How to Sand Auto Body Filler for a Smooth Paint Job

Auto body filler (commonly known as Bondo) is essential for repairing dents and dings before painting a car. But the secret to a seamless repair lies in the sanding process. Using the right grits and technique ensures the filler blends smoothly with surrounding metal for a paint-ready surface.

Why Sand Auto Body Filler?

Sanding shapes the filler, removes excess material, and creates a smooth transition between metal and repair area. Without proper sanding, repairs remain visible after painting and can cause premature paint failure.

Tools You’ll Need

• 9x11 in wet/dry sandpaper sheets
• Sanding block or longboard sander
• Orbital sander (for large repairs)
• Body filler spreader and hardener
• Masking tape and tack cloth

Best Grit Sequence for Body Filler

• 80 grit: Rough shaping and leveling filler.
• 150 grit: Refining the surface and removing scratches.
• 220 grit: Blending repair into surrounding paint/metal.
• 400 grit: Final sanding before primer.

Step-by-Step: Sanding Auto Body Filler

1. Let filler cure. Ensure the body filler is fully hardened before sanding.
2. Start with 80 grit. Shape the repair area using 80 grit (25-pack) on a sanding block for control.
3. Smooth with 150 grit. Switch to 150 grit (50-pack) to refine and reduce deep scratches.
4. Blend with 220 grit. Apply 220 grit (100-pack) to feather the edges into surrounding surfaces.
5. Finish with 400 grit. Use 400 grit (25-pack) for a smooth, primer-ready finish.
6. Clean thoroughly. Wipe with a tack cloth before applying primer.

Special Cases

For deep dents, apply filler in thin layers and sand each layer progressively. For minor scratches or shallow repairs, starting at 150 grit may be sufficient.

Pro Tips

• Always use a sanding block to keep surfaces flat.
• Feather edges gradually to avoid noticeable repair lines.
• Don’t rush—let filler cure completely before sanding.

Aftercare

• Prime repaired areas immediately after sanding to prevent rust.
• Store leftover sandpaper in a dry, flat place to prevent curling.
• Use automotive-grade paint for lasting results.

FAQs

• Can I sand body filler by hand? Yes—hand sanding offers better control for small repairs.
• Do I need to wet sand body filler? No—dry sanding is standard, but wet sanding can be used for final grits.
• What grit before primer? 400 grit gives the best balance of smoothness and adhesion.

Watch & Learn

Get professional repair results with eQualle’s 9x11 in wet/dry sandpaper sheets, available in 25, 50, and 100 packs. Shop automotive sanding sheets here.