Installing cement backerboard is one of the more popular choices for a shower wall substrate. Cement backerboards include Hardiebacker, Durock, Fiberboard, wonderboard, and similar products. These materials bridge the gap between expense and effectiveness. When installed properly they will give you many, many years of durable shower construction.

The advantage of cement backerboards is that, while not waterproof, they are dimensionally stable when wet. That just means that when they get wet they do not swell up. Any swelling behind tile is a bad thing. It will lead to cracking grout, tile, and all sorts of bad things.

Waterproofing your studs

To install the backerboard you must have a vapor barrier between it and the wooden wall studs. While the backerboard will not swell when wet, your wall studs will. You must prevent any moisture from reaching them. The preferred material for a vapor barrier would be 4 mil or thicker plastic sheeting which can be purchased at places like Home Depot or any hardware store. You can also use tar paper or roofing paper, the thick black paper used under shingles. Although I personally do not use that, it is an acceptable barrier.

Starting with your bare wall studs on your shower walls simply take your plastic sheeting and staple it to the wall studs completely covering the entire surface which will be inside your shower. You can also use silicone instead of staples to adhere it to the studs. Make sure you overlap all the edges. Just hang it all up there like you’re hanging wallpaper. You want it covering the framing enough that if you were to spray the walls with a hose the wall studs and framing would not get wet.

At the bottom of the barrier you will want it to overlap on the shower side of the tub or shower base. That is you want it so that any water that runs down the plastic sheeting will roll off into the tub rather than behind the tub. Overlap the lip of the tub or base and silicone the back of the barrier to keep it in place.

Installing the backerboard

Now for the backerboard. Lay out your backerboards for the best fit on the walls. They can go up vertically or horizontally, it makes no difference. With a regular tub surround with a five foot back wall it is usually easier to use two horizontal sheets along the back wall and one vertical on each of the sides. (This assumes 3 X 5 foot backerboard sheets.)

All backerboards are cut by scoring and snapping. You do not need a saw for them. While there are special scoring tools specifically for this you can easily do it with a regular utility knife. While all these backerboards are essentially identical in their effectiveness as a substrate, some are more easily cut. Durock, in my opinion, is the most difficult. I personally prefer hardiebacker or fiberboard. Make sure you check the website for whichever you choose for specific instructions.

To fasten the backerboard to the framing you have a couple of choices. A lot of professionals simply use galvanized roofing nails. While this is perfectly acceptable, I prefer screws over nails when possible. Hardi makes specific screws for their backerboard which can also be used for all backerboards. These are manufactured with ribs beneath the head of the screw which help it cut into the backerboard and countersink so the head is flush. If your local big box or hardware store carries them, they will be in the tile section. You can also use just about any type of corrosion resistant screw. Anything that can be used for an outside deck can be used for your backerboard.

Fasten your backerboard to your shower framing with a screw or nail about every 8 – 12 inches. I would also suggest using a straight-edge along your wall while doing this so that you can shim out any areas where the wall studs may not be straight. The flatter your backerboard is installed, the easier your tile installation will be. Take your time, the beer isn’t going anywhere.

Allow for movement!

You do not want to butt the backerboards against one another. You need to leave a small gap at every change of plane. That includes corners, walls to ceilings, and walls to tubs or floors. There needs to be room for expansion and contraction.

Wood moves – always. It’s just a fact of life. The secret to dealing with the movement is to ensure the movement will not interfere with the tile. Leaving this small gap will allow for movement of the sheets enough so that they do not force against one another and push out. While the backerboard itself is very stable, you are still attaching it to wood.

If you have a tub or shower base you will also want to stop the backerboard about 1/8 inch above the lip. You do not want to run the board over the edge of the lip because it will cause the backerboard to bow out and your wall will not be flat. It will also allow the tub or shower base to move a bit – it’s attached to the wooden studs as well. Tubs also move when they are filled with water. You need to allow for that movement.

I usually leave about a 1/16 to 1/8 inch gap between the sheets of backerboard. This allows for thinset to lock into the entire thickness of your backerboard when you tape and mud your seams. We’ll cover that part in a minute.

Don’t allow for movement! (Confused yet?)

