Auto & body
Prepping car bondo for paint
Shape with 80. Feather with 180. Finish with 320.
Body filler is forgiving but it tells the truth in paint. The three-grit climb that turns a rough bondo patch into invisible repair.
The climb
The exact sequence, in order.
- 180
Shape the filler
Long board (DA file) or hard hand block. Cross-hatch passes to find high spots.
Reach for
3M Pro Grade 2.75" × 25yd Sanding Roll — 80 Grit
- 2180
Feather the edges into the paint
DA sander with a soft pad. Work outward in concentric passes.
Reach for
Mirka Gold 5-inch Hook & Loop Disc Assortment
- 3320
Final smoothing before primer
By hand or ROS at low speed. Light, even pressure.
Reach for
Indasa Plusline 220-Grit 9×11 Sheets (50-pack)
Watch out for
The things that quietly ruin the job.
- ·Sand bondo dry, always. Bondo absorbs water and will bubble under paint.
- ·Don't skip 180. Going 80→320 leaves scratches the primer will telegraph through.
- ·Feather edges aggressively — a hard transition line will show in paint.
Questions people ask
The practical part.
How thick can I apply bondo?
Most fillers are rated to 1/4" max. Thicker means more sanding and a higher chance of cracking later.
Primer after 320 or 600?
High-build primer goes over 320. Sealer or basecoat-ready primer wants 600. Match the climb to the next product.
Keep going
Adjacent jobs.
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