Answer
For paper mache before painting, use 220 on rough spots, then 320 or 400 lightly.
Why it happens
Paper mache is delicate, so it needs light smoothing rather than aggressive sanding.
Recommended grit
Use 220 for rough high spots, then 320 or 400 lightly before paint.
Wet or dry
Dry.
Success check
The surface is smoother without tearing or fuzzing badly.
What to do
- Let the paper mache dry completely.
- Sand only high rough spots with 220.
- Refine lightly with 320 or 400.
- Wipe dust gently before paint.
Avoid: Do not sand damp paper mache.