If your shower framing is such that you cannot place the edges of all the backerboards directly over a stud you will need to add more studs. You may do this with regular 2 X 4’s screwed to the present framing vertically or horizontally as needed. You must make sure that every edge of the backerboard is supported so if the wall is pushed or leaned on in that spot it does not move. You want solid walls.

Final step

The last thing you must do is mud and tape your seams. Similar to regular drywall all of your in-plane  joints must be taped. To do this you just use regular thinset and alkali-resistant fiberglass mesh tape. You can find the tape in the tile section – it’s similar to regular fiberglass drywall tape, but it specifically manufactured to be alkali resistant. Make sure it is alkali-resistant because your thinset contains alkali which will gradually erode regular tape thus defeating the purpose.

There are two ways to address the corners. The industry standard, and the way you should do it, is to tape and mud the corner joint as well. Most backerboard manufacturers recommend this, as do the handbook standards. I only do that about half the time – I’m a rebel like that. 8)

*The other half of the time I only tape and mud the in-plane joints – the gaps in the same wall, not the corners. With the corners I fill the gap with silicone. I do this to allow the different planes of the walls to move in different directions, which they will do whether you like it or not. Allowing this movement in the substrate compensates for excess stress in certain applications. This is something that I do, it is not industry standard and you will likely not find anyone else recommending doing this. So when you get the conflicting information about this – that’s why. :D

Fill all the gaps in your seams with thinset (you left gaps there, right?) then embed the tape into it. Then go over the tape with more thinset to smooth everything out. This will lock everything together and give you a continuous, solid substrate for your tile. That’s what you’re looking for.

When properly installed cement backerboards will create a rock solid, extremely durable substrate for your tile installation. Taking time and care to solidify what is behind or beneath your tile is the only way to guarantee a lasting installation. Your tile is only as durable as what it is installed upon.

As always if you have any questions at all please feel free to leave a comment.

Hardiebacker Website

Durock Website

Need More Information?

I now have manuals describing the complete process for you from bare wall studs all the way up to a completely waterproof shower substrate for your tile. If you are tiling your walls and floor you can find that one here: Waterproof shower floor and wall manual.

If you have a tub or pre-formed shower base and are only tiling the walls you can find that one here: Waterproof shower walls manual.

{ 1498 comments… add one }

Leave a Comment

  • Nathan

    Do you recommend doing the upper wall sections before creating a shower base? I am starting from bare studs, and wasn’t sure whether to build the shower base first, or put the upper sections of drywall and cement board around the shower. I don’t want to mess up my shower base while installing the shower walls and drywall.

    • Roger

      Hi Nathan,

      I do the floor first, tile it, then do the walls. But you can do it in whichever order you want.

  • Ron

    Is it okay to waterproof the showerwalls with Red Gard, but then traditional waterproofing (vinyl sheet) on the shower pan?

    • Roger

      Hi Ron,

      Yes.

      Sorry for the delayed response, my spam filter went ape shit last week for some reason, I just found your comment in the spam folder, I hope the answer found you in time.

  • Tracy

    I have already lay down my shower liner now I’m ready to put down the backer board, can I screw it in or what should I do.

    • Roger

      Hi Tracy,

      Screw what it? You can screw the backer into the studs, you can not screw the backer into the studs through the liner.

  • Scott Nelson

    Hi Roger,
    For the shower pan I plan to build, the subfloor is 3/4″ plywood with a 1/2″ durock underlayment. Can I install a preslope over the durock? Do I treat it like a cement floor? If it’s not recommended to install a preslope over durock, instead of trying to rip it out, can I glue & screw a 1/4″ plywood underlayment over it?
    Thanks,
    Scott

    • Roger

      Hi Scott,

      You can go over the backer just like concrete. No worries.

  • Greg

    Im getting ready to install hardibacker in my shower, however I have already poured and finished my preslope, liner, and final mortar bed. So the hardibacker will be run right up to the showerpan and stop instead of being embedded into the shower pan to add more stability to the bottom edge that I cant screw into because it would compromise the liner. Should I chip out the final layer of deck mud, or am I ok?

    • Roger

      Hi Greg,

      You are fine. You can place one drywall shim on the studs above the liner, they are the same thickness as the liner, which will bring the back of the backer flush with the face of the liner, then you don’t need to screw into the bottom of it.

  • greg

    The back of my shower wall is painted cinderblock can I tile on top of that without a backerboard and would I need to remove the paint?

