The proper underlayment can fill the need correctly
A successful tile installation is contingent on its foundation, which means it is crucial to determine the condition of the subfloor and substrate and what appropriate underlayment is required
For a beautiful and long-lasting tile installation, every facet of the job needs to be completed properly according to tile industry standards and best practices. The key element here is the foundation of the installation.
Determining the feasibility of each installation is dictated by the subfloor or the substrate. Can tile be bonded to the substrate? Is it flat enough? Are there low spots that need to be addressed? Does it need to also be level? Does it need to slope to a drain or perimeter edge? Whatever the answer, the surface may need significant attention before any tile is applied.
When these questions are answered, the prep work begins. In order to correct these issues, there are a myriad of products that solve specific issues. Knowing which ones work appropriately can be critical to the success or failure of the project. Given the ever-changing and fast-paced appearance of new product introductions, the market requires the tile installer or tile contractor to stay abreast of these new technologies.
Backer board, as a category, has been around since the late 1970s. The development and mass production of this product revolutionized the tile industry by providing a tile-ready surface in the form of a sheet or panel for floors, walls and ceilings. Some of the products in this category fall under an American National Standard Institute (ANSI) designation while others hold an American Society of Testing Materials (ASTM) label. These products are grouped in the Tile Council of North America (TCNA) Handbook as “Backer Board.”
- Cement backer board was the first product in this grouping. It was originally known as concrete backer units or CBU, a designation still maintained in the ANSI document, which dominated the market for a number of years. Interior installation specifications are housed in ANSI A108.11, while the material specifications are found in ANSI A118.9 or ASTM C1325. Cement backer board products can also be installed on exterior applications as found in the Handbook detail W202E, where the “E” represents exterior. It is the only backer board rated for exterior use.
- Coated Glass Mat Water-Resistant Gypsum Backer Board, as its name designates, conforms to ASTM C1178 and is used in wet or dry areas on floors, walls and ceilings over wood or metal wall studs or over wood subfloors.
- Glass Mat Water-Resistant Gypsum Backer Board conforms to ASTM C1658 for use on walls and ceilings in dry areas over wood or metal studs and ceiling framing.
- Fiber-Cement Backer Board is a dispersed fiber-reinforced cement backer board designed for use on floors, walls and ceiling in wet or dry areas and is applied over wood or metal wall studs and wood subfloors. General interior installation specifications are found in ASTM C1288.
- Fiber-Reinforced Water-Resistant Gypsum Backer Board conforms to ASTM C1278 and is used on floors, walls and ceilings in dry or wet areas over wood or metal wall studs and wood subfloors.
- Cementitious Coated Extruded Foam Backer Board conforms to ASTM C578 and ASTM D4068 and is used on floors, walls and ceilings in dry or wet areas over wood or metal wall studs or wood subfloors.
As a general rule on floor applications, backer boards require a supporting layer of thinset mortar or other product, as directed by the manufacturer. Fastening the board and seam treatment should strictly follow the manufacturer’s recommendations. Failure to do so can void the manufacturer’s warranty.
Floor underlayment preparation materials
In order to obtain a floor or wall surface that is flat enough to receive tile, provisions need to be made to correct the surface irregularities. For tiles with all edges shorter than 15 inches, the maximum allowable variation of the substrate is 1/4 inch in 10 feet from the required plane, with no more than a 1/16-inch variation in 12 inches. However, for tile installations which include large-format tile, those with one edge at least 15 inches in length or longer, the maximum allowable variation is 1/8 inch in 10 feet from the required plane, with no more than a 1/16-inch variation in 24 inches when measured from the high points of the surface. In order to meet or exceed these requirements, normally a troweled-on patch or Self-Leveling Underlayment (SLU) is used.
