An Anti Fracture Membrane protects tiles from cracking due to the horizontal movement in the substrate (base floor). The membrane will allow the substrate to move independently from the tiled surface. The membrane bridges any movement in the substrate therefore not allowing that movement to transfer to the tiled surface resulting in a cracked surface. Even though the membrane is secured to the substrate and the tile is adhered to the membrane, the membrane stretches where needed preventing or reducing stress transference eliminating cracks to occur in your floor.
There are many different forms of anti fracture membrane available. One of the most effective is the anti fracture membrane made of a multi weaved fabric reinforced with a plastic netting. This type of membrane is purchased on a roll which is approximately 36 inches wide. In installation the membrane is applied using a modified thinset that is notched trowelled to the substrate surface. The fabric is then applied to the thinset and smoothed with a trowel working from the middle out. This will eliminate air pockets between the fabric and thinset and insure maximum adhesion of the membrane.
Crack isolation membrane is used synonymously with anti fracture membrane. The material and procedure is the same as the antifracture membrane but crack isolation addresses existing cracks in the substrate. Some companies provide smaller width rolls of fabric in their kits that are used for crack isolation when installing a crack isolation membrane; the fabric should overlap the crack at least three inches in each direction. Use crack isolation membrane and only addressing existing cracks in your subfloor may be a cost effective measure at the time but it does not insure future cracks from developing in you subfloor that may eventually transfer to your tiled surface.
Cleavage membranes are usually some form of fabric that is installed over the subfloor. This membrane is not adhered to the subfloor but is allowed to move independently. Many tile contractors have used 15 lb. felt paper for years and continue to use is as a cleavage membrane. When used in areas of high moisture such as a shower area, entry or basement, the fabric only membrane will deteriorate over time. To overcome this problem a mortar base is installed over the membrane and wire is embedded into the mortar for added strength.
Waterproof Membrane is a water proof material used primarily in showers and spas. Waterproof membranes are now widely used as a shower pan (instead of a copper pan). The waterproof membrane is a rubberized material approximately 40 mm thickness and sold on a roll. The membrane is approximately 36 inches wide and come with available corners. Adhesive can be purchased to mend pieces together. Caulk also is available for the areas that need to be water tight like around the shower drain. Some companies sell a two part system. This involves applying a liquid first to the substrate and then embedding a reinforced fabric into the liquid. A finish coat of liquid using a brush or roller is applied in the end to insure a waterproof area.
Wherever your floor is located it is an essential that some type of anti fracture membrane is applied to your sub floor before adding the tile. It is an extra step in the tile installation but will prevent cracks in the future.