The first layout consideration in floors is based on vision. Where will the eye first fall? Sometimes this is at the point of entry into the room. If the room has multiple entrances, the eye may naturally travel to the longest wall. I would say that in the case of a bathroom, the eye would first go to the base of the shower or tub. Each room must be considered individually. Sometimes in layout there are many choices that will work. We need to pick the one we feel will "look" the best. Where do we start?
In the case of tiling one room, take measurements in both directions. Compare these measurements to the tile and joint size chosen. This will indicate whether full tiles or cuts are necessary. If you end up with tiny cuts, less than 1/2 tile, at one wall, it will be more visually appealing if you shift the field so that larger fuller tile is used even if you have to cut at both ends.
It is also necessary at this time to include in your measurements if any trim pieces are to be used. In the case of cove tile and the like, room for the tile must be added to your measurements and allowances made.
In my experience, the best approach is to identify the longest wall and establish the first "working line." Working lines are lines on the floor made with pencil, marker, or chalk line. These lines can and will possibly be moved several times during layout. If you are using chalk lines, do not spray the lines with clear lacquer until all of the lines are made.
Tile Doctor Tip: When you identify your longest wall, make your first working line far enough from the wall for at least one trowel. This allows you to use the line and still apply a bond coat between the first tile set and the wall.
To establish the line, measure out from the longest wall at two places and make reference marks. If the room is large, over 6-8 feet, use a chalk line. If not, you can use a straight edge and pencil.
Tile Doctor Tip: ;When using a chalk line, be sure that you carefully align the chalk line with the reference marks and pull the line as tight as possible prior to snapping it. Also, place the chalk line as close as possible to the reference marks, while aligning it, without actually touching the surface. When the surface is touched, chalk will be left. Additionally, always retract the line into the tool for each line snapped. The chalk line is of no value without chalk.
Now you have your first working line properly spaced from the longest wall allowing room for a trowel pass between the line and wall. This first line is placed after you have established where the field of tile will start. We now need to check the room for square. This is accomplished by making a perpendicular line on an opposing wall at the exact spot the tile needs to be placed. Use the reference marks again to establish the line. Now you have a choice. A Large roofing square can be compared to the intersecting lines and an estimate of square can be made. A better method is the mathematical approach called the "3-4-5" method.
The 3-4-5 method is derived from geometry, which calculates the dimensions of a triangle. In practice, a measurement is made down the longest wall line from the intersection of the two lines. A reference mark is made at 4 feet. Next measure down the other line and make a reference mark at 3 feet. Now measure the distance between the two reference marks. If the measurement is 5 feet, the walls are square. If they are not an adjustment will need to be made.
Tile Doctor Tip: This is an important measurement: "If you start out square, you will end square."
Now it's decision time. Will spacers be used or will the installation be "grid set?" There are advantages to both. Let's talk about spacers first.
Spacers can be used if the tile is nearly perfect in square and size when compared to each other. I can illustrate this thought by saying that if the room is large there will be many tiles involved. Lets say there are 30 6″x6″ tiles in the length of the room and 20 6″x6″ tiles in the width. Spacers are used and the tiles are not quite the same size. Let's say they vary 1/32″ each. All that needs to be done is multiply 1/32″ 30 times and you get the picture. Those nice straight lines you started out with now looks like a snake.
Spacers will work very well if the tiles are uniform and the room is relatively small. If spacers are used, only the original lines are necessary when the installation is started. After the installation is started, it is mandatory to occasionally check square by measurements using a straight edge or chalk line while the installation is in progress.
Tile Doctor Tip: Spacers must be removed after the job is completed and cured prior to grouting. In my opinion, it does not matter whether the spacers are thin or not. There will not be sufficient grout depth at tile intersections if spacers are left in.
This leads us to the grid set method. This method is preferred if the installations are large, multi-room, the tiles are irregular, or if special patterns are involved. The advantages to this method far outweigh the additional time involved in laying it out.
It works like this. From the original lines established, grids are chalk lined onto the setting surface. The grids are marked on the entire surface in both directions from the original lines. This step forms boxes that the tile will be set in. What size are the boxes? This will depend on the tile size and the installer's ability. The box must be large enough to accommodate the application of the bond coat by notched trowel while not too large to make setting difficult. The lines also must be established with perimeters that include the tile and grout joints. Look at the diagram and photographs of this method in use.
This method is also preferred as it allows the installer to view the entire installation and cuts prior to one tile being set. Also, with this od, an installer can start anywhere in the project and the grout joints will line up. It is especially desired if there are any structures within the field of tile like that of islands or special designs.
Let me illustrate this dialog by a suggestion. Let's say that the tile chosen is 12″x12″ and the grout joint chosen is 3/16 inch. I would pick a grid or box measuring 24 3/8″ 24 3/8″. This leaves a grout joint between the two tiles and at two ends. The tile would be set within the box or grid always orienting the tiles in the same two sides of the box wherever on the floor they are placed. For example, look at the floor and decide where you will orient the tiles within the grids. Then always repeat this orientation in each box within the installation.
One other method exists in layout and this method utilizes a "metal tile rack." This tool is made of steel rod, which is as thick as the desired grout joint width. After the setting bed is placed, the rack is laid down and the tiles are placed in the rack and beaten in. The rack is then removed leaving the tiles in place. Grids and working lines need only to be established for the rack and not the tile. This method is particularly useful when the installation method is a fresh mortar bed and pure cement bond coat. This method is not seen very often. However, it is still used.