Most of my new/old house has ceramic tile on concrete and there are several places that have ‘hollow’ spots. I am guessing that the previous owner/installer did not use enough thinset in these areas. There is a creaking sound whenever I walk over some of these spots. So I have a couple questions. Short of taking out the tile, is there any preventive measure that I can do to stop the tile from eventually cracking and popping out? The carpet in a bedroom has been removed and I can see the thinset for the tiles in the doorway to the hallway. Two of them sound hollow and I can see that the thinset does not reach the tile. Is there a way to add thinset (or something else) into the grooves of the existing thinset to reinforce the tile? Thanks for any help.

I need help! How do I put down a tiled bathroom floor with a drain off center?