Answer
Let wood filler dry, level it with 120 or 150, then blend with 180 and 220.
Why it happens
Filler must be leveled after it dries and then blended into the surrounding wood scratch pattern.
Recommended grit
Use 120 or 150 to level dried filler, then 180 and 220 to blend.
Wet or dry
Dry.
Success check
The filled area feels level with the surrounding wood.
What to do
- Let the filler dry completely.
- Level the filler with 120 or 150.
- Blend with 180.
- Finish prep with 220.
Avoid: Do not sand soft or uncured filler.