Answer
Between marine varnish coats, use 320 or 400 after the coat cures. Use 600 for very fine final prep.
Why it happens
Each cured coat needs light scuffing so the next coat can level and bond.
Recommended grit
Use 320 or 400 between cured varnish coats. Use 600 for very fine final prep.
Wet or dry
Dry unless the varnish instructions allow wet sanding.
Success check
The coat is smooth, dull, dust-free, and ready for the next coat.
What to do
- Let the varnish cure as directed.
- Scuff lightly with 320 or 400.
- Clean dust completely.
- Apply the next coat in a clean area.
Avoid: Do not sand soft varnish or sand through edges.