Answer
The primer scratches were too deep or not fully refined. Sand the primer with 320 or 400, then use 600 when a finer paint surface is needed.
Why it happens
Paint can reveal coarse primer scratches when the primer was sanded too aggressively or the grit sequence was skipped.
Recommended grit
Use 320 for primer leveling, 400 for normal paint prep, and 600 for finer prep before topcoat.
Wet or dry
Use dry sanding for most primer prep. Use wet sanding only when the primer is fully cured and water-safe.
Success check
Primer has a fine, even scratch pattern with no visible coarse lines before paint.
What to do
- Let primer dry or cure before sanding.
- Use 320 grit to level visible primer texture or scratches.
- Move to 400 grit for normal paint prep.
- Use 600 grit when a finer topcoat surface is needed.
- Use a sanding block on flat panels to keep the surface even.
- Clean all sanding dust before paint.
- Inspect under good light before applying topcoat.
Avoid: Do not paint over 180 or 220 grit scratches unless the coating system specifically allows it.