I have a 1910 craftsman home, which all of the original horsehair plaster. There is an area of the living room where the wall is cracked and at the base of the crack, the finish coat is seperating and falling off (I can see that the cracking continues through the base plaster). I intend to use Big Wally's plaster magic to reattach the plaster to the lathe, but once this area is secured, how should I patch the missing finish coat? Will joint compound work over the horsehair? Should I use plaster of paris? I appears that this spot has been patched before.