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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  • Paula Moody

    We are replacing a tub surround with tile. We have drywall. We were going to install a backer board then tile. Is there a schluter edge product that would edge both the backer board and tile? Or should we use something different than backer board?

    • Roger

      Hi Paula,

      It depends on the size of your tile. I believe the thickest profile schluter makes for the edge is 3/4″, but I’m not sure about that. You can always get a 1/2″ and install it backwards to cover the drywall, then another butted back-to-back with it for the tile.

  • Laurie

    I bought the Kerdi membrane pdf and still a bit confused and hoping you can help. We have drank the orange Kool-Aid and are full on board with Schluter products. Doing a tub surround – we are using Kerdi board, a 12X12 porcelain tile and edging with 1/2″ Rondec. Where/how do I transition from the Kerdi board to the drywall? I want the tile to stop at the edge of the tub and not come past. The drywall will be painted. I “think” the best approach will be to use Kerdi band between the drywall and the Kerdi board, so I bring the drywall into the tub 2″ so that Kerdi band will end right where I want the tile to end?

    • Roger

      Hi Laurie,

      That is absolutely correct. That is the best way to do it.

  • Ted

    Hi Roger,

    I am tiling an alcove Bathtub and have a few questions. I am using 7/16″ Hardie backer board which will meet up with 1/2″ greenboard on the backside of tub (32″ side of tub that is opposite shower head). How do I go about covering this transition with waterproofing and tile? Will the 1/16″ gap be an issue? Also, the tile I am using does not have a matching bullnose. Should I use a schulter edge? If so, should the tile overlap onto the greenboard?

    Another question I have is on the opposite wall (32″ side of tub with shower head), there is an outside corner. How would I go about ending the tile on one side of the corner and then have it meet up with drywall on the other side or the corner in order to get a good finished edge look?

    Any help would be greatly appreciated. Thank you

    • Roger

      Hi Ted,

      It depends on what type of waterproofing you’re using. The gap will not be an issue. Yes, you should use a schluter edging. Yes, it should overlap the greenboard.

      I normally run the schluter edge right up the corner.

  • Tyson H.


    I followed the instructions per your manual for the shower (all CBU but joints with thinset and mesh). The question I have is about the drywall to hardiebacker transition. I taped that and used joint compound over it so the wall was smooth where the tile meets it. The joint compound extends 3 inches onto the backer board. The tile will not extend over this joint any more than 6″ (25%) Is the joint compound a suitable substrate for 12″ x 24″ porcelain tile? See picture, taken before I added joint compound. In retrospect, I should have maybe just gone over the transition and leave the gap in there.

    • Roger

      Hi Tyson,

      Unless you cover that joint compound with a waterproofing of some sort it needs to be removed anywhere that lies inside the shower. Water will eventually disintegrate it. You can go over that transition with thinset, you can sand, prime and paint it just like drywall mud.

      • Tyson H.

        Do you think rolling RedGuard over the entire joint would be sufficient?

        Or, should I just take a knife and trim it, remove the joint compound on the CBU and go back over it with thinset? The thinset is so “sandy” which is the reason I used the joint compound at the top. However, I definitely don’t want the tile to come loose and fall off the wall.

        • Roger

          If you get good coverage on it and make sure you go past the compound on the shower side (so water can’t sneak in the side) you should be just fine.

      • Tyson H.

        Thought I would provide this update, supports your recommendation. Custom Building Products, who manufactures RedGard, just called me. They said you can prime joint compound with RedGard diluted with water in a 4:1 ratio. This will ensure good adhesion. Then go back over it with a second coat of RedGard undiluted. CBP said that RedGard is latex based so it can be painted with latex paints but the manufacturer recommends where RedGard extends beyond the tile to skim coat it with Speed Finish, also their product sold at HD, to smooth out the rough RedGard surface. Then paint over that. Easier to use thinset, sand it and then skim coat it as you recommended but thought I would provide this for your readers.

        • Roger

          Thanks Tyson. :)

  • Jeremy McMillin

    Hi Roger,

    I made a mistake redoing my shower. I installed cement board (wonderboard 1/2″) In the shower after putting in the shower pan liner and then pored the shower pan (pre-slope first of course). Realizing that my wonderboard to drywall transition at the top of the shower is going to be about 1/8″ off (drywall is a little thicker). I tried to just install shims at the top of the stud near the transition, but this is causing corners not to be quite square. Do you suggest I remove the shims and use thinset and alkali resistant tape to bride the seam and try to flush it out at top? I plan on tiling (subway tile) past the transition on the top and sides, just not sure exactly how to proceed).

