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.
Thank you so much for your advice to use thinset to add the 1/4″ backerboard over the reguarded Hardibacker. My new problem is that my impatient husband couldn’t/wouldn’t wait for your reply. It’s up with adhesive. Any suggestions where to go from here? Sigh…
Hey Paula,
Yup, cover it all with redgard so it’s sealed up. Or, and this would be best, pry it off of there and put it up with thinset – which will never come loose. Of course your husband was impatient – we’re guys, it’s what we do.
Hey Roger,
Another question about construction adhesive(liquid nails). I’m planning on overlapping the joint at the backerboard/drywall in my shower surround with a 3″ wide bullnose border tile. I’m going to use thinset mortar on the bb side(2″) and liquid nails on the drywall side(1″) of the border tile. I was also going to bridge the same gap between bb and drywall with tape imbeded in mortar then RedGard over the joint and drywall only as there is vapor barrier elsewhere hopefully in an effort to prevent future cracking between the bb and drywall. What do you think?
Thanks, Neal
Hey Neal,
No reason to use liquid nails at all on the drywall side – you should use thinset for all of it, thinset will adhere to drywall just fine. If you tape and mud that gap with thinset and use redgard over it that area will be waterproof as well as prevent cracking – sounds like a good plan!
Hello again,
I have a question regarding the backerboard in the tub surround area. We have already put up the backerboard, mudded, taped, remudded, siliconed where the backerboard meets the tub flange, and reguarded the whole shebang twice. We have since realized that we need to build up the backerboard with another layer where we will be installing a glass accent boarder. I am concerned about putting up the backerboard with screws because although I can patch and redguard the screw holes from the front I can’t where the screws continue into the original layer of backerboard and into the wall. So, is it possible/permissible to apply the 1/4″ build up of backerboard with constuction adhesive, or a similar material therefore eliminating any perforation of the original redguarded backerboard? Also, I can’t mesh as tape it as we have already set all of our tile below this accent area. Any suggestions would be greatly appreciated and as always, thank you in advance for your advice.
Paula
Hey Paula,
I absolutely love easy questions – thanks.
Do not install liquid nails on your shower wall – won’t work. Do not screw through your waterproofing – defeats the purpose.
What you can do, though, is install the 1/4″ strip of backerboard for your accent directly onto your redgard with thinset. It’ll work just fine and it won’t go anywhere. And you don’t need to use any mesh tape on it – it’s just a spacer.
Roger,
We really appreciate you helping us DIY’s! My question is about the backerboard starting above the tub flange, rather than overlapping it, how will I span this 1″ gap with tile down to within caulkable distance of the tub surface? And then grouting between tiles that vertical 1″ gap up to the bb? In your picture about the weep holes, the tile appears to be within 1/8″ of the tub and then caulked horizontally along the tub which is what I want to duplicate.
Thanks, Neal
Hey Neal,
The tile can actually hang over that gap. As long as you have your moisture barrier running down and over the tub flange it won’t hurt anything at all. Just install your thinset all the way down to the bottom of the backerboard and install your tile to it. The 1″ or so at the bottom isn’t actually attached to anything. You can pack thinset in there behind the tile if you want – it uses less grout that way. It won’t stick to the plastic but once it cures it will leave a solid backing behind there for your grout. You do want to leave a 1/16″ – 1/8″ gap between the tile and tub for caulk or silicone.
Hi Roger,
I had a contractor install a tub surround. He put up plastic water vapour barrier over the wood framing on the external wall (long side of tub) then placed Durock cement board, then thin set, them tiled. However, on the front and back end of the tub, he omitted the water vapour barrier and placed the durock cement board against the framing and then thinset and tiled. Should he have placed water vapour barrier on all sides? When I asked him, he said since the front and end wall of the tub are internal walls I did not need the plastic water vapour and that the cement board alone would be enough. I’m worried that water will seep into the cement board and affect the wood framing. Also n the floor, he levelled it with cement then tiled over it. He did not use an uncoupling membrane to prevent cracking. His reasoning is that the house is about 100 years old and should have settled already so he is not concerned. Should I still be concerned?
Thanks for your help,
Mary
btw, Great site!