    • Roger

      Hi Greg,

      You’ll need to at least rough up the paint to get a bond with whatever method of waterproofing you plan on using over it, then you can tile directly to it.

  • Shaun (a different shaun)

    THANK YOU. Wow. Youtu6e makes my head hurt.

    I remodeled wifey’s bath a few years ago and was “freshening up” a bit before tackling next one. I haven’t used redguard before so wanted to see if I had missed anything else.

    Only question.

    If I want the tile to stop flush with the front of the tub – do I stop the backer board there as well (as opposed running past a bit for a buffer)?

    Last time, I went one full tile (2.5″) past the front of the tub to deal with any water that might escape there. Now I want to stop flush – if I DO stop backer there, should I use green board (or similar) to abut to front of tub or will painted drywall suffice?

    Thanks!

    • Roger

      Hi (a different) Shaun,

      You can run it past the tub, or leave it flush with the face and silicone between it and the drywall (drywall is fine). If you go past it backer can be finished and painted just like drywall.

  • Missy

    Hi, these are the best, simplest instructions I’ve found so far, thank you! Question: I’m finishing the shower in a roughed in bathroom. Plumbing and shower pan are already there. When I install the cement board, do I need to cut out access to the pipes themselves or can I simply cut holes for the shower head pipe and the knob area? Thanks!

    • Roger

      Hi Missy,

      Only for the things that will stick out of the tile, the shower head and controls.

  • Colleen Terman

    I am wanting to tile shower walls. I keep finding different opinions/methods and just need a straight forward answers. Does backerboard need to be taped and mudded? Does it have to be sealed with a primer or waterproof sealant? The drywallers . . . have mudded into the shower area on top of the backerboard about 8 to 10 inches. I have been told that the thinset will not adhere the tile to the mudded area. Is this correct? And then the next question is if the thinset will not adhere to this area, how do I fix it?
    Thanks so much! This is so flippin’ confusing.

    • Roger

      Hi Colleen,

      Yes, backerboard needs to be taped and mudded. Yes, it needs to be waterproofed in some manner, either a barrier behind it or a membrane over it. Thinset will bond the tile to it, the problem is that the mud may disintegrate when it gets wet – and it will get wet. At that point the mud will become unbonded from the wall, even though the thinset will still be bonded to it. It’s not a thinset issue, it’s a mud issue. It can be sanded off.

      You may want to download my free shower waterproofing manual, it will help with most of your questions.

  • Rich

    Roger I completed my pan & curb following your info and I have to say that all went fairly well, but I don’t think I want to do another curb…ever.
    A couple of questions…if you will.
    1. I finished my final mortar in the pan and then at the end I turned the drain up to the tile height. There is a little void under the drain at this point. Is there any concern there? Should this be filled before tiling? I could squeeze some thinset in there.
    2. My curb isn’t perfect by any means. Can I skim coat where necessary with thinset to pretty things up a bit?

    Thanks for your unusual kindness!

    • Roger

      Hi Rich,

      1. No worries about the void. You can put thinset there if you want, completely your choice.
      2. Yes.

  • Riveter

    Hi Roger, We are going to use silicone in the corners , where the planes meet, in our shower surround and tape the 3 hardiboard planes. When we tape and thinset the gaps on each plane, how long should we wait before starting the redguard application?
    And do we spritz the hardiboard with a spray bottle of water right before we prime the walls with the the first coat of diluted redguard?
    Thank you again. You are absolutely the kindest person in the world. Everyone seems to know about your website. XXXOOO

    • Roger

      You need to wait until the next morning for the thinset to cure before redgard. No need to spritz the backer, the primer coat takes care of that.

  • Darius

    Hi Roger,

    I’m at the stage of hanging the dura rock backerboard on the shower walls. I’ve read where you suggest leaving a 1/4 gap between the bottom of the backerboard as well as where you’ve suggested using silicone at each plane change.

    My question is where do I silicone on the edge between the bottom of the walls and the deck mud on the floor? I’m not sure if I’m filling that gap with silicone or if I should apply a bead of silicone several inches up on the pvc liner on the wall which will adhere to the backer board when I mount it.

    Thanks for all of your information that you’ve made available.

