When 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!
What 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.
Now 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.
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I’ve had to shim my CBU aprox 1/4″. Will I be able to transition it to the existing drywall (which obviously I can’t shim since its already installed). Both are 1/2″, though I’m hoping like you said the CBU will be a tad less, which will help reduce the difference. Any other tips. Love the site!
Hey Rudy,
Shimming it out that much isn’t going to allow for a clean transition. You can use some sort of transition strip or decorative tile to cover up the excess height. You can also float the drywall up over a larger area to cover it up.
Whilst reading this page again to soak up the wisdom on dry-wall to backer board transitions something has occurred to me. When tiling part way up a wall and you have a horizontal transition of backer board to dry wall in between the vertical studs is there any special technique you would recommend?
Hey Paul,
No need to put anything else there. Just screw the backer to the studs and tape and mud that transition.
Roger,
I replaced a section of drywall with cement board above a shower so i can tile the ceiling. The problem I’m having is that the cutout measures 38″x 38″and the cement board is 3′ x 5′. Is it ok to tape and fill a one inch gap on each side? How do you handle awkward gaps that are too small for a strip of cement board but bigger then desired 1/8″?
Hey Tex,
I’ll normally cut the three foot piece down to within a foot or so and fill in the entire foot. I prefer to have pieces of board no smaller than a full tile, and have the seams offset from where the tile edge will be (so the grout line is not over a seam). Sometimes it’s just easier to cut it down to the size between studs and just make your seam on the stud. I never have slivers smaller than four inches or so – they’ll normally bust as you try to screw through them when they’re that small.
I am in the midst of a bathroom remodel and having torn out the tub I am confronted with an 1-1/2 drain line. Some places will allow this as code for a shower; it seems some places do not. This 1-1/2 inch drain drained the old tub (which was only being used as a shower) faster than a tile elf drains a six pack. What gives? Why do I need to use a 2 inch drain because its a dedicated shower? Can I use a reducer on the vertical just below the drain before it goes into the P-Trap? If you need 2 inch drains for showers, why do some companies sell 1-1/2 shower drains?
This is enough to drive a man to drink………..more than usual. But, I digress…….
Hey Paul,
The reason is simple – tubs will hold water, up to about 75 gallons. A shower base will hold about 7. If there is a problem with your drain it’s gonna destroy the rest of your bathroom quickly. A two inch drain both drains water more quickly and does not clog or get plugged up as easily. If you need to have a 2 inch by code (and it should be everywhere in my opinion) then it needs to be run that wide all the way back to the stack where it ties into either a two or four inch drain. Some companies sell 1 1/2″ drains because that’s what they make and they hope you won’t notice until it’s too late to return it.
Well, that’s my guess anyway, the real reason? Who the hell knows.
Sorry to be obtuse if this is in the info… I am asking questions of a builder and want to make sure the shower is built correctly especially to prevent water damage. How do you butt up drywall to backer board and prevent the moisture in the backer board from being absorbed into the drywall? I know he is butting up factory edges. Thank you, Robin
Hey Robin,
There should be a 1/16″ – 1/8″ gap between those. That gap should be filled with thinset and taped and floated with alkali-resistant mesh tape, then floated with more thinset. While thinset is not waterproof it will not wick water out of the backer, the thinset is more dense, the water will run through and out of the backer before running into the thinset to the drywall.
Thanks so mch for all your help, Roger,
Robin
Oops, Just realized my labels were out of order there… Here is a graphic with the correct labels. Sorry about that!
http://i42.tinypic.com/2zgxaon.jpg
In my opinion yes, it’s a bad idea. Unless you are installing HUGE tile there is absolutely no reason to have 1/4″ of thinset behind it once it’s installed. Even with 18×18 marble I only had about 3/32″ between the back of my bullnose and the 1/2″ drywall. You are WAAAAY overthinking the amount of space kerdi takes up behind the tile. It is made to install on the same plane as whatever surface you tile. If you do decide to do that you are committed to having a shitload of thinset behind your tile and kerdi in order to come out to the correct plane. That much thinset will shrink, which means once you set it and walk away it’s not gonna be in the same place you left it when you come back – it’ll be shrunk into the wall a bit from the thinset shrinking. And it will do that inconsistently. You’re asking for a hell of a lot more problems than that has the potential to solve.
Use 1/2″, go to the same plane, and silicone the 1/16″ gap.
Roger thank you!!!!
Thank goodness I found you BEFORE wasting time and money. I will do exactly as you said.
And for what it’s worth- I am a graphic designer by trade, and I think your Photoshop skills are quite impressive, all things considered
Thanks again!
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