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. 
*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. 
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.
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.
I am working on my second bathroom, this time with just a shower base. The debate over the cement board over the flange is still very confusing. I am trying hard to make it work over the flange, but my shower base flange is going to require 5/16″ shimming. This will put the Hardibacker and drywall out of plane by about the same amount. I have studs added in that area in the event of adding a shower door. If I added drywall shims on the drywall side, would that help and anyway I can make this look right. On a side note. I am back to leaning on using Redgard over plastic. To me it just seems more logical to stop the water prior to getting through the Hardibacker. Yet some suggest online that Redgard is just a marketing product.
Hi Tom,
First – Redgard is NOT just a marketing product. That’s bullshit. It’s a legitimate waterproofing product. If you use redgard simply stop the backer above the flange, silicone between the flange and the backer, then paint redgard all the way down over that (including the bottom of the backer) and onto the flange itself. This leaves you a solid waterproofing layer all the way into the basin.
Can you put Hardi backer down on top of shower bed because mud slab was short
Hi Henry,
No. But you can use more mud.
Above you gave a benefit of using cement backerboards… what are the cons? And how does that compare to Denssheild?
Hi Jay,
The biggest drawbacks are the weight and workability of cement boards. They’re a pain in the ass. They are also not waterproofed, densshield is. With backerboards you need to waterproof either behind them or over them, densshield is already waterproof.
If I’m pouring a mud pan can I install my rubber membrane first install my hardy backer down to the membrane and then pour my mud Pan to the hardy backer on the walls or do I have to pour the pan first and then run the hardy board down to the pan ?
Hi Joe,
You can do it either way. If you run the backer first leave it about 1/2″ or more off of the liner. It can wick water if it’s touching the liner.
Thank you
What would you say is a minimum thickness to pour a pan ? This customer does not want a 4” curb because of a disability so I’m trying to keep it low. Do you think 1 3/4 on the outside and 1 1/4” in the middle of a 5’ x 4’ shower is enough ?
Thanks
Hi Joe,
That’s plenty. Technically you should have a MINIMUM of 3/4″ at the drain, ideally 1 1/2″. 1/4″ / ft. from there works out for what you’re planning.
I have green board on the ceiling, cement backer on walls. What should I use in the corners between ceiling and walls where cement board meets greenboard?
Hi Arvel,
Thinset and alkali-resistant mesh tape.
Hi Roger, I’m a DIY guy and am working on a remodel of our shower/tub. Doing a lot of research but I have a question about topical membrane on hardiebacker. I already bought the hardiebacker but haven’t installed yet because I can’t seem to find much information on anyone actually using a topical membrane on hardiebacker. Yeah, there are one or two, but googling/searching those terms should provide a sh!tload of info. Only thing I’ve found out is that you should really wash the hardie board very well and that you should dilute and prime the hardie board with said topical membrane then coat to recommended thickness. Due to lack of info should I even use hardie board or should I just use another cement board such as durock / wonderboard.
Hi John,
Hardi is just fine with a topical membrane over it. A LOT of people misuse cement backerboard names, so there are likely a lot of hardi installations being called durock, etc. Also I’m sure there are a lot simply being referred to as cement backerboard installations.
I have done hardi installations like that a LOT. It works just fine. Yes, you do have to wipe it down (this is to remove dust which would prevent a proper bond – hardi has a lot of dust on the surface due to the manufacturing process) and prime it, which ensures a solid bond by filling open pores, which the full topical membrane chemical composition may be too large to fill, first. (That just means that some of the open pores in the hardi may be smaller than the membrane, diluting it seperates the individual molecules and allows it to penetrate).
Hi Roger- so I have a slight problem after putting the wonder board over the rubber liner it sticks out farther than the top wonder board pieces (bows kind of) and we are using single sheet walls ( full marble sheets) do I need to stop the wonderboard once I hit the rubber liner? How do I prevent the bottom where the rubber liner is from being out farther send the top of the shower walls?
Hi Alyson,
There are two methods (no, you can’t stop the board above the liner). You can shim out the board so it is even with the face of the liner – two drywall shims on the studs above the liner accomplishes this. Alternatively you can notch space out of the studs at the bottom the thickness of the liner, creating a ‘pocket’ for the liner to sit into flush with the face of the studs.
