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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tony

Hi Roger_
I have a problem which is not shower related but has to do with such transition. I am trying to install a mosaic backsplash. Normally I’d just attach them to drywall which is the case for 2 of the walls here but on the 3rd wall there is too big of a gap between counter and the wall (bigger than width of the tile). I have been thinking about screwing a 1/4 cbu to studs but on top of the existing drywall to close the gap. This wall (or the planed cbu) will terminated to a perpinducular wood panel (fridge wall panel) on the left, wall cabinet on top, and counter on bottom. :?: My question is regarding the right side were its perpindicular to drywall which would also be covered with same mosaic (continuation of backsplash). Is this solution really a solution at all. Do i have to tape the cbu to drywall at all since both covered in mosaic and no water in this area. I really appreciate your input and apologize if my question is unrelated to the topic. Thanks Tony

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Roger

Hi Tony,

That will work just fine on a backsplash. You can use a pencil rail or what is called a ‘mud edge’ to cover the end that is not terminating at a vertical stop.

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daren

Hello,
I have already installed hardiebacker and taped it up. I also taped the edges where the hadiebacker (shower wall) meets the wall of the bathroom (greenboard). I sealed this transition already with mud and tape thinking I was well outside of the shower…after planning my tile layout I realized the bullnose needs to be placed directly on the seem to make it for right. Being the the backerboard in the shower is not flush with the wall and sits back what is the best way to even it out? I was told to Feather thin set from the bathroom wall arross the backer board and to bring it far out to make a smooth transition between The greenboarand backer board. Is this correct and do I need to do anything to help the thin set stick to the hard thin set once it dries??.how should i proceed to make the two flush?? Thanks

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Roger

Hi Daren,

That is the correct way to do it. The new thinset will bond just fine to the cured, you don’t need to do anything special to it.

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Matt

Thanks Roger. So, it sounds like I should not cut the height of the bullnose to match field tile grout lines but instead just play around with placement to find an aesthetically pleasing layout? Thanks – Matt

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Roger

Hey Matt,

I would. You can always cut the bullnose down, they always seem to be noticeable on the cut end, though.

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Matt

Hi Roger,

I’m in the home stretch. Shower with tile (porcelain) base and surround. The shower wall is a couple inches out (proud) vs. the bathroom wall so I planned to do a tile return with bull nose.

The field tile is ~ 10″ tall and the matching bullnose is ~ 13″ tall. What is the typical approach? Cut the bullnose to ~ 10″ tall so grout lines match field tile? Other?

Thanks in advance. — Matt

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Roger

Hi Matt,

Normally if you cut the bullnose the cut edge will show. I would begin by offsetting the bullnose by 1/3 halfway up the wall. It’ll jog from the 1/3 in both directions, but not enough to be noticeable. And your next question is why not 1/2. :D Because it’ll be noticeable.

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Matt

Thanks Roger.

I did some dry fitting and made some more precise measurements. The field tile is 9 7/8″ tall with a 1/8″ grout line. The bullnose is 13″ tall.

With the bullnose offset by 1/3 half way up, there are points where the field tile grout lines are missed by 1/8″ (either before or after). Seems like this might look strange. Am I thinking about this correctly?

Thanks,

Matt

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Roger

Yes, but you’ll only have two of those. If you begin in the center one will be 7 feet high and the other at 1 foot high. It’s about the only way you can make non-matching bullnose sizes like that look decent. Play around with it, whatever you think looks best is the best option. :D

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Jason

Slight variation to the posts I have read thus far on this topic. I have removed old tiles/sheetrock to studs, but my cut is along tile that will remain over sheetrock. So I am butting up new hardiebacker 1/2″ (with a little gap, of course, to an existing sheetrock/tile layer. Mesh tape won’t fully overlap the seam. This is the reality on most of the sides where I removed tile/sheetrock and replaced with hardiebacker. My question is: Do I use thinset in these gaps without the tape? Do I use silicone? Do I use thinset and tape, but with no overlap since none exists? If the answer is remove another row of tiles to expose more sheetrock, I’m afraid I’ll be redoing the entire shower and not just this one section. Where the tile is stuck, it’s stuck.

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Roger

Hi Jason,

I would just use silicone to prevent water from wicking into the drywall side. As long as it sits flush with the drywall it’ll be fine.

