How Do You Install HardieBacker Board on Cinder Block in a Shower?

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HardieBacker is a common underlayment for tile.
HardieBacker is a common underlayment for tile. (Image: blue tile background image by Galina Barskaya from Fotolia.com)

HardieBacker brand cement board is a popular substrate for ceramic tile and stone. Cement boards are highly moisture resistant, and bond well with thinset mortar; this makes them the preferred underlayment for shower stalls. HardieBacker is typically fastened to wooden or steel studs, but it can be applied to cinderblock. Cement board can be installed using common hand tools. Get a helper for this project.

Things You'll Need

  • Dust mask or respirator
  • Straightedge
  • Carbide-tipped scoring tool or utility knife
  • Thinset mortar
  • Notched trowel (1/2 in. by 1/2 in. )
  • Five gallon bucket
  • Hammer drill and 5/32-inch bit
  • 1-1/2-in. #8 flathead tapcon screws
  • Drill with Phillips bit

Cut the HardieBacker to size. Place the straightedge on the cut line, and score it with the scoring tool or utility knife. Bend the cement board at the score line to cut it.

Mix the thinset mortar in the bucket with clean, room-temperature water. Mix the mortar thoroughly until all the powder is moistened, and add water until the mixture is the consistency of toothpaste. Allow the mortar to set, or “slake,” for five to 15 minutes, then remix it. There are slight variations between brands of mortar; read the instructions on the bag.

Apply the mortar to the cinderblock wall using the notched trowel. Hold the trowel at a 60-degree angle to the wall, and work in a semicircular sweeping motion.

Press the HardieBacker board firmly and evenly into the bed of mortar. The surface tension of the mortar is normally enough to hold the HardieBacker in place.

Drill holes for the screws using the hammer drill. The exact pattern and spacing of the holes isn’t important since the mortar is ultimately what holds the HardieBacker in place. Ten to 15 holes per 3 ft. by 5 ft. sheet will do the job. Keep the holes at least 3/8 in. from each edge and 2 in. from each corner.

Drive the tapcon screws into the holes drilled in the previous step. Drive the screws flush with the surface of the HardieBacker board. Allow the mortar to cure overnight before tiling.

Tips & Warnings

  • Make sure the cinderblock surface is clean and free of loose material before applying the mortar.
  • If the cinderblock wall is stable, you may be able to apply tile directly to it with mortar.
  • HardieBacker board contains silica compounds. Silica dust will damage the lungs if breathed. Wear a dust mask or respirator when cutting it.
  • Wear eye and ear protection when using power tools.

References

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