Installing Cement Backerboard for Tile in a Shower

by Roger

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.

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Dan

Hi Roger,
I have a question regarding blue board. I have installed DensShield in a shower surround, and I’ve sealed and tiled the likes up to the ceiling. I was curious if you can tile over blue board on a ceiling. The shower is a single head, non-steam shower. Originally I was just planning on painting the ceiling, but after looking at it I was thinking I might be better off tiling. What are your thoughts on tiling on blue board?

Reply

Roger

Hi Dan,

Yes, you can tile over it on the ceiling. It’ll be fine.

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Dan

Awesome! Thanks for the quick reply

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Mary

I am building a new house, bathrooms have 9 foot ceiling. the sheetrock guy had blue board up in the three bathtub showers. I made them take it out and put in cement board to the ceiling because I am running my tile to the ceiling…. In my Masterbath, walk in shower that is about 7 x 5, the put cement board up to about 8 foot and then at the top, they have blue board. Shouldn’t this be cement board at the top too, or will it be ok that high up being blue board? Again, I am tiling all the way to the ceiling. In my 3/4 bath they did the same thing. I am tiling to the ceiling in that stand up shower as well. Can I tile over the blue board and is the OK since it is that high up? Thanks.

Reply

Roger

Hi Mary,

Provided the showers are not enclosed (with a header across the entrance which traps vapor at the ceiling) then your waterproofing and substrates are only required to go three inches above the shower head. You can tile directly over it, it’ll be fine.

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Rhi

Hi,
We recently bought a house and started remodeling the bathroom. Due to a problem with the floor we needed to add some height. We were told to use cement board on the floor and that we would need to seal it prior to placing the linoleum down. What do we use to seal it

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Roger

Hi Rhi,

I have no idea who told you that but it probably should have been just regular plywood under linoleum. You can seal it with a mixture of 1 part glue (that you’re using for the linoleum) and three parts water.

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Mark

Hello – I have a question regarding installing the cement backer boards. I used your guide and created a shower pan with the oatey liner as described in your traditional guide. The water flood test was successful. I was going to use the plastic moiture barrier behind the cement backer board. However, I changed my mind to use Redguard as this seems the better choice with a niche. Now I am using your other guide (liquid topical shower waterproofing). My shower pan is complete and I am unable to embed the cement backer boards.

1) Should I install the cement backer board without embedding into the pan and just Redguard paint them from top to bottom and leave my shower floor as is?

2) The backerboard will be installed to the ceiling. I am only tiling to above the shower head and not tiling to the celing. I plan on painting to the ceiling above the tile line. Should I redguard all the way to the ceiling for complete coverage on the backerboard and paint over the redguard with normal paint?

3) When hanging the cement backer boards, do I stop adding screws above the oatey liner (approx 8 inches up the back wall)? My concern is 8″ of unscrewed backer board at the bottom of the shower stall. I figure I shouldn’t be screwing there. Just looking for confirmation.

Reply

Roger

Hi Mark,

1. Yes

2. No, only redgard up to where you’re installing the tile, just paint the rest.

3. You can install fasteners down to three inches above the finished height of the curb. It’s normally easier to place two drywall shims (the same thickness of the liner) on the studs above the liner so it lays flat all the way down.

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Mark

Wonderful. Thank you for the quick reply.

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Ross

Hi Roger,

Thanks for the info and support!
I realized a potential situation today while working on the shower.

1) The drywall that is on the wall is 5/8. Hardie board, and other backerboards, run 1/2. What is the best way to to solve this drop down in thickness? I hope its not to tear down the sheet rock and replace with 1/2 sheetrock. My idea is 1/8 shims along the studs to make the difference but that is a crap ton of shimming. I can not find 1/8 plywood if it exist. I will have this problem on the top and side of all shower walls. The walls are 10′ and the shower “cutout” doesn’t go all the way to the ceiling.

2) On the exterior wall I am replacing the insulation R-13. I am also adding insulation to interior so my wife can sleep and not hear the shower in the early AM. If the insulation I install has a “vapor retarder” built in do I still need to put up plastic vapor barrier or would I be creating a moisture sandwich?

What to you suggest Shower Sensei :rockon:

Ross

Reply

Roger

Hi Ross,

Shims are the way to go. I know it’s a pain in the ass. :D Regular drywall shims stapled to the front of your studs will work just fine, just put your barrier over them. Using a barrier will not create a moisture sandwich, there is nothing between the two barriers, that is only when using a topical membrane and your substrate is between the two.

