Answer
For drywall corners, use 150 or 180 lightly, then 220 for final smoothing before primer.
Why it happens
Corners are easy to over-sand because pressure concentrates on a narrow line.
Recommended grit
Use 150 or 180 for joint compound corners, then 220 for light final smoothing.
Wet or dry
Dry.
Success check
The corner is smooth, feathered, and ready for primer.
What to do
- Let joint compound dry fully.
- Use 150 or 180 with light pressure.
- Feather the edges away from the corner.
- Use 220 for final smoothing before primer.
Avoid: Do not press hard into the corner line.