This story shows how to accurately marking layout and reference lines.
Perhaps no other task requires more precision than marking reference and layout lines. These lines keep your tile square to the room and evenly spaced.
Mark reference lines perpendicular to each other. Save time setting tiles by locating these lines where a grout joint will fall when you install the tile. You can use your layout sketch to find this point, but it's better to dry-lay and space at least one row of the actual tiles in both directions. Mark the edge of the tile, then snap the lines.
Next mark layout lines to establish grids for laying tiles in sections. How many you use depends on how complicated your layout is, how quickly the adhesive sets up (its working time), your skill level (if you're less skilled, use more lines), and the size of the tile (large tile will generally mean fewer lines). Establish a grid with which you feel comfortable (about 2-foot squares are a good size to start). Measure from the reference lines in both directions by an amount that equals several tiles (plus grout joints) and snap lines at these points.
About five minutes to measure and snap each line, more if dry-laying tile to establish lines
Laying out floors: tape measure, chalk line Laying out walls: tape measure, 4-foot level, chalk line
Reading a level, measuring accurately
Surface preparation, installation of backerboard
Layout sketch, loose tile, spacers
Snap a chalk line at the points you have marked. Repeat the process between the other walls. Use the 3-4-5 triangle method to square the lines. Measure from each of these reference lines distances equal to an even number of tiles and joints, and snap layout lines at these points.
Hold a 4-foot carpenter's level vertically on the wall and at least 2 feet from a corner, preferably on a plane where a grout line will fall. Adjust the level until the bubble indicates it is straight up and down. Taking care not to disturb the level, trace a penciled line down its edge. Extend the line to the floor and ceiling by snapping a chalk line over the one you have marked.
Position the level horizontally on the chalk line, about midway up the wall and preferably on a plane where a grout joint will fall. Adjust the level until the bubble is centered in the glass and scribe a line along the level. Extend this line with a chalk line. You don't have to check the intersection for square with the 3-4-5 triangle method.
From each line, mark the wall at intervals that correspond to an equal number of tiles (include the grout joints) and snap layout lines.