Answer
Before polyurethane, use 180 then 220 on bare wood. Between cured coats, scuff lightly with 320 or 400.
Why it happens
Very coarse scratches can show through finish, while overly fine sanding can reduce finish grip on some woods.
Recommended grit
Use 180 then 220 before applying polyurethane. Between cured coats, use 320 or 400 lightly.
Wet or dry
Dry before the first coat; dry or very light wet sanding between cured coats only if the finish instructions allow it.
Success check
The wood is smooth, dust-free, and still has enough tooth for finish.
What to do
- Sand bare wood through 180 and 220.
- Remove all dust before applying polyurethane.
- After a coat cures, scuff lightly with 320 or 400.
- Clean dust before the next coat.
Avoid: Do not use 1000+ grit on bare wood before polyurethane.