    Darius

    • Roger

      Hi Darius,

      You don’t, I only meant the change of planes in the corners. The bottom doesn’t need anything, it just hangs there flapping in the wind. Well, hopefully not flapping…but you know what I mean. :D

  • Rich

    I have a bit of confusion I am hoping you can clear up.

    My question is on the mortar pan mixture. Using the Quikcrete 3:1 topping and getting it to a 5:1 is completely understood when you consider the weight. I called Quikcrete regarding their product and asked if the sand/topping product was packaged by weight or volume. They claimed that the 3:1 ratio is by volume not by weight. That was a while back, so I ended up mixing the preslope at a 4:1 ratio (1 bag + 15 Lbs sand). Recently I called them back to clarify their info before pouring the final slope. When I asked the same question concerning the contents of their product I received a different answer. I was told that it was packaged by percentage and proportions depending on what region of the country you were from, that it may be 3:1, 4:1 or 5:1; they were not sure. I am from Minnesota, explaining that to them they could not answer their percentage and proportion run-around. There is approximately 4 gallons of material in a Quikcrete topping/sand bag (that makes 3 gal. of sand to 1 gal cement) and also there is 4 gal. of sand in a 30 lb bag of sand. I don’t know why, that’s the way it worked out when I emptied them both by gallon, and that is why I called Quikcrete a second time.
    Not sure what exactly is in the bags that I bought. I am hoping you will make this all sensible.

    Thanks again…

    • Rich

      I need to apologize for the error above concerning the sand. The bag of sand I used was actually 50 lbs, so I used half (25lbs) to one bag of the sand/topping compound. That should of put me close to 5:1 by weight which is the way I believe it is packaged. I found a local distributor of their product and that is what they told me. Quikrete was not willing to make that claim. I find that when you start asking questions confusion presents itself.
      Anyway, sorry for the confusion from my end. :whistle:

    • Roger

      Hey Rich,

      How am I supposed to make it sensible when they don’t even know what they make? :D

      Bottom line is this (well, a couple of bottom lines, I suppose…): The ratio I provided works well. Whether you have their 3:1 or 5:1 it will still work, as a good mud mix can be anywhere from 4 to 6.5 to 1. It’s a matter of personal preference (how the mud works), it will not compromise the mud deck at all.

      • Rich

        Thanks for the input…
        My pan is looking good and ready to go.
        I shouldn’t bother with confused desk folk. :bonk:

        Your endeavors are appreciated.

  • Shaun

    Roger,

    Should I use thinset for mudding the seam where the cement backerboard meets the drywall outside the shower? I will be installing a bullnose tile over the seam; however, I want to paint the rest of the drywall.

    • Roger

      Hi Shaun,

      You can use that or regular drywall mud, provided it is not inside the shower. Thinset can be sanded and painted.

  • Rich

    Roger,

    What is the best advice…and why?
    Should the backer-board be installed after the completion of the mud-pan or before the finished mud pour, after the liner?

    Thanks…Rich

    • Roger

      Hi Rich,

      Best advice: It depends on your waterproofing method.

      Why: Because different methods require different tie-ins to the base.

      • Rich

        Ok…

        So I have a water barrier on the studs, over the liner.
        Which way would be a smart choice? Backer-board first, before last mortar pour or after completion on pan?

        Thanks again…

        • Rich

          Let me correct my typo…the “on” at the ending of the last message was suppose to be an “of”. Not that you wouldn’t have caught it, just trying to make life easier. Wasting time here I suppose doesn’t translate to easier. :-P
          My obvious next question, at least what I am pondering is this: If I install the CBU after the completed pan, holding it up ¼ – ½ inch off the mortar pan, I cannot screw to it 4 ½ inches from the bottom (top of the mortar) to be safe, I’m thinking ,not to penetrate the liner too far down, if at all…correct? If that is the case, will the bottom of the wall over time want to bow from moisture and separate/crack the tile and cause me unwanted misery because it wasn’t fastened securely? It would seem that to imbed the CBU in the mortar guarantees this problem being eliminated. If having no vapor membrane on the studs is the way for embedding the CBU, then that is a cheap fix at this point. I would rather pull it and apply a liquid membrane. Perhaps there is no issue here.
          Of course I am not sure what you are going to suggest…maybe having the vapor barrier on the studs is the way to go if embedding the CBU and I can move ahead the way it is.

          Thanks for your online support.

