Set a level on the subfloor to verify that it is square and level. Inspect all of the sheathing to make sure there is no damage to any of the sheets. Brush off any dust and debris from the area with a broom and dust pan.
Measure the length and width of the floor in the room. Write down each number and multiply the two together to get the total square footage of the room. Divide the number by the square footage of a sheet of Hardibacker, which is 15, to figure how many sheets will be needed.
Spread thick dry-set mortar along the corner of the room where the first sheet will be installed. Spread it out with a trowel. Smooth the surface until it is even across. Set the first sheet of Hardibacker on top of the mortar at the corner leaving a gap of 1/8-inch from the edge of the wall for expansion.
Drive Hardibacker screws every 8 inches throughout the entire sheet. Keep the screws at least 2 inches from each corner of the Hardibacker and 3/4-inch from the edge. Set the fastener heads flush with the surface of the Hardibscker when driving them in place.
Spread out the mortar in the next spot and place the second piece of Hardibacker next to the first, leaving a gap of 1/8-inch between the two to allow for expansion. Install this piece and all of the remaining pieces in the same manner until reaching the end of the first side.
Measure and mark on the final piece of the first side where the cut will need to be made for it to fit. Line up a T-square along the mark. Score along the mark with a utility knife. Repeat the process until the board can be snapped in two. Install this piece just like the previous pieces were installed and continue in the same manner until the room is complete.