Sanding drywall mud? Any way to do it with a hand sander without it umm snowing? I tried wetting it?

and that just made a disaster zone of ruined sandpaper, this kind is nontoxic so it isnt dangerous I just wonder how many weeks I will be cleaning up drywall powder. I have about 160-180 sq ft I have to do
Update: the previous owner destroyed(painted with the outdoor marine paint??? weirdos) the existing tile and all we could do was rip it out and it was floor to 2/3 the wall up on our whole kitchen, so that is why there is so much area with drywall mud, we used it to smooth the wall and now are sanding it to the point where... show more the previous owner destroyed(painted with the outdoor marine paint??? weirdos) the existing tile and all we could do was rip it out and it was floor to 2/3 the wall up on our whole kitchen, so that is why there is so much area with drywall mud, we used it to smooth the wall and now are sanding it to the point where we can texture it.
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