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.