Answer
For high-build primer, level with 320, then refine with 400 or 600 before paint.
Why it happens
High-build primer is designed to be sanded, but it must be leveled with a grit that cuts without leaving deep final scratches.
Recommended grit
Use 320 for leveling, then 400 or 600 before paint.
Wet or dry
Dry for leveling; wet at finer stages only when the coating system allows it.
Success check
The primer is level, smooth, and has a uniform scratch pattern before paint.
What to do
- Let primer cure as directed.
- Block sand with 320 to level texture.
- Refine with 400 or 600.
- Clean thoroughly before paint.
Avoid: Do not paint over unlevel primer texture.