Answer
For firm foam, use light pressure with 220 or 320, then 400. Soft foam may tear instead of sand cleanly.
Why it happens
Foam is soft, so coarse grit and heavy pressure can rip the surface instead of smoothing it.
Recommended grit
Use 220 or 320 for shaping firm foam, then 400 for light smoothing.
Wet or dry
Dry.
Success check
The foam is shaped without torn chunks or rough gouges.
What to do
- Use only light pressure.
- Shape firm foam with 220 or 320.
- Refine lightly with 400.
- Stop if the foam tears or crumbles.
Avoid: Do not use heavy pressure on soft foam.