Manufacturer Roundtable: Crack Isolation and Uncoupling Membranes
For this month’s manufacturer roundtable, we wanted to find out more about crack isolation and uncoupling membranes. The reason for these products is clear—to keep cracks in the substrate from transferring into the tile—but what is the difference between them, and where does the term “anti-fracture” fit in? We also asked our panel of experts to weigh in on considerations to keep in mind while working with the products.
Participants are: Annika Oeing, Ardex’s marketing communications manager; Jay Conrod, Laticrete senior product manager; Karen Dhanota, marketing and communications specialist for M-D Pro; Dan Marvin, MAPEI’s director of technical services; Brian Petit, vice president of operations for NAC Products; Richard Hung, marketing communication manager for Parex/Merkrete; Tim Abbott, CEO of Proflex Products; Sean Gerolimatos, director of research and development for Schluter Systems; David Stowell, Schonox/HPS North America’s technical director; and Alan Kin, technical sales manager for Texrite.
Q: What are the differences between anti-fracture, crack isolation and uncoupling membranes?
Marvin: “There are really no ‘anti-fracture’ membranes; this is a misnomer. No membrane installed behind tile can completely protect against fracturing of the tile. Force from above such as heavy rolling loads, impacts and lateral stress from lack of movement joints can still cause tile to fracture.
“Crack isolation membranes are designed to keep cracks that originate in the substrate from propagating up through the tile and grout. They do this by being ‘stretchy’ and dissipating the force from the crack into the membrane instead of allowing it to move up into the installation.
“Uncoupling membranes serve a similar role but do it in a different way. Instead of being made of stretchy materials, typically they have two layers that are adhered together. The bottom layer is attached to the substrate and the top layer is adhered to the tile. This allows the two layers to ‘uncouple’ from each other when force is applied from below, and the whole installation acts as more of a floating floor than a rigidly bonded installation.
“There is a great deal of overlap between these products but they both have strengths and weaknesses. For a concrete slab where cracks have either already started or are likely to begin, a crack isolation product is sufficient. All this product has to do is protect the tile from the cracks.
“Uncoupling membranes typically replace a layer of the substrate (for instance, a thicker cement backer-board) so you will often find them in wood-frame construction where finished floor height is a concern. They are also often used where floor deflection may be a concern, such as in elevator cabs or access flooring. It’s important to follow the directions for the products you select.”
Conrod: “Typically, crack isolation and anti-fracture membranes are terms that can be interchangeable. However, the ceramic tile and stone industry uses the term ‘crack isolation’ as the proper term to address these membrane types. These products are designed to isolate tile and stone finishes from minor, in-plane substrate cracking. These membranes can also have additional characteristics such as waterproofing and sound reduction properties. They can take the form of liquid-applied systems, sheet goods and trowel-applied systems.
“Uncoupling membranes are typically plastic membrane systems geometrically configured to provide air space between the tile and substrate to allow independent movement between the two and limit the transfer of stresses. These membrane types can also have additional features, including a mechanism to receive floor warming cables, as well as waterproofing and sound control.
“In some cases (mainly in residential applications), the membrane types can be interchangeable. However, the features of certain membranes might be better suited for a specific application due to service ratings, compatibility with other installation materials and the overall project requirements/specification. Consult the membrane manufacturer for specific information on this matter.”
Hung: “Crack isolation membranes are available in two types. The first type is liquid-applied. It is described as a thin section, load-bearing, monolithic membrane that inhibits the transfer of new or existing cracks from the substrate to your tile installation. This type of membrane is single-component and can be applied with a flat trowel, roller or brush.
“Being that these membranes are in a liquid state when applied, they will conform to any form or irregular shape. The science behind liquid membranes is to allow the absorption of energy into the membrane, thus not allowing the crack to transfer through to your tile installation. This type of crack isolation does not raise the tile height, allowing for seamless transitions.
“The second type of crack isolation membrane is a sheet membrane. These membranes come in rolls of varying widths. They are made of chlorinated polyethylene (CPE) with a polyester fabric laminated on both sides. Unlike the liquid membrane, sheet goods are usually bonded to the substrate with a thin-set mortar and rely on a crack’s movement to ‘slip’ underneath the sheet good and not allow the crack to transfer through to your installation. This type of crack isolation does not raise the tile height either.
“Uncoupling mats are installed with a thin-set mortar between the substrate and mat. These types of products are sold in rolls and are generally 3/16 in. thick, which will add height to your installation. Currently, there are no ANSI or ISO standards for uncoupling mats.
“All of these products will work over most common substrates including concrete, OSB and plywood. When it comes to substituting one product for another, the biggest difference between these types of products is the height added. Liquid and sheet membranes will not add height, but uncoupling mats will.”
