Answer
For body filler, shape with 80 or 120, refine with 180 and 220, then finish with 320 before primer.
Why it happens
Filler needs shaping with coarser grit, then refinement before primer.
Recommended grit
Use 80 or 120 for shaping, then 180, 220, and 320 before primer.
Wet or dry
Dry.
Success check
The filler is level and the scratch pattern is fine enough for primer.
What to do
- Let body filler cure fully.
- Shape with 80 or 120.
- Refine with 180 and 220.
- Finish with 320 before primer.
Avoid: Do not wet sand uncured or porous body filler.