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What is Post-Tensioned Concrete and Can I Install Tile Over it?
QUESTION
I was told that my concrete slab is a post-tensioned concrete slab. What does that mean and can I install tile over it?ANSWER
Post-Tensioning is a method of compressing the concrete with high-strength steel tendons and end plates installed prior to pouring the concrete that counteracts the natural tensile forces created by subsequent loading of people and equipment. The stress is applied with hydraulic jacks after the concrete has hardened. Post-tensioned slabs generally have less deflection, less cracking, and in theory are more stable than traditional concrete with rebar if installed correctly.Generally speaking, the two recommended methods for installing tile over post-tensioned concrete is TCNA F111 Non-Bonded Mortar Bed application over a cleavage membrane for ceramic tile or natural stone installations for On-Ground or Above-Ground Concrete applications. Or TCNA F113 method over an ANSI A118.12 Crack Isolation membrane only for ceramic tile installations for On-Ground or Above-Ground Concrete applications.
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Question: My bathroom contractor built our new shower pan with 1/4 of it on the existing floor tile, 1/4 of it on the thinset that was left after removing one row of floor tile, and 1/2 of it directly on the slab. This doesn’t make any sense to me. This creates a length wise slope in the curb towards the shower wall. Is this going to cause any long term problems or violate any building codes or industry standards? We can’t find anything remotely like this in any of the standards documents you have referred to such as ANSI or TCNA. Thank you very much for your reply.
It is an odd configuration. You have to rely on the original tile to be structurally sound and adequately attached. If the original residual thinset mortar was tenaciously attached to the slab then it would be ok to bond over it.
There is no industry standard or manufacturer of installation products who would recommend this installation configuration. In theory, bonding over the tile has a greater chance to be problematic, but if it is stable and the tile was properly and adequately bonded to those surfaces, and you don’t get any extreme temperature fluctuations or and seismic movement, it could possibly perform satisfactory. There are not guarantees other than what the installer will offer.