Roger, great information, especially for a new DIYer like myself!! I have a few questions though. I’m remodeling my bathroom and I’m at the point of installing the backer boards. I have to shim them to be flush with the sheetrock. If I were to go with the plastic behind the backer option, I would go over the shims, correct? Also, would the screws mounting the backer board compromise the plastic sheeting? I’m on the fence between plastic sheeting for a vapor barrier and Redgard. I have a cast iron tub with a lip on the edge, so I understand the sheeting process of leaving a gap between that lip and backer board, as the sheeting will allow water to run off into the tub, but how would that gap work with using Redgard, as there would be no plastic to guide the water into the tub?
Thanks in advance for all your help!!
Hi Drew,
Yes, the plastic goes over the shims. The screws will seal after they are driven in and the backer is placed over them (it creates a dam water runs around, they don’t magically seal…). With redgard you would place the backer against the tub, silicone the gap and paint redgard all the way down to the tub.
Great article. Thank you!
Question. I am getting a lot of conflicting information about waterproofing. My tile guy wants to use the method you describe (with 10 minute building paper), but I am reading in a lot of places that this method is not long lasting and that using surface membrane or paint on (eg., RedGuard) waterproofing. Would you please let me know what you have seen from your experience and education in terms of longevity of the different methods. Thank you!
Hi Art,
The traditional method described above will last as long as you want, provided it is installed correctly. I have ripped out 40 year old showers built with this method. Either one will last as long as you need if it is installed correctly.
Do i need to install a drywall behind the cement backerboard?
Hi Frank,
No, it goes directly to the studs.
I am installing a 36 x36 new shower pan is it recommend to install plastic or roof paper on 2x4stubs before hardie dboard for water moisture barrier???
Hi David,
Absolutely, unless you’re using a topical waterproofing membrane like redgard or kerdi. You need to have a barrier in there somewhere, either over the studs or over the backer.
I bought your manual on liquid topical shower waterproofing and so far it is saving me from enormous headaches and binge drinking. I understand that you hang the backer first then pack the slope (so the backer ends up embedded). Is it necessary with Hydroban to do anything to the slope-to-backer transition before applying? I know you thinset slurry the sandy slope first, but I’m just wondering about thinsetting some tape on from the backer to the slope or just leaving it as is. Thanks!
Hi Ethan,
No, you do not need to do anything to that transition.
Hello Roger, enjoying your site with a few cold ones. I’m adding a shower in the basement, fiberglass base with Hardi tiled walls. 2 of 3 sides of the shower base have a lip. Was planning vapor barrier to studs before Hardi, and understand your recommendation to silicone barrier to lip. What’s the best way to maintain waterproofing for the side with no lip? Something other than plastic barrier? Attaching pic for clarification. Thanks for the help!
I’m not a tile guy, but I am a plumber… This shower base is not the type used for an alcove, the base in you’re pic is made for a corner application
Tom is right, you know.
You can silicone the back of the barrier to the vertical part of the lip about 1/4″ or so, so the tile covers it. But it certainly isn’t ideal with the incorrect base.
Hi Chief,
Fold the plastic over onto the horizontal arm of the base, silicone the back of it to that arm, install your tile then cut off the excess plastic at the base of the tile.
Roger,
First time doing anything like this at all. I’ve put my preslope in and I’m about to install the liner after I finish evening out the preslope (fingers crossed it’s correct).
I’ve read on here to not put any screws into the backerboard below 8 inches or so.. I’m planning on leaving a small gap at the bottom as recommended. I’m worried about the bottom of the backerboard bowing inwards because there are no screws closer to the bottom of the wall. Am I missing something?
Hi Zac,
I don’t know.
You do need to compensate for the thickness of the liner by either notching out the studs so the liner sits flush with the face of them, or shimming out the studs above the liner so the backer sits flush with it. This way it doesn’t bow out at the bottom of your walls.
Hi Roger,
Question on this part:
“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.
