This urethane adhesive is used for crack suppression and waterproofing. The manufacturer recommends fiberglass tape reinforcing at inside corners for waterproofing application.
One area of ceramic tile installation that has been receiving increasing attention from both manufacturers of setting materials and consumers is that of crack isolation and waterproofing. Today's building practices call for faster construction while at the same time wanting higher performance of the end product. Current fears about mold contamination, both founded and unfounded, are also driving increased sales and use of waterproofing products in applications that were not previously considered for such measures, such as complete waterproofing of tub areas, floors and countertop applications. These concerns have both increased the sales of existing products and caused new products to be introduced to the marketplace with others to follow.

Crack isolation and waterproofing systems may be desired when ceramic tiles are specified over problem-prone substrates or waterproofing is desired or required. One of the most important considerations in their use is they are part of an installation system. Waterproofing systems are currently covered under ANSI A108.13, installation of load bearing, bonded, waterproof membranes for thinset ceramic tile and stone. Currently, there is no standard for crack suppression though one is soon to be introduced. In four years of teaching a generic membrane class using 10 different systems, I can assure you of one thing: no two products are alike relative to installation requirements. Though some products may appear to share similar application techniques, all they are is similar.

Roll applied membranes are very easy to use for crack suppression or waterproofing applications. They dry rapidly but if flood testing is required, a 3- to 7-day cure time is recommended depending on the product used.
Adherence to industry standards and manufacturers' instructions is required to achieve proper product performance. Many membranes may be used over both wood and concrete floors. Crack suppression membranes may be especially useful over existing finished flooring that is to be remodeled or rehabilitated. Regardless of the substrate being covered, crack isolation systems can reduce potential damage to ceramic tile on substrates that provide less-than-perfect conditions. Sometimes these same membranes can perform as a waterproof system with slightly different application procedures. Most are sold with a limited warranty, which varies widely by manufacturer. The warranty would be a prudent consideration in the selection and installation of a membrane system. It is absolutely essential that you read the manufacturer's instructions completely before any work begins. Thinbed, load-bearing membranes are high-tech, high-performance materials, but only if they are installed according to specification we will take a look at a few of the many systems available.

Trowel applied membrane systems are typically composed of a liquid and powder and possibly a reinforcing fabric. First, the setting bed is prepared as it would normally be for the direct application of ceramic tile. Most require pretreatment of cracks and/or corners. Application usually consists of keying the material into the substrate with the flat side of the trowel followed by combing the material in a singular direction and another pass with the flat side of the trowel to smooth the surface. There are a few key elements to success using these systems. The notches act as a gauging device in this application. There is a specific film thickness required for this type of system to perform. Typical failure occurs from either engaging the substrate with the trowel, leaving a void, or failure to reinforce the corners. These are the simplest of systems to use but probably one of the most demanding on troweling techniques.

This CPE membrane can be installed with either adhesive or latex modified thinset. Proper application of the manufacturer's bonding sealant to the seams is required for both waterproofing and crack suppression.
Roller applied membranes are a little more user friendly. Their installation instructions vary dependant on desired performance. For crack suppression, typically the cracks must be pretreated. For waterproofing, cracks and inside corners are typically treated. On floors, full field application of fabric is typical in areas requiring waterproofing. A wet coat of the liquid or paste is applied with a paint roller, working a small area at a time. While this application is still wet, the fabric cut for the space is laid over and pressed into the wet paste followed by an additional application. With some systems, full fabric application is not required on walls, only pretreatment of cracks and corners. Trowel applied membrane systems can be extremely versatile, covering setting beds that would otherwise be very difficult to waterproof. If desired, relocation or waterproofing of control joints is not always possible with trowel or roller applied systems. Check with the manufacturer of the specific product you are using if you will be encountering control joints.

Synthetic sheet membranes are made from chlorinated polyethylene, polyvinyl chloride, and other materials, are available in a variety of lengths and widths, and vary in performance from manufacturer to manufacturer. Generally speaking, these membrane systems have polyester or fiberglass netting bonded to each face so they may be attached to subfloors, and tile to the top surface. Bonding on both sides can often be done with latex-portland cement mortar. With some brands, the sheet may be bonded to the subflooring with glue allowing the tile installation to proceed quickly and without worrying about disturbing the bond between the sheet and the subfloor, a major consideration when using thinset mortar to bond the sheet to the floor. However, when using glue to bond the membrane, it is important to know the moisture vapor and alkalinity level of the slab.

Manufacturers have strict guidelines on vapor emission and alkalinity. Using adhesive over a slab that has excessive vapor emission can prove disastrous. Regardless of the bonding material used, the sheet has to be pressed into the surface of the subfloor. With thinset mortar, this is usually done with a 75- or 100-pound sheet vinyl roller. When using organic adhesive (because it is so sticky), the sheet can be smoothed down with the roller or even a flat trowel. Like all other types of membrane, it is essential that the setting bed surface be prepared using the same criteria required for the direct application of tile - if the surface is not smooth and flat enough for tile, it is not smooth and flat enough for a membrane. With this type of membrane, care must be taken to avoid trapping air below the sheet. This can cause air pockets to form that can seriously reduce the compressive strength of any tiles installed directly above the pocket. Particular attention must be given to any overlapping and sealing seams between neighboring sheets when the main objective is to keep the installation waterproof. Seams may be closed with a solvent or sealant, not to be confused with caulk; there IS a difference. Consult with the manufacturer for specific recommendations.

