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I am building a shower. The entrance is framed by 2x4s. On the outside of the shower there is drywall butting up against the 2x4. So, there is only enough room for a 3/4” strip of hardibacker. I’ve tried predrilling and countersinking, but the hardibacker is still breaking at every screw hole. I’m thinking about gluing it down with construction adhesive instead. Thoughts?

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  • My question is why are you only installing a 3/4" strip of hardibacker on the edge on the door edge? – Programmer66 Jun 16 '20 at 14:28
  • Since it's outside the shower I'd just use 1/2" plywood there. – isherwood Jun 16 '20 at 14:45
  • I would not glue, backer is really not made to piece narrow pieces together. use some mortar and fill the gap. – Ed Beal Jun 16 '20 at 15:00
  • Imagine a 2x4. The edge of the 2x4 is 1.5”. The 5/8” drywall leaves about 3/4”-7/8”. – irrational Jun 17 '20 at 1:03
  • There is no gap. It is the side of a 2x4. Only 3/4-7/8” is exposed because of the 5/8” drywall. – irrational Jun 17 '20 at 1:05
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The solution I came up with was to predrill, just through the cement board, and then using roofing nails. The predrilling and the flat head of the nails kept the cement board from splitting.

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If it's breaking, then it isn't well supported on the back (or you're driving the screws too far, or your pre-dilled holes are too small). The official website says that it should be mechanically fixed at 8" on center for wood, or 16" on center for metal.

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  • A 3/4 wide strip will break every time. I never predrill backer the backer screws do the job fine. – Ed Beal Jun 16 '20 at 14:39
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With a strip that narrow you would be better off to put some screws / nails in every 6-8” below the surface and fill the strip with mortar embed mesh in the top surface for maximum strength.

The problem Your screws need to be 3/8 or more away from the edge Of backer board a 3/4 wide strip will break every time.

it is best to fill it embed some fiber mesh for strength. The screws/ nails in the wood will be enough for it to hold onto.

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