Do I Need A Sub-Floor On Indoor Concrete Slabs?
You may tile directly over indoor concrete slabs.  In some extreme circumstances you
may find it necessary to use a self-leveling cement if the floor isn't flat enough to
provide a smooth enough finish for your satisfaction.  An anti-fracture membrane can
be used for additional reinforcement but is not typically necessary.  The only
preparation required is to clean the floor.  Use a polymer or latex modified thinset
mortar for the best installation.
TM
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