Are you referring to only the edges that run vertically? or are you also including the horizontal edges? We placed two 3x5x1/2″ Hardie on the back wall of our tub surround. The 5′ long edges run horizontally. When i push on the horizontal edges of the backboard (between the vertical studs), they do push in slightly. We will be tiling with 12″x24” tiles. It seems everything I have looked at, noone runs 2×4’s horizontally to support those edges…only the edges that run vertically. Is this normal and acceptable movement or should I take down the hardie and add horizontal 2×4’s?
Thanks,
C
Hi Christi,
Just the vertical seams.
And yes, I realize this reply is likely too late, but the info will be here for others in the future. Sorry for the delay.
Roger,
Do I need to put up Sheetrock before installing the backer board in a shower?
Hi Dave,
No.
I have built the pan and I am in the process of installing the backer board. My dilemma is that I want to use redguard but the shower has an outside wall. As I understand both the membrane and plastic is a bad idea. Will redguard serve as the vapor barrier between the heated air and the insulation if I remove the plastic sheeting? or will I be better off not using the redguard?
Hi Jay,
Yes it will.
And yes, I realize this reply is likely too late, but the info will be here for others in the future. Sorry for the delay.
Hi Roger,
You’ve been very helpful and love my dog way to much to mess this up??. So my 2 shower liners have passed the leak test. Preparing for final slope. You said that hanging the cement board now would give you a nice surface to draw line on to make a the final slope but I need to leave a 1/4 to 1/8 inch space between? Some of the cement board is already up. We did not put plastic behind it we plan on using redguard. Is that ok? How do I waterproof the space between final deck mud and cement board when it is 1/4”-1/8” above shower floor. Also was also planning on using fiberglass tape on seams do I need to put pieces of tape over screw holes. Thanks for your help
Hi Alissa,
Yes, if you are using redgard (good idea) then you do not want plastic behind it. Hang your backer up so you have enough space for that gap, then draw your line 3 1/2″ above the final height of your top deck (read through this). You do not waterproof that, the liner should run a foot or so up behind it, and water on the wall will run down the face of the redgard into the liner. Gravity solves the rest. No, you do not need tape over the screws.
What kind of caulk should I use in corners when I am taping cement board seams? Mold resistant paintable caulk since I will put seam tape in it and mortar just up to the corner caulk when I do the in-plane seams? What kind of caulk would you recommend? The redgard needs to stick to it. I like your instructive website. I’m trying not to set the cats on fire.
Hi Linnae,
100% silicone. The redgard will not stick to it, but it doesn’t need to. You still need to tape and mud the seams once you silicone them.
Thank you Roger! I’ll mud them when as I’m installing the tile. Today is a Silicone/seam tape and RedGard day!
Hello. I need something clarified please. for my shower the cement board is all taped together with thinset except the vertical corners. i used 100% silicone without tape on those. Do i then tape and thinset over that silicone then redgard the shower?? thank you
eric
Hi Eric,
Yes.
And yes, I realize this reply is likely too late, but the info will be here for others in the future. Sorry for the delay.
My tile guy left an inch and a half space between the lip of the cast iron tub and the cement board. Then he started to install the 12 by 24 tiles. Heonlyput 1 row the next day he didn’t want to use the same patern of tile. The tile was already set to the wall. He useda hamer to smash the tile to remove it. When he did he smashed all the cement board. I asked if he had to replace the cement board, he said No that the tape that holds thecementboard together was till there so he could fill it with mud and put the tiles back up. I feel uncomfortable with his procedure. My insurance company wants it redone. The contractor will not remove all The tile he installed to complete the shower suroundandis saying whether it is fine. I just can’t believie have a goid solid back behind my tile, especially being the first row of tile. What should I do? Except the job or get a new tile guy to take down all tiles and cement board and redo the entire shower surround?
Hi Brenda,
Get a new tile guy! That’s BS and it doesn’t sound like he even waterproofed the shower. There should be NO gap there either.
The largest gap at the lip of the tub surround should be 1/8 – 1/16 , then mud tape and mud, right? So with smashed cement board around the bottom I don’t have a sturdy waterproof shower surround, especially with the cement board that was smashed is on the first row of tile on the 2 short walls. He is insistent that the job is done correctly and will go to court to stand up for his job. I’m sure it will last a bit but I wasn’t ever planning to retile. What do I tell him? How do I prove he is wrong?
