Sanding Auto Body Filler: Smooth Repairs Before Paint

Auto body filler (Bondo) is essential for repairing dents and imperfections, but without proper sanding, it leaves uneven patches visible under paint. The secret to seamless car repairs is sanding filler with the right grit progression. This guide walks you through sanding body filler for a flawless, paint-ready surface.

Why Sanding Body Filler Matters

Body filler cures hard but uneven. Sanding shapes the repair, feathers edges into surrounding panels, and creates a smooth surface that primer and paint can adhere to. Skipping sanding leads to wavy panels and visible repair lines.

Tools You’ll Need

• Wet/dry sandpaper sheets (80–400 grit)
• Sanding block or longboard sander
• Body file (for heavy shaping)
• Vacuum and tack cloth
• Automotive primer
• Respirator, gloves, and safety glasses

Recommended Grit Sequence

• 80 grit: Rough shaping and leveling filler.
• 120 grit: Refine shape and smooth ridges.
• 220 grit: Blend edges into surrounding paint.
• 320–400 grit: Final prep before primer.

Step-by-Step: Sanding Auto Body Filler

1. Apply and cure filler. Let it harden completely before sanding.
2. Shape with 80 grit. Use 80 grit (25-pack) sheets to carve down high spots.
3. Smooth with 120 grit. Switch to 120 grit (50-pack) for refining the repair.
4. Feather edges with 220 grit. Use 220 grit (100-pack) to blend into the car’s surface.
5. Finish with 320–400 grit. Lightly sand the entire repair for a paint-ready surface.
6. Clean the panel. Vacuum and wipe with tack cloth before priming.

Special Cases

For large dents, use a sanding longboard to keep panels flat. For small repairs, a block sander provides more control. Always sand in long, even strokes to avoid dips.

Pro Tips

• Apply thin filler layers instead of one thick coat—it sands more evenly.
• Always sand in crosshatch patterns for smoother blending.
• Check progress with a guide coat (light spray of contrasting paint) to reveal low spots.

Aftercare

• Prime immediately after sanding to protect against moisture.
• Store leftover sandpaper in a dry place to prevent clogging.
• Inspect under bright light before painting—any flaws will show once painted.

FAQs

• Can I skip 80 grit? No, it’s crucial for shaping hardened filler.
• Do I need to wet sand filler? No, dry sanding works best—save wet sanding for primer and paint.
• What if I sand through filler? Reapply a thin layer, let it cure, then re-sand.

Watch & Learn

Sanding body filler properly ensures invisible repairs under paint. Stock up on wet/dry automotive sandpaper—packs of 25, 50, and 100 available in all grits. Shop body filler sanding sheets here.