Home Improvement Expert Danny Lipford

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How to Secure Cement Backer Board to a Plywood Subfloor


Our builder installed our tile floor on ¼” thick cement board, and the tiles are moving and popping up. Is there any way to fix this easily? -Karen

It sounds like the cement backer board was not attached properly to the subfloor using thin-set adhesive, screws, and fiberglass tape on the joints. If that’s the case, unfortunately, there’s no quick fix for this problem other than removing the tile and cement backer board and starting over.

While using 1/4” thick—rather than 1/2” thick—cement backer board is acceptable, how you install the backer board and attach it to the plywood subfloor is as important as how you lay the tile on top of it.

Here’s the right way to attach cement backer board to a plywood subfloor:

  1. Make sure the joists are wide enough for the span and spaced on 16” centers to provide a sturdy floor with no bounce.
  2. The plywood subfloor should be at least 5/8” thick on 16” centers (3/4″ preferred) and securely attached to the joists preferably with screws.
  3. Layout the cement backer board at right angles to the plywood subfloor so the joints in the backer board are staggered and don’t fall on joints in the plywood. Leave a 1/4″ gap between the backer board and walls and 1/16” gap between the sheets of backer board.
  4. Mix up and apply a modified thinset to a large enough area of the plywood subfloor to cover each piece of backer board using a 1/4″ x 1/4″ notched trowel.
  5. Position each piece of backer board in the thin-set, press in place, and attach using special backer board screws on the spacing recommended by the backer board manufacturer.
  6. Cover the joints in the backer board with fiberglass tape embedded in thin-set adhesive and allow to set before tiling.

Good luck with your project,


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5 Comments on “How to Secure Cement Backer Board to a Plywood Subfloor”

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  1. Tilton Davis Says:
    March 30th, 2012 at 10:18 pm

    I am putting down a Nuheat pad under my ceramic tile. I was planning to staple the cemnet board to the subfloor instead of screwing it. Is there a problem with screws in the cement back board and under tile heating…? Reading this article makes me think I am going to have trouble with tile shifting if there are only staples instead of screws holding the cement board to the subfloor plywood. I plan to use thinset between the cement board and plywood. Can you comment/advise me…? Thanks.

  2. garry elliott Says:
    July 10th, 2012 at 11:30 am

    hello, why does my bucket of pre-mixed thinset morter say do not use to install backer board to sub floor? thanks

  3. john brown Says:
    December 10th, 2014 at 3:35 pm

    Can I install backer board using thinset only? Grout lines have cracked. I have pulled up the tile and smoothed out the old thinset. I have a heated floor and cannot use screws. Is there anything that will adhere backer board to the old thinset? Or is my only option to take up everything down to the subfloor and start from scratch<

  4. Arturo Racelis Says:
    April 1st, 2015 at 11:48 pm

    I’m installing a prefab shower pan (36″x48″) and while I have ensured that the plywood subfloor is nailed down and level with my super solid floor joists, is there a need for a thinset mortar between the plywood subfloor and the backerboard? I’m putting cement mortar on top of the backerboard to serve as “base” to set in my prefab pan (as suggested by the manufacturer). What’s the purpose of such a step before laying the cement mortar as foundation for my prefab shower pan? Most research I’ve done does not address my kind of situation. Any response is highly appreciated. Thank you!

  5. Bob Preston Says:
    September 25th, 2015 at 6:59 pm

    I’ve installed 1/2″ cement board (wonder board) over 3/4″ hardwood floor. A very sturdy and strong substrate. I started by placing 30# roofing paper to act as bond break to avoid squeaks before installing the cement board being sure to stagger joints. Is thinset truly necessary?

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