I had someone try and unfortunately I wasn't there when he did it. He told me he mixed spackle and plaster but after a day or 2 it was cracking all over the place and after 3 or 4 days it was still wet, I could stick my finger into it, in some places over an inch deep. I guess this guy had no idea what he was doing so I figure I'd try it myself. How do I go about doing this? Do I mix plaster with spackle, and if so how much? Or do I have to fill the holes with sheetrock or something for the spackle to grab. Thanks for your help.