We had a professional contractor remodel our home 5 years a go. At the time, we had a sunken living room which the contractor filled with concrete in order to bring it to the same level as the rest of the house. We had ceramic tile laid on top of the concrete. Over the years, the grout line has separated where the original concrete meets the new concrete. I have removed the cracked grout line but am not sure what to do to prevent any new grout from cracking in the future. Someone suggested mixing cement grout with caulk. The grout lines are only 1/8". Thanks for your help.