Uncoupling type membranes offer features beyond those of most fully adhered flat membrane systems but require full field application to be effective.
Peel and stick membranes are yet another version of sheet membrane systems. They are usually asphalt based with fabric facing one one side of the sheet, peel and stick membranes offer an alternative to the synthetic sheet membranes. Peel and stick membrane systems require that a primer be applied to a clean, prepared surface so the sheets will adhere properly. Because of their thickness at overlapping seams, peel and stick membrane systems usually require a particular strategy for spreading the tile bonding mortar to avoid the appearance of a "hump" where the tiles pass over a seamed area. A potential drawback for asphalt based peel and stick membranes are that they have a tendency to soften when exposed to direct sunlight. This may be problematic for tiles installed next to a south-facing window or on an exterior application. Make certain that the membrane manufacturer approves your particular application. Solvents also typically affect these types of membranes. If aggressive floor care measures are used or the floor will have chemical exposure, consult with manufacturer prior to application.

The Tile Council of America handbook has this year added the term uncoupling membrane. The definition is a system that separates the finished surface from the substrate to allow independent movement between the two and prevent the transfer of stress to the tiled surface. There are several manufactures of these systems. While a sheet type membrane, they typically have different performance properties than other systems. Among the advantages, the system is they allow for elimination of the control joint relocation required with other systems. Uncoupling membranes also allow for vapor transmission that can have a negative effect on most other systems. They can be used either for crack suppression or waterproofing with an additional seaming fabric. They also may be used as a substrate in lieu of additional underlayment or over green concrete. These systems are installed using a suitable thinset mortar.

These are the current type of systems available there continues to be widespread use of untested products never intended for ceramic tile membrane systems. Uses of roofing felt, sheet vinyl, scribing paper, or scrim reinforced Kraft paper with unknown values, glued or unglued to concrete slabs have a long history of failure. These products typically lack the performance features and criteria that would allow effective control of concrete fractures and wood movement without transmission of cracks through the finished tile surface. They exhibit low bonding strength against the expansion and contraction of both the tile and the substrate. In the case of concrete, they also typically lack ability to be exposed to or are not designed for prolonged moisture exposure common in a bonded application. A while back, I received a call from a national homebuilder that gave some interesting statistics on the effectiveness of their use. Prior to using the glue-down felt method over concrete, they were experiencing a 40 percent failure rate during the warranty period. Use of roofing felt cut the figure down to a 20 percent failure rate. They found this risk to be acceptable, as the subcontractor was always judged liable and provided free repairs or replacement. There are many fully warranted and industry approved membranes that probably would cut the product failure rate down to 0 percent. Due to minor cost differences, this builder was not interested as he had a ready source to assume liability during the warranty period, the tile contractor. After the warranty period that liability would pass to the consumer.

It is worth noting that except in the case of gross error, installation or otherwise, ceramic tile floor systems must usually pass through several years of seasonal changes for such failures to take place. This is due to minimal seasonal or thermally induced movement of the installation relative to the force required to produce failure. Installations that have "tented," that is, risen from the floor surface, also typically have no movement accommodation joints at the perimeter as recommended by all tile, membrane, and installation material manufacturers and contained in industry guidelines. These products and methods continued to be widely used. The initial financial savings realized by using such methods and untested products often results in a huge replacement cost to the unsuspecting end user at a later date. Always use industry recognized and approved products and methods for any type of membrane application.

Diagnosing the substrate and selecting the proper membrane system requires some good familiarity with not only the substrate but also the performance requirements of the installation. All membrane systems require solid support and with few exceptions recommend an L/360 deflection rating. They all require adequate surface preparation otherwise their performance characteristics may be greatly diminished. In the case of crack suppression, the contractor must make an estimation of the nature of the crack: is it active and moving or dormant and stable? Is it caused by a structural failure? Is there a problem with the structural or subfloor materials? Can the crack(s) be expected to continue advancing into the slab? If the installation is over wood construction, what structural members (or lack of) are causing or contributing to potential damage of the tile and installation system? If the substrate deteriorates because of a structural problem, it is highly unlikely that any crack isolation or waterproofing system could protect tiles or substrate installed over such a surface. On the other hand, if the problem is rooted in the substrate materials, crack isolation systems may help to reduce potential damage. If there are no cracks in the structure surrounding the crack in the subfloor, if the surface height of the substrate on either side of the crack is the same, and if the crack width does not exceed manufacturers' requirements, thinbed crack isolation systems can be effective at reducing tile damage and in the case of waterproofing, protect the substrate. Too many flaws might be an indication that the entire substrate is in poor condition and that additional cracks may appear as time goes on rendering attempts at crack suppression and waterproofing ineffective. Proper assessment of the substrate is critical to the success of the installation and requires good knowledge of substrate materials.

Another important consideration in all crack suppression and waterproofing membranes is provision for movement accommodation. In the application of crack isolation systems, most allow only relocation of control joints, not elimination as commonly done. Manufacturers provide very specific instructions on how these joint are to be treated. In the case of a true expansion joint, the joining of two structures such as in a room or building addition, none allow for expansion joint relocation. This can be of even larger concern if the application also requires waterproofing and should play an important part in the selection process. Use of any membrane does not change the requirement of all manufacturers to provide for movement in the tile installation as outlined in the TCA Handbook under EJ 171 or the American National Standards. Providing protection against substrate movement is not possible unless the substrate has some place to move. Following the recommendations of the manufacturer and adherence to industry guidelines will result in a profitable installation for you and achieve the performance your customer expects.