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Q.Are the new trowel-applied membranes used for waterproofing showers as good as sheet membranes? Are some better than others?

A.Contributing editor Michael Byrne, a tile setter and consultant in Los Olivos, Calif., responds: I started using sheet-membrane materials in the early 1970s and was an early adopter when NobleSeal TS came on the market. Today, I still use TS, but I use liquid — or trowel-applied — membranes as well. And by the way, liquid-applied membranes are not exactly new — their use by first-century Roman tile installers is well documented.

Since I tend to upgrade from the tile industry’s minimum standards, I generally use liquid systems designed for continuous immersion — rather than value-engineered materials that offer only limited water-shedding protection. When I have a choice, I prefer to use Bonsal’s B-6000 and its companion reinforcing fabric for waterproofing. I also use Custom’s 9240 system. These materials have an important property in common: When properly applied and cured, they will not re-emulsify if exposed to moisture.

Do liquid-applied systems work as well as sheet membranes? It depends. The most critical factor — aside from the tested performance and suitability of a particular product — is how carefully the system was installed. In my consulting work, I have seen many examples of mediocre systems that have provided long service because the installer followed all the rules, and in some cases applied a third or fourth layer of liquid instead of the minimum one or two. I have also inspected installations where top-of-the line CPE sheet materials failed because the installer did not follow the manufacturer’s directions. And I’ve inspected liquid systems that were applied properly but nevertheless failed because the system was not rated for the application.

With so many different waterproofing and crack-isolation membrane systems to choose from, a designer or installer needs to have a firm understanding of an installation’s intended use and select the most appropriate level of protection. While some of the components may appear similar, performance levels of all tile membrane systems are definitely not the same. All brands have unique application and installation requirements and limitations, and they all have unique viscosities: Some are thin enough to shoot with an airless sprayer, some are gels that can be spread with a brush or roller or notched trowel, while others are site-mixed pastes so thick and viscous they can only be spread with a notched trowel.

Regardless of which membrane I choose, I always try to use thinset and grout from the same manufacturer. Because I install tile in many different applications, I’ve learned the skills required to install any type of waterproofing system. Equally important, I insist on treating surface prep and the installation of waterproofing, crack isolation, and sound reduction membranes as costs separate from that of tile installation.