Do You Have Enough Mortar to Accommodate Large Format Tile Installation?

Large format tile is the most popular installation choice for flooring these and for good reason. It can make a space look larger and displays fewer grout lines across a floor. But when you install this tile you need to ensure that you have enough mortar to accommodate the natural tile warpage that tends to come with large format tile. Plus with tile sizes getting larger and longer, this need is only getting increasingly important. Let's take a look at this a bit more in depth.

As Tile Gets Larger, Warpage Tends to Increase

In the past, we used to consider 8" x 8" tile as large format. Needless to say, large format tile is a lot larger now and warpage has become more of a concern. The CTEF website states, "According to the Tile Council of North America (TCNA), the allowable warpage of a tile is as follows: The ANSI A137.1 (The American National Standard Specifications for Ceramic Tile) defines allowable warpage according to the type of tile. For Pressed Floor Tile in the Calibrated category which is commonly used on floors, the allowable warpage is listed as follows: Table 8: Pressed Floor Tile (does not include porcelain) – When measured as described in the ASTM C485, Warpage Edge, the warpage of each tile in the sample lot shall not exceed 0.75% (0.08 inch) along the edge nor 0.50% or 0,08 inch on the diagonal. From this formula the allowable warpage can be determined. Today’s popular larger tile sizes can be 6” x 36”, one meter by one meter or larger and include an industry standard allowable amount of warpage (where the center of the tile is higher than the edges or ends)."

More Warpage Means More and Different Mortar

To support this warpage you need LHT mortar, otherwise known as large and heavy tile mortar. Technically, there is not an established standard but there is one in the works. According to CTEF, "Selection of the appropriate trowel notch size is best determined by checking the mortar manufacturer’s data sheet or on the back of the bag. Normally, LHT mortars allow for a ½” mortar thickness after the tile has been embedded. "LHT mortars allow the mortar to be spread with a thicker configuration than conventional thin set mortars as seen in the attached photo. This additional amount of mortar, when troweled in a straight-line pattern, is designed to support the edges of the tile fully as well as the center which many times can be higher due to the tile warpage. "Without this needed support, the tile is very susceptible to breakage under a concentrated load point such as a woman’s high heel, which can exert over two thousand pounds of pressure per square inch. Additionally, this lack of mortar or empty space can produce a hollow sound under normal foot traffic which is unpleasant and most times, unacceptable."

Back-Buttering is the Right Path

The right mortar is the first step, but you should also back butter the tile. Essentially this is the application of a skim coat on the back of the tile. It will create a better bond as well as fill the warped area. According to the TCNA Handbook, "All corners and edges of the stone tiles must be fully supported, and back-parging, or back-buttering, is recommended in all areas. Coating the back of the tile, however, does not constitute coverage, which is the area where the mortar makes contact with the tile and the substrate.” Leveraging a combination of the right mortar and back buttering should meet the minimum standards of 80% coverage in dry areas and 95% coverage in wet or exterior areas. The only thing to be cautious about is making sure you do not exceed the maximum thickness of the mortar permitted by the manufacturer.

How do you Ensure the Right Coverage?

According to the CTEF, "The best and most effective way to confirm that this minimum requirement has been met is to occasionally remove a tile. A good tile mechanic meeting the requirements of qualified labor, as recognized by the Tile Council of North America, will use this procedure regularly to ensure that the consumer is getting what they deserve, a high quality, long lasting, and trouble-free installation." Of course if you have any installation or tile questions, our team of tile experts are here to help. Stop by any of our convenient tile store locations across South Florida