Tried it damp. Tried it wetter than damp. Tried it wet. Tried a wall scraper:
View attachment 110595
That didn’t work. Then I tried a heavy duty floor scraper with a blade that could do some damage:
View attachment 110596
That didn’t work.
But an 80 grit flap disk… that worked. It left the wall a little too damaged.
The best I’ve come up with has been the wire wheel cup on an angle grinder. That knocks the sand off the wall, then I can smooth it out with my palm sander and a drywall screen.
I don’t have all my tools here, so I’m limited in what I can try.