I tore up the old tiles which were on a wooden underlayment. I installed Wonderboard and screwed the hell out of it. Then installed all the tiles using thinset. Waited 24 hours then grouted. Well a week went by and 2 tiles would make a noise when you walked on them. After removing the 2 tiles I noticed that the thinset didn't harden. These 2 tiles are not next to each other and are in the middle of the floor. I cleaned up the areas and applied thinset to 2 new tiles and installed them. Well it's been 12 hours later and one of the tiles seems to be ok but the other still seems loose.
Can't figure out why 2 tiles in different areas are acting up. If worse comes to worse I'll cut out the wonderboard under the tiles and install 2 new pieces and try again. No one used this bathroom for almost week after the tiles were set. All tiles, wonderboard, thinset, grout were in the house for a week before the work was started.
Email me with any recommendations, Thanks