          • Roger

            The backer will not move once it’s installed. You CAN embed it into the mud, it won’t hurt anything. The proper way is to leave the gap, though, because backer will wick water up. Provided you have your barrier installed properly this does not create problems.

        • Roger

          After completion of the pan, leave 1/8″ – 1/4″ gap between the top of your mud and the bottom of the backer.

          • Rich

            Once again, thanks for all your friendly service.

            Hope your Holidays are a little greener than usual. :guedo:

  • He'd bid

    should I install hardy board ruff side out or smooth side out?

    • Roger

      Hi…uh…’He’d bid’, did your parents hate you? That’s a terrible name for a kid. :D

      Hardi says smooth side out, I say it doesn’t matter.

  • Mike

    Hi Roger,

    Thanks for all of the detail in this article.

    I’ll be installing backboard and tile for a tub/shower. I have 4.5″ deep wall cavities (older home) and I’ve sprayed closed cell foam for about 3″ worth on exterior facing walls(old wood exterior slats). Since this is a water and vapor barrier protecting from exterior moisture, I assume it will put somewhat a barrier on the shower side too. The studs are still exposed where the backer board meets wood. My question has to do with the fear of creating a double vapor barrior. I could put the plastic sheeting across the whole wall which would cover studs(great) but leave a 1 inch gap between sheeting and closed cell spray foam.

    What’s your opinion? Is the 1 inch gap enough for air flow? What if I drill some air flow holes between each stud so that each cavity can vent sideways?

    Thanks in advance!

    • Roger

      Hey Mike,

      That won’t be a problem. The issue arises when you have a substrate trapped directly between two vapor proof barriers with no space between them. Your construction will be fine.

      • Mike

        Thanks Roger, makes sense now. Have a great day!

  • L (LANELL)

    Roger
    Easy for me is Durock. Extra work and expense is buying more ‘stuff’. The wall is not my handiwork and is lumpy. :bonk:

    Thanks

  • L (LANELL)

    Hi Roger

    About not attaching Durock to block. I drilled and screwed other things to it with what was told were proper screws. Lots of screws just in case. I have worn out and have many more masonry drill bits. But if no screws will keep it up , as they have for me elsewhere, what easy store bought mix to screed over block could I get at box stores or where I have bought laticrete things. Still waiting on glass estimates from FOUR places, BTW.
    Thanks mucho

    • Roger

      You can screw it (to a wall, it will last), there is just no reason to when you can skim coat it with regular thinset or just go right over it with your waterproofing. You’re creating extra work for yourself.

  • Ross

    Roger,

    Regarding the corner edges where the walls meet I’m not sure if I should silicon and be a rebel or keep to industry standard and tape/mud. I’m using 6×6 porcelain with a horizontal mosaic row if that helps determine. 1/8 grout line.

    When you use the silicon method what it the reason for half the time you doing it that way, why not all the time?
    What is throwing me off is why james hardie doesn’t mention this (like you state in your article), however, your silicon method makes perfect sense.

    • Roger

      Hey Ross,

      The size of the gap determines whether or not I put silicone in there. You can fill it with silicone then tape and mud. The two do not do the same thing. The tape and mud ties it together to compensate for movement, the silicone prevents water wicking. The tape and mud with silicone in the gap will not wick enough water to do any damage before it dissipates or drains.

  • L (LANELL)

    I will have to use something to level out block wall since it would never work to TILE on. And thinset only levels up to 1/4″ as I recall? So no Durock directly drilled and screwed to block wall. Ok.

  • L (LANELL)

    Next problem /question. I have one wall that was thin cedar strips over concrete block wall (condo wall, end unit). I wondered whether to leave the metal 1″ thick metal square strips I screwed to block as studs.Or would be better to take them down and Durock over the block directly. Just bare block, only painted on outside of Condo. Would be easier. The corners of abutting walls I have put very sturdy corners in. So, Durock over block? This will be topical drain and Hydroban troweled.

    • Roger

      You can install durock to the studs you’ve created or you can remove them and hydroban and tile directly to the cinder blocks. Do not attempt to install durock to a concrete wall.

      • John Walls

        1) “Do not install Durock to concrete”—
        Why? Because it’s hard to do or because of some other issue–compatibility, expansion, or something else?? Does this apply only to Durock or would the same apply to Hardi or any other cement board?
        2) Why is thinset limited to 1/4″ for leveling?

