My buddy and I have gotten into a bit of a dispute on facebook, here's what he asks:
I keep hearing tiling an unlevel floor will result in tiles coming up. This reason makes no sense to me. The only reason a stable but unlevel floor will have tiles come up is if the bond between the cement and floor or tile fails. This failure should have NOTHING to do w/levelness of the floor, correct?
My response goes something like this:
Here's the thing: Unless you use a LOT of paste underneath the tiles (which won't dry out properly so will crack fast) then you will have a potential for a lever situation once the paste that's under an uneven one does dry out (because it will). Then that will cause disruption under the other tiles. Can't you just lay another level of backerboard to try and get things mostly level?
The more the floor is uneven the more you will have to use extra cement, which means it won't dry out at the same time. Here, I'll go ask the pros for you to see what you can do since apparently you don't like my idea of asking them.
Am I on the right track? What can he do to reduce the risk of the tiles coming up if the original floor is uneven?
FWIW: He's refinishing an older townhouse that he purchased in Houston, TX (in case age/location makes a difference)
after feedback from Tester101 (much obliged) the actual problem is a wavy and uneven concrete floor. It's for the living room, so there's not really any real risk of water.