Wetting not only allows you to scrape it off easily, but there is no
dust, as with dry scraping. What you have is acoustic beading
(styrofoam), mixed with sheetrock mud (wet gypsum), and it has been
sprayed onto your ceiling. This was initially a common commercial
application, back in the 50s, 60s & 70s, that eventually moved into
our homes, 70s & 80s. Yes, use drop cloths or visquene. You don't
want to be mopping or vacuuming your floor, to remove that stuff from
I've found, using a 8" sheetrock paddle is easiest for scraping and
gets the most off with one swipe.
Once off, you will likely need to float your ceiling sheetrock, again,
but most likely just one floating.