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Ceramic tiles have many of the same layout requirements as other floor coverings, and it is likely that most of the tools required for it are already in an installer's tool kit. Tile industry layout requirements are relatively simple and can be boiled down to two guiding principles: tiles should be centered and balanced, and no cut tiles less than half the size of a whole tile should be installed (within reason).

Tile layout begins with a grid of lines plotted on the subfloor for backerboards and other materials, followed by a second grid of lines to guide the position of the tiles.

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Measuring the Installation Site

Measure the installation site to see if it is reasonably square, straight and can be tiled successfully. If there are severe problems, a written notice should be presented to the building owner before any additional work is done. Generally, the preliminary layout starts along the longest wall, preferably an exterior wall, but it may also begin at some arbitrary focus designed for the installation.

For the greatest accuracy, two reference lines intersecting at 90 degrees and centered need to be plotted on the floor with a pencil or chalk line, or projected by a laser. A laser square can significantly reduce the time spent completing a layout, but the process for locating individual lines is more or less the same (Image 1).

To check a room for square, project the first reference line parallel to the longest wall. For a more precise and useful layout, this line should be centered within the floor. Locate the second reference line at an angle of 90 degrees to, and at the center of, the first line.

Check for accuracy by comparing the projected lines against the measuring square before tiling or extending the layout grid into adjoining rooms. From these two center lines, distances to the surrounding walls can be determined, and the ultimate layout grid can be established based on the scale of the tile and grout-joint dimension.

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Measuring the Tile and Grout-Joint Dimension

The grout-joint dimension is determined by adding the desired joint width to the average dimensions of the tile. To do this, align 10 tiles along a straightedge with the squared edge of each tile touching (no joint). Measure them and divide the total length by 10. Add the desired grout-joint width to reach the grout-joint dimension. Multiples of this number can be used to help balance the positioning of the tiles and the location of the grid (Image 2).

The joint running the perimeter of a tiled floor is of special importance. Tile edges should never be in direct contact with any restraining surfaces. Therefore, a movement joint must be made wherever the installation abuts a hard surface.

The movement joint should never be less than the width of a grout joint, and never less than 1/4 inch. The 1/4-inch minimum movement-joint dimension needs to be figured into the layout of the tiles.

Plotting the Layout Grid

Referring to the grout joint list's whole-tile dimensions, I use a measuring tape to determine the best possible positioning. I measure off the two reference lines so the grid will run straight and true from one side of the floor to the other. The two reference lines are also invaluable when plotting lines for inlay panels or other distinct features.

The size of the layout grid ("How many lines do I snap?") is largely determined by an installer's reach. For installing tiles up to 12-inches square, a grid of lines spaced every 36 inches works for me, with tighter spacing for 16-, 18-, and 24-inch tiles. In addition to guiding the placement of the tiles, the layout lines can be used to stage tiles in preparation for their installation (Image 3) on large floors.

On relatively small floors less than 6 feet wide, a grid of lines may not even be needed if the tiles can be aligned against the two reference lines. For bathroom floor installations using tiles larger than 12-inches square, only one line may be required. For 12-inch-square tiles and smaller, more lines are usually required.

Whatever the size or configuration, the final layout should be done just before the tiles are installed. In situations where neither or just one reference line will be used as layout lines, a different color chalk should be used for the grid lines to avoid confusion. Double check all dimensions before committing them with chalk or pencil lines to the setting bed. Use a vacuum to remove excess chalk dust.

A layout grid that includes lines between all whole and cut tiles allows a swift installer the option of installing both whole- and cut tiles at once or at different times. When assistance for mixing thin-set, staging tile and making cuts is available, all the tiles should be installed as the work proceeds. On residential projects greater than 300 square feet where a helper is not available, it may make more sense to install the whole tiles one day and save the cut tiles for the next.

Layout lines accurately indicating the whole-tile perimeter of the installation can dramatically improve an installer's precision. With a surrounding grid of layout squares indicating the general field of tiles in place, the installer's output should improve as well. A good layout can help minimize the inevitable irregularities that are a part of every building project, and help maximize profits by enabling the installer to lay down tile with confidence.