Warpage and Lippage
When the Specification for Ceramic Tile American National Standard was first revised in 1988, large format tiles were 8 in by 8 in and 12 in by 12 in. Today, however, the ceramic tile industry has grown far more complicated, as 12 in by 24 in, 18 in by 18 in, 24 in by 24 in, and larger tiles are manufactured in abundance. This has notably proliferated the problem of lippage in modern ceramic tiles. Lippage is the height in variation of adjoining tiles, or the “differences in elevation between edges of adjacent tile modules.” Lippage is not only undesirable in appearance, but it can also introduce trip hazards.
Tile lippage can be the result of many factors, one of which is the allowed warpage of the tile modules. Since modern tiles can be manufactured at dimensions larger than ever before, particularly the rectangular ones, which possess extreme long-to-short-side rations, warpage can cause unavoidable lippage (or even the perception of such a condition). ANSI A137.1:2021 – American National Standard Specifications for Ceramic Tile establishes allowable tolerances criteria for each type or category of ceramic tile to prevent hazardous or otherwise unwanted warpage.
The allowed warpage information in ANSI A137.1:2021 is derived from ASTM C485-16 – Standard Test Method for Measuring Warpage of Ceramic Tile. For example, in ANSI A137.1:2021, in reference to calibrated pressed floor tile, the standard states that, in accordance with ASTM C485, warpage edge should be at minimum “-0.75% or -0.08 in (-2.0 mm)” and at maximum “0.75% or 0.08 in (2.0 mm)”.
ASTM C485-16 – Standard Test Method for Measuring Warpage of Ceramic Tile
ASTM C485-16 – Standard Test Method for Measuring Warpage of Ceramic Tile addresses a test method that details the procedures for measuring the corner, diagonal, and edge warpages of ceramic tile. It is applicable to the following ceramic tile categories:
- Square Tile (2 in by 2 in or larger)
- Oblong Tile (no facial dimension smaller than 2 in)
- Square and Oblong Tile (no facial dimension smaller than 2 in)
- Nonrectilinear Tile (larger than 4 in2)
- Trim Tile (meeting the one of the four previous dimensions)
- Square or Oblong Tile (facial area less than 4in2)
The actual testing method of ASTM C485-16 makes use of an Edge and Diagonal Apparatus and a Corner Apparatus to measure the warpages of ceramic tile samples. With this information, the method can then be employed to calculate the deviation of the ceramic tile from a flat plane, which is expressed as convex (positive) or concave (negative) warpage in relation to the tile face.
The exact procedures for carrying out this method are detailed in the standard.
ASTM C485-16 – Standard Test Method for Measuring Warpage of Ceramic Tile is available on the ANSI Webstore.