DuckMuck is correct, Kerry. You must have some sort of membrane between the thin-set mortar and the concrete floor. Grout remains fairly porous even after sealing, particularly in a shower setting. I've had great success - twice - using a paint-on, very rubbery coating whose name escapes me. I got it at either HD or Lowes - I suspect they still carry it. It came in a gallon size paint-type can. A fairly bright pink in color. I put two or three extra heavy coats and never had any problems. Much simpler solution than the thick, heavy, floppy, pain-in-the-arse rubber membrane. Good luck! nk

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