Answer
For pitted rust, use 80 or 120 to remove loose rust, then refine with 180, 220, and 320 before primer.
Why it happens
Pitting means corrosion has eaten into the metal, so sanding can remove loose rust but may not erase deep pits without removing metal.
Recommended grit
Use 80 or 120 to remove loose rust, then 180, 220, and 320 before primer.
Wet or dry
Dry.
Success check
The loose rust is gone and the remaining surface is clean enough for primer.
What to do
- Remove loose rust and debris.
- Sand with 80 or 120 to cut corrosion.
- Refine with 180, 220, and 320.
- Clean and prime the metal promptly.
Avoid: Do not assume fine grit will remove deep pits.