Home Repair and Paint Guide

Ceramic tile subflooring must be able to carry heavy loads without movement. This is especially true when installing ceramic kitchen floor tile. Heavy appliances, cabinets, and other items will place a lot of stress on the subfloor. Flexing of the support structure will cause the tiles to crack in a short period of time.

If you decide to apply ceramic tile over an existing floor, make sure it is flat, solid, and well bonded to the subfloor. Cracked tiles might indicate that there has been excessive flexing. This is especially true where the room is on the second level of your house.

Vinyl or linoleum should be removed for best results, but you can also cover it with a proper underlayment such as cement board.

Tile can be installed over an existing ceramic tile floor long as it’s level and in good condition. You may have to roughen the surface of the tile if it’s too glossy.

Remember that installing ceramic tile over an existing floor will raise the height of the entire floor. This will reduce the height of the cut-ins along the bottom of cabinets. A lot of people don’t know that these cut-ins allow room for your feet when standing in front of a counter. Making these too short will cause you to catch a toe on the cabinet edge when approaching the area. Doors are another problem. Getting the floor too high will close the gap at the bottom.

Concrete backerboard (cement board) is the standard material for ceramic tile subflooring. Backerboard has a solid concrete core and is faced on both sides with fiberglass. It can’t be damaged by water and is the ideal solution for bathroom and kitchen installations.

Cutting backerboard is a lot like cutting drywall. Using a framing square, score your cut line a few times. You can use a regular utility knife for this, but you’ll go through a lot of blades. A special carbide-blade cutter works better. Break the board by applying pressure until it snaps apart along the score line.

Cement board is installed over a wood subfloor using the same type of thinset mortar that you use to set tiles. Use the flat side of a notched trowel to spread the thinset out where the sheet of backerboard will be placed. Then use the notched side of the trowel to comb out the adhesive. Secure the sheets with galvanized nails or backerboard screws about every 8 inches. Stagger the joints so they don’t line up with one another or fall directly over the joints of the subfloor. Leave about 1/8″ space between the sheets and fill these gaps with thinset mortar using a taping knife.

A concrete slab is a great underlayment for tile as long as it’s stable and flat. Move a straightedge over the surface and mark high and low spots. Low spots can be filled in with a leveling compound and high spots can be ground down with a rubbing stone or grinder.

Small cracks in the slab must be covered with a crack isolation membrane to prevent the tile and grout from developing stress fractures. Crack isolation membrane is a thin, slightly flexible layer between the slab and the ceramic tile. The idea is to allow a small amount of horizontal movement in the underlayment without damaging the tile.