How to Tile a Floor
Tile is permanent, waterproof, and beautiful — and unforgiving of a bad substrate. Get the floor stiff and flat, set tile with the right trowel and full mortar coverage, and the setting and grouting go smoothly. Tap “Add to my materials list” as you go.
1Check and prep the subfloor
The floor must be stiff — deflection no more than L/360 of the span — and a wood subfloor needs ~1⅛” total thickness. Fasten loose spots, fill lows, and make sure it’s clean, flat, and dry. A bouncy floor cracks tile.
2Install cement backer board
Over a wood subfloor, comb thinset with a ¼” trowel, set ¼” cement backer board, and screw it down every 6–8”, leaving ~1⁄8” gaps and taping the seams with mesh tape in thinset. (Over a sound concrete slab you can tile directly.) The tile calculator includes backer board and screws.
3Waterproof wet areas
In showers and tub surrounds, apply a waterproofing membrane over the backer before tiling. A typical dry bathroom or kitchen floor doesn’t need it.
4Dry-lay and snap layout lines
Find the room center, snap two square chalk lines, and dry-fit tiles outward so you avoid thin slivers at the walls — full tiles where the eye lands, cuts at the perimeter.
5Set the tile with the right trowel
Match the trowel to the tile (~¼×¼” for small tile, up to ½×½” for 12×24”), comb straight ridges, back-butter tiles over 8”, and lift one occasionally to confirm ~80–95% mortar coverage. Use spacers, then let it cure ~24 hrs before grouting.
6Grout, then seal
Pack grout diagonally with a rubber float, sponge off the haze, and fill the ¼” perimeter gap with silicone, not grout. Once the grout cures, seal it.
7Reinstall the baseboard
Finish the room by reinstalling baseboard (and shoe molding) over the tile edge. The calculator sizes your baseboard run.