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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Great information!

Question is my shower pan has a 1 inch or so flexible plastic flange that attaches on 3 sides – against the studs (it’s maybe 1/16″ thick). Should I go over that with cement board and stop say 1/8″ over the actual shower pan surface?



Hello. I installed 4mil vapor barrier and durarock. Can I silicone caulk and tape with thin set all corners? Can I silicone caulk any seams as well as tape and thin set?


steve dunn

Great site. Just tearing out a spa tub to install a 4 x 6 shower.



I’ve been poring over your blog for the last couple of weeks (thanks for all this, btw), devising a plan for shower wall tiling around an in situ tub. I’m prepared to take it down to the studs and hang backerboard (and waterproof, of course) and planning to grout with spectralock epoxy grout. The question I have is: since I am using epoxy grout, can I thinset the backerboard corners and grout the tile corners? Or should I silicone the backerboard changes of plane and caulk the tile corners? Also on the list of possibilities I guess would be thinset backerboard corners and caulk tile corners, and silicone backerboard corners and grout tile corners. Using a light grey grout so not having to color match would be great, but bulletproof is the most important consideration, no? Waterproofing with hydroban and tiling with 4×8 ceramic. My understanding after much reading is thinsetting the backerboards together at the corners would resist the tendency of the walls to move relative to each other. Wondering if the strength of the epoxy grout you have touted lends itself to this approach, versus as you say at times, things are going to move and this should be allowed to certain degrees, i.e. plan for mobility in joints with silicone and caulk.


Seth Finkelstein

When you tape and mud, do you fill the gaps you so diligently left, tape then go over with mud again? Or do you just tape and then mud over the tape only? Doesn’t it defeat the purpose of leaving gaps if you fill gaps between backerboard with thinset?



Ed Birchler

Excellent article. It is very helpful.
I do have a question. I have an exterior shower wall with a window that I am planning on tiling around the window.

What do I do with the backer board and tile for the edges around the window?

Thanks for your help!


maggie darr

Hi. I hope you can help! I’m concerned. I just had a standard bathtub converted to shower. He just used cement board. I paid 4 thousand without door yet. Hoping my shower will hold up and did I overpay?



Hi Roger.

I love the site and the manuals. I’m learning far more about tiling than I imagined there was to know.

Do I need to do anything where the backboard meets the floor? Thinset? Silicon? Just leave it?




We’re having a house built and our builder skipped most of these steps in tiling our shower walls. They did not install a vapor barrier, nor did they tape and mud the seams. Also, part of the backer was broken off on the edges, so I’m concerned if a piece of tile were to get hit too hard, it could chip. Does code require those steps and they are technically in the right despite poor standard of excellence? Thanks!



Should I tile the shower pan before I install the duroc?



Yes, tile the floor first.


Kyle Kanter

Please notify me of answers to the above comments. Instead of hanging backer board myself, I leave it to a professional. But it’s worth the research to know what the proper method is, so I know what to expect from the “professional”.



Great info. What do you do for the gap between the cement board and the floor?


Farzad Fana


Doing a tub/shower surround. I put up 6 mil moisture barrier and a layer of cement board. This layer has joints (left a about an 1/8″ gap as per your recommendations). I want to add a second layer of cement board on two of the walls. My question is should i tape/mud the joints on the first layer of cement board before adding the second layer? Or tape/mud the joints on the second layer only? Many thanks.



I wouldn’t double up backer board. Start with a layer of plywood (the proper thickness) and then add your cement board.


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