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joe

I am asking if this will be an acceptable solution, or if there is something that will work better to fill the gap. :bonk:

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joe

Hello, and thanks for all you put out there. Like many I wish i would have located your help sooner.
My issue is my Duroc backer is about one inch above my final mud bed. I was just going to use the same stucco mix that I’m going to use for the curb to build up to it. Hoping this will be an acceptable solution. I am using red guard for the waterproofing.

Reply

Roger

Hi Joe,

Yes, you can use the same stuff to fill that gap.

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joe

I have been looking at that gap for about three weeks. wife wants to kill me, but you Roger saying yes just made it all better. Thanks very much.

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Brother

Have boxed in the entire shower with backer board . She has now decided that she does not want tile on the ceiling, Can I paint backer board

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Roger

Hi Brother,

Yes.

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Duane

Hi Roger,

I’m working on tiling a tub surrounding in an existing house. I have gotten to the point where I have the 500 hardibacker boards up but now realize that they are not all flush with the existing drywall (should have bought your books earlier…). What is the maximum amount of differential that you can fix by “floating” out the seam to smooth it out (some boards are close to flush, others have an offset of ⅛” or so). Not excited about removing boards to shim, but also don’t want to be creating issues for me when I move to the tiling step…

Thanks!

Reply

Roger

Hi Duane,

1/8″ shouldn’t be a problem at all to flush our your walls.

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Joe P

I’m having a bit of a problem. I’m following the liquid topical shower waterproofing guide and in here it says “So let’s start with the easiest part – getting the screws flush”. I want to know what trick you’re using to get these darn things flush! I’m using 500 Hardibacker with the longer hardibacker screws. Before I go on, let me first express my hate for the square bit.

How do you not strip these things every time?! They’re driving me bonkers!

Once I figured out how to keep them from stripping 1/2 the time, I was able to get the screw into the backerboard for the most part but I’m still having trouble getting the head flush. In about 20% of the cases it goes in nicely but the rest of the time it stops as the head hits it. I’ve tried using a variable speed drill and an impact driver and both result in nearly the same result. One technique that sort of worked was drilling it in then reversing it before the head touches, then drilling in again with force. Is there a better way?

Another issue I’ve noticed is that when drilling, the screw punches some excess crud out the back of the backerboard which sits between the 2×4 and the backerboard, making it so it’s not quite flat.

What tips do you have for these two issues? Also, how terrible is it if the head of the screws are sticking out slightly on the shower walls?

Reply

Roger

Hi Joe,

Screw them until they stop, reverse it, then take another run at it. Don’t stop before they hit the board. Square bits come in different sizes, you need #2 size. Replace often. Press the board against the stud as you screw in to keep it from blowing out chunks in the back. If they are sticking out 1/16″ or less you should be able to make up for that as you set the tile.

I know it’s a pain in the ass. I hate it too. :D

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Joe P

When you say to use “regular thinset” for mudding the in-plane joints, what the heck is “regular” thinset? Modified? Unmodified? Pre-mixed? Self-mixed? Let’s just say that I’ve never used any sort of thinset before :bonk:

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Roger

Hi Joe,

It’s any thinset that comes in a powder which you mix with water. Pre-mixed anything is not thinset. When I typed regular thinset what I meant was ‘NOT drywall mud’. :D

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Randy

Roger, we have a new house with a tile shower – both the walls and the floor are tiled. There are a few small cracks in the grout in the corners where the walls meet. There us a gap at the grout line at the bottom where the floor tile meets the wall. I’ve noticed that water seeps out from this crack for several hours after the last shower of the day. I know water will wick up the wall thru this space but the amount of water seems to be excessive. Is this much water normal? I’m concerned about mold developing over time in the grout close to the wall where the water seeps out. I’ve considered sealing this area with silicone but am concerned about trapping moisture behind the wall. Is there a good solution to this? You told Keri to silicone where the wall and floor tile meet but you told Jeff the silicone would serve no purpose. I must be misinterpreting something. Thanks.

Reply

Roger

Hi Randy,

I told Keri to silicone there rather than grout because grout cracks. I told Jeff to silicone there because grout would crack. But silicone is not required, it is aesthetic. The grout needs to go, if you silicone then the water will run down your floor waterproofing (if your substrate is properly constructed) and into the drain through the weep holes as intended. That amount of water is probably normal. It seems like a lot, but if you put it into a glass it won’t actually be much at all.

