Both sheet- and liquid-applied anti-fracture membranes play a critical role in protecting tile and stone installations against cracks moving from the substrate into the tile. This month, Floor Covering Installer talks to the experts to learn more about anti-fracture membranes and find out what’s new in the category.

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Sheet vs. Liquid

Whether sheet-applied or liquid-applied, anti-fracture membranes are used to separate stresses and movement in the substrate—or mitigate stresses that have already caused movement and cracking in tile and stone installations.

“In either case, the membrane is designed to act as a buffer layer between the substrate and the floor above it,” explained Dan Marvin, director of technical services for MAPEI. “If cracks develop in the substrate, the crack is stopped at the flexible membrane, instead of telegraphing up through the floor.”

“The relief of stresses incurred by deflection, crack movement, thermal expansion or contraction or moisture expansion occurs in one of two ways,” explained Mark Albonetti, installation and technical specialist for M-D Pro’s Prova brand. “Some sheet-applied systems incorporate air cavities into the membrane. These air cavities remain empty as the material is bonded to the substrate on the bottom and the ceramic tile setting material is applied to the surface of the membrane. These air cavities absorb the differential movement between the substrate and the ceramic tile and setting material. Prova-Flex is an example of this type of membrane.”

With several sheet and liquid anti-fracture membrane options on the market, knowing exactly when and how to use both types of membrane is important to a successful installation.

“Sheet membranes are usually a fabric-reinforced bituminous formulation with a rubberized adhesive layer that requires either a latex- or epoxy based-primer for interior or exterior applications,” said Jay Conrod, Laticrete product manager.

Typically applied over a primer, sheet membranes are ideal for larger applications like shopping malls and airports. With no drying time required, sheet membranes allow installers to quickly and easily cover expansive areas and begin installation immediately after application.

“The primer is applied to a clean, dry substrate and will set-up to a tacky state in about 20-30 minutes,” noted Dave Hanna, NAC Products’ marketing manager. “Once it is tacky, the sheet membrane may then be applied. Tile or other hard surface flooring may be installed immediately after the membrane has been applied to the substrate.”

Coming in rolls of a flexible material with elasticity, sheet-applied membranes have the ability to stretch and elongate while remaining bonded to the substrate, stated James Roberts, ceramic industry specialist for M-D Pro. “This ability to stretch and elongate makes it useful over wider substrate cracks, and one of sheet’s biggest advantages is its ability to offer up to 3/8-inch crack isolation.”

While both sheet and liquid anti-fracture membranes provide waterproofing properties, some sheet membranes also offer vapor barrier properties.

“One of the main advantages of a sheet-applied membrane is that it is applied after the substrate is installed and all penetrations can be waterproofed,” noted Albonetti.

However, liquid-applied membranes—which are commonly made from a latex rubber base—are easily applied and ideal for use in housing developments, office buildings, multi-family construction and commercial installations.

“Liquid-applied membranes are a single- or multi-component membrane which are trowel-, roller- or even spray-applied,” said Roberts. “Some liquid-applied crack isolation membranes are even used as the setting material for the tile or stone.”

Typically requiring more than one coat, the drying time of liquid-applied products can be anywhere from 30 minutes to hours between coats. According to Conrod, drying time depends on a variety of factors including but not limited to substrate conditions and temperature, air temperature, and relative humidity.

“Where the difference comes into play is usually applicator preference or application requirements,” said Conrod. “If only a crack isolation product is specified, then it may come down to price.”

What Installers Need to Know

Whether working with sheet or liquid, the most important application step occurs before opening the bucket or box, commented Marvin. “Read the technical data sheet. Every product has a suitable range of temperatures and moisture levels over which they can be installed. The technical data sheet will spell out the steps required for a problem-free installation.”

Installers may assume that all membranes are installed the same way. A common mistake when installing sheet products is not paying attention to the primer instructions and the timeframe allowed prior to installing the actual membrane, said Conrod. Liquid-applied products can be more sensitive to drying conditions between coats and after the final coat, prior to the topping application.

“The manufacturer’s recommendation for installation temperature ranges should be strictly adhered to for both installation, transportation and storage of all products,” stressed Conrod. “The manufacturer should also recommend moisture vapor emission limits and/or hydrostatic pressure requirements that could negatively impact the performance of anti-fracture products. If the substrates are not structurally sound, clean and free of dirt, oil, grease, paint, laitance, efflorescence, concrete sealers or curing compounds, these products will exhibit adhesive failure, requiring costly mitigation and repairs further down the road.”

Manufacturers also noted that cutting corners when applying both liquid- and sheet-applied membranes to save money or time can end up a costly mistake in the long run.

“When applying fabric membranes [installers] may spread too little mortar, using an undersized or worn out trowel,” said Duane Farley, national account manager and technical specialist, Canada, for M-D Pro. “They may also spread too much of an area. Both of these scenarios can cause the mortar to skin over, causing poor adhesion and possible failure.”

Farley added, “When applying liquid membranes they may put it on too thin or too thick. Too thick will take a very long time to dry/cure and if too thin the membrane will be weak in both the anti-fracture and waterproofing. They also may not give a second coat to ensure proper coverage and performance.”

Marvin added, “Neither of these [types of membranes] is suitable for out-of-plane cracks. When one side of a crack is higher than the other, it points to structural issues in the substrate. Putting a flat, stretchy layer on top will not fix the problem. Also remember that crack isolation membranes shouldn’t be used to cover up movement joints. These joints should be honored up through the tile to prevent cracking.”

From hands-on training sessions to helpful written material and online demonstration videos, manufacturers say they are doing their part to make sure installers know how to properly use their liquid and sheet anti-fracture membranes. They also recommend installers seek information from industry organizations such as the National Tile Contractors Association, and using resources like the Tile Council of North America‘s (TCNA) Handbook for Ceramic, Glass and Stone Tile Installation.

“Our industry is constantly changing and the installation material manufacturers are improving products and their applications, but there are a few that have been dependably used for crack isolation installations and will be for the foreseeable future,” added Conrod.

What’s New on the Market?

Manufacturers are constantly unveiling advancements in both sheet and liquid applied membrane technologies.

“NAC revolutionized the way decorative floors were installed with the inception of the first self-adhering Elastomeric Crack Bridging anti-fracture membrane, ECB,” said Hanna. “ECB and ECB 75 sheet membranes are bitumen-based products designed for use over surfaces that require crack isolation/anti-fracture protection.”

According to Conrod, typically the crack isolation products on the market today will offer a dual purpose, such as waterproofing and crack isolation, or sound control and crack isolation--and some will perform all three.

“Some of the more current popular products that also have crack isolation properties are uncoupling membranes, such as Laticrete Strata_Mat, or a specialized product that acts as a thin-set, crack isolation and sound control product all-in-one, like Laticrete 125 Sound & Crack Adhesive,” he said.