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Neil Garber

Just bought your ebook on waterproofing a tub enclosure. Gonna use the paint-on membrane method. But first, a problem:
I’m trying to work around existing plaster walls, above and next to the alcove. Finished, the alcove is 59.5 inches. Where it’s down to the studs, it’s 61. I need to shim to 60 for the new tub, that’s simple enough, but what do I do with the walls? The plaster is about 3/4 thick. If I shim ( will probably need to sister nailers) and install 1/2 board, that means I’ll have the board sitting at the top of the lip and proud by about 1/4 on each side. Does that sound right? Thanks.

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Roger

Hi Neil,

Yes, that does sound right. The backer can stick out over the flange as much as you want, it just can’t be behind it.

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Lost DIYer

Hey Roger-

Curveball for you: whilst I was away from my bathroom project, a buddy put up 1/4″ Hardiebacker on my shower wall. No problem, cause Hardiebacker says the 1/4″ board is suitable for shower walls. However, now my backer to drywall seam is off by a 1/4″. Can I slap a second layer of 1/4″ board over the first to make it flush? And if so, should I put thinset between the two layers, or liquid nails, or…? Or will just screwing the second layer to the stud suffice? Thanks in advance for the advice.

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Roger

You should remove the 1/4″ and replace it with 1/2″. 1/4″ should not be used on shower walls, the height difference is just one reason, it doesn’t create enough stiffness between the studs. If you must, though, just put another 1/4″ layer over the first, nothing between.

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John

I am confused. You mentioned the backer board to dry wall transition was beneath the bullnose tile. I thought we weren’t supposed to stick tile to dry wall. What am I missing? Is half the bullnose tile stuck to dry wall with thin set? Thanks.

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Roger

Hi John,

Yes, half of the tile is stuck to the drywall. Where did I say you can’t stick tile to drywall? What I HAVE said, continuously, is that you can not have drywall as your substrate inside a shower or wet area, but you can absolutely stick tile to it. It just can’t be inside the shower where water will disintegrate it. :D

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Amanda

The fiance’s dad helped us install the cement board along the edges of the tub and drywall. I have a couple of questions I will do my best to describe:

1. Uneven backerboard placement on tub rim: the back wall is flush with the lip of the tub, however the long tub wall and wall with plumbing is recessed from the lip of the tub 1/8″-1/3″. The wall with the plumbing contains two shelves, which are secured in multiple places to the studs, and makes it difficult to remove. If I compensate with thinset my fear is it will be noticeably protruding.

2. How do I address 1/3″-1/2″ gaps between the cement board and the top edges of the ceiling? The future father-in-law said not to worry about it, but I’m concerned it’s too large to tape and seal over.

I asked to put the project on hold until we resolve these issues. Any input would greatly be appreciated!

Thanks.

Reply

Roger

Hi Amanda,

1. The only way to solve that is to either remove and shim the wall out or use more thinset beneath your tile. You can do it with thinset if you make sure to use a straight-edge and keep a flat plane. If you do not then the protrusion at the bottom will be noticeable.

2. That is no where close to too large to tape and mud, it’ll be fine.

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Amanda

Thanks Roger, you have been an incredible help!

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Maxim

Really helpful site you have. Thanks

Could use some advice with my scenario of having a hardiebacker wall lining up against drywall with the hardiebacker being about 1/8″ deeper than the surface of the drywall. The drywall cut is fairly good so I’m considering just putting a bull nose pieces down the line and filling the gap with drywall mud as I go over it after the tile is in place. It’s too late for shims unfortunately. Do you have any other ideas how to approach it?

The other question is about the wall to ceiling transition. Should I tape (the alkaline resistant stuff or otherwise) here? Skip it and just tile as high as possible and fill it in with silicone? I’d really rather not repaint the ceiling if I can avoid it and my tile is nearly white so I’m thinking generous use of white silicone for any remaining gap.

Pictures here to help visualize (I hope links are ok).
http://imgur.com/a/NqTZ5

Thanks!

Reply

Roger

Hey Maxim,

That would be your best bet if you can’t shim it anymore.

Just leave about 1/16″ between the wall tile and ceiling and silicone it.

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Jason

When tiling around just the tub, I plan on going up to about 10″ from the ceiling and maybe 6″ past the tub so I can bring it down to the floor. What do you recommend.

I love the way you made shower shelves in the picture. What did you use to finish off the edge of that 2nd shelf.

Thanks

Reply

Roger

Hi Jason,

I normally take the full tile straight up from the tub edge then have the bullnose run down to the floor. The tile extends the width of the bullnose (normally 3″) outside the tub. The shelves just have bullnose on the edges.

