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Unread 10-16-2019, 07:01 PM   #3145
cx
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If you actually want crack isolation, DG, in your proposed scenario, you put down a cleavage membrane (your RedGard might arguably suffice if you just gotta use some, but unnecessarily expensive and not as effective) and an un-bonded, reinforced mud bed of a minimum 1 1/4" thickness with welded wire mesh in the vertical center. Probably the very best possible treatment if you have any questions about your slab. It's also the mud bed of choice where the size of the tile installation area exceeds 100 square feet, the technical size limit for bonded mud beds.

If you want to do the thinner bonded mud bed, though, you gotta bond it. You could, I suppose, add your RedGard to the top of the mud bed as a crack isolation membrane if you want.

As for your slab being "uneven," the technical requirement for either type of mud bed is that the concrete substrate be flat withing 1/4" in ten feet. That requirement is also disregarded on a regular basis.

Floor mud beds have been used for many decades in many variations over many and varied substrates in many and varied conditions and shapes. The currently accepted methods are published in the TCNA Handbook - F111 and F112 being the two pertinent to your SOG installation - and you can refer to those and then deviate to your heart's content. But if you want to have industry backing in the event of a problem, those are the methods you probably want to follow.
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