An underlayment is necessary when laying a ceramic tile floor in an area that is going to be exposed to large amounts of moisture such as: bathrooms, kitchens, entry ways and laundry rooms. Cement underlayment is one of the better options to choose from as it is water proof and makes most surfaces sturdy enough to support the ceramic tile. The most common type of cement underlayment is cement board. Most cement board is manufactured using Portland cement to make it completely water proof.

Things You Will Need

cement board
thin-set mortar
1/2" galvanized deck screws
power drill
Y4" trowel
power saw with masonry blade
utility knife

Step 1

It will be necessary to obtain these materials: cement board, thin-set mortar, 1/2" galvanized deck screws, power drill, Y4" trowel, power saw with masonry blade and utility knife. You will want to clean the area that you are going to apply the underlayment thoroughly. Once cleaned ensure that the surface is dry before moving on. A wet surface will make the mortar more likely to come loose. Once you have gathered all of the required materials and cleaned the surface you can begin the process of laying the mortar.

Step 2

To begin with, you will need to mix the mortar according to the product's label. Once the mortar is mixed, using the trowel, you can apply it to an area that is large enough for one sheet of cement board. Apply the mortar in a figure-eight pattern. Once the mortar is applied lay the sheet of cement board. Be certain that the cement board's seam does not run along any seams of the subfloor. Once the cement board is laid, fasten the sheet with the deck screws every six inches along the edges and eight inches throughout the rest of the sheet. You will want to countersink the screws slightly to maintain a flush surface. Continue doing this until the entire floor is covered with the cement board, using the saw and utility knife to cut any special areas.

Step 3

Once the cement board is laid it is time to go back and tape the seams with fiberglass mesh tape. Go back with the thin-set mortar and cover the screw heads and seams. Feather the mortar over the screw heads and seams to create a smooth surface. Be sure to feather the mortar out away from the seams to make the smoothest seam possible. Once the surface of the underlayment is completely smooth allow the project to cure for at least two days before beginning the tiling project.

Once the cement board is laid and sealed, you will have a flat surface that is ready to be tiled. The underlayment will provide a water proof barrier that is stable enough to protect any tile that is set on it.

Tips & Warnings

Make sure that you use the proper blade when using a power saw to cut cement board as you will damage any blades that are not intended for this.

Make sure that all underlayment is level. If there are any screw heads sticking up it may damage the tile.