This article concludes a series of three, focusing on the recently-revised ANSI A137.1 standard, which categorizes ceramic tile by type and outlines the performance that each tile type must achieve in order to be labeled A137.1 compliant.
The first article defined the five main tile types covered by the standard, listed the destructive and non-destructive laboratory tests that are used to measure tile performance and application suitability, and outlined the sampling of tiles for testing. The second article discussed important performance characteristics and testing for glazed tile: resistance to abrasion (wear), thermal shock, and freeze/thaw cycling. This article covers the dimensional characteristics of ceramic tile, and the amount of variance in size and shape allowed for boxes of tile labeled A137.1 compliant.
What are facial dimensions, wedging, and warpage?
Facial dimensions are length measurements of the sides of a tile, typically measured to the thousandth of an inch. For example, a tile nominally referred to as “12x12” might actually have sides that measure 11.756 inches, which is longer than 11-3/4 inches by 6/1000 of an inch. When measuring to this degree of accuracy, commonly each side of the same tile will have different measurements. The individual measurements of each side of each piece of tile in a sample are averaged together to provide the average facial dimension of the sample. For example, if 80 pieces of tile were measured, the average facial dimension of the sample would be the average of 320 measurements.
Wedging is the squareness of a tile’s corners, or the amount of variation from a tile having perfect 90-degree corners. The amount of wedging measured is expressed as a percentage, based on the tile’s facial dimensions.
Warpage is the curvature in a piece of tile, or the convex or concave shaping of the face of the tile due to changes that occur during firing and cooling. Edge warpage is measured at the center of a tile’s edge, and diagonal warpage is measured in the center of the tile. Both are expressed as a percentage, based on the tile’s facial dimensions.
How much variation in facial dimensions, wedging, and warpage is allowed?
This depends on the type of tile. The A137.1 standard contains a separate table with the dimensional requirements, or tolerances, for each of the five main tile types: mosaic, glazed wall, pressed floor, porcelain, and quarry. Some of the tile types are further subdivided into the categories natural, calibrated, and rectified, each of which has separate dimensional tolerances.
Natural tile is tile that does not go through a sorting (or calibrating) machine, and therefore is allowed the greatest amount of variation in size and shape, sometimes to intentionally produce a more handmade or rustic look. Calibrated tile is sorted by size so that only tiles within a small range of variation will be boxed together. Rectified tile has extremely tight tolerances that can only be achieved by mechanically cutting or grinding tiles after firing. By subdividing the tile types in this way, the tile manufacturer has a way to communicate the level of dimensional precision that a batch of tiles will have. To find out the allowable amount of wedging, warpage, or variation in facial dimensions for a given tile, you would have to reference the table for that tile type as well as the appropriate section in the table (natural, calibrated, rectified), if applicable.
Example: If you wanted to know how much variation is allowed in the facial dimensions of quarry tile, you would refer to the quarry tile table, which contains only one set of dimensional tolerances. The caliber range (the range of tile sizes that may be boxed together) allows a maximum variation in the size of the tiles of ±0.75% of the average facial dimension of the sample or ±0.09 inches, whichever is less. This means that for a batch of quarry tiles with an average facial dimension of 8 inches, it is acceptable to find tiles as small as 7.94 inches (8 – 0.75% of 8) and as big as 8.06 inches (8 + 0.75% of 8). In this example, the maximum allowed size variation among tiles is .12 inches, which is a little less than 1/8 inch.
If the quarry tiles were 13x13 instead of 8x8, the cap on the allowable amount of size variation would apply instead of the allowable percentage, because the cap (±0.09 inches) is less than the allowable percentage (0.75% of 13 = 0.0975). In this example, it would be acceptable to find tiles as small as 12.91 inches (13 – 0.09 inches) and as big as 13.09 inches (13 + 0.09 inches). The caps on the allowances provide an upper limit so that, as tile size increases, the amount of warpage, wedging and size variation allowed cannot increase beyond what is reasonable for a quality product.
In contrast to the allowances above for quarry tile, calibrated porcelain tile is allowed the lesser of ±0.50% or ±0.08 inches, and rectified porcelain is allowed only ±0.25% or ±0.03 inches. In practical terms, this means a batch of calibrated porcelain tile with an average facial dimension of 12 inches could have tiles ranging from 11.94 inches to 12.06 inches-a batch of rectified porcelain tile with an average facial dimension of 12 inches could only have tiles ranging from 11.97 inches to 12.03 inches.
What is the impact of the new tolerances for wedging, warpage, and variation in facial dimensions (caliber range)?
Variations in facial dimensions, wedging, and warpage affect the look of the finished tile installation and determine the minimum grout joint width required to work with the tiles. To produce an attractive installation, the installer needs a grout joint width of at least three times the amount of size variation present, a recommendation that has recently been adopted as an ANSI installation standard. The amount of warpage present determines how much lippage may be present, particularly when an offset pattern is used.
Across the board, the new dimensional tolerances allow markedly less wedging, warpage, and variation in facial dimensions, obliging manufacturers to supply ceramic tile that accommodates the modern trends toward narrower grout joints and patterns that require flatter tiles. Furthermore, by establishing dimensional requirements for rectified tile, the new A137.1 should reduce the occurrence of problems between contractors, owners, and design professionals with regard to acceptable patterns and required grout joint width.
Now the tightest tile standard in the world, adoption of the revised A137.1 standard ushers in a new level of quality expectation, not just for the domestic industry, but also for all manufacturing countries that supply the U.S. with ceramic tile.