With that, let’s start on product and performance expectations for crack suppression membranes. To allow for addressing the meatier issues in some depth we should start with the simple statement “if it sounds too good to be true, it is.” That saves me a lot of typing and the magazine valuable space in explaining the obvious. Membranes are not supporting structures nor will allowing for a half inch of movement be either a true statement or of any value to you in the installation. In selecting the right products, you need to make a realistic assessment of the intended use of the floor and include consideration of the maintenance chemicals and procedures. An elevator lobby for a condominium project has very different performance needs from the powder room in the penthouse suite. Likewise a shopping mall is much different than the dentist office vestibule. It is entirely possible that one product could be used in both applications, however, I would stop short of saying it’s likely.
Crack suppression membranes are often highly deformable can offer great elasticity and the ability to resist great amounts of movement. These same features may also mean it has 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 to change the light bulbs. The type of substrate should also be included as a consideration. Is it dry concrete or does the slab have possibly poor site drainage or other problems such as an excessive water ratio in the 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 may be very different than OSB over a crawl space. A membrane used on OSB over a crawl space can be as nearly 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 use of the floor and limitations of the product prior to the installation. Some of this may sound to a few like it is not in the realm of the installer’s responsibility. If you are the knowledgeable flooring professional who was hired to do the job, it is your responsibility to know the benefits and limitations of your trade products.
Membrane placement in the flooring sandwich is another consideration. In the testing process, a thin layer of setting material in 1/8” thickness with 100% coverage is used in establishing the performance values of the membrane product. Yet often we see a bonded crack suppression membrane under a mortar bed or ¾” or more of medium bed mortar. The crack suppression abilities of a membrane are very limited when placed anywhere other than immediately under the tile. The further away from the tile interface the less likely they are to provide you with the crack suppression abilities you seek. To get the best performance out of a membrane system they need to be located as close to the tile surface as possible. Any prep work such as floor fill or correcting out-of-level conditions should occur prior to the placement of the membrane.
Without exception, the one item most often consistently 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 are designed to control where cracking will occur. That the joints will crack at some point in time is relatively certain. In the case of random 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. For floors with lengths greater than 25’ total, movement joints need to be placed in the field of installation. In such installations perimeter joints alone will not provide the necessary movement accommodation. Crack suppression membranes, by design, dissipate energy; they 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. No joint, no stress removal, and cracked grout or loose tiles are not out of the realm of possibilities.
The above is a brief description of what we who look at failed jobs see consistently when jobs go bad. We also hear a fair amount of “I’ve been doing it this way for years and never had a problem.” Nobody is saying that each and every time you don’t take the appropriate measures to ensure a successful installation, a failure will occur. The reality is only a small percentage of jobs where proper installation practices have not been followed will fail. These failures may be near term, after a few years, or long term, 15-20 years. In most instances, either the home has been sold or the building remodeled, and who installed the floor will be long forgotten. But, many will fail and if you are fortunate enough to still be around you may find yourself unfortunate enough to be fixing problems that remained masked for many years. You would be surprised at how long you can be held accountable for your actions; it certainly is longer than the one year most think, depending on the state you live in. Why take a chance on failures? Follow the instructions and put it in right the first time.