Answer
Feather paint edges with 220 or 320, then refine with 400 or 600 before primer.
Why it happens
The edge between old paint and bare or repaired areas was not blended gradually enough.
Recommended grit
Use 220 or 320 to level the edge, then 400 or 600 for finer primer prep.
Wet or dry
Dry for shaping; wet can be used at 600 for fine finishing where suitable.
Success check
The repair edge feels smooth and cannot be felt with a fingertip.
What to do
- Clean the repair area.
- Sand the paint edge with 220 or 320.
- Blend outward with light pressure.
- Finish with 400 or 600 before primer.
Avoid: Do not leave a hard paint ridge before primer.