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kyle

I have a question about taping outside corners of Hardibacker. I installed a recessed shelf in the shower wall, using 2×4′s and hardi board. How do I tape the inside and outside corners of the shelf? One guy told me to use the metal corner sheetrock joint tape combo. I didnt think that was correct due to moisture. Whats your take?
Thanks :bonk:

Reply

Roger

Hi Kyle,

NO CORNER BEAD! (smack that guy) It is not really necessary to tape it in a niche, but you can use the alkali-resistant mesh tape and thinset if you want to.

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Newt

We built a partial wall for a new walk-in shower. By partial, I mean it doesn’t go all the way to the ceiling and it’s open-ended. It wobbles. We have put about ten thousand screws into it but it still wobbles. Will it stop doing that after sheetrock & cement board go up? I’m guessing (seriously-I’m a rookie) this is not suitable to tile if this condition exists?

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Roger

Hi Newt,

Yes, it will solidify once you get the substrate on both sides of it. It will still move a bit, but once you get tile installed it won’t move.

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lee

Just bought a house with a stand alone shower that has never been finished. Has plumbing, studs, then greenboard that is taped floated, textured and painted. No shower pan yet we have to pour one. My question is should I leave the greenboard, redguard over it, then install backer board on top? Or should I demo down to the studs, put in red guard, then backer board?

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Roger

Hi Lee,

You should remove the greenboard. It doesn’t belong anywhere near a shower. You can not use redgard over greenboard. If you want to use redgard you would install the backerboard then install the redgard over the face of it, not behind it. The tile is installed directly to the redgard.

Reply

keri

I have a question about where tile meets shower base. We installed our cement board with gap at bottom so it doesnt touch tile shower floor. After we tile, can we just fill the gap with grout or do we need to use silicone? Thanks

Reply

Roger

Hi Keri,

You need silicone where the wall tile meets the floor tile.

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Brendon

Perfect. Thanks a ton for everything you’ve done here.

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Ray

You mention plastic up between the studs and backer board? My shower is in the basement, I have rigid insulation against the poured concrete wall and a plastic sheeting against that. I have placed a 2×4 wall against that. I am undecided if I need to place more insulation between studs, or leave it open to allow breathing. My concern is if I place more plastic sheeting up, won’t I potential have a sealed barrier, that could build up mold and mewdew?
Or leave the insulation out, and only have the studs between plastic?

Thank you.

Reply

Roger

Hi Ray,

Either should be fine. It’s normally just sealing the backer or substrate between the two layers that causes problems. A larger area like 3 1/2″ between studs allows more vapor dissipation than a sealed 1/2″.

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LaNell

Hi Roger…I think I have a similar mess , uh..scenerio One end of my shower will be a concrete block wall that is standard Fl. Concrete bunker build so other side is stucco/painted exterior Half inch cedar strips on vertically in the 30″ wide space and I don’t want to build it in. This is my gutted to studs rebuild so have to work with what I have. Anthing need done to bare block but drill and screw Durock to be Hydrobanned on top? I am in climate that rarely varies from 80 degrees and 80% humidity.

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Roger

You can just hydroban the block and tile right to it.

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Jeff in SK

Hey Roger!

The mother-in-law’s bathroom is coming along nicely, but I have a question regarding finishing the bottom edge where the tile/wall meets the shower base:

So, when the cement board was installed, we left a small gap between the CBU and the shower base flange as you recommend, and filled it with silicone to seal that space. The plan is now to paint the Redgard overtop the silicone and onto the shower base (it will be masked off so that no Redgard will show once the tile is on).

My question is this: After we install the tile to within 1/8″ of the top of the shower base and grout everything (including weep holes!), is it necessary to silicone the bottom edge of the tile against the shower base being that there is already Redgard overtop of the silicone to prevent any moisture getting into that gap?

Thanks again in advance!!
Jeff

Reply

Roger

Hi Jeff,

No, you don’t need to silicone it at all. Silicone at the bottom in a properly built shower is only for aesthetic purposes, it doesn’t serve any purpose at all as far as waterproofing. All waterproofing is behind your tile, as it should be, as you’ve stated.

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Brendon

Regarding silicone below the bottom row of tiles, how doesn’t it prevent water that gets behind the tiles and runs down the plastic from getting back into the pan? Does it go back through the tile, above the bottom line of silicone? Is silicone not actually waterproof?

Reply

Roger

Hi Brendon,

Silicone is waterproof. And it does prevent it unless you install weep holes.

Reply

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