filler with hardener, spread thin layers, then sand and prime. The details are what decide whether the repair stays invisible. This guide covers which Bondo product to use, the right mix, and the sanding grits that give a smooth, paint-ready finish.
Which Bondo Product Do You Need?
| Job | Product | Ready to sand |
|---|---|---|
| Dents and dings, general bodywork | Bondo Original Filler | About 20 min |
| Same jobs, done faster | Bondo Fast Dry Filler | About 15 min |
| Small holes and rust-out, up to 1/2 in. | Bondo Short Strand Fiberglass Filler | About 30 min |
| Larger holes, up to 1 in., and cracked fiberglass | Bondo Long Strand Fiberglass Filler | About 30 min |
| Small, hard-wearing repairs such as alloy wheels | Bondo Extreme Metal Reinforced Filler | About 20 min |
| Pinholes, scratches and the final skim coat | Bondo Glazing & Spot Putty (no hardener) | About 20 min |
For a one-off fix, the Bondo Body Repair Kit comes with pre-measured filler and hardener pouches, so there's no guessing the mix. Browse every option in our body fillers category.
What You'll Need
- Body filler and cream hardener
- Plastic spreaders and a clean, non-porous mixing board
- 80 grit and 180 grit sandpaper or sanding discs, plus a sanding block
- Wax and grease remover, a tack cloth and primer
- Gloves, safety glasses and a dust mask
How to Use Bondo Body Filler: Step by Step
1. Clean the area
Wash the panel with soap and water, then wipe it with a wax and grease remover. Filler won't stick to wax, oil or silicone.
2. Sand to bare metal
Sand the damaged area with 80 grit to remove paint, primer and all rust. Go 1 to 2 inches past the edge of the damage so the filler grips clean metal all around. Clean again and let it dry. If you leave rust under the filler, it will bubble through later.
3. Mix filler and hardener
Scoop filler onto your mixing board. 3M's guide is a 3-inch strip of hardener for a 3-inch puddle of filler, and that's also the most you should mix at once. Fold and press the two together with a spreader until the color is even, with no streaks. Don't whip it, because that traps air bubbles. Never put hardener into the can, and never return mixed filler to it.
Too little hardener and the filler stays soft and gummy. Too much and it cures too fast, cracks or bleeds through paint.
4. Apply in thin layers
You have about 3 to 4 minutes before the filler starts to set. Press a thin first coat firmly into the metal so it fills the scratches, then build up in thin layers, each a little wider than the last. Build slightly above the surrounding panel so you can sand it down level. Several thin coats beat one thick one.
5. Let it cure
Wait about 20 minutes for Original Filler or 15 minutes for Fast Dry. When ready, the filler is hard and a fingernail won't dent it. Work above 45°F (7°C), because cold slows the cure.
6. Sand to shape
Rough-shape with 80 grit on a sanding block, working in an X pattern across the repair so you don't dig low spots. Finish with 180 grit or finer and featheredge the edges into the paint. Run your palm over it with your eyes closed, since you'll feel high and low spots before you see them.
7. Glaze, prime and paint
Fill any pinholes or fine scratches with a skim of glazing and spot putty, then sand it smooth. Wipe with a tack cloth and apply 2 to 3 coats of primer once the filler has cured for at least 45 minutes. Then sand the primer and paint following your paint system's instructions.
Common Bondo Mistakes
- Filling over rust or paint. The repair lifts or bubbles within months.
- Using filler on holes. Standard filler isn't for holes. Use a fiberglass-reinforced filler or a body patch behind the hole.
- Applying it too thick. Heavy layers crack and shrink. Pull the dent out first so the filler only needs to be a skim.
- Skipping primer. Bare filler soaks up paint and shows through as a dull patch.
FAQ
How long does Bondo take to dry?
Bondo Original Filler is ready to sand in about 20 minutes and Fast Dry in about 15 minutes at room temperature. Fiberglass-reinforced fillers take about 30 minutes.
Can Bondo be used on plastic bumpers?
Standard body filler is made for metal, fiberglass and wood. It isn't flexible enough for most plastic bumpers, which need a flexible bumper repair product.
Is Bondo body filler the same as Bondo wood filler?
No. Wood filler is formulated for doors, trim and rotted wood. See our Bondo wood filler guide for that job.
What about small paint chips?
For rock chips and light scratches, the Bondo Scratch & Rock Chip Repair Kit is faster than full bodywork.
Need help choosing a filler or abrasive? Shop body fillers at Strobels Supply or contact our team.