Abbott: “Anti-fracture and crack isolation membranes are basically the same and can come in different types, such as peel-and-stick , liquid-applied and glue-down. Even some adhesives and thin-sets offer crack isolation. They are designed to keep movement from 1/16 to 3/8 in. from transferring through the assembly and cracking the tile, grout or both. One thing to keep in mind is that the crack isolation only covers horizontal movement and never vertical.
“The idea behind an uncoupling membrane is that it can absorb the movement of a subfloor before it results in loose or cracked tiles. The bottom line is that anti-fracture, crack isolation and uncoupling membranes are all trying to accomplish the same thing by preventing any cracking from the substrate to transfer through the tile assembly and cause a failure.
“The typical crack is caused by settling of the concrete or shrinkage, and when a saw cut is placed in the slab to try and control where the concrete will crack. Membranes may be placed over these types of cracks but if you have a cold joint—where an existing slab meets up with a new slab—that joint must transfer through the tile assembly.”
Petit: “One of the differences between crack isolation and uncoupling membranes is that a crack isolation membrane that meets the ANSI A118.12 method can flex with the substrate. With expansion and contraction in a substrate, the crack isolation membrane will remain bonded to the substrate and move in-plane with the expansion and contraction. It is designed to be the weak link in the system, taking the stress off of the hard surface flooring and preventing cracks in the flooring. An uncoupling membrane does not flex with the movement in the substrate; it uncouples or ‘breaks’ from the substrate.
“Crack isolation membranes are typically installed by applying primer to the substrate, then peeling and sticking the membrane. You can then immediately start setting your hard surface flooring. Uncoupling membranes are installed using thin-set mortar, which must cure before flooring installation.”
Kin: “Crack isolation membranes are thin layered materials, either liquid-applied, available in pressure-sensitive rolls or as sheet products which are laminated or adhered to the surface with tile mortar. These membranes can be used for both partial and full coverage. An uncoupling membrane can only be used for full coverage.”
Oeing: “Anti-fracture and crack isolation are often synonymous with one another. Crack isolation refers to isolating an existing crack to make sure it doesn’t transfer through the tile. Anti-fracture refers to trying to prevent cracks from transmitting through the tile. The same material is used in both products; the reasoning behind the application often leads to how it’s named.
“Uncoupling membranes isolate the tile from the substrate, effectively neutralizing movement stresses between the substrate and tile, and thus eliminating a major cause of cracked tile.
“If a job calls for an anti-fracture product, a product with the name crack isolation can be used and will aid in preventing cracks from transmitting through the tile. As the old industry adage goes, there are two types of concrete: ‘concrete that has cracked and concrete that has yet to crack.’”
Dhanota: “Crack isolation and uncoupling membranes are similar; however, uncoupling membranes are typically a thicker product. If a job calls for a crack isolation product, an uncoupling product can be substituted. However, you cannot use an uncoupling product for partial coverage.”
Q: What should installers know before working these types of products?
Kin: “The installer should be mindful about whether the installation will use partial or full coverage, then decide which available products best suits the installation. All membranes allow for full surface coverage; partial coverage may not be applicable for uncoupling membranes.
“For partial coverage, be mindful to properly extend the membrane over the crack by three tiles wide per the manufacturer’s directions. This three-tiles-wide rule should be understood and bid appropriately for the increase in labor and materials, especially when dealing with large-format tiles. In some situations, due to the abundance of minor cracks appearing on the jobsite, it may be more cost-effective to coat the entire area and gain full crack suppression.
“Additionally, make sure to understand proper liquid-applied thicknesses, don’t apply a pressure-sensitive product onto peaks or divots, use the proper mortar for laminated membranes and ensure you have the product in the correct orientation when using uncoupling membranes.
“Large cracks of 1/8 in. or greater and/or cracks that show an uneven rise or ledging, bending or folding will not be protected by any of the treatments already mentioned. The structural surface condition should be addressed with the builder and it should not be expected that any of the systems will hold or prevent tilework from this type of movement.”
Gerolimatos: “If a membrane is specified for use over cracks in a concrete slab using the partial coverage method, as called out in Method F125-Partial from the TCNA Handbook, the appropriate choice would be a crack isolation membrane. If a membrane is specified for use over a single-layer plywood subfloor, as per Method F148 from the TCNA Handbook, the appropriate choice would be an uncoupling membrane. There will be other examples that fall in a gray area where one or both types of membrane may be suitable. All parties (contractor, architect, owner, etc.) should agree upon the course of action that fits their needs and expectations.”
