Answer
Remove most adhesive first, then sand with 180 or 220. Finish with 320 before paint.
Why it happens
Soft residue can smear and clog sandpaper if it is not removed carefully first.
Recommended grit
Use 180 or 220 after scraping/cleaning residue. Use 320 for final prep before paint.
Wet or dry
Dry for residue removal; wet only after residue is gone and the surface allows it.
Success check
The residue is gone and the surface has an even prep scratch pattern.
What to do
- Remove as much adhesive as possible by scraping or cleaning.
- Sand remaining residue with 180 or 220.
- Replace the sheet when it loads up.
- Finish with 320 before paint if needed.
Avoid: Do not grind soft adhesive into the surface with heavy pressure.