When tiling over plywood, you should always put down a layer of cement backer board first, as it provides the necessary support for the tile. Follow these steps to seamlessly install a cement backer board.

    1. Prepare the Plywood Subfloor

    Preparing the plywood subfloor is crucial for ensuring your backer board and tiles don’t crack, shift, or become loose later. Rushing this first step often leads to a bigger headache down the road. 

    Start by inspecting the subfloor for loose boards, protruding nails, or uneven spots. Hammer down any raised nails and refasten loose boards with drywall or deck screws. Then, fill any large gaps in the plywood with a polymer-modified patching compound. Allow the mixture to fully cure before moving on.

    Next, sand down any high spots to create a flat, even surface. Pay close attention to seams between plywood sheets, then sweep and vacuum the subfloor thoroughly to remove dust, debris, or loose particles. Finally, you can apply primer to seal the plywood surface, which enhances adhesion and prevents moisture issues. Allow the primer to dry fully before applying thin-set.

    2. Cut Cement Backer Board To Fit

    When installing cement backer board, you should create custom pieces to fit around doors, walls, and other obstructions. Here are some tips:

    Make several passes with the knife to cut through the fiberglass mesh.

    Mark the shape first and cut along the line.

    This helps create tight seams.

    Use a rasp to smooth the edges.

    …when cutting backer board to protect against dust. Work in a well-ventilated area.

    They can be used for small spaces like around plumbing fixtures.

    3. Install the Cement Backer Board

    With careful measurements and the right tools, you can achieve a professional fit with your backer board installation. To begin, lay the cement backer board into the thin mortar, making sure to overlap any seams in the plywood subfloor by at least four inches. This overlap creates a strong, continuous foundation. 

    Next, fasten the backer board using an impact driver and backer board screws, making sure to space the screws four inches apart around the perimeter of the backer board sheet and eight inches apart across the center. The perimeter screws prevent the edges from curling. Take care to leave a 1/8-inch gap between the backer board sheets and stagger the sheets so that the four corners don’t meet at a single intersection. The gaps account for expansion and contraction.

    Cover the seams between the backer board sheets with fiberglass mesh tape. The mesh tape creates a continuous surface and prevents cracks from forming. Spread a thin layer of thin-set mortar over the taped joints to seal the seams and create an even plane. Once the mortared joints have cured, you can start setting the tile. Allow 24 to 48 hours for the thin-set mortar to fully cure before applying the tile.

    4. Tile Over Cement Backer Board

    Once your cement backer board is fully installed, you’re ready to select and lay the floor tile. You can achieve beautiful results with the right materials and some simple techniques.

    Overview video of the process: https://todayshomeowner.com/concrete/video/tiling-over-concrete-and-wood-floors/

    To start, let the thin-set mortar cure for 24 to 48 hours before tiling. This prevents the backer board from shifting.  Use a notched trowel to apply a layer of thin-set mortar over the backer board, spreading even layers across small sections at a time. Press tiles into the mortar firmly with a slight twisting motion. Use tile spacers to create consistent grout lines.

    Today’s Homeowner Tips

    I recommend working in small sections so the thin-set doesn’t dry out before tiles are applied. Follow drying times on the product packaging.

    As you work, clean excess thin-set from the tile faces with a damp sponge before it dries. Finally, allow the thin-set to cure fully (usually 24 to 48 hours) before applying grout between the tiles.

    With proper thin-set application and tile installation techniques, your new tile floor or wall will last for many years to come.

    Related: Using Warped Cement Backer Board When Tiling a Floor

    So, Is Installing Cement Backer Board a Good DIY Project?

    Installing cement backer board requires some specialized tools and materials, but it is a project most dedicated DIYers can take on. The process mainly involves careful surface prep, accurate cuts, and proper thin-set application — all skills you can learn with some research and practice. 

    That said, first-time tilers may want to hire a professional for peace of mind and to ensure it’s done correctly. 

    FAQs About Installing Cement Backer Board

    How thick should cement backer board be for flooring?

    For floor installations, use 1/2-inch or 5/8-inch thick cement backer board. The thicker board provides better support and prevents flexing.

    What type of screws should be used to install backer board?

    Use corrosion-resistant backer board screws with sharp threads to grip the cement fiberboard. Avoid traditional wood screws as they can cause cracks.

    Should the seams be taped when installing backer board?

    Yes, use fiberglass mesh drywall tape over all seams and corners to lock the two separate sheets together and prevent any movements. Embed the tape in a layer of thin-set mortar to create a waterproof seal.

    Can backer board get wet during the installation process?

    Avoid getting the backer board wet, as moisture can compromise the integrity over time. We recommend working in sections to allow the thin-set mortar to fully cure before moving on.

    Is thin-set the same as mortar when installing backer board?

    Thin-set mortar is a specialty adhesive mortar explicitly designed for bonding cement backer board. Traditional mortars don’t provide the same adhesion, so I recommend double-checking that you’re using a thin-set mortar before you start your tiling project.

    Editorial Contributors
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    Amy DeYoung


    Amy DeYoung has a passion for educating and motivating homeowners to improve their lives through home improvement projects and preventative measures. She is a content writer and editor specializing in pest control, moving, window, and lawn/gardening content for Today’s Homeowner. Amy utilizes her own experience within the pest control and real estate industry to educate readers. She studied business, communications, and writing at Arizona State University.

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    Lori Zaino

    Lori Zaino is a freelance writer and editor based in Madrid, Spain. With nearly two decades of editorial experience, she’s written and edited for publications like Forbes, CNN, Insider, NBC, Newsweek, The Points Guy, The Infatuation, and many others. Having just completed her first home renovation, she’s more interested in home improvements than ever, dedicated to bringing you fresh and accurate content to help you update your living spaces.

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