    • Roger

      Hi Jeremy,

      Yes, the thinset and tape are likely your best bet at this point short of removing the wb and shimming the whole wall. You’ll at least get a smoother transition.

  • Steve C

    Two questions:

    1. I read in one of the comments that you should NOT use both a vapor barrier AND Redgard. Why not? I was planning on putting a plastic water vapor in, then Hardieboard, then redgard, then tile. I don’t see why it would hurt to do both.

    2. I put in a prefab shower pan. I’m then putting in 1/4″ shims on the studs so the backer board will lay over the shower base flange. I want to use 1/2″ backer board (rather than 1/4″) for added durability. That means that the cement board will be higher than the drywall where the two meet. How can I transition the two without an eye sore? Bullnose tile won’t work since the cement board isn’t flush with the drywall.

    • Wade

      I would go one route or the other, why spend more when you can do one or the other ? I honestly wouldn’t shim and cause yourself more problems like trying to flush up your drywall. You don’t need the board to go over the flange of the pan either. Once the board is in it’ll normally sit slightly above it and you seal between the board and the pan. then tile over the flange. You’ll just want to put a good bead of silicone between your tile and pan bottom. you shouldn’t have to worry to much with proper maintenance. I just wouldn’t want you to cause yourself more headaches and possibly having to tear something apart because it just isn’t working for you like you want.

    • Roger

      Hi Steve,

      1. Because anything trapped between the two (vapor condensation, for instance) can not dissipate and will lie dormant waiting to grow mold. This is commonly referred to as a mold sandwich. Don’t do both, it is one instance where overkill is definitely a negative.

      2. Leave the 1/2″ backer above the tub lip, without shimming it out, and run the tile down to the tub. The backer should still stick out further than the tub lip, so the tile will go right over it and you’ll have a flush transition to the drywall.

  • Elizabeth

    I am actually installing tile to my entire bathroom wall but only halfway up. How do you suggest I go about this? Should I cut the existing drywall (with textured plaster) at the height desired and install cement board the use this method at the seams? I’m worried I’ll damage the upper part of the wall and have to do a complete demo. Also, should I use some sort of chair rail at the seam to hide any small discrepancies?

    • Wade

      If you’re doing halfway up a wall, that’s not around the flow of water from shower, you could use just the drywall, or if you want to make sure it’s bombproof. You could take cut out the drywall, and add cement board in its place. Since it’s not really needing to be waterproofed like a shower you could just fill it in with some drywall joint compound tape it up, then tile over it, texture over it, or whatever cement board accepts joint compound and texture pretty readily. So whatever think may be better for you try either of those ways. I’d recommend if they aren’t huge tiles, and they’re in an area that isn’t getting blasted with water just tile over the drywall area with some mastic. If it’s going to be wet go the mortar cement board route.

      • Roger

        ^^^He’s right. :) I would ensure that the particular tile you use is suitable with mastic. If it’s a natural stone or a large format tile you need to use thinset.

        • Elizabeth

          Thank you both for your advice. I would use the drywall except it’s been textured (plastered?) And so it’s not flat enough. I’ve been today not to mount the backer board onto the drywall. I’m using 2×3 inch ceramic subway tiles so they are not heavy. I already have the thinset as I’m using it for the floor so I was planning on using it for the wall as well.

          • Wade

            The texture shouldn’t be so huge of an issue, the mortar would be that squishy buffer between the texture so the tile should level out. of course if there are bows in the wall you’ll have to tweak a couple tiles here and there to level them out also.

        • Colleen

          Just curious about using thinset over the texturing mud. If the texture mud is water-soluble, how will the thinset affect it?

          • Roger

            Hi Colleen,

            It won’t. Even water-soluble mud requires it be soaked in water for an extended period. That is normally longer than the required curing time of your thinset, at which time the thinset has utilized all the moisture and will, in fact, leach any moisture from the mud while doing so.

  • Shawn Jones

    Hey there can you sand/plane down the dry wall to make it flush with the backer board and install a tile rail to keep it neat?

    • Roger

      Hi Shawn,

      Yes you can. No problem with that at all. You do want to cover the bare gypsum with something after sanding it down, regular drywall mud works fine. You don’t want bare drywall core under your tile, it isn’t that stable.