That is correct about the gap. The tile substrate has been compromised, period. If the substrate is compromised it compromises everything installed over it. Don’t let him BS you, he would lose his ass in court. Ask him to show you on the manufacturers website, or in the TCA manual, where his shitty fix is an approved method.
Thank you for your help. This was an insurance job. I’m trying to find out how much money is left on the claim to get someone else to redo the floor and shower surround. It has been a nightmare. We were without a bathroom for 2 1/2 months and still having leaking from shower plumbing, besides the tile job. I can’t thank you enough for your expertise! Have a great day!
Thank you so much for you advise. This is an insurance job. I have to see how much money is left for me to hire a new tile guy and redo the job. Have a great day!
I have gotte so much knowledge from your website, thank you for sharing your time and experience.
I’m using NobleSeal (similar to Kerdi) and it says it has crack isolation. Does that negate the need to mud and tape the seams? I know backer seams don’t go flush when you mud and tape them, but if you tile while you tape it’s all good. In this application, the mud and tape will have to dry prior to installing the membrane and I’d hate to have lumps on my wall.
Hi Dan,
If you’re using a sheet membrane like nobleseal or kerdi you do not need to tape and mud your seams.
Can you address a shower niche? I framed out a niche with 2×4, used flashing and planning to cut cement board and tape and thinset. Should I also use finerglass tape, redguard or silicone?
Hi Chris,
If you go over it with redgard that would be ideal.
Ok so cement board, thinset the corner and Redguard. Should I use the fiberglass seam tape or is the taped and thinset joins good enough?
Additionally I did vapor barrier behind the cement board about 7 feet. I left 1 foot at the top for ventalation. There will be tile almost to the ceiling. can I Reguard the entire Cement board area. I keep hearing about this mold sandwich, not sure how if the area is water tight. Thanks for your advice.
If the backer is trapped between two vapor barriers moisture can still form between them. Think about the outside of a glass of ice water after it sits in the heat for a bit. Condensation, no matter how small, can build up over time and begin to feed mold. That said, you have an open area at the top for moisture dissipation, so you’ll be fine.
I don’t understand how you finish the space between the horizontal part of the shower base and the bottom of the cement board when you leave the cement board 1/8″ from the top of the shower base flange. I get that you don’t want to push the cement board out by overlapping the flange and make a bulge at the bottom. Do you just leave the flange showing? My shower base also says to put screws with washers right above the flange to attach it to the stud wall. So I am also figuring I need to account for these. I plan to notch my studs but am wondering if I can avoid that and somehow make the tile to base transition look good.
Thanks for creating and maintaining this website.
Hi Ryan,
You don’t do anything there. Leave the flange showing and the tile just hangs over it down to withing about 1/16″ of the base.
Ah. Guess I should mention I am doing a pebble wall. Does that change your answer? Don’t think I can hang those down very well. Gonna have to notch and recess the base I think.
Oh.
In that case you need to either notch and recess the base or shim out your wall stud and run the backer over the flange lip down to within 1/8″ or so of the base.
You are awesome. Bought your manuals on liquid topical waterproofing and tile tips. Worth every penny. In it it states you put your Hardibacker up first and then form your mud pan. Do you just embed the walls in the pan? If so, does it matter if the bottom edge is butt against the floor? Thanks in advance for your help!
Hi Jim,
Yes, I embed the walls in the pan. With topical membranes it doesn’t make any difference. You do need to leave them up off the floor about 1/4″.
Hi,
I’m ripping out old vinyl or linoleum shower walls that the previous owner put in our back unit. The sheeting had been glued onto plywood. The seams had been caulked but eventually failed and the vinyl sheeting has started rotting.
I’m ready to drape plastic sheeting and then install hardibacker, then tile these walls, but wondering if the plywood will cause a problem, or if I need to rip that off to get to the studs. I’d much rather not! The ply has been nailed in, not screwed, so it would be quite the process to remove it.
Thanks,
Hi Colleen,
Sorry, the plywood really has to go. Plywood moves WAY too much to be behind a tile installation. It’s likely at least part of the reason the seams in the previous surround failed.