Let it continue to dry. Sand the surface using 60-grit sandpaper. Wipe with a damp cloth or clean with a wet/dry vac. Repeat Steps 2 and 3 four times. On the 4th sanding, use 220-grit sandpaper.

In it, the creator shows the use ... wet while sanding. When it’s smooth to the touch with no perceptible imperfections, you’re done with that grit. Wash down with water and wipe dry ...