I will soon be tiling our shower in our basement finish and I have a few questions. I have done some floor tile before, but this is my first opportunity with a shower. Installing a 30"x60" wide shower pan. I will be using 1/2" Hardibacker for the shower area, 97" ceilings. I will be leaving the recommended expansion gap between all boards covered with Alkali tape and thinset.

  • Is this expansion joint also needed between the Hardibacker and ceiling drywall?

  • If so, what is this area sealed with?

  • On the back wall, should I fill the expansion joint between the Hardibacker and drywall with Alkali tape and mortar there as well?

  • What's the best way to go about where the Hardibacker meets the lip of the shower pan? Another expansion joint? Does it go over the lip and sealed at the bottom with silicone?

I'll be waterproofing with Regard. 


1 Answer 1


I was told a decade ago when doing the same thing to not worry about expansion joints in the panels but instead do them where the corners are as the expansions come from shifts in the walls in relation to the floor - basically anywhere that the tile isn't flat but makes a change in plane. In those areas use white silicone caulk not grout. Seems to have worked fine.

As for expansion joints between the cement board and the wall itself - didn't put anything like that in. Only put plastic in between the board and the wall. I'm not sure you would want the cement board floating against the wall.

  • + for plastic behind the cement board.
    – Ed Beal
    Feb 2, 2021 at 16:29

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