What is an isolation membrane? Should I use one?
An isolation membrane is one made for the specific purpose of isolating ceramic or stone tile from movement in the structure on which it is installed. It can come in a couple of different forms — trowel applied or sheet membrane. Either one is good, but the preference is usually for the sheet membranes, because of their greater tolerances for movement. To use an isolation membrane just as a general rule, it’s not necessary. If you have any question at all as to whether or not there would be too much movement in your subfloor without it, then yes, it should be used, whether it be over concrete or wood frame. NOTE — isolation membranes will greatly decrease the chance of your tile cracking if your movement is lateral (side to side– in the case of concrete cracks, ones that open and close). However, there’s not a membrane made that will address the problem of vertical movement. If you have cracks in a slab where one side of the crack is higher than the other, or in wood frame, where an
