Drywall to Backerboard transition in tiled showers

by Roger

drywall, backerboard transitionWhen you tear out and rebuild your shower walls you are left with a transition between the old, existing drywall and the new stuff – cement backerboard or drywall (if you’re using kerdi). Whaddya do with it? And how do you do it? And why am I the one asking questions – that seems backwards.

If at all possible, when you remove the old stuff you want to cut a straight line down the drywall to make for a clean transition. If it isn’t straight or was simply torn out without any regards to actually rebuilding it, then find a spot where you can cut a straight line from top to bottom. You want to have a level line for your transition.

So before you begin you want something similar to that horrible graphic right there I just created with a bottle of scotch and my toes. The left side is looking into the wall cavity with one stud, that big brown looking thing? Yeah, it’s supposed to be a wall stud. You are not allowed to give me crap about my lack of Photoshop skills!

drywall, backerboard transitionWhat we need is a way to shore out the new substrate (backerboard) to be solid and on an even plane with the existing stuff. We have a very, very specialized item for this. Listen carefully, because it’s a deeply guarded secret. Ready?

It’s a  2×4.

Take a 2×4 and cut it to the length of either the entire wall or simply from about six inches from the top to six inches below the bottom. The latter is often the only way to do it – you still need to be able to get it into the wall cavity over the tub and around the other studs. It needs to fit in there.

Just take the 2×4 and get it into the wall. Turn it so that the width (3 1/2″) is split between the open space and the existing drywall. There will be 1 3/4″ behind the existing drywall and 1 3/4″ to screw the backerboard to. Once it’s in there it will look nothing like that second horrible graphic – but it will give you the gist of it.

You can see 1/2 of the 2×4 and the dotted line on the drywall outlines the other half. Just screw right through the drywall into the stud to hold it in place.

drywall, backerboard transitionNow you can take your cement backerboard (or whatever your substrate is going to be) and place it up to the edge – leave about a 1/16″ gap between the backerboard and drywall. Then just screw through the edge of your substrate into the other half of the 2×4.

Make sure you measure whatever product you’re using for your substrate. Your existing drywall is likely 1/2″ thick – your substrate likely is not – it is probably a touch smaller. To get them even and on the same plane you can use regular drywall shims behind it.

1/2″ backerboard is rarely 1/2″! It is often smaller – make sure you measure it and shim it out as necessary. Once you get it installed you still need to tape and mud the seam. Just use the same alkali-resistant mesh tape and thinset that you’re using for the rest of the backerboard seams. Don’t know what I’m talking about? Read Installing backerboards on walls for shower tile.

Once that’s all finished you can install the tile as normal, just like the photo below. The transition is directly under the bullnose tile on the edges of the shower. And yes – you can paint right over the thinset if you need to.

Tiled shower with backerboard transition

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Hi Roger, when our shower was tiled years ago, the top tile was actually a tile cut in half (no bullnose, etc). I am ripping these top half tiles out and replacing with a full, properly bullnosed tile. The durarock is flush to the drywall and I am not going to rip out a half tile width of drywall and section in pieces of durarock. So, I will be placing the tile half on the durarock and half on drywall. Any suggestions for best adhesion? Thanks!



I need help with getting a level plane on my tub surround. The hardie board is sunk in where it meets the drywall. What can I do to correct this?



My Hardie Backer Board is not on the same plane as the drywall outside the tub. The drywall is thicker by 1/2″ How do I correct this, please? Plus the guy who installed it left 1/2″ gaps between joins in some areas, is this ok? Should I apply thin set, then tape and more thin set over tape? I am having to do it myself as I discovered the man I hired was arrested, and in the county jail. Any info would be truly appreciated.



Roger, Hopefully this is an appropriate category for this question, others didn’t seem right. My Kerdi membrane shower is progressing nicely, or course learning as I go. Today’s question: because I changed my tile layout plan as I went along, the top tile will end above the Kerdi. Kerdi ends about 79″ above finished shower floor but top tile is 1″ above that. Is this acceptable with silicone chaulk along tile/Sheetrock edge? Or do I need to add some more Kerdi? Thanks in advance.



Question: I am replacing a ceiling in a bathroom and the tile on the wall goes all the way to the ceiling. When I put the greenboard on the ceiling how do I join with the wall tile (where the tape and then mud would go if it was drywall or green board and not tile on the wall)?



Hi Manny,

You can’t unless you remove the top row of tile, then it’s just tape and mud as normal. The best you can do without doing that is silicone and hope it doesn’t move much.



I am installing a tile shower in my basement, and will need to transition from existing drywall to hardiboard. When you install the 2×4 this way, is it strong enough to hold when installing screws through the backerboard and into the 2×4? Will it push the screw heads through the sheetrock as there is nothing behind it to support it?



Hi Rastussir,

Yes, it’s strong enough, unless you’re trying to push the screws in with undue force. Never had any issues with that.


Eric Sadler

I squared up my walls and leveled up my studs. The I put up the hardiboard. In certain spots where the hardiboard and my sheet rock meet it is unlikely even. The hardiboard comes out fear there than the drywall. Not sure what to do.



Hi Eric,

If you don’t want to pull down the backer and shim out the drywall (who wants to do that?) you can always float the drywall up to flush with the backer and repaint.


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