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Gil

Ok, thanks for your response and that makes things much clearer for me. I really benefited from your download on waterproofing. One last question if I may? When tiling the bottom coarse, which would be last I assume, how much would be figured for a gap above the tub ledge? The grout line width or something narrower to just allow for moisture flow?

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Roger

I normally go 1/16″ to 1/8″ above the tub.

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Ladd

Hi Roger,

I am installing a 1/2″ hardiebacker substrate with a transition to an existing 1/2″ drywall. The transition occurs on a stud that needs to be shimmed out in order to be even with the other studs that the backerboard attaches to. But if I shim it out to the point where it becomes even for the substrate, it will be out almost 3/8″ past the drywall. What should I do?

Thanks!
Ladd

Reply

Roger

Hi Ladd,

You’ll need to either shim out the drywall as well, or shave down the studs on that wall so they are in line with the last stud the drywall is attached to.

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Frank

Roger,

I may have what is the reverse of this problem. I did a new install of a tub in my basement. I had to frame out further than the existing wall by roughly a half inch. I installed a plastic wall surround directly to the studs. Now I’m wondering the best way to tie these two walls together. Again, the wall is just offset by a half inch. Should I just trim it with a quarter round?

Thank you,

Frank

Reply

Roger

Hi Frank,

Do you mean the shower substrate sticks out 1/2″ past the wall? Or the other way around? If the former then you can use 1/4 round, a schluter trim turned backwards or a ‘mud cap’ trim edge. If the latter then shim out your shower wall. :D

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Tom

Hi Roger,

I’m using 1/4″ drywall over my existing drywall to make the transition to the CBU flush. But, I am using large 12×24 wall tile in the shower finished off with bullnose on the edges. Because of the large tiles I’m using a 1/2x 1/2 x 1/2 square notched trowel. I’m afraid that the thickness of the thinset, several coats of Redgard and the tile itself will create such a large “lip” and it will not look good. Should I shim out the drywall more than 1/4″ or do something else?

Thank you,
Tom

Reply

Roger

Hi Tom,

The bullnose goes from the tile to flush on the wall. If there is build-up that is how to compensate for it, that’s what it’s for.

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Chris

Hi Rodger,

Before reading this site, I made a booboo. In my sheetrock to backerboard transition, I used mold resistant mesh tape and joint compound. There’s about 4 inches of jc on backerboard. Will it be a problem Hydroban-ing over this or should I sand it down and redo it correctly. Thanks!

Reply

Roger

Hi Chris,

Go ahead and hydroban over it.

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Larry

Hi Roger,

I am tiling a kerdi board shower and decided I don’t want to try tiling the ceiling. I have already installed kerdi board on the ceiling and used unmodified thinset and kerdi fabric over the screws and corner joints. Can I skim a coat of thinset on the ceiling to make it smooth and paint it instead of tiling it? Thanks for your help.

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Roger

Hi Larry,

Yes, and thinset can be sanded and finished just like drywall (you’ll need to prime before paint).

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Larry

Thanks for the quick response. Do you mean dry sanded as in with sandpaper after the thinset dries or do I use a damp sponge when the thinset is starting to set to smooth it?

Also, do I prime and paint with latex or oil based?

Thanks again.

Reply

Roger

The sandpaper or sponge will work. Using both works better. Either paint will work, I prefer latex.

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Madi Ha

Hello, My husband and I are installing tile into our bathroom we have removed all of the sheetrock from behind it and replaced with hardboard, however there is a 1/2 inch gap between the hardboard and the sheetrock that is on the walls. How do we correct this?

Reply

Roger

Hi Madi,

Tape and mud it with thinset and alkali-resistant fiberglass mesh tape.

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Gil Costa

HI Roger,

I am using your traditional waterproofing method of a plastic vapor barrier under 1/2 ” durock which butts up with 1/2″ green board at the edge of the tub base much like your diagram above. The problem I ran into is that I used a finished edge on the drywall and a cut edge on the cement board at the transition resulting in an uneven transition by approximately 1/8 inch in spots. Can I even this off with thinset when I overlap with tile? and if so, how can I finish the edge of a bullnose edge which will sit a little higher when completed? I am thinking caulk. Also, on the topic of caulk, do I caulk the corners of the shower instead of grouting if I caulked them before tiling?

Reply

Roger

Hi Gil,

Yes, that can be compensated for with thinset as you set your tile. Silicone (or caulk) to finish the edges where the bullnose meets the wall. Yes, you always need to silicone your corners (in the tile as well).

Reply

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