I have a problem with my slab. I bought the house and found that they had replaced the piping overhead because the pipe leaked in the slab. When I repaired the slab to keep it from pushing up, I chisled out about 3" on each side, then used concrete to repair it. It is starting to lift again, cracking the slab, and I need to solve this so that I can tile the floor with ceramic tile. How can I prevent this from happening again? Should I have used plastic cement to repair this or is there another product that is better? ANY HELP WOULD BE GREATLY APPRECIATED! Thanks.