Seaming HardiBacker to Drywall

Question

I'm rebuilding my shower and using HardiBacker (1/2" thickness) in that space. I've then got normal green-board drywall that I'll be transitioning to. I figure that I'll tile up to the edge of the HardiBacker.

The real question here is whether I should seam the HardiBacker to the drywall using:

• (A) normal tape and drywall mud

• (B) paintable caulk

• (C) something else or some other solution like tiling over the seam by an inch or so, etc.

I've seen some interesting answers online like (A) and (B), and I can see advantages to each - (A) would make for a pretty smooth surface transition while (B) would allow for a permanently flexible (since the two different materials should in theory expand and contract at different rates), waterproof transition that could be repaired if a crack were to form and could be covered with grouted caulk. So in short, does anyone have some thoughts or suggestions?

A few additional notes - I'm planning to over-engineer this shower by putting Schluter Kerdi liner over the HardiBacker as I like the idea of redundant waterproofing solutions, and I like the idea of using something like KSL1400 (a prebuilt shower pan with integrated liner and slope).

Answer 1

When I did my shower, I lined it up so the Hardi/drywall seam was about 1" before the edge of my shower tiles. Then I just covered this seam with mesh tape and thinset. So when I laid tile, it overlaid onto the drywall by about 1". I then used a caulk matched to the grout color run along the outside edge of the tile where it met drywall.

The tile edge is a good 5" outside of the tub, so I wasn't too concerned with water getting through the grout onto the drywall.

This gave me a nice clean edge and avoided having to try to get tape/mud smooth on the hardibacker. I've never had any expansion issues with the different materials.