Roughly 25 years have passed since membranes first gained a meaningful foothold in tile installation. In that time, we’ve gone from the availability of several products to what I’m quite sure would be 50 or more, and that is only counting legitimate products designed specifically for tile installation. There are an untold number of products out there commonly used for various tile membrane purposes that were never designed for that reason.
For instance, Duct Tape is still commonly used as a crack suppression product. Prior to the development of and later testing standardization of tile membranes, many products were used to aid in crack prevention, and chief among them was Duct Tape. Somehow people felt that bonding a tile over a 2-inch strip of tape was going to stop crack transfer through the tile surface. Many continue to think they can straddle a tile over a crack with a strip of a tile membrane. What was Duct Tape originally designed for? Certainly not crack suppression and not taping ducts; it was designed to seal ammunition cases in World War II!
There are three main areas of use for membranes in tile installation -- waterproofing, crack isolation and sound suppression -- all of which are typically bonded. There are additional types of membrane materials and methods not covered under industry standards that may or may not be bonded (depending on product and application) such as uncoupling membranes, cleavage membranes or slip sheets, drainage mats, vapor diffusion membranes and those that allow installation over green concrete. We will focus on two of the more common applications for which standards exist. But first, a word about standards: No standard is perfect. Sometimes, performance areas in a standard are ignored because consensus cannot be reached. On other occasions, standards may contain watered down performance values so a broader range of products will meet the requirements. There is merit to compromise, as high the performance values can make selection both limited and expensive. Without standards, we are left with only lofty claims of somebody’s marketing department. Products meeting standards offer assured performance levels to those who use and specify a product. It’s important to keep in mind standards are created to establish minimum performance criteria for use of a given product. Minimum is a key word. Just because a product meets a standard, that doesn’t mean it’s designed for any and all applications.
Take waterproofing for example. There are many degrees of waterproofing. Does it need to just shed water, like a shingle roof? Shingles might work great on a roof for waterproofing, but they would make a poor swimming pool liner. Some waterproofing products are also designed to shed, not hold. Others are rated interior, but not exterior -- where one would anticipate they would remain wet much longer. Water vapor, such as in a steam shower, isn’t addressed in standards at all, making it a buyer-beware category of use. In crack isolation, are you looking for protection against tile breakage due to continuing shrinkage cracking, or is it your desire to relocate some saw joints? Different load levels, traffic and environmental conditions all affect product selection. While a product may meet standards, it doesn’t mean it’s suitably rated for your specific application. When in doubt, ask. It’s very common to find jobs where the products used weren’t suitable for the application after failure has occurred.
By far, waterproofing is the most critical application of direct-bond membranes. The applicable standard is American National Standard Specifications for Load Bearing, Bonded, Waterproof Membranes for Thin-set Ceramic Tile and Dimension Stone Installation A118.10. Their job is to prevent positive liquid water migration into the substrate and adjoining surfaces. Available in both liquids and sheets, they have a wide range of performance levels. Quite often I hear, “I won’t use XYZ because ABC is half the price and easier to use.” There is a reason most manufacturers make four to six waterproofing products, and it isn’t so they can have just as many price points. Each has its own focus. Selecting the right product requires knowledge of the intended use. Many installers take undue risks utilizing recommendations and installation techniques other than those specifically recommended for a product by the manufacturer because, “I do it this way all the time with XYZ,” even though you chose to purchase ABC because it was less expensive. That’s not the way it works. The substantial differences between products are only revealed when the instructions are read. The biggest issues I see in the field are lack of film thickness and required corner reinforcement.
Lately, some of the installer-created hybrid systems have come on the radar. In these styles, a combination of waterproofing products are used on the same project because one portion of one product is easier than the other and vice versa. When this happens, all I can say is, “Good luck to you. You created the system, so now you’re the one carrying the liability.” My experience tells me that this doesn’t always work out as intended.
These membranes are designed to suppress cracks caused by horizontal in-plane movement of the substrate, not vertical displacement. While crack isolation membranes are intended to minimize the potential for a crack passing from the substrate through to the finished tile or stone installation, they may not always be 100% effective. It’s particularly important when dealing with a cracked substrate to locate and fill expansion joints with a suitable sealant or prefabricated expansion joint for the membrane to perform properly.
Movement joints in the substrate need to be carried through the tile installation. Use of a membrane to relocate control joints is a proprietary function of a membrane product as represented by the manufacturer and not part of any TCA method or ANSI standard. When used for their crack-bridging abilities, most manufacturers require a three-tile wide band of application. A few will allow for a smaller band width by requiring a single tile be fully supported by the membrane. From my perspective, think of shock absorbers. Membranes transfer stress from one area to another. They aren’t storage devices, so soft joints must be used to absorb the energy transfer.
In later articles, we’ll explore the installation of these and sound attenuation membranes in greater depth. The first and foremost decision to be made when using any membrane is proper selection and realistic performance expectations by all affected parties. Creating that thought process is the mission this time. If you have any specific areas of interest, please let us know and we will try to incorporate them into an upcoming issue.