Cleavage Membrane

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What is a cleavage membrane or slip sheet?

These terms are synonymous and refer to the sheet used between the mortar bed and the substrate. This sheet prevents the mortar bed from bonding to the substrate and allows it to “slip” if there should be movement in the substrate.

What is the difference in a mortar bed and cleavage membrane installation and a thinset installation using an anti-fracture membrane?

In the mortar bed installation, the mortar bed is not bonded to the concrete – rather it is isolated from cracks in the concrete by the cleavage membrane. This allows the tile to “float” over the concrete.

In the thinset installation, a crack isolation/anti-fracture membrane is bonded to the concrete. Tile is bonded (with thinset) to the surface of the membrane. The internal make-up of this membrane is such that movement in the concrete is not directly transferred to the tile. The membrane compensates where needed to prevent or reduce force transference. These membranes are either trowel applied or sheet applied. In many cases, multiple components or steps are part of the system. Performance also varies. It is important to check with the crack isolation manufacturer regarding their installation instructions and intended use.

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