I had some water damage to the ceiling of a small bathroom and need to remove the plaster, but I don't want to invest in a reciprocating saw (plus they're scary to use overhead).
you could also try a rotozip.
plaster is much harder than drywall and you will be forever trying to cut plaster with a drywall saw...rip it out with a hammer...
Depends on the thickness of the plaster. I have seen it over half an inch thick. It is harder than drywall and will dull the saw like fast. So, I would first get a narrow chisel( or large flat bladed screwdriver) and a hammer will do for the removing of the plaster. You may also have wire mesh embedded in that plaster so wire cutters are handy. After that point you are down to the wooden slats. Saw works on wood. But if you are just fixing the plaster, just chip out the old and put in new. You did not really indicate why you had to go so deep. I would have leveled out the plaster, which may mean adding some more...then sand flat, spray the stain with a coat of Kilz(out of a spray can.) Then when dry, repaint the ceiling.
The primary difference between drywall and plaster is the backing. The wood lath backing often used behind plaster can easily be cut by a normal drywall saw. A good knife would almost work.
