This reply is probably a bit too late however I just came across the post... As far as the crack in the ceiling (or walls) with any lath and plaster, you don't have to worry about any special "plaster mixtures" once used in the good 'ol days. Modern day drywall compound will work just fine, and this is how I managed to fix many cracks in my new/old...(1)Widen the crack with a flat head screw driver,not too much though, just as wide as the screwdriver head itself. (2)Fill with drywall compound (poly filla drywall compound will work, or any other premixed compund) (3) cover crack with drywall PAPER TAPE, not the drywall mesh tape. (4) re-apply the drywall compound with a putty knife and allow to dry for 24-48 hours. Keep the room temp. between 60-75 degrees celcius. Good Luck.