Ceramic tile can be used on walls, floors and countertops. Ceramic tile, however, is not flexible, and it should be bonded to a firm base (also called the substrate) that will not bend or flex. In areas where water is a problem, like the bathroom, the base must also be waterproof.
Traditionally, tile setters bonded the tile to a sturdy mortar bed that consisted of a 11/4-inch-thick layer of cement troweled over wire lath nailed to the framing. Today builders use gypsum drywall as a backing in rooms where moisture is not a problem. In bathrooms, showers and other wet areas they install cement backer board.Cement backer board, also called CBU (cementitious backer unit), consists of a thin layer of concrete sandwiched between two layers of fiberglass mesh. It is available in 30-by-60-inch sheets and is an excellent waterproof tile base.
When tiles are bonded to the substrate, the grout will crack, and the tiles will pop loose unless the wood is thick enough to resist bending. Most subfloors are 3/4-inch plywood (older floors may have 1-by-6 boards).
Even with the addition of a 3/8-inch plywood underlayment, the floor may flex if it absorbs too much moisture. Many tile setters prefer to use underlayment to expand at different rates without disturbing the tiles above.
It should be bonded, not nailed, to the subfloor with latex-cement mortar. The adhesive bonding allows the subfloor and the underlayment to expand at different rates without disturbing the tiles above.
The adhesive is troweled onto the substrate with a notched trowel, then the tiles are carefully set in place. Generally, they are filled with grout. Grout is available in two different forms, sanded and non-sanded.
After the adhesive has set and dried (drying time will vary with different brands of adhesives) the gaps between each tile are filled with grout. The primary purpose of the sealer is to make the grout less susceptible.
A grout saw can make it easier. A grout saw has a short carbide-tipped blade designed to rake out the old grout. Move the saw back and forth to loosen and remove the grout but be careful not to chip or damage the tiles.
Allow the tiles time to dry, then mix a new batch of grout according to the package directions. Apply pressure to force the grout into the gaps. Wait about 30 minutes for the grout to set, then wipe the entire area with a round-cornered sponge.