Conrod: “Before working with crack isolation and uncoupling membranes, installers need to determine the type of application needed, the type of tile or stone to be used, and whether or not the project may require any waterproofing properties, as these factors will affect which specific products can be used.
“For a quick turnaround, sheet membranes are preferred. With trowel-applied products, contractors can often save on labor costs as they can often apply crack isolation and a thin-set in one application.”
Abbott: “Some important things to know are the limitations of the crack suppression system, the proper mortar to use, TCNA EJ171 placement for movement joints and leaving room around the perimeter for expansion and contraction, and the size of the tile being installed.”
Marvin: “Both liquid-applied and sheet-applied membranes should show that they comply with ANSI A118.12, the standard for crack isolation. This standard requires that the membrane can keep a crack of at least 1/16 in. in width from propagating from the substrate into the tile layer.”
Hung: “As always, it is recommended that you follow manufacturer recommendations for installation substrate requirements. Know that when going over approved wood substrates, these products will not strengthen or add integrity to the floor. Deflection values must be met prior to installation. For installations over concrete, check with the manufacturer for information regarding approved substrate types and what is required when slab moisture is present.”
Petit: “Be familiar with the Tile Council of North America (TCNA) Handbook, which contains a significant number of installation methods that demonstrate the proper installation guidelines for both crack isolation and uncoupling membranes.”
Dhanota: “The substrate must be clean, flat, dry and structurally sound. If there are any expansion or control joints, they must be honored all the way through the system.”
Q: What is your latest product in the category?
Stowell: “The Schonox iFIX [rollable adhesive] system with Schonox AB [uncoupling membrane] acts as a waterproof, crack isolation membrane for cracks up to a width of 3/16 in. When installed as a crack isolation membrane on floors and after a drying time of approx. 16 hours, Schonox APF [fiber-reinforced self-leveler] may be installed directly over Schonox AB without the need to prime.
“Schonox HA [rollable sealing membrane] also acts as a crack isolation membrane without waterproofing requirements. The membrane is applied in a one-coat application at the required thickness. Apply a thickness of 1/16 in. to isolate cracks up to 2mm; apply a coat of 1/32 in. to isolate cracks up to 1mm. After complete drying of approx. 16 hours, Schonox APF or Schonox AP [self-leveler] may be installed over the crack isolation membrane without the need for priming.”
Marvin: “Liquid-applied membranes such as MAPEI’s Mapelastic CI are typically easy to install and can isolate up to 1/8 in. cracks. Sheet-applied membranes like our Mapeguard 2 require a primer before installation, but can be tiled immediately after they are installed. These types of membranes are often found in high-volume locations such as shopping malls. Mapeguard 2 has been tested to withstand in-plane cracks up to 3/8 in. wide.
“Uncoupling/underlayment membranes such as MAPEI’s Mapeguard UM need to be rolled into the mortar below with a heavy roller, then the ‘cups’ should be filled with mortar as the top is troweled. While there are differences in opinion about the type of mortar to use with uncoupling membranes, MAPEI’s testing has shown that our polymer-modified mortars work very well with our membranes, as well as those of our competitors.”
Conrod: “Strata_Mat is a next-generation, high-performance uncoupling mat for use under ceramic tile and stone installations in both residential and commercial applications. The unique patent-pending design of Strata_Mat provides for an enhanced mechanical bond and faster drying of the mortar, allowing shorter time to grout. Strata_Mat can be used with both modified and unmodified mortars.”
Petit: “ECB Classic has been an industry leader in crack isolation since its introduction 35 years ago. The ability to immediately walk on the ECB membrane once it is installed and be open to traffic, especially in mall applications, sets it apart. ECB Classic offers protection up to 3/8 in. of structural movement, along with resistance to moisture vapor transmission.”
Dhanota: “Prova Flex-Heat is a multifunctional, 6mm thick membrane that features exclusive Vapor Management and Shear Stress Control systems to provide anti-fracture and uncoupling properties.”
Hung: “Hydro Guard SP-1 is a fast-drying, liquid-applied, waterproof and crack isolation membrane composed of modified elastomeric copolymers. With excellent elongation, adhesion and high-strength properties, Hydro Guard SP-1 provides a 100% waterproof membrane that limits the transfer of substrate cracks to the finished ceramic or stone tile surface. It also exceeds ANSI A118.10 and A118.12.”
Abbott: “The newest addition to the Proflex line is UCM. This uncoupling membrane features specially formulated, patented fill, which addresses projects that require waterproofing, sound control and crack isolation. Proflex UCM can be installed using non-modifed thin-set or Proflex HMA multi-function waterproofing adhesive. It can be used over pre-existing flooring and almost any substrate, as well as for any job requiring a shower pan, exterior drainage mat or waterproofing membrane.”