Answer
Between polyurethane coats on stairs, use 320 or 400 lightly and avoid sanding through edges.
Why it happens
Between-coat sanding should level small defects without cutting through edges or tread noses.
Recommended grit
Use 320 or 400 lightly between cured polyurethane coats.
Wet or dry
Dry unless the finish instructions allow wet sanding.
Success check
The coat is lightly dulled, smooth, and dust-free before recoating.
What to do
- Let the coat cure fully.
- Scuff lightly with 320 or 400.
- Use very light pressure on tread edges.
- Remove dust completely before the next coat.
Avoid: Do not sand through finish on stair nosing or edges.