Protective Membrane Systems
It is entirely possible for a tile installation to last for the life of the building, provided that the installation is properly specified, installed and maintained. When a wet area or flexible structure calls for ceramic or stone tiles, a protective membrane system should be part of the installation.
There are three types of thin-bed membrane systems: waterproofing, crack-isolation, and sound reduction. The three types offer two methods of application: a manufactured sheet requiring an adhesive for installation, and liquid-applied membranes that are site-built with a liquid or paste and reinforcing fabric. They are all designed for application between the tiles and their setting bed, and some do double- or even triple-duty. For example, the Noble Co. makes a membrane system for sound reduction that also acts as both a crack-isolation and waterproofing membrane.
Sheet-membrane systems are composed of a core, made of plastic, asphalt, or other materials, bonded to one or more layers of fabric reinforcing.
Crack-isolation membranes may be applied in one of two ways: full-coverage or bandage. Full-coverage membranes cover an entire floor or wall surface, while bandage systems cover only the area immediately surrounding a crack. Cracks in a structure are always accompanied by movement. Crack-isolation membrane systems remove the tiles from direct contact with a shrinking or expanding setting bed, resulting in fewer cracked tiles.
With full-coverage applications, all the tiles in an installation are protected. Therefore, movement is concentrated where the membrane ends, e.g. at the perimeter of a floor. With bandage systems, since only a small segment of the tiles are isolated from the setting bed, movement is concentrated in the soft joints immediately surrounding the cracked or affected area. The drawback of the bandage method is that, as the setting bed continues to move, tile joints in the affected area may in turn continue to widen or narrow beyond what is acceptable. Excessive movement toward or away from the hard perimeter of most full-coverage installations, however, can be resolved with relative ease. To avoid contact between the tiles and a hard perimeter, the excess tile can be trimmed with a dry-cutting diamond blade. Where a crack is developing along the perimeter, a thicker baseboard molding can be added to mask the appearance of movement.
Waterproofing membranes are installed using the same methods and techniques for installing crack isolation systems, except more care must be given to minimize the overlapping of sheets or reinforcing in the design phase, and in reducing leaks during the installation. Waterproofing membranes need to flex and yield to normal structural movement without disintegrating. Manufactured sheet systems contain an integral reinforcing fabric, while liquid-applied systems rely on reinforcing fabric installed on-site, where it is embedded in liquid or paste. Where specified (or where common sense dictates), the membrane reinforcing must be continuous at upturns, or at other changes in direction. Without a reinforcing fabric, cracks are likely to occur when movement tugs at the membrane.
Some applications, such as bathtub shower walls or bathroom floors, need a membrane system that only has to shed water or hold a small amount of standing water. Another type of waterproofing membrane, commonly referred to as a shower pan, must be able to contain and hold water and channel it to a drainpipe. Shower pans are usually found at the base of a shower stall, but with a few slight variations, they can also used as waterproof liners for tiled sunken tubs, pools, and fountains. Shower pans are usually associated with mortar-bed installations, but special drains now permit thin-bed membranes to be used for some shower pan applications.
While some compromises can be made on interior applications, exterior tile applications subject to water exposure require a sloping substrate (a crowned walkway or a sloping deck), a drainage layer, and a membrane rated for exterior use. The installation needs to have positive drainage so rain or snowmelt runs off the tile surface quickly. This can be done with a system of drainpipes, or by simply allowing excess water to run off the surface away from the structure.
Sound-reduction membranes, when designed and installed properly, reduce sound in two ways: By isolating tiles from direct contact with the substrate, and by blocking airways through which sound waves can travel. In some ways, they are installed like waterproofing membranes; the membrane must be continuous, so lapping up or around when there is a change in direction is a common installation feature. For example, when installed on a floor, a typical sound-reduction membrane installation specification calls for an upturn of a specific height wherever the floor meets a wall surface.
Use the right materials. There are numerous membrane systems that have been tested specifically for use on thin-bed tile applications. When reasonably specified and installed according to manufacturer’s instructions, most give dependable service. Problems arise, however, when light-duty systems are specified for heavy-duty applications, or when the installer fails to accurately follow label directions (this is one of the leading causes of tile installation failure). Problems may also develop if inappropriate or untested materials are used as waterproofing. For example, some installers may apply one or more coats of a “waterproofing liquid,” such as a Thompson’s WaterSeal, thinking that it will stop the transmission of water or moisture through backerboards, plywood, or other substrate material. Unfortunately, such materials only protect the treated material, doing nothing to stop water penetration through the structure.
Scribing felt, tar paper, and other types of construction papers, glued to a substrate with mastic, are sometimes used as crack-isolation membranes under thin-set mortar and tile. The idea may have developed from the tile showroom practice of setting display tiles on an easily removable surface. Nevertheless, the materials have proven to be ineffective for thin-bed crack isolation applications, and not a single thin-set mortar manufacturer recommends their use.
Rather than use untested or unapproved materials or methods that place responsibility for liability in the hands of the installer, use membrane systems made specifically for use on tile installations. Membrane application requires some education, training, and attention to detail, but the basic skills should be familiar to most floor covering professionals, and the rewards of profit are there for the contractor who knows how to do it right.