        I’m asking because I need to install granite or tile on a fireplace front. It’s an Isokern modular masonry fireplace (blocks of ground up volcanic rock that have been molded together with a binder of some sort). Unfortunately, the fireplace face (firebox and smoke dome) is out of plane with the surrounding wood framing by about 1/2″. So, I need to taper the fireplace face from 0″ to 1/2″ (with thinset, I assume) to flatten the surface to match the framing, then install Hardi over the whole assembly (framing and fireplace), and then install the stone or tile on top of that. Note that much of the load taken by the Hardi would be from attachment to framing, and also note that Isokern allows nails or screws up to 1″ long to be used for drywall attachment to the face. Also, note that changing the framing to match the fireplace is not a reasonable option at this point. I would appreciate your advice on this.

        • Roger

          Hi John,

          1. Because there is no way to reliably fasten cement board to concrete that will last long-term with continued use. And it is redundant. Cement backer (yes, it applies to all of them) is a product used in lieu of cement. It gives you a cement-based substrate for tile where cement is not available.

          2. Because a bed of thinset over 1/4″ will shrink considerably over time, throwing your tile installation out of whack and cracking your grout.

          If you need to put a wall in-plane with a concrete-based product as your substrate use wet mud. It is 1 part cement, 4 parts sand and 1/2 – 1 part powdered masonry lime. That is what you float your wall out with, not thinset. Once cured it is stable, solid and will not shrink. It is still the absolute best wall substrate available.

  • Amanda

    Hi Roger,

    We are renovating the Master bath in the house we recently bought (it was terrible!). You’re site has been a great resource! We did a mud pan with the PVC liner (pre-sloped!). We’ve got backerboard up and are planning to Redgard after we mud & tape the seams of the backerboard.

    We read that we could install the backerboard before the second mud bed (embedding it in the floor) or install it afterwards with a 1/4″ gap above the floor. We opted for the later, as that is what the backerboard manufacturer indicates in their instructions. Our gap above the floor ended up being closer to 1/2″-3/4″ on one side – we put the cut side down and it unfortunately broke a bit jagged, so the gap varies a little – and 1/4″ on the other wall.

    Now our question is, do we need to fill this gap with something, so we can Redgard all the way to the floor? I’ve searched around, but it seems that most people just say to embed the backerboard in the mud (too late!). If we do need to fill the gap, what should be used – thinset & tape, caulk? Since there is no vapor barrier behind the backerboard b/c we’re doing the Redgard, I’m worried about water wicking up behind the backerboard through the gap. Any advice would be much appreciated!

    Thanks!
    Amanda

    • Roger

      Hi Amanda,

      You don’t need to fill it with anything, tile can just hang over it. Water is not going to wick up the board if there is not a constant source of moisture into which it is embedded (like your top mud deck :D ).

  • John Walls

    Roger, I’m new at this, so please accept these questions in the spirit in which they are intended—educate me.
    1)Regarding the requirement that every edge of backerboard be supported:
    a) I have a case where the studs range from 2 to 6 inches from the corner. Should I still put in more framing or is this close enough? What about using metal corner clips here (instead of more lumber), like the kind used on regular gyp board for two-stud corners?—Like the Prest-On Corner Back. Do you think the cement board would be too weak or fragile for this? Or maybe the clips would be too weak for this particular service?
    b) What about the horizontal edge just above the tub—do I need horizontal blockers across there to support the cement board bottom edge? Same question at the top if I don’t go all the way to the framing top plate.
    c) Would the answers to the above be different for granite slabs (or engineered stone) instead of tile? Maybe the slabs would be more forgiving since they are in one piece and not grouted?
    2) Regarding leaving expansion gaps between cement board corners:
    If these gaps are then filled with thinset and then embedded in tape so as to lock everything together, then what good is the gap from an expansion perspective? It seems that the expansion function of the gap is eliminated. You mention that you use silicone in the corners sometimes (instead of tape embedment). Why not all the time? Why do you think the manufacturers recommend tape embedment instead of caulk? Help me understand this.

