You can either use cement backerboard or a waterproof underlayment membrane.
Ceramic tile isolation membrane on wood subfloor.
In addition they provide a stable substrate for tile installation on oily asphalt or extremely smooth surfaces for which adhesion is a problem.
Uncoupling membranes are primarily designed for use over concrete slabs and subfloors especially ones with defects such as depressions or high moisture levels.
Firstly what i consider a crack isolation membrane is one that has and a118 10 rating.
An uncoupling membrane disconnects tile from its concrete subfloor and prevents cracking in the slab from being transmitted upward to the tile job.
If the tile is being installed in a bathroom consider applying an isolation membrane over your wood subfloor to further protect against expansion and contraction.
Ditra allows for ceramic tile application over single layer plywood or osb subfloors on joists spaced up to 19 2 488 mm o c.
If your subfloor is plywood you will need to lay down something as plywood will expand and contract causing your tiles to crack and or pop loose.
Most tile membranes are also designed to provide waterproofing if installed according to specifications.
You can either roll on a liquid latex membrane or use a peel and stick crack prevention mat over the entire concrete subfloor.
A 3 4 inch plywood subfloor on a joist structure with 24 inch spacing needs the extra thickness of cementboard or the floor will flex and the tiles will crack.
In fact i know that some are.
This type of cracking can be easily avoided in the tile layer either by installing the tile on a mortar bed set over a cleavage membrane method f111 for example or by installing the tile over a crack isolation membrane using a thinset method.
Uncoupling membranes aren t recommended for tiles smaller than 2 inches square and should not be used when covering old hardwood flooring due to adhesion problems.
Tcna does still show a single layer t g subfloor with an uncoupling membrane f148 but i don t know anyone in the tile.
The membrane would be much easier for you to work with as it is thin lightweight and flexible and easy to cut.
So just because a membrane is an upcoupling membrane doesn t mean that it isn t a crack isolation membrane.
Uncoupling tile has been successfully installed for thousands of years by incorporating an uncoupling layer or forgiving shear interface within the tile assembly.
If installing over an appropriate wood surface sand the wood to make it smoother and remember that the installation will work better over a subfloor at least 1 1 8 inches thick.
To prevent that movement from creating cracks in your grout and tile install a crack prevention membrane after the concrete subfloor is clean flat and free of cracks larger than 1 8 inch.
