I do not think tiling a shower floor is as easy as just directly tiling ontop of the original concrete floor...from my understanding, above the wood subfloor...should be mortar, then some sort of PVC membrane, another layer of mortar, and then the actual floor tiles...water inevitably seeps through the grout lines in a tiled shower floor and will run through the mortar, collect in the membrane, and then be directed to the drain hole where the excess moisture is allowed to run off via small weep holes...it is actually a very elaborate installation that takes a bit of skill...

My best guess from what you are saying is that you do not have the proper installation underneath your new tile floor to deal with the excess moisture that runs underneath the tiles...

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