Millions of square feet of sheet-applied crack isolation membrane are successfully installed every year under natural stone and ceramic tile. Yet there are an increasing number of membrane failures occurring. It is important to address this problem because cheaply made products are giving quality crack isolation membranes an undeserved reputation. Why is this happening? There are a couple of factors that typically contribute to membrane failures, including adhesion (or rather, a lack of adhesion) and deterioration/emulsification, or lack of primer between the membrane and substrate.

Fabric separation

One of the main reasons some sheet applied (peel and stick) membranes fail is due to fabric separation. Some laminated sheet membranes have a low tensile strength and separate from the elastomer (rubber/asphalt) base. You can easily check this by trying to separate the fabric from the rubber, if it separates, do not use it; it can be very expensive to repair.

Professional-grade sheet membranes generally use the extrusion method of manufacturing. This process creates a semi-encapsulating, high-strength bond between the fabric and elastomer. The fabric material can range from natural to higher-performing synthetics. One system utilizes non-woven polyester fabric laminated to both sides of the membrane. Either way, make sure the fabric layer does not separate from the membrane.

Primer failure

Some membrane systems use water-based latex primers that can re-emulsify. Adhesion with the substrate is then compromised—especially if there is water vapor present from the concrete floor. This causes the adhesion to break down and a possible failure of the finished floor.

Careful consideration of a membrane system should be studied prior to installation, including the performance data, the manufacturers’ recommendations for a suitable substrate and condition of the substrate.

Membrane primers are essential and developed to a high strength, non-emulsifying formulation. The primer should be formulated to rapidly cure in place and provide a surface that permanently bonds with the adhesive base of the membrane. Once applied to the substrate, the primer cures in approximately 20-30 minutes and forms a permanent bond to the floor with applied pressure.

Following are some considerations when choosing a crack isolation membrane.

  1. Demand Performance Data. Long-term installation success depends on the ability of the crack isolation membrane system to meet all 10 of the A118.12 standard’s tests for crack isolation membranes. The two most critical are shear strength after accelerated aging and long-term water emersion. Poor performance or failure of these two tests indicates the membrane will not provide the adhesion necessary for a natural stone or other hard surface flooring installation. Insist on seeing results from all 10 performance tests.
  2. Follow Installation Instructions. A successful installation begins by reading and following the installation instructions developed by the manufacturer. There are important variations between installation procedures that can lead to failure if not properly handled. For a porous substrate or when a patching or leveling compound is used, some manufacturers call for an additional treatment of the slab before the primer is applied. These products can be very absorptive and may need to be sealed before applying the membrane’s primer. Existing cracks or control joints may need to be addressed prior to primer application as well.
  3. Note Manufacturer Cautions and Conditions. A crack isolation membrane may not be the answer for all types of flooring situations. A substrate with vertical sheer or an uneven floor may not benefit from the use of a crack isolation membrane. It is important to know and understand the suitable substrates for the membrane application. What product limitations and expectations can be anticipated when using a particular membrane?
  4. Perform a Bond Test. A bond test may be the only way to know if a membrane system will bond securely to a substrate. A bond test is merely a small installation of membrane over a surface in order to determine if sufficient bonding can be achieved. It is performed by priming a small section of the worst part of the floor and placing a 1’ x 1’ section of membrane according to the membrane manufacturer’s instructions. After a 24-hour cure, check membrane adhesion to the substrate.
    Make a cut in the center of the sample with a knife and peel it back. Transfer of the rubberized compound should be evident and the membrane should be difficult to remove. If it is removed easily without evidence of transfer, do not proceed with the installation. Call the manufacturer for corrective action.
  5. Use Quality Setting Materials. It is crucial that the proper setting material be applied for successful hard surface flooring installations. Large format tiles installed via the thin-bed method require a medium-bed mortar meeting ANSI A118.4. The use of a 1/2” by 1/2” U-notch or square-notched trowel is usually recommended for applying the medium-bed mortar. Most national brand medium-bed mortar companies use a larger aggregate in the matrix, which creates a stiffer, stronger mass under the large-format tiles or stone.
    DO NOT use a standard A118.4 latex mortar not designed for large-format tiles, as they have a smaller aggregate and may retain too much water contributing to the warpage and failure of the tile. Some green marbles and absorbent clay tiles will require special setting materials like an epoxy mortar or a rapid-set mortar specifically designed for natural stone.

Crack isolation membrane systems serve an important purpose and when installed correctly, can provide a lifetime of protection for a flooring investment. Careful consideration of a membrane system should be studied prior to installation, including the performance data, the manufacturers’ recommendations for a suitable substrate and condition of the substrate.

Reading and following the manufacturers’ installation instructions, the performance of a bond test, and the use of a quality setting material appropriate for the hard surface flooring being installed should also be observed. Following these guidelines can go a long way towards ensuring the successful installation and long-lasting beauty of the hard surface finished floor.

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