Answer
Dirty water can drag grit and residue across the surface. Rinse the surface, change the water, clean the sheet, and continue with the same grit before moving finer.
Why it happens
Loose abrasive particles, removed coating, or dirt in the water can act like coarse grit and create swirl marks.
Recommended grit
Stay with the current grit until the dirty-water marks are removed, then refine with the next finer grits such as 1500, 2000, and 3000.
Wet or dry
Use wet sanding with clean water. Rinse the sheet and surface often so residue does not become an abrasive slurry.
Success check
The surface shows a clean, uniform wet sanding pattern with no new random swirls.
What to do
- Stop sanding when new swirls appear.
- Dump dirty water and rinse the container.
- Rinse the sheet and surface thoroughly.
- Inspect for trapped particles on the sheet.
- Continue with the same grit until the new swirls are removed.
- Move to the next finer grit only after the pattern is clean and even.
- Use fresh water for final fine grits.
Avoid: Do not keep sanding with cloudy, gritty water. It can create scratches that look like swirl marks.