Jun 4, 2012
“Across the length of the tile, it is warped like a banana with a .047˝ gap in the middle,” said the contractor. “This is minor, but the customer is pitching a fit. To compound matters, the samples in the showroom are perfectly flat, and I just received notice that she is protesting the charge with her credit card company.
“I sold the material only, and her installer brought it to her attention,” he continued. “She has accent lights close to the wall in the ceiling which cast a shadow over the lippage down the wall in the shower where she wants it. As far as I know, the ANSI spec says this warpage is within tolerance, but I’m caught in a legalistic defense here. If I hide behind the rules, I’m going to get hit hard. Any advice?”
“This is a question we run into very frequently. ANSI A137.1.5 Table 10 Porcelain Tile shows a formula and a maximum allowable-edge warpage for calibrated and rectified tiles. Your tile does fall within allowable warpage factor as you describe it. There are many installation issues that need to be met with large-format tile that are more challenging than smaller tile.
“First, any tile which has one edge 15” or longer is considered ‘large-format tile’ and will need a substrate twice as flat as standard tile, so instead of 1/4” in 10’ and 1/16” in 1’ flatness requirement, we now need 1/8” in 10’ and 1/16” in 2’ flatness,” Whistler said. “This is specified in ANSI A108 and 2011 TCNA Handbook editions. Even with these improved substrate flatness requirements, there is still allowable lippage – which we can call human error allowance, or slump factor – that are allowed in addition to the inherent lippage that is introduced by inconsistencies in the tile itself.
“Second, many tiles, and particularly these plank-shaped tiles, are specified to be installed with offset grout joints,” Whistler continued. “The most commonly specified is the ‘running bond’ or 50% offset with the grout joint centered on the adjacent tile. This exacerbates lippage issues since you are placing the two low points of two tiles next to the high point of the adjacent tile. Small grout joints can also lead to more noticeable lippage, even when within acceptable limits.
“To help these issues, ANSI and TCNA now both have standards that large-format tile be installed with no greater than 33% offset, and that grout joints be no smaller than three times the facial variation of the tile supplied to the project,” Whistler added.” Tile manufacturers also frequently supply installation guidelines that give minimum joint width and offset recommendations for each product.
”Third, wall-washing type lighting, or any source of lighting that is ‘washing’ parallel to a tile installation will tend to accentuate the visual presence of lippage, even in very acceptable tilework,” he said.“ The NTCA Reference Manual has a very good document explaining this phenomenon, and gives very good tips on how to alleviate this problem.
“Last, there are installation tools available that can help install large-format tile in a more easily-achieved lippage-free manner,” Whistler concluded. “These are a type of mechanical-edge setting system that help keep the surfaces of tiles flush with one another during installation and also during the initial slump and shrinkage time that occurs with the most commonly used mortars.” Examples include the Tuscan Leveling System and QEP’s L.A.S.H. system.
For more information, contact NTCA at 601-939-2071 or seek out the assistance of a Five Star Contractor in your area by entering this address in your browser: https://www.tile-assn.com/Member/FiveStar.aspx?mid=84.