    • Roger

      Hi John,

      a. 2-6 inches is fine provided you tape and mud the corners. DO NOT use a metal corner clip or bead – they rust.
      b. No, you do not need horizontal backers at the top or at the tub.
      c. No, same answers.
      2. It isn’t any good. That’s why I fill the gap with silicone first, than tape and mud. The silicone allows for expansion (in a lateral swelling sense) and the tape and mud tie the two backers together so they move as one. Manufacturers recommend taping and mudding, because most of their specs are dealing with a simple wall construction without taking wet areas into the equation.

      • John Walls

        Roger, thanks for the reply. I have a few followup questions:
        a) Would you still have an issue with corner clips if they were galvanized or zinc plated? Also, they should be behind the waterproofing (for a topical installation), right? Also, do you think there would be a problem structurally? Just asking for future reference.
        2) If you use Kerdi for waterproofing, do you still need to tape embed the corners? Will Kerdi be strong enough for this on its own, or do you need the extra strength provided by the tape in the corners? You mention this in your eBook, but I think the Kerdi thing may apply only to in-plane seams and not corners?

        • Roger

          1. I would have no problem at all with any material provided it was installed behind a topical waterproofing. no structural issues I can see.
          2. No, the kerdi does the same thing as the tape and mud.

  • lucy

    Hi, Love your site and humor.

    1. Down to studs. Purchased hardiebacker. Want to be sure I am understanding correctly. The hardibacker goes 1/8 above the tub lip. Fill the 1/8 space with silicone and all other spaces where hardi meets.. Then thinset/mortar, tape. Dry 24 hours then use 50/50 water/redgard to prime hardi then 1 to 2 more coats of 100% redgard. Then thinset/mortar over redgard to tile.
    2. The stink pipe is in betwwen studs on right side of alcove. Previously, the paint would chip (tiling that part now though with the remodel). Can/should I cover the pipe with plastic so it doesnt sweat on hardi? Using redgard so I dont want the moldy sandwich problem.

    3. Put in skylight above tub area using greenboard with plastic underneath.Not redgarding that so it should be okay, right?
    Thank you so much!

    ;)

    • Roger

      Hi Lucy,

      1. Yes, absolutely correct!
      2. Yes, you should cover it with something. A small area such as that won’t create a problem.
      3. It should, it depends on how hot you like your showers. :D

      • John Walls

        Does the Hardi lap the lip or not lap the lip?
        —-The eBook says to shim out the Hardi enough to just clear the thin 1″ tall lip on the tub flange so that the Hardi can lay flat on the lip and extend down and over the lip to 1/8″ above the wide (2″ to 4″) flat ledge of the tub. So the Hardi laps the lip.
        —-The above post makes me think the Hardi should stop 1/8″ above the top of the 1″ tall tub lip (i.e. Hardii, then 1/8 gap, then top of the skinny lip). The Hardi doesn’t lap the lip.
        —-Am I lost in terminology or is it just a case of either way is OK?

        • Roger

          You can do it either way. I prefer the hardi shimmed and over the lip, but that may create problems outside the shower where it meets the regular walls. Either one works fine provided you have a sealed transition from the barrier to the lip or from your membrane to the lip.

          • John Walls

            Roger, thanks for the response. Makes sense to me.

            But, is the answer different if I use Kerdi instead of Redgard?
            I just finished the Ebook for a Kerdi tub/shower wall.
            If I am interpreting it properly, I think it requires doing it like Lucy described (don’t lap the lip) Then silicone the Kerdi to the vertical portion of the tub lip. Is that correct? There isn’t a wall cross section in that book, but I think this is what the photo is showing.

            I need to get some contractor bids and I don’t know what their capabilities are in my locale (like have they ever heard of Kerdi). I had planned on having the wall all flat, shimmed, and ready before talking to them, but it sounds like maybe I need to pick a system first–right?

            • Roger

              If you use kerdi do not lap the lip. You can, but it’s not necessary at all. You are overthinking this, the only thing to be concerned with is having a waterproof plane (continuous) from the wall into the tub. There are MANY ways to do that, I’ve only touched on two.

              Different contractors have different methods, these are mine. I have no idea how the contractors in your area work, so I don’t know that you need to pick a system first or not. I will tell you that I absolutely REFUSE to install tile over any substrate at all that someone else has prepared. I never do that, I’m the one that warranties it, I’m the one that pays if something goes wrong. So if you called me I would kindly refuse unless you took it down to bare studs. I’m an ass like that. :D