How to Install Cement Board

By
Lee Wallender
Lee Wallender
Lee Wallender

Lee has over two decades of hands-on experience remodeling, fixing, and improving homes, and has been providing home improvement advice for over 13 years.

Learn more about The Spruce's Editorial Process
Updated on 05/28/23
In This Article
Project Overview
  • Working Time: 30 mins
  • Total Time: 1 - 2 hrs
  • Yield: Install four sheets of cement board
  • Skill Level: Intermediate
  • Estimated Cost: $85 to $100

Cement board, commonly sold under trade names such as Durock, Hardiebacker, and WonderBoard, is now the standard underlayment used for ceramic, porcelain, or stone tile laid with thinset mortar adhesive. Cement board is used for most floor tile and has all but replaced plywood and drywall backer materials for wall-tile applications in wet areas like showers and tub surrounds.

Yellow electric drill installing cement board

The Spruce / Liz Moskowitz

Cement board forms a durable, stable base for tile, and it has no organic materials (unlike drywall, greenboard, or plywood) so it is not prone to mold, rot, shrinkage, or decomposition due to moisture. Ceramic tile laid over cement board is one of the most durable floor or wall surfaces you can install.

How to Use Cement Backer Board

Typical Cement Board Sizes

Cement board is most commonly sold in 3 x 5-foot sheets and in thicknesses ranging from 1/4 inch to 5/8 inch. A 3 x 5 panel of 1/4-inch cement board weighs about 30 pounds; a 1/2-inch sheet, 36 to 44 pounds. Larger, 4 x 8-foot panels are also available, but their weight makes them hard to manage for DIYers.

Choose a sheet thicknesses based on the application:

  • Floors: A 1/4-inch minimum thickness is needed, but thicker panels are also fine. 
  • Walls: Use 1/2-inch or 5/8-inch-thick cement board, not 1/4-inch. The extra thickness is needed when spanning the studs and it provides a solid base for the tile.
  • Countertops: 1/4-inch, 1/2-inch, or 5/8-inch-thick panels are all suitable for countertops. 

How to Cut Cement Board

You will need to cut your cement board to various sizes to suit your project. Knowing how before you start your project can keep you from making costly errors. Cut the cement board with a utility knife and a T-square.

  1. Score the board: Score the cement board deeply with two or three passes with the knife, using the square to ensure a straight line.
  2. Snap the board: Snap the waste area of the sheet back to break the board along the cutting line.
  3. Cut the back: The two sections of the cement board will remain attached by the mesh. Cut the fiberglass mesh along the backside of the board, as applicable, to complete the cut.

To make round or curved cuts, use a jigsaw with a carbide blade or a drill and a hole saw bit.

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What You'll Need

Equipment / Tools

  • Bucket
  • 1/4-inch notched trowel
  • Drill-driver
  • T-square
  • Utility knife
  • 4- or 6-inch drywall knife

Materials

  • 4 cement board sheets
  • Thinset mortar
  • Cement board screws
  • Self-adhesive cement board mesh joint tape

Instructions

How to Install Cement Board on Floors

  1. Assess the Substrate

    For ceramic tile floors, the cement board usually rests on a plywood subfloor (minimum 5/8-inch-thick exterior-grade plywood or OSB). If new ceramic tile is being laid on an existing floor, the cement board can usually be laid right over the existing floor finish, provided the floor is in good shape and the extra thickness is not a problem

    Tip

    There is no need to install cement backer board on a concrete substrate—ceramic tile can be applied right over concrete, provided the surface is flat, smooth, and free of significant cracks. Just be sure to add a decoupling membrane like Schluter Ditra to prevent concrete cracks from transferring to the tile.

  2. Plan the Installation

    Make a rough plan for the cement board sheet layout, based on the area to be covered and the size of the cement board sheets. The joints between the sheets should be offset by the joints in the plywood (or other) subflooring by at least 8 inches, for maximum floor stiffness. If necessary, plan to start the first row of sheets with a partial sheet to create the offset.

