Tile Grout Joints: Alignment versus Uniformity

Using spacers when laying floor tile will make grout joints straight. This is a commonly held belief but it is unfortunately incorrect. As any experienced tile installer knows, spacers are more likely to hurt the installation than help it.

But how can spacers, which virtually guarantee grout joint uniformity, be a bad thing?

It has to do with the allowable dimensional variation in the size of the tiles and the inconsistency of the wall dimensions across a room. If the individual tiles were all the same size and the corners of the room were perfectly square, then spacers might be useful. However, manufacturing limitations of tile and imperfect site conditions require tile installers to make slight adjustments to the grout joint, which spacers would otherwise preclude, in order to maintain grout joint alignment.

According to ANSI A137.1, Standard Specifications for Ceramic Tile, a calibrated porcelain tile is allowed to vary in its facial dimension by up to 0.08 inch, equating to a total variation by as much as 0.16 inch. In other words, a tile can vary in size by more than 1/8 inch. Similarly, the wall-to-wall dimension can vary drastically when taken from opposite ends of a room. If spacers are used, the grout joints may have a uniform width but they won’t line up, resulting in an aesthetically unappealing installation.

To accommodate imperfections in the tile and backing walls, installers should snap a grid of chalk lines on the floor to dictate where the grout joints will fall. For example, if the tile is 12-inch by 12-inch nominal, a tile setter may snap chalk lines every four feet in each direction. The installer would then lay tile inside the grid, lining up a corner of the tile on the intersecting grid lines every four feet. This will ensure there is grout uniformity within each four-foot section of floor. When the tiled floor is viewed in its entirety, all joints won’t be homogenous but they will be aligned, which is the more important visual consideration.

When it comes to layout, the chalk line grid should be snapped on the floor in the precise position to eliminate or minimize cut tiles, and it should generally be parallel to the longest or most prominent wall in the room. The grid is kept square using the largest possible Pythagorean triple for the size of the room. For example, the installer would snap a right triangle of eight feet, 15 feet and 17 feet, or a right triangle of five feet, 12 feet and 13 feet. In smaller rooms, the triangle may be three feet, four feet and five feet.

Now that the need for variable grout joint width to maintain proper grout joint alignment has been demonstrated, let’s examine what the American National Standards Institute (ANSI) says about allowable variation in grout joint width.

ANSI A108.02, General Requirements: Workmanship for Tile Installation, states, “To accommodate the range in facial dimensions of the tile supplied for a specific project, the actual grout joint size may, of necessity, vary from the grout joint size specified.”

This language is vague. It does not give a specific value for allowable variation; however, it does alert the end-user that a certain amount of inconsistency in grout joint width is unavoidable.

Scott Conwell is director of industry development and technical services at the International Masonry Institute (IMI). He leads the institute’s tile, marble and terrazzo industry development program, and is the creator of IMI’s masonry detailing series, an online collection of construction details and technical information that sets the industry standard for architectural details on masonry, tile, stone and terrazzo.