  • Prentis

    Can I add a backer board to the drywall before tileing

    • Roger

      Hi Prentis,

      You can, but why would you? You should not have multiple layers of different products in your substrate behind your tile. It would be better to remove the drywall and replace it with backerboard. That would also keep everything at the edges flush.

  • GWB

    Your info is very helpful. Thanks (and the graphics are fine :cool: ).
    I’m currently replacing an old all-in-one tub-and-surround with a new tub and tile on the walls.
    When I get to the ceiling (drywall, as far as I can tell) with my backerboard, should I run the backerboard up _behind_ the drywall if there’s a gap? Or just _to_ the drywall, then tape and thinset the corner? (If the thickness of the backerboard is the same as the gap between the ceiling drywall and the wall studs, then I assume I should just go _to_ the drywall.)

    • Roger

      Hi GWB,

      Either way will be fine.

    • Nick

      Drywall or backerboard on walls usually supports edges of ceiling drywall. At my home, after I removed a section of wall drywall, the ceiling started to droop down! Granted it took several months. The ceiling drywall edge ran parallel to the joist and apparently a cross member wasn’t provided, so the wall drywall was really supporting the ceiling drywall.

  • John Adams

    I replaced a tub and put new backer board in. I had to shim the backer board out to the tub edge because the stud-to-stud opening for the tub was a little large. Now the backer board doesnt come out flush with the existing drywall there is a 1/2″ step down to the walls outside the tub. Any ideas how I could put and edge around it after I tile the tub area ?

    • Roger

      Hi John,

      Get a schluter tile profile and flip it around upside down behind the tile to cover that 1/2″. I’ve also used 1/2″ rounded pencil rails down those reveals.

      • Diwakar

        Hi Roger,
        I’m facing a similar problem, with 24” of stud, using 3/4” kerdi board. It transitions to the existing 1/2” drywall outside the bathtub. If I use an upside down schluter profile, then I’m not transitioning with the kerdi band to the drywall like they suggest then? Also, where that profile would meet the step down drywall, would it best to use caulking for any imperfect drywall edge? And of course, end the tile with the profile, right?
        Thank you so much for your guidance in advance

        • Roger

          Hi JD,

          You can not use the kerdi-band when you do that, but you can silicone between the 3/4″ and 1/2″. This method uses two pieces of schluter there, the one upside down to cover the kerdi-board (you can get 1/4″ height schluter), then one regular one used correctly on that to cover the tile edge.

          • Diwakar

            Roger, you da man. You’re awesome! Thank you for your guidance. Not being in construction and not having done anything like this, I appreciate the awesome idea of having 2 profiles – 1 upside down and 1 regular with the caulked edge transition. Genius!

  • Lynne

    Probably a stupid question…but having trouble picturing exactly what to do…in order to match up the differing heights of the cement board and the drywall, the shims under the cement board–are they along the entire length of the board, or just the last few 2×4’s to angle it correctly?

    • Roger

      Hi Lynne,

      The entire length of the board. You want the wall completely flat, not bowed out to meet the drywall.

  • Paul Radvansky


    I used Durock cement board on my shower walls a ready for tile. Whats your opinion on Redgard as an extra level of protection in waterproofing. Is this overkill? If I use the Redgard will the adhesive called for in the Redgard product be as effective as the Type 1 adhesive for tile?

    • Roger

      Hi Paul,

      If you don’t have a vapor barrier behind your durock, you NEED to have a barrier over the face of it. So yes, redgard would be a great option. If you do have a vapor barrier behind it then no – you don’t want the redgard – it will cause more problems. Type 1 is a MASTIC, you want to install your shower tile with thinset, whether or not you use the redgard.

  • 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?


    • 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.

      • Keith Knauss

        Thanks, Roger. I’m confusing myself more now. If I tape and mud, should I use fiberglass tape and thinset? Or can i get away with joint compound?

        • Roger

          Hi Keith,

          You need to use thinset.

  • 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??

  • 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?

  • 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

    • 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?

  • 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?

    • 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.

  • 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?

    • Roger

      Hi Daniel,

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

  • 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.

    • 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.

  • 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.

  • 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.

    • Roger

      Hi Sissy,

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

  • 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.

    • Roger

      Hi Cheryl,

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

  • 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?

    • 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″.

  • 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).

    • Roger

      Hi Jackie,

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