Answer
For rust before painting, use 80 or 120, then refine with 180, 220, and 320 before primer.
Why it happens
Loose rust needs removal first, then the metal needs a finer scratch pattern for coating prep.
Recommended grit
Use 80 or 120 for rust removal, then 180, 220, and 320 before primer.
Wet or dry
Dry.
Success check
The rust is removed or stabilized as required and the surface is evenly prepared for primer.
What to do
- Remove loose rust and debris.
- Sand rust with 80 or 120.
- Refine with 180 and 220.
- Finish with 320 before primer if a smoother prep is needed.
Avoid: Do not paint over loose rust dust.