Step 1 - Measure the Area
You will first need to measure the area that you plan to install the cement board in. Take your tape measure and get the length and width of the room. Multiply the two numbers together to give you the square footage that you need. Most cement board comes in 3'x5' sheets so you can divide this number by 15 square feet. Once you get this number, you might add an extra sheet just to be safe.
Step 2 - Apply Thinset
Before you can put in the cement board, you will need to apply thinset to the wood subfloor. Many people skip this step and end up with problems down the line. Use a trowel to apply the thinset evenly to the surface of the floor. This will provide a nice and consistent surface for the cement board to be attached to.
Step 3 - Put the Cement Board in Place
After you have applied some thinset to the floor, you will need to press the cement board down into it. Make sure that you press it down firmly and evenly across the board.
Step 4 - Screw the Board in Place
Once the cement board is firmly down into the thinset, you need to screw it down into the floor. Use screws that are long enough to go down through the board and into the subfloor below. You will notice that there are many holes in the surface of the cement board. Each one of these holes needs a screw in it. Use your electric drill to screw in the screws. You can nail the cement board in place as well if you are more comfortable with this method. However, screws traditionally work better for this application.
Step 5 - Cut the Cement Board
In order to fit the cement board into the room, you will need to cut it to size. You ccan use a saw but this will most likely create a lot of dust in the room. Another way to do this is to use a carbide tipped blade to score the surface of the cement board. Keep scoring it until a defined line has been made in the board. At this point, you should be able to break the board cleanly on the line.
Step 6 - Cover the Seams
Selected from: https://www.doityourself.com/stry/how-to-install-cement-board