I am painting some rooms in my mom's house. There are crack that need repair. The worst are in ceiling. One runs down the center of the ceiling. I took off the loose plaster. It is not joint compound but very hard plaster. The seam between the gypsum or whatever they used in the ceiling is almost like concrete filled with about 1/2 inch gap with something like concrete.The plaster is so hard that I think it will mess up more if I take more off. Almost all of it is not wide enough to use tape and joint compound. I was thinking of using Quik -rete instead and keep wet troweling until it dries. Do people think this would work?
Plastering is a system.Base,scratch,finish. With that being said the first thing you would have to do is reattach the edges of the crack back to the lath. If you do not do this the crack will just come back.It is loose plaster. I have used this system http://www.plastermagic.com/faq.php
I saw it on a DIY program and gave it a try.It worked like a dream. Good Luck.