An isolation membrane is used when ceramic tile is going to be laid over where there is a hairline crack in the floor that will be under the tiles.
If there are hairline cracks in the floor under the tiles, they could result in the horizontal movement of the floor along the cracks. There could also be movement from expansion joints, cold joints, or any other type of joints. The isolation membrane forms a barrier between these and the tiles.
Purpose of Isolation Membrane
The aim of the isolation membrane is to ensure that problems in the floor don’t transmit themselves to the tiles when they’re put down. Failure to do so could cause the grout to crack, and possibly cracking in the tiles themselves.
Once the isolation membrane has been put on the floor surface, the tile is installed on top of it in the normal way. Be aware than in many cases an isolation membrane will also offer other kinds of protection for the tile floor that will go over it. As ceramic tile becomes thinner and more prone to reacting to cracks in the floor below it, the isolation membrane will become more and more important.