Answer
Use 120 for heavy marks, then 180 and 220. Sand with the grain where possible.
Why it happens
The previous grit pattern was not fully removed before moving finer.
Recommended grit
Use 120 to remove heavy marks, then 180 and 220 for prep.
Wet or dry
Dry.
Success check
The wood feels even and has no isolated deep scratch lines.
What to do
- Sand with the grain where possible.
- Use the grit that still removes the visible lines.
- Step through 180 and 220.
- Remove dust and inspect under good light.
Avoid: Do not skip directly to fine finishing grits on rough wood.