How to Install HardieBacker Board in a Shower Tub Surround

Measure the square footage for the walls around the shower tub surround. HardieBacker comes in sheets that have 1/2-inch 4-by-8-foot or 1/2-inch 3-by-5-foot dimensions that are used for wall installations. Add 10 percent for errors in installation. If the 4-by-8-foot sheets are going to be used, then divide the total square footage by 32 to determine the number of sheets needed to cover the walls. If 3-by-5-foot sheets are going to be used, then divide the square footage by 15 to determine the number of HardieBacker sheets to get. Always round up to the nearest whole number.

Measure where the HardieBacker edges will land on the wall. Ensure there is adequate framing to support the HardieBacker edges. HardieBacker is installed with 1 1/4-inch exterior counter-sinking screws. There are screws that are specifically made for HardieBacker, as well. The screws are installed 3/8 to 3/4 inches from the edges and 2 inches from the corners. 2-by-4-inch lumber is the minimum recommended size for the proper framing for HardieBacker. If the width of a wall cannot be covered with a single sheet, then the joints between the corners must be staggered. Each joint must end on a different stud in the wall to be considered staggered. 3-by-5-foot sheets will typically cover the walls on a standard tub surround with minimal cutting and minimal joints.

Measure the distance across the walls and cover all the studs with a moisture barrier, such as roofing felt paper. Measure and mark the first piece of HardieBacker with a chalk line. Leave 1/8-inch gap in each corner of the tub surround for expansion and contraction. Leave additional 1/8-inch expansion joints every 12 feet, if any wall exceeds that distance.

Score the HardieBacker with a carbide tipped scoring blade on the chalk lines, using a 4-foot level as a guide. Stand the HardieBacker on its edge and snap HardieBacker along the scored edge. Install the HardieBacker with 1 1/4-inch exterior counter-sinking screws on the wall leaving a 1/4-inch gap along the bottom edge near the tub. Install the 1/4-inch exterior counter-sinking screws every 8 inches around the perimeter of the HardieBacker and on every stud with the first screws starting 2 inches off the corners. Do not install screws within 2 inches of the corners.

Cover all the walls with HardieBacker. Measure and mark any HardieBacker that will have any plumbing fixtures penetrating through the wall before installing the HardieBacker over them. Use a carbide tipped masonry bit to drill the holes. For larger holes, use a circular saw with a carbide tip blade.

Measure each joint and corner and cover with mesh joint tape. Mix latex thinset that complies with American National Standards Institute A118.4 regulations and water together until the mixture has the consistency of peanut butter. Spread the thinset over all the joints with a margin trowel without leaving humps or baring the mesh joint tape. Allow the thinset to dry overnight. The HardieBacker is now ready for tile.