Answer
Pinholes need a thin skim coat, not more sanding. After it dries, sand lightly with 220.
Why it happens
Air pockets or thin filling can leave small holes that sanding alone will not fill.
Recommended grit
Use 220 for smoothing after applying a thin skim coat.
Wet or dry
Dry.
Success check
The patch is smooth with no visible pinholes before primer.
What to do
- Wipe away sanding dust.
- Apply a thin skim coat over pinholes.
- Let it dry fully.
- Sand lightly with 220 before primer.
Avoid: Do not keep sanding pinholes deeper.