In today’s tile market, there is a vast array of tile products to meet the consumer’s needs and desires. However, just because a tile product is for sale on the shelf doesn’t mean that it is applicable to every job or design. Determining the suitability of a tile to a particular pattern needs to be determined before the installer is ready to begin his or her work.
The Tile Council of North America (TCNA) Handbook, under the heading of Grout Joint Size, Layouts, and Patterns – System Modularity (currently page 41), it states, “Nominal sizes only provide a general idea of tile size and cannot be relied upon as an indicator of size compatibility or pattern compatibility with other tiles having the same nominal size, including for tile from the same tile line. Grout joint sizing or patterns can only be determined based on actual tiles ready for installation.”
Modularity or as it is known in the ANSI A137.1 (American National Standard Specifications for Ceramic Tile) “System Modularity” is defined as, “Tiles of various nominal dimensions are sized so that they may be installed together in patterns with a common specified joint width.”
The key point of these definitions is that all the grout joints in the pattern are to have “a common specified joint width,” meaning that each joint is the same size. In the case of a stack joint or running (brick) bond, the tile is all running in one direction, but when the tile pattern calls for the tile to be turned ninety degrees, the difficulties begin.
For a tile to be modular, the width of the tile must allow for a grout joint when it is turned at right angles to the adjacent tile. For instance, a basketweave pattern requires two tiles in a north/south direction with two tiles directly next to them going in an east/west direction. The problem occurs when two tiles are butted tightly together against the long side of the adjacent tile and are flush with the long side ends. When this occurs, there is no room for a grout joint. If a grout joint is created between the two tiles, the outer edges do not line up.
As seen in the image, the width of four tiles is exactly the same as the length of one tile with no room for the three grout joints.
Interestingly, the manufacturer of this tile has a disclaimer clearly printed on the side of the box and on their technical data sheet stating, “Tile is not modular” providing a very clear meaning – don’t use it in a pattern. Often times a tile is selected for color and/or shape with little or no attention to its ability to be used in a pattern. The real difficulty arises on installation day when the installer is faced with the prospect that this is not going to work and must tell the consumer about the problem. This is the wrong time for this discussion. It should have occurred in the selection and selection process.