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Cement board bowing problem - bathtub backsplash

Cement board bowing problem - bathtub backsplash


Old 06-17-19, 10:05 PM
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Cement board bowing problem - bathtub backsplash

I am redoing the tile backsplash in the bathroom. I have the old tile and cement board removed, and in the process of reinstalling the new cement board, I have noticed a problem that is causing the cement board to bow/flare outward. The lip of the bathtub is not flush against the framing. In some cases, there is a gap more than 1/4 inch. As such, if the cement board is installed so that it sits over the bathtub lip, it bows outward since the studs are effectively too far "recessed."

I'm hoping the 3 photos and 1 drawing illustrate what I'm talking about.

What is the best possible solution? My current plan is to install 1/4" plywood on top of the studs to cover the gap, then install the cement board on top of the plywood. The end result would allow the cement board to remain perfectly straight without any bowing.

See the final attached drawing for an example.

Is there any problem with this approach? Any better approach? If I were to go this route, I'm assuming I could just screw the cement board right on top of the plywood (making sure to set them in the studs, not just in the plywood). I will be doing all of the waterproofing op TOP of the cement board with AquaDefense, not behind it.

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Last edited by PJmax; 06-17-19 at 11:20 PM. Reason: reoriented/resized pictures
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Old 06-17-19, 10:16 PM
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I always shim the studs out like you suggest.
Old 06-18-19, 05:25 AM
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Yes, shim out the studs as needed. Plywood works for bigger thicknesses, then luan and even tar paper for fine adjustment.
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