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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My house was drywalled with 5/8″ rock. So I bought Hardibacker that say’s it is .42 and 5mm plywood (why they carry one metric sized sheet, I don’t know) that is .20, ripped the ply down to 1.5″ strips and tacked them up to the studs. Then I put the first hardibacker up figuring .42 + .2 = .62 which is awful close to .625 or 5/8″ rock. Well, I knew the sheetrock crew made amazingly nice walls, I didn’t realize that meant they floated every square inch of the rock with mud to make them smooth. So my 5/8″ walls are definately more than .625. Trying to figure out how to make up the difference. Should I take down the .2 ply and put up .25 or just staple paperboard shims to everything? Since I’m gonna put 1 5/8″ hardi screws through everything I thnk it shouldn’t make a difference, but then again I don’t like that much cardboard in my walls. Any opinion?
Just a note, just bought an impact driver today. I have had a really good cordless 18v Makita drill for years (like 10, been through 2 sets of batteries, yes I may be sentimentally attached to that drill) that I have used to drill 2 1/4″ holes, drive lags, etc. However, when putting those screws into Hardibacker 500 it just couldn’t sink them flush. So I gave up and bought a new impact / drill combo and man, what a difference. That impact thing you have to be careful not to overdrive the screws. Hardibacker must own Makita or something and found a way to make us upgrade our old reliables (that and they quit making batteries to fit my old reliable). If anyone out there is thinking of putting up Hardibacker and don’t have an impact driver, I’d recommend getting one.
I would probably just remove the .2 and use thicker ply shims. That’s a lot of cardboard. It won’t make any difference, but if you’re like me it’ll still bug you.
Yeah, an impact driver makes a world of difference! I actually do own two makitas, even though I’m a DeWalt whore.
Good drills.
Thanks! And thanks for a great site!
Roger,
I appreciate the article you wrote. Very helpful.
Regarding the drywall section, where the cement board and the dry wall meet (well there will be a small gap filled in with thinset and taped appropriately), but noentheless, I was wondering if it is necesarry to give 1/8″ gaps on the rest of the drywall? (for example, where the drywall meets the floor, meets the ceiling, and meets any other walls) Do you need 1/8″ gaps there as well or only for the cement board areas?
Hey Chris,
Only in the cement board areas. The drywall transitions get taped and mudded with drywall mud. You should leave a space there to lock in the drywall mud, though.
Roger,
To confirm, you suggest to use drywall mud and drywall tape for the cement board/drywall transition seam? (Instead of thinset and alkali-resistant mesh tape as used in the hardiebacker to hardiebacker seams).
Thanks for your help,
Chris
Nope, sorry. Mesh tape and thinset for the backerboard – drywall transition (and any backer area you’re taping) and just tape and drywall mud for drywall only.
WHAT IF THE TRANSITION LANDS WAY AFTER THE TILE ENDS CAUSE OF STUD PATTEREN AND PIPES IN THE WAY?NO ROOM DO YOU STILL USE THINSET CAUSE IT WILL BE OUTSIDE OF THE SHOWER AREA?
THANKS
JESSE
Hi Jesse,
Yes, you can still use thinset outside of the shower area.
This site is a lifesaver.By far some of the most credible bathroom information on the web.
I’m replacing the drywall on the lower half of a tub surround with hardibacker. Unfortunately there is a small section towards the rear wall (8″ approximately) where I am unable to remove the drywall. I am going to join the hardiebacker this section. The two planes meet at edge of the tub flange – slightly behind the corner where the back wall and side wall meet.
My questions:
1)Should I leave a space between the backerboard and drywall?
2) Should I do anything to waterproof the edge of the drywall at the butt joint? Apply thinset over the edge and Redgard on top?
3)Should I caulk this corner joint? Is it ok to put Redgard at this corner (which is also an intersection of drywall and hardiebacker)?
4)I need to shim the studs to account for the tub flange (1/8″) – can i put Redgard on top of drywall shims?
Thank you!
Clarification on question 1 – talking about a space at the butt joint. Should I tape and mud the joint?
Do not tape and mud the corner. Just fill with silicone and redgard it.
