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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Keith Knauss

Hi Roger,

I am redoing a bathroom with a 3×3 shower. I hung Denshield in the shower enclosure to the ceiling. The ceiling is green board. We are planning on tiling the shower walls all the way up to where it meets the ceiling (but not the ceiling itself). Do i need to tape/mud the inside corners between the Denshield and ceiling green board? Or can i just leave it and tile it?

Thanks!
Keith

Reply

Roger

Hi Keith,

You can do either. If you do not tape and mud to the ceiling you need to have a solid silicone line between it and the tile when you’re done.

Reply

Liza

We are redoing our bathroom and the tub we had had the 3 walls built into it. When we pulled the tub out there was no dry wall behind it just the studs. Do we have to put more dry wall up and then the backer board or can we just put backer board up??

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Bill D

Hi Roger, I gutted my small 5 x 8 bathroom. Starting a remodel from a clean slate. Tiling 3 walls to the ceiling for a new shower where a tub once was….Using 1/2 Hardie backer for these 3 walls. I will ultimately transition from the Hardi backer to green board for the remainder of the bathroom. For all transitions from Hardi backer to green board, I will use drywall tape and mud. In addition, I am leaving the drywall on the ceiling and will cover with 1/2 green board. Studs are 16″ on center. Will I have any issues using 1/2 green board over the existing (nail pops everywhere) drywall?…..or should I just demo the ceiling and use 5/8 green board? Do you see any other issues with my approach?

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stefanie

I tore down my rotted shower walls the tile went behind the floor tiles .. they are tiny square ones .. I put up backerboard which sits on a concrete 2 iunch sorta so called edge .. ithe board and cement is flush but when I put the new tile against the wall there is a small gap between floor and tile the new tile wants to slide behind the floor tiles what do I do

Reply

Roger

Hi Stefanie,

Not too sure what you have going on there. Can you build out that gap using deck mud to get everything flush before setting tile on it?

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Mark

This is a follow-up to Jackie’s question regarding transitioning from cement board to drywall. Given the effort to make the entire cement board surface of each wall a monolithic structure by using thinset and mesh at the seams of the cement board, will there be a potential cracking issue at the seam between the cement board and drywall if the drywall isn’t part of the monolithic mass of cement board? And even if you use thinset and mesh at that seam, will the drywall move with the cement board, or will the drywall tear when the monolithic mass of cement board tries to take the drywall with it?

Reply

Roger

Hi Mark,

It sounds like you have WAY too much movement in there to be concerned with something as small as a drywall transition. :D Drywall and backer will expand and contract at different rates. However, taping and mudding the changes of plane with either drywall mud or thinset will be more than adequate to hold them together without problems.

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Daniel G

Hi Mr. Floor Elf Sir!

I recently installed .41 inch backerboard next to 5/8 inch drywall without using shims. I now understand this was a mistake! Is there any way to make this joint work (such as a schluter and thinset with no tape) or am I completely doomed to going backwards and replacing the backerboard to properly level?

Reply

Roger

Hi Daniel,

You’re doomed. Unless 1/4″ backer over the existing will flush it out for you.

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Rick

I am redoing my bathroom and tearing out the shower walls. First question is what is the best boards to use to avoid mold. I have heard several options and some from what I was told would be overkill. (1) Only tear out the existing mortar and apply mortar and chicken wire over it–no need for tear out (2)tear out to studs and use greenboard mortar/chicken wire over it (I always thought greenboard was frowned upon because of the humidity and moisture) (3) greenboard covered with redgard and don’t really need mortar/chicken wire because it would be a floating wall (4) using backerboard with mortar and chicken wire. I have heard about denshield boards but they are rather expensive.

Reply

Roger

Hi Rick,

Why are you intent on mudding your walls? No, greenboard should be nowhere near your shower. Densshield boards are a hell of a lot less than redgard. You should remove everything down to the studs, shim out densshield to flush with your bathroom walls, then install tile. Forget the chicken wire and all that.

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Susan Jimemez

We hired someone to do our bathroom and he forgot we wanted the tile off set and he tiled half up one wall of the shower when we noticed it. He then took the tile off and it reaped up some of the green board behind it and he covered it with joint compound which he said would be like cement and he tiled over it and said that there was no need to put new green board. my husband and I are worried about mold. Is this okay to do and if so should we make sure to seal the tile and grout twice after he is done tiling so mold doesn’t occur.

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Sissy

Hi, I am tiling shower walls in a basement bathroom. I had already installed green board before I decided to tile. Is it ok to put the cement board over the green board? I sure hope so because I worked on it all day?. I did put a moisture barrier over the green board before I installed the cement board. Any advise would be much appreciated.

Reply

Roger

Hi Sissy,

Not really a good method, but it should be fine.

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Cheryl

Hi, I’m redoing my shower. Im using mold and resistant drywall. I don’t want to take it off now but, are drywall screws ok, can I apply a thinset over the drywall and use waterproof ing membrane after. I know its alot but drywall is up.

Reply

Roger

Hi Cheryl,

You can use schluter kerdi over drywall. That is the only approved waterproofing membrane for use over drywall.

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Richard A

Is it ok to stack 1/2″ (.42″) and 1/4″ to transition to 5/8″ drywall? Anything need to go between them?

Reply

Roger

Hi Richard,

Yes, you can, and no, nothing goes between them. But it would be easier to put 1/4″ (actually should be 1/8″) shims over the studs, then install the 1/2″.

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Jackie

Hoping you can help! So we are completely redoing our whole bathroom in our old house. We are planning to tile in the bath all the way up to the ceiling. We are in the process of installing the cement backer board but have just realized we are unsure on how to handle the joint between the backer board and the ceiling. Can you give me some tips on this? We came up with the idea to use drywall in the last 6-8 inches so we could just use drywall tape and mud, but seems there should be an easier way. Also I’m fearful there will be a bit of a gap between the wall and the ceiling(the old tub surround must’ve been thicker).

Reply

Roger

Hi Jackie,

You can use regular drywall tape and mud from the backer to the drywall. It works on backer as well.

Reply

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