Hardibacker is a type of board used as an underlayment when installing tile in bathrooms. It is a mould- and moisture-resistant cement board that can also be used for various other applications. Hardibacker is sold in 3-by-5-foot sections and installs very similarly to drywall. It is screwed to the sheathing underneath or the studs in the wall for installation around a shower. This moisture-resistant barrier helps protect the sheathing underneath from water damage and supports the tile on top of it.
Measure the square footage of the room. Run a tape measure across the length and width of the area where the Hardibacker will be installed and multiply the two together for the total square footage. Divide that number by 15, which is the square footage of a sheet of Hardibacker to figure out the total number of sheets needed.
Wipe off all of the sheets prior to installation with a clean rag. Run the rag over the entire sheet to remove all the dust. This will help the bonding process between the boards and the tile.
Line up the first sheet of Hardibacker in the bottom corner of the room. Drill in 1-1/4-inch Hardibacker screws into the sheets at each dot marked on the sheets. Insert a screw 2 inches from each corner of the Hardibacker where the dots are located and every 8 inches around the perimeter.
Insert the rest of the screws at the location of each dot along the inside of the Hardibacker. Butt the second piece up to the first and leave a 1/8-inch gap to allow for expansion. Install the second piece just like the first and continue down the first side of the room until you reach the end.
Cut the last piece of the first side to size, if necessary. Measure and mark the cut line with a pencil and line up a T-square. Score along the T-square with a utility knife. Grip the board on both sides and snap it in two. Install the piece just like the previous pieces. Continue in the same manner around the room until all of the Hardibacker is installed.
Cover up all seams with cement backer board tape. Run the tape over each seam to seal the gaps. Cover the tape with thin-set mortar. Spread the mortar over the tape with a trowel.