There are a lot of terms used when it comes to purchasing crack protection for tile floors, and confusion seems to occur when the various terms are mentioned. I have even seen it digress into heated arguments about the merits of one over the other. So what really is the difference between the three commonly used products?
Under the National Tile Contractors Association glossary the following is listed: Crack Isolation - Prevention of transfer of cracks from the substrate through the tile or stone when substrate is subjected to horizontal movement of cracks. However, for Anti-Fracture and Crack Suppression, the definitions simply read “See crack isolation.” So why the difference in terms? Since the development of thin-set mortar, the tile industry has struggled with the problem of cracking and reflective cracking in direct bond tile and marble. Reflective cracking is caused by the transference of movement from the substrate directly through to the bonded tile. Among the causes are tiling over a concrete control joint, unforeseen cracks developing in the concrete, and movement or seasonally induced moisture movement of wood panels to which the tile may be adhered.
The damage can result in expensive repairs and finger pointing, which harm the reputations of installers and manufacturers alike. The problem became more acute in the 1970s and ‘80s as tile products grew in size, and with availability shifting from 1/2” thick 6” by 6” quarry tiles or mosaics installed over floating mortar beds to larger and thinner tile formats directly bonded to various substrates. There were many field engineering attempts to solve the problem of cracking in direct bond applications, ranging from duct tape or fiberglass mesh over cracks to utilizing the back of linoleum sheet goods to cover the whole floor.
Manufacturers took note and began seriously working on a solution. Once several industry stalwarts had developed successful products, they sought to develop a standard for direct bond membranes possessing movement capabilities. As others joined the fray and after a number of contentious meetings for many years, the accepted term for these products was defined as crack isolation.
This was followed by publication of a standard in 2005, ANSI A 118.12 American National Standard Specifications for Crack Isolation Membranes for Thinset Ceramic Tile and Dimension Stone Installations. Some manufacturers felt their products posed capabilities accommodating greater movement than that under standards, and chose to call their products anti-fracture while others chose to use the term crack suppression.
Regardless of the terminology used, the standard is based on crack isolation. There are no quantifiable ASTM tests that demonstrate any additional properties in membranes other than those contained in the A118.12 standard for crack isolation.
Let’s now look at the product and performance expectations for crack isolation membranes. Some manufacturers make wild and unsupported claims of performance. To allow for addressing the meatier issues of membrane use in some depth we should start with the simple statement, “If it sounds too good to be true, it probably is.”
Membranes do not add to the support of the tile, nor are they intended to mask structural deficiencies. In selecting the right products, you need to make a realistic assessment of the intended use of the floor. An elevator lobby at street level for a condominium project has very different performance needs from the powder room in the penthouse suite. Likewise, a shopping mall is much different from the office vestibule. It is entirely possible that one product could be used in both applications; however; I would stop short of saying it is likely.
Crack isolation membranes are often highly deformable, can offer great elasticity and the ability to resist a certain degree of movement. These same features may also mean a relatively low resistance to compression such as a fully loaded hand truck, or in some not so unusual instances for commercial applications, a pallet jack or scissors lift used to change the light bulbs.
The type of substrate and in-service conditions are an important consideration in the selection process. Is it dry concrete or does the slab have possibly poor site drainage or other problems such as an excessive water ratio in the concrete mix, causing high vapor emission? It may be lightweight gypsum and a sealer needs to be applied. In wood structures, plywood over a finished basement is very different than OSB over a crawl space. A membrane used on OSB over a crawl space can be nearly as problematic as an installation over damp concrete in areas of high moisture or rainfall when the crawl space is not properly ventilated.
You should always know the conditions and use of the floor as well as limitations of the product prior to the installation. As a knowledgeable flooring professional, it is your responsibility to know the benefits and limitations of products you specify to be installed.
Another consideration: What is the size and type of material to be installed over the membrane? I bristle a little when somebody categorically says, “Our product is fine for tile and stone.” As we know, there are many types of tile. However, only quarry tile is used for testing the crack bridging abilities of a membrane under standards. Quarry tile is very deformable and may not be representative of a ceramic or porcelain tile.
Stone is very intolerant of any movement without an accompanying fracture. Every vein in stone is a crack waiting to happen. If your project is of any size and involves the installation of thin tile or stone flooring over a membrane, it would be very prudent to ask whether the manufacturer has any crack suppression data related to the particular type of tile or stone you are using. While not a frequent occurrence, it is not unheard of for a membrane to be too compressive and thin stone or tile too inflexible for use over certain types of membranes, especially in commercial applications.
Without exception, the one item most often missing in membrane installations is the lack of any movement joints or failure to carry control joints through to the next closest grout joint. Crack suppression membranes do not eliminate the need for movement accommodation joints. On the contrary, if membranes are to perform their task, they need a place to move to.
Control joints and/or movement joints are designed to control where the movement will occur. That the control joints in concrete will crack at some point in time is relatively certain; these joints must be carried through the surface of the tile installation per manufacturer instructions.
In the case of random concrete slab cracks, the energy of the cracking is stored in the membrane for transit to a predetermined location. That location would be the movement accommodation joints in the field and/or expansion joints at the perimeter of the installation. When the total area of the floor is greater than 25’ in length, movement joints need to be placed in the field of installation. When exposed to sun or high moisture conditions, including high levels of ground water, they need to be placed even closer. Under either condition, perimeter joints alone will not provide the necessary movement accommodation.
Crack suppression membranes, by design, dissipate energy. They also store it for transit just like a truck hauling a load. Once the energy of the movement arrives at its destination (the movement accommodation joint), it unloads and is ready for another trip. It is entirely futile to use a crack isolation membrane without accommodating the anticipated movement.