- 1). Mix 1/2-cup of trisodium phosphate in a bucket with a gallon of hot water. Scrub the concrete subfloor vigorously with a scrub brush. Rinse well. Let it dry for 48 hours.
- 2). Lay two chalk lines over the middle of the floor with a snap line, perpendicular to each other so they intersect at the center, and divide the floor into four squares. Set a square at the intersection as you snap the lines, adjusting them, if needed, to make sure the lines are exactly 90 degrees from each other.
- 3). Use a notched trowel to spread mortar over the center of the floor, in a few square feet, at one of the four corners formed by the intersection of the lines.
- 4). Lay the first tile in the corner of the intersection. Press in more tiles around it, with spacers between them.
- 5). Continue spreading mortar and setting tiles, working toward the perimeter of the room. Keep the grid straight along the snapped lines. Cover the entire floor, cutting the edge tiles, as needed, with a tile cutter.
- 6). Let the mortar set overnight. Pull out the spacers.
- 7). Grout the floor with a grout float. Press the grout into the lines while squeezing it off the surface. Wipe up the excess grout with a damp sponge.
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