A cleavage membrane lets the mortar bed slip
Cleavage membrane and slip sheet are two names for the sheet placed between a mortar bed and the substrate. The Tile Council FAQ says the sheet keeps the bed from bonding, so the bed can slip if the substrate moves.
How that differs from a bonded membrane
In the mortar-bed assembly the bed is isolated from cracks in the concrete and the tile floats over them. In a thinset assembly the crack-isolation membrane is bonded to the concrete and the tile is bonded to the membrane with thinset. The membrane's makeup keeps slab movement from transferring directly. Those membranes are troweled or sheeted, often in more than one step, and performance is not uniform.
Read the system, not the nickname
The FAQ tells the reader to check the membrane maker for instructions and intended use. A slip sheet under a mortar bed and a bonded anti-fracture layer are not interchangeable names for one detail.
Source
Fetched 2026-10-11 from Tile Council cleavage membrane FAQ. The sentences above follow that page. They are not a contractor promise.
Related notes
- Tile notes index
- A crack-isolation membrane stretches; it does not replace movement joints
- A mortar bed is a packed layer, bonded or floating
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