I did what dodgeman said and it worked great. You need to be sure that there are no loose tiles or cracks in the floor that would indicate a problem because this would just transmit to your new floor. The height is the possible bummer but I would much rather have a slightly elevated floor with a nice corian or marble threshold at the door than have to bust out a mud job floor (jackhammer). I used a belt sander and a 5" disk sander (or you can get a rubber pad for your elec. drill) with very aggressimve grit sandpaper, garnet if possible (the reddish stuff) as garnet is the second hardest substance on earth. I basically sanded the shine right of the ceramic tile. I used thinset mortar with latex bonding agent (milk) instead of water to make sure to get a grip.