Answer
Use a sanding block or flat backing pad instead of bare fingers on flat areas. Start with the grit that levels the grooves, then refine with the next finer grits.
Why it happens
Bare fingers create uneven pressure points, so the abrasive cuts deeper under each finger.
Recommended grit
Use 180 or 220 to level light grooves, then refine with 320 and 400. Use 120 only for deeper grooves.
Wet or dry
Use dry sanding for most leveling. Use wet sanding on water-safe surfaces during finer refinement.
Success check
The surface looks flat from a low angle and no finger-shaped grooves remain.
What to do
- Stop sanding with bare fingers on flat areas.
- Wrap the sheet around a flat sanding block or backing pad.
- Start with 180 or 220 for light grooves.
- Use 120 only when grooves are deep enough that 180 does not level them.
- Sand evenly across the full area, not just the groove.
- Move to 320 and 400 after the surface is level.
- Check the surface from a low angle before finishing.
Avoid: Do not press with fingertips on flat surfaces. The pressure marks can become visible after finish is applied.