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Self-Adhered Crack-Isolation and Sound Control Membranes

DETERIORATION OF MEMBRANE PRIMER ADHESION – When installing a membrane over concrete slabs, it is generally recom mended, and required by some membrane manufacturers to test for pH and moisture vapor transmission through the concrete slab. Moisture that can accumulate beneath a membrane can deteriorate many of the primer products used to adhered mem branes due to the high pH of damp concrete.

Problem

Cause

Cure

Tile installed over membrane is loose, lifted, or has suspect hollow acoustic sounds; when tile is removed, tile remains adhered to membrane, and membrane can be removed easily from the concrete; membrane primer may be soft and wet.

Elevated pH from the excessive moisture in concrete deteriorates membrane primer and adhesive interface of membrane.

Always vapor transmission testing on concrete slabs prior to installation of membrane. Check with membrane manufacturers for specific requirements. Some manufacturers require relative humidity to be <75% when tested according to ASTM F2170, (relative humidity test), or moisture vapor transmission to be below 3lb./1,000 sq. ft./24 hrs. when tested according to ASTM F1869 (calcium chloride test). conduct moisture

SHRINKAGE OF CEMENT MORTARS – Do not use thinset mortar in thickness greater than recommended by thinset product manufacturers or by industry standards (3/32-3/16 in. [2.4-4.8 mm]) thickness to install/level tile over membrane, as increased shrinkage of the thinset mortar may occur, which could exert stress on the membrane and result in loss of membrane adhesion. Large and Heavy Tile (LHT) mortar is typically formulated to control shrinkage when used from 3/16-3/4 in. (4.8-19 mm) thickness, and are acceptable for use over membranes.

Problem

Cause

Cure

Tile installed over membrane is lifted, or has suspect hollow acoustic sounds.

Improper use of cement based mortars; each type of mortar has thickness limitations based on formulation to control shrinkage.

Follow manufacturer and industry standard recommended guidelines for thickness of thinset and large and heavy tile (LHT) mortar. Provide wire reinforcing and control joints in thick-bed mortar installations to control shrinkage when installing tile over a membrane.

FLOWABLE HYDRAULIC CEMENT UNDERLAYMENT (FHU)/SELF-LEVELING UNDERLAYMENT (SLU) – As a general rule, do not install thin, flowable/self-leveling underlayments over membranes; level the substrate before installation of the membrane. Similarly, certain flowable/self-leveling underlayment products may also deteriorate due to sensitivity to moisture accumulation beneath a membrane. Always consult with FHU/SLU product manufacturer on this issue, as some products are not suitable for installation under membranes. FHU/SLU products typically undergo initial expansion and contraction while curing, and could crack or delaminate when installed over a flexible surface with an absorptive fabric scrim.

Problem

Cause

Cure

FHU/SLU product cracks or delaminates from membrane after installation.

Initial expansion and contraction of FHU/ SLU while curing may cause cracking or delamination of FHU/SLU when installed over a flexible membrane; fabric scrim absorbs moisture and shrinks upon drying.

Do not install thin, self-leveling underlayments over membranes; level the substrate before installation of the membrane. Check with product manufacturers, as some special products are available if this application is necessary.

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NTCA Reference Manual | 2024 / 2025

Chapter 4 | Membranes