  3. Mix and Apply the Mortar

    Mix a small batch of thin-set mortar as directed by the manufacturer, mixing the dry powder with water in a bucket. Apply a mound of mortar to the subfloor, then spread it out in an even layer, using a 1/4-inch ​notched trowel. Cover an area just large enough for the first cement board sheet.

    Thin-set mortar dry powder scooped with measuring cup to mix with water in white bucket

    The Spruce / Liz Moskowitz

  4. Install the First Sheet

    Place the first sheet over the mortar bed. The rough or embossed surface of the sheet should face up, as applicable. Allow a 1/4-inch gap between the edges of the sheets and all surrounding walls. Fasten the sheet with cement board screws, using a drill-driver, making sure the screws are flush with the surface of the sheet or are slightly recessed. Space the screws 8 inches apart across the entire sheet.

    First cement board sheet fastened with cement board screws with yellow electric drill

    The Spruce / Liz Moskowitz

    Use only cement board screws and alkali-resistant cement board joint tape. Standard screws and drywall joint tape will corrode or deteriorate from contact with cement board.

  5. Add More Sheets

    Use the same techniques to apply mortar and lay and fasten the remaining sheets in the first row, spacing the sheets 1/4 inch apart and leaving a 1/4-inch gap at all walls.

    Cement board score cuts made with utility knife

    The Spruce / Liz Moskowitz

  6. Install the Remaining Sheets

    Continue installing sheets to cover the entire area. Remember to offset the joints between the cement board and any underlying plywood and to gap the cement board sheets by 1/4 inch. Mix fresh mortar only as it's needed to prevent it from drying before you can use it up.

    Cement board joints offset with mesh joint tape

    The Spruce / Liz Moskowitz

  7. Tape and Mud the Joints

    Apply cement board joint tape to all of the joints between sheets, adhering the tape with its self-adhesive backing. Mix more thin-set mortar and, using a drywall knife, cover the taped joints with a thin layer, much as you would do when mudding drywall joints. Tool the mortar with the knife so the tape is covered and the joints are flat and smooth. Allow the mortar to cure completely, following the manufacturer's recommended drying time.

    Cement board joints covered with thin-set mortar by drywall knife

    The Spruce / Liz Moskowitz

How to Install Cement Board on Walls

Cement board on walls also uses the same techniques, but in this case, there is no layer of mortar behind the cement board as it is screwed directly into the wall studs. Consult the cement board manufacturer for recommendations on using a moisture barrier between the board and the wall studs. This may be thick plastic sheeting or another type of water-resistant membrane.

  1. Assess the Substrate

    For highly wet areas, such as showers and bathtub surrounds, cement board typically is attached directly over the wall studs, although the studs may be covered with an intervening moisture membrane. (Some cement board products may not require the underlying membrane if the seams are properly waterproofed.)

    Tip

    In wet areas, never install cement board directly over drywall or green board. Instead, first, remove the existing surface material, then install the cement board over the studs and membrane, as applicable.

  2. Place the Cement Boards

    Stagger the cement boards on the wall, making sure that four corners never meet. Avoid forcing the boards together. A slight gap will compensate for the expansion and contraction of base materials and studs. Similarly, avoid forcing the edges of cement boards against floors, ceilings, or other surrounding areas.

  3. Screw the Boards in Place

    Screw the cement boards onto the wall, placing the screws every 8 inches. Every stud that runs behind or along the perimeter of a cement board must be fastened to the board.

  4. Tape the Joints

    Apply fiberglass mesh tape on top of all seams. Wherever tape strips meet, be sure to overlap them slightly. Avoid doubling-up tape as much as possible.

  5. Fill the Joints

    Use the drywall knife to apply thinset mortar to all taped joints. Force the mortar through the holes in the mesh tape. Run the knife along the top of the seam to even it out on each side.

  6. Feather the Joints

    If there are humps of thinset mortar, feather the mortar out across the board. The cement boards must be as flat as possible for correct tile installation. To feather, begin the knife on the highest area, then drag the knife, gradually reducing the amount of mortar.

When to Call a Professional

Installing cement boards in shower stalls and bathtub surrounds can be more difficult because the areas need to remain water-tight. You may want to call tile installers for wet areas.