Hi Ander,
Any place your backer butts to or against the drywall should have a 1/16″ – 1/8″ space between the two. If the seams are on the same plane then tape and mud it, if there is a change of plane (corner) fill the gap with silicone. After you do that coat the entire area with redgard to waterproof it, including the corner. Yes, you can put redgard on the shims.
Hello Roger
We are building a new house and I will be tiling a walk in master shower. The plan is to use Kerdi over the Hardy Backerboard on the walls and ceiling. You have previously directed the backerboard joints should be filled with thinset and taped and floated with alkali-resistant mesh tape. This is probably a foolish question but is the thinset modified or un-modified? Also, any problems using the Kerdi on the ceiling? I’ve never put tile on the ceiling so any advice regarding proceedure is greatly appreciated. Thanks
Hey Warren,
Not a foolish question at all, especially given that Schluter tends to confuse the modified-unmodified debate with absolutely everything. For taping and mudding the seams it really makes no difference. When using kerdi in your shower you actually do not need to tape and mud the seams – the kerdi does the exact same thing all in one step.
Kerdi is fine on the ceiling. Just make sure to give it a good day to cure before hanging tile on it. I have a post about ceiling tile here: Installing tile on a shower ceiling.
Hello again,
I have to tell you, I took your advice and it worked great and looks good so far. I scrapped the sheetrock and put up 1/2″ hardi board. (took down the plastic vapor baiirier first, its on exterior wall. I have purchased kerdi membrane, thats why I took down the vapor barrier. Everything looks great except for one problem that I hope you can help me with without takking down the hardiboard. Here it is, on the back wall, the hardiboard butts up to the old sheetrock. I have a little depth problem between the two with the hardiboard about 1/8″ lower than sheetrock. Is there something that I can use to fill this? and if not, can I just shim that 1 stud where they meet, I could do this by backing out the screws and slide a shim in there. I jus didnt want to have too much of a outward bend with the hardiboard from the stud to the right of it. I really dont want to take all the hardi board off and shim every stud. Could I use a little thinset to fill or even joint compound on the hardiboard since I am putting kerdi over the hardibaord. If thinset and kerdi will stick to the joint compound, moisture should not get back there. Please let me know.
Thanks
Hey Jim,
Ideally I would remove that piece and shim all the studs – but you already knew that.
You can float that out with thinset from the drywall to get a flat surface. Stay away from the wall mud. No water will get back there behind the kerdi – but the thinset has water in it and it may soften the wall mud, that’ll create problems. You can float anything back there with thinset. I would maybe put the shims on the outer part as you’ve described and float out from there toward the inside corner until it’s relatively flat – then embed your kerdi with a straight-edge to ensure a flat substrate.
Hello, Roger. Thank you for all the solid information you share with all those who come to see and appreciate.
I am in the process of a bathtub with tile surround remodel. Tub is in and good to go and I am moving on towards the tile. The tub fits tightly against the plumbing wall and the 5′ side. But on the back corner of the tub, there is a 5/8″ gap from the framing and nearly a 3/8″ gap were the tile will meet the drywall. That is an exterior wall and it is badly out of square, as I found out when I replaced the flooring on this 2nd floor.
I have some potential solutions:
1. Tear out the drywall on the entire wall and shim as needed. I would rather not do this, as there is a window with corner bead and I would have to paint adjacent walls and ceiling.
2. Make the 5/8″ shim on the far corner, 3/8″ on the other, and shim accordingly in between. This would cause a need to float the drywall out as far as possible to maintain appearance of flatness. And if so, could I thinset and tape the drywall/cbu joint even with the cbu being proud 3/8″ (maybe slightly less than 3/8″)
3. Plane and cut studs accordingly. Probably too difficult and time consuming.
4. I had thought the easiest thing to do might be to shim accordingly and use 1/4″ backer, but I am not sure just how beefed up the framing would need to be. Maybe 8″ on center or maybe run 2×4 on the flat horizontally at 8″ on center (or closer together if necessary). This also might be a little time consuming on it’s own in addition to dealing with insulation on this exterior wall. There would only be an 1/8″ or so to float the drywall out.
