The old phrase, “Necessity is the mother of invention,” is applicable to many of the things we encounter in everyday life and the installation of tile is no exception.

Consider a potential commercial job with an on-ground concrete slab (TCNA Handbook F113) that includes floor drains and the installation of a 12” x 12” tile in a straight pattern with 3/16” grout joints.   

The substrate, according to the plumbing code, must slope at a minimum of 1/4” per foot while ANSI A108.01-2.6.2.2 states, “They (the approved substrate) shall be dry, stable, well cured, and for tile with all edges shorter than 15 inches, shall have a maximum permissible variation of ¼" in 10 feet (6 mm in 3 m) from the required plane, and not more than 1/16” variation in 12 inches (2 mm in 305 mm) when measured from the high points in the surface.” 

This provides a real challenge to the tile installer since the soon-to-be-installed tile must follow the slope to drain to effectively evacuate the liquid and meet the flatness requirement of the ANSI standard. 

How does the installer do this? The short answer is that he/she can’t, but the ANSI Specifications provide some guidance. 

Under A108.02-4.3.7 it states, “Lippage – guidelines, explanation, and caution: Lippage refers to differences in elevation between edges of adjacent tile modules.” Included under this section, the provided chart states that for Pressed Floor and Porcelain Tiles with a grout joint width of 1/16” to less than ¼", the allowable lippage is 1/32”. 

It further states, “Caution: This chart does not apply to tiled floors sloping to drains. Lippage will be present when using tiles 6” x 6” and larger over interior and exterior conical surfaces sloped to drains. The larger the tile unit surface area, the greater the lippage. Cutting the individual units can reduce the amount of lippage but may not eliminate lippage.”

The solution as suggested above is seen in the above image. Note that nine 12” x 12” tiles are split diagonally while two pieces are split diagonally in both directions, allowing them to follow the slope of the concrete while minimizing visible lippage and a possible tripping hazard.

As tile installers, we are often called on to work tile miracles. In this case, by following the industry standards and guidelines along with some creativity, the problem is solved, providing the owner with a good-looking and safe installation while saving the tile industry from another black eye.