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Types of Membranes

PURPOSE : This document is intended to identify and define the different membranes that can be associated or incorporated into a ceramic tile installation. CLEAVAGE MEMBRANES A cleavage membrane is a thin layer of material within a tile assembly that is loose laid (floating) or mechanically attached but not bonded. Cleavage membranes are incorporated below the mortar setting bed in a thick-bed tile installation when the backing or substrate surface can be damaged by water, is not continuous, is cracked, or is dimensionally unstable. The cleavage membrane separates the backing surface from the mortar setting bed and tile, allowing the mortar setting bed to be unbonded and free floating, and thereby not subject to the instability of the backing surface, preventing reflective cracking. When a cleavage membrane is incorporated, the setting bed is required to be reinforced with lath or wire, see ANSI A108.1A. Cleavage membranes are always materials that are moisture resistant. Cleavage membranes do not necessarily form an impermeable membrane that will hold water, but are intended to provide other materials some protection from moisture and vapor. Typical cleavage membranes include roofing felt, reinforced asphalt paper, asphalt laminated paper, polyethylene sheeting, chlorinated polyethylene (CPE) sheeting, polyvinyl chloride (PVC) membrane, or high-solids, cold-liquid applied membrane. ANSI A108.M-2.8.1. provides the specific requirements for these various materials. Some of these same materials can be used as a vapor retarder membrane. See Vapor Retarder Membranes. CRACK-ISOLATION MEMBRANES Crack-isolation membranes (sometimes marketed as anti fracture membranes) for thin-set ceramic tile and dimension stone installations act to isolate the tile or stone from minor, in-plane substrate cracking meet ANSI A118.12. These membranes may be bonded to a variety of substrates approved by the manufacturer. The contractor should check with the manufacturer to determine the limitations of crack movement the specific material will tolerate. There are two basic types of crack-isolation membranes: sheet applied and liquid applied. Sheet Applied Membranes are usually provided in rolls consisting of a flexible material with some amount of elasticity that allows the material to elongate while remaining adhered to the substrate. Some of these membranes have integral reinforcing fabrics to enhance the tensile strength of the material as well as provide a better bonding surface for thin-set mortars.

Liquid Applied Membranes may be single or multi component membranes applied in a liquid form using a trowel, roller, or sprayer. These membranes cure into a continuous crack isolation membrane, which allows direct bonding of ceramic tile, usually with latex Portland cement mortar. Some liquid applied membranes require embedding a fabric into the membrane to increase tensile strength. The TCNA Handbook addresses Crack-Isolation Membranes in Methods F125-Partial and F125-Full. F125-Partial is for specifying application of a Crack-Isolation Membrane over existing in plane cracks when the material is applied only in the vicinity of the existing cracks. F125-Full is for specifying the Crack Isolation Membrane to be applied throughout the installation to protect against existing cracks as well as future in-plane cracking that may develop. WATERPROOF MEMBRANES Waterproof membranes for thin-set ceramic tile and dimension stone installations function as barriers to positive liquid water migration meet ANSI A118.10. Among these are sheet applied membranes and liquid applied membranes, which can be bonded to a variety of manufacturer approved substrates. Sheet Applied Membranes are usually provided in rolls consisting of a waterproof, flexible material that is to be adhered to the substrate. Some of these sheet applied membranes have integral reinforcing fabrics to enhance the tensile strength of the material as well as provide a better bonding surface for thin set mortars. Liquid Applied Membranes may be single or multi component membranes applied in a liquid form using a trowel, roller, or sprayer. These membranes cure into a continuous waterproof membrane, which allows direct bonding of ceramic tile, usually with latex Portland cement mortar. Some liquid applied membranes require embedding a fabric into the membrane to increase tensile strength. LOW PERM WATERPROOF MEMBRANES Low perm waterproof membranes are membranes meeting ANSI A118.10 and have water vapor permeance values of 0.5 perm or less, determined per ASTM E96, Procedure E (desiccant method at 90°F) and 90% relative humidity. Manufacturers should be consulted when water vapor is of special concern, for example in steam rooms, because not all waterproof membranes are effective at retarding vapor transmission. Not all waterproof membranes meeting ANSI A118.10 are low perm waterproof membranes.

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NTCA Reference Manual | 2024 / 2025

Chapter 4 | Membranes