5. Another thought I had would be to add new drywall over the other drywall.
You have any ideas for me? I think I like the 1/4″ cbu, I just don’t know how much framing it will take to be acceptable. I could also put in 1/2″ plywood in between the studs but that would be a pain and would require lots of blocking, would lose some r-value and it would be a little challenging to maintain flatness.
Long question with some rambling, I know. Let me know what you think.
May we all find truth,
Daniel
One other possibility I just thought of would be to shift the tub to that back wall so that I would only have 1/4″ in the far corner and could pad the plumbing wall out 3/8″, if there is enough room that the drain can shift this much(it is all pvc and may have enough flex to move back 3/8″) and the shower valves won’t be left too far back in the wall. I definitely don’t want to redo the shower valves. If the shower valves were too far back to do this, perhaps I could use 11/32″marine plywood, and then thinset 1/4″ cbu to the ply and screw to the ply only? I wonder if anyone has tried that one lol. Even if that would work which i suspect it wouldn’t be strong enough, where would I put the vapor barrier? Behind the ply or marine grade ply perhaps I suppose but don’t we don’t want that gaining moisture. Waterproofing the cbu may be better in that case.
Lots to sort out but thanks for everything,
Daniel
and what the hell P.S>
I will be ordering one of your shower books in the near future as I am sure it is quite informative.
And so that you can understand why I would do this, I forgot to mention that the plumbing wall is 36″ and goes to drywall corner bead, which is why that would be a lot easier to deal with and I certainly would have done that to begin with had I checked the rough opening more carefully.
Sorry if this has been a bit much.
Thanks,
Daniel
Hey Daniel,
First of all lose all the ideas that incorporate any type of plywood behind your wall. Even marine grade will expand and contract due to temperature differential and humidity. I would probably shift that tub the 3/8″ and get it nice and solid there. Then shim out each stud in the corners so that a 1/2″ backer will sit appropriately over the tub flange. Once you have all the corner studs shimmed out, shim out all the studs between them using a straight-edge. Just place a straight-edge along the wall with each end on the corner studs then fill in the spaces between them on the other studs to meet the straight-edge. Although the walls may not be square, the tub should be, just shim out the studs so they meet the tub appropriately.
I am starting with my bathtub ceiling. Do to little help and time,I will be doing a small area each night can I spread a thin coat of thinset on my cement board and spread and notch the backside of my tile with thinset. That way when I start and stop I won’t get to thick a layer on my cement board.
Yup, no problem with that at all.
The transition is a little off between the hardibacker and the sheetrock. I’m going to stop the tile very close to the transition. The wall is non-textured, so I need a very smooth transition. Can thinset stick to the drywall mud? If I feather it out with thinset, then I get a bumpy wall. If I feather it out with drywall mud, then I get drywall mud onto the hardibacker side?
Hey Ben,
Thinset will stick to drywall mud. The problem is that drywall mud may disintegrate when wet. If you don’t have waterproofing over it then thinset sticking to it will do you no good.
So perhaps a thin layer of redgard over the drywall mud prior to adding thinset and tile?
Yup, that’ll work fine.
Hi Roger,
So regarding the drywall-backerboard transition…do you create the seam with the alkali-resistant tape and thinset at the same time that you are laying tile like in your post on how to install backerboard for floor tile. Or do you do it a step before and wait until the thinset dries at the seam before the tile is laid?
My specific concern is the proper step to paint the drywall. I’d like to do it before I set the tile and paint all the way to the shared seam with the backerboard. But if there’s a step between the seam creation and tile laying, then maybe I could
I plan on having about an inch of bullnose tile covering the drywall over the transition but it would be nice to not have to paint that edge after the tile is installed. It would also be nice to not have to paint the thinset and just have the thinset stop just before the edge of the bullnose and then caulk the edge with the drywall.
Any help would be greatly appreciated, Roger! You rock! Thanks!
Eric
Hey Eric,
You can actually do it either way. I do it at the same time because I don’t have time to wait around until it cures before I lay tile, it’s actually easier to do it the way you are thinking. So yeah – you can do it like that with no problems at all.
You rock!
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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