Answer
For a fiberglass tub, avoid coarse sanding. Test 1000, 1500, then 2000 wet on small marks only.
Why it happens
Tub surfaces have a finish layer that can be cut through by coarse sanding.
Recommended grit
For small surface marks, test 1000, 1500, then 2000 wet in a hidden area.
Wet or dry
Wet.
Success check
The mark is reduced without cutting through the finish layer.
What to do
- Clean the tub surface first.
- Test a hidden area before visible sanding.
- Wet sand lightly with 1000, 1500, then 2000.
- Stop if the finish becomes uneven.
Avoid: Do not use coarse grit on a fiberglass tub surface.