Floor patch materials come from a variety of manufacturers and are used to obtain the required plane for tile installations. Most of these products are latex-modified and require mixing with potable water. Some non-latex powders are jobsite mixed with latex liquid provided by the same manufacturer. These patch products are designed to tenaciously bond to the properly prepared surface and fill low areas, also known as bird baths, as well as flatten out high spots. This entire exercise is the best way to “fix the floor or wall.”
A SLU is designed to flatten or possibly level a floor surface prior to installing tile. The floor surface must be properly prepared and primed with the manufacturer’s recommended product and allowed to dry.
Three critical factors in a SLU project are accurately measuring the water for the mix, using a mixer that maintains the proper speed and mixing for the recommended time. Too little water can impede the flow of the mixture, while too much water can cause the aggregate to sink to the bottom — separating from the other components, yielding a weak and powdery surface. If the speed of the mixer is too slow and/or not for the correct amount of time, the product will not be properly combined and may not function as specified. Additionally, have enough help to mix, move, pour and smooth the product within the allotted time.
Once poured onto the floor, the SLU should be moved into place with a gauge rake having adjustable legs to control the product thickness. When completed, a surface smoothing tool is moved across the surface to break surface tension and flatten the SLU. Allow the recommended dry time depending on the environmental conditions before installing tile.
Many architectural plans and specifications require the floor to be level. This is especially true for highly specialized medical and technical equipment that require a perfectly level floor. In this case, the application of the SLU requires more diligence and attention to detail. When completed, the bubble of a spirit level or transit must indicate a truly level surface — or not.
Unfortunately, some not-so-well-trained or poorly informed tile placers (not tile mechanics or installers) have the mistaken idea that whatever is in the back of the truck or left over from the last job is appropriate to patch the low or high spots. This is entirely wrong. The use of thinset or even the newly designated large and heavy tile (LHT) mortars are not designed to repair these surface irregularities. Consumers should be wary of contractors who say that underlayment products are not needed and add unnecessary cost to the project. Watch out for this one; a recipe for failure from the beginning. The least expensive price for the job may be the most expensive in the long run.
Waterproof membranes, conforming to ANSI A118.10, are available in sheet and liquid forms being usable with both vertical and horizontal thin bed and thick bed installations of tile. Some of these products have integral reinforcing fabrics for tensile strength and minor crack-bridging properties.
Crack isolation membranes
Crack isolation membranes, conforming to ANSI A118.12, for thin-bed ceramic, glass and stone installations act to isolate the tile form minor in-plane substrate cracking. These products must be load-bearing and bonded to the substrate in order to function properly. In some cases, the trowel-applied products can be used as the adhesive for the tile. Other products within the scope of this category are allowed to cure or are applied as sheet goods and are then used as the substrate for the tile.
An uncoupling membrane is a plastic membrane system geometrically configured to provide air space between the tile and the substrate to allow independent movement between the two and limit the transfer of stresses. These membranes are not characterized by ANSI or ISO standards, but must achieve 50 psi or greater shear bond strength in seven days per the test method in ANSI A118.12 Section 5.1.3. Consult the manufacturer’s written literature for specific installation details.
Bonded sound reduction membranes
Bonded sound reduction membranes, conforming to ANSI A118.13, are intended to reduce the floor-to-floor impact insulation class (IIC) sound. These membranes may be trowel applied, sheet or composite materials that are bonded to a suitable substrate so that tile can be bonded directly to the membrane.
The interesting thing about the products described here is they may need to be used in conjunction with each other in order to provide a suitable surface for a quality tile installation. The floor may need to be flattened with a patch or SLU anywhere from just a skim-coat to as heavy as 6 inches. The surface may further need the advantages offered by a backer board or one of the membranes mentioned above.
Whatever the case, always follow the manufacturer’s guidelines and when possible, use products produced by a single manufacturer. These two prerequisites along with using qualified labor, installers who meet the requirements of a Ceramic Tile Education Foundation (CTEF) Certified Tile Installer (CTI) or Journeyman from the IUBAC, will enhance consumer confidence and ensure a beautiful and long-lasting tile installation. Everyone wins.