Crack Isolation Membrane
Sometimes concrete slabs or poured gypsum underlayments can develop small cracks because of seasonal movement. These cracks can “telegraph” up through the floor tile and show up as cracks in the grout or tile.
To prevent this you should install a crack isolation membrane (sometimes called an “anti-fracture membrane”).
An isolation membrane is a thin, slightly flexible layer between the underlayment and the tile. The tile sort of “floats” on this layer. If there is horizontal movement in the underlayment, the membrane stretches a little to absorb the movement – not the tile.
We’ve used two types of isolation membrane. One is a thin layer of a rubbery fabric that we glue to the surface of the concrete.
The other is a gooey material that we roll out like very thick paint. Once the isolation membrane has dried, you install the floor tiles right over the top of with thinset mortar.
Electric floor warming kits have become very popular. For the most part these are easily installed by a do-it-yourselfer. But check carefully with your building department. These mats require some electrical work and there may be regulations or restrictions on how much work can be done by a homeowner and when a licensed electrician has to be involved.