I am attempting to fix a cracking tile floor in my Master Bath floor - the 12"x12" tile was laid about 18 months ago, using cement-fiber backer board over plywood. The joists are 24" o/c, engineered 2x4 construction.

Soon after installation, the grout started to crack, and recently, one of the corners of a tile is showing some deflection relative to it's neighbors. I don't want this to propagate to the tiles under the vanity, and have to take that out, so I would like to fix it soonest.

I believe that if I just dig out the tiles and re-set, they will eventually crack again; I'm assuming that the sub-floor will need to be reinforced by entering the ceiling from below before doing this. Are there any other suggestions out there for doing this in a less intrusive fashion? I'm aiming for "good enough" here - I don't want to do a shoddy job, but I don't want to pull up the whole floor and relay it myself just to make it perfect.

Thanks ... 0064Jake