Covering floorboards with ceramic tile is like covering any other type of flooring, except for the floor preparation. It is important to start with a clean, level surface. This may require some extra time, but it will ensure that your tiles have a long life. Once you've made sure that the surface is clean and level, all you have to do is install cement backer board, trowel on thin-set mortar and lay your tiles as you normally would.
Clean and secure the floorboards you want to cover. Sweep up, then vacuum the corners to remove any dust and debris. Use screws to secure any boards that may be loose. If any boards are broken or rotten, replace them. Set all nail heads or screws below the surface of the wood.
Check that the floor is level by pushing a 1.2 m (4 foot) carpenter's level around the floor and marking any dips or rises. Apply self-levelling, liquid floor leveller to any spots that aren't level.
Measure and cut sheets of 1.2 m (1/2 inch) cement backer board with a circular saw to cover the floorboards. Lay the backer boards perpendicular to the floorboards. Screw the backer boards in place, spacing your screws about 15 to 20 cm (6 to 8 inches) apart, following any specific instructions for the backer board.
Dry-fit your tiles to check for layout and measure any cuts before you add glue. Lay the tiles, starting from the far wall and working toward the door, putting tile spacers between them. When you reach side walls and doorways where a full tile will not fit, measure and cut tiles to fit, factoring in the spacing between tiles for the grout line.
Trowel on premixed thin-set mortar. Cover only as much of the floor as you'll be able to tile before the mortar starts setting up -- see manufacturer's directions for specific directions, but try not to put down more mortar than you can cover in 20 minutes. Use tile spacers between each tile to keep them square. Continue tiling your way back through the room until all tiles are placed except the ones along the wall.
Measure the distance from the last row of tiles to the wall to get your cut. If the wall is not square, you may have to vary the cuts on individual tiles, so measure and mark them one at a time. Cut the tiles with a wet saw, lay down thin-set and put them in place.
Mix the grout to about the consistency of peanut butter. and apply it using a rubber grout float to push it into the spaces between tiles. Use a large sponge to wipe off excess, rinsing your sponge in a clean bucket of water and continuing to wipe as you go. Allow the grout to dry. Use a sponge to clean the grout haze from the entire floor the next day.
If you are laying tile in an area that gets particularly dirty or is subject to moisture, spray or wipe on a grout sealer.
Wear safety goggles when using a wet a saw.