Hey Lorca,
Yes, he should have installed a vapor or moisture barrier on all walls surrounding the shower. The fact that he installed the tile with thinset tells me that he isn’t doing anything improperly on purpose – he likely simply doesn’t know better. Since it is just a regular tub surround and not a full shower or steam shower or anything of that sort it will likely be fine. Although it would have been better (and proper) with a full barrier I don’t think it’s anything major.
As far as your floor he is correct that the concrete should have already settled. I still would have used a membrane but it’s actually done all the time and usually doesn’t create problems. I wouldn’t be too concerned about it.
Roger,
Can Hardie backer be finished and painted particularly the area above the shower tile.
Hey Joe,
Yes it can. It may be better to use a primer on it first because it tends to suck moisture out of whatever you put on it.
Hey Roger,
I am using Hardibacker and running it all the way up to my shower ceiling. Do I need to tape the joint where the Hardibacker meets the ceiling? If so, do I just use the mortar on the cement board and drywall, then tape? Hope this makes sense.
Hey Randy,
Yes, you do need to tape that joint. Just use regular thinset and fiberglass (alkali-resistant) and you can paint over the thinset if you need to.
Hey Roger, I am tiling my shower. So far I have the floor done (pre-slope, liner, and top layer) and have just installled the concrete board with a 1/4″ gap to the floor. I will be using Redgard as the waterproofer. Do you mud and tape in the corners where the CBU meets the floor?
Hey Brian,
Do not tape and mud that plane change. That may allow moisture to get behind your redgard and wick up your cement board. Fill that gap with 100% silicone, or a ‘backer rod’ and silicone then paint the redgard directly onto it. A backer rod is sold at hardware and big box stores and is essentially a styrofoam rod used to fill excessive space before caulking – it won’t wick water. You need to separate the backerboard from the top mud deck, which will get saturated, with a waterproofing of some sort to prevent water from getting behind your redgard.
I am doing a complete demo on my shower stall which includes removing the shower pan.
The 2 wall that are concrete and the other 2 are metal studs. What do I have to do to the concrete walls so I can install the backerboard and what size do you recommend for the walls.
Hey Jason,
You can place ‘furring studs’ against the concrete walls to install backerboard to. It’s basically a wooden (or metal) studded wall installed right against the concrete wall. You can also use a topical waterproofing membrane like kerdi or a liquid like redgard and apply it directly to the concrete wall and tile right to it. The advantage of that is you don’t lose any space in the shower – the studded wall will bump it out.
I prefer 12×12 or larger on shower walls, but that’s just a personal preference. There is no real set size for shower walls – whatever you (your wife) like will work just fine.
Since my last inquiry I have done a complete demo of the shower, replaced defective 2×4’s, tore out the mud bed down to the slab.
The drain was two piece cast iron on to PVC. I was able to remove the 3 bolts and remove the top of the two piece unit. What is left is the bottom portion of the unit which is flush to the building slab. The original installation did not have a pre slope. The installer had simply built up a 1 1/2″ curb around the 2×4 base that is nailed to the slab. I have removed this as well.
Do I need to now remove the bottom portion of the drain so that I can raise it to allow for the 1/4″ pre slope to go under the drain base to your recommended thickness? I believe that I do?
Do I chip out the old metal drain? It appears that the concrete that surrounds it has been removed and replaced at another time? I don’t want to screw this up and the local plumming supply had no useful information. The information that you supply on your site is great and has provided me alot of faith that I can do a semi professional job
Hey Joe,
Yes, unfortunately the drain will need to be raised. Your pre-slope should be a minimum of 3/4″ thick at the drain so the flange will need to be raised to that (the top of it). Alternatively you may be able to use what’s called a ‘drain extender’. It is basically a second bottom flange which is bolted onto the current one to raise the top of the drain. I’ve used them a couple of times and they’ve worked just fine.
Tell the meatheads down at the plumbing supply shop to get you one of those for your drain and you may not need to chip it all out of there.
So if you leave a gap between your tub lip and the bottom of the cement backer board, do you need to tape this gap? Also when you lay your tile, do you mortar the bottom line of tiles to the tub lip and the cement backer board or only the backerboard? It seems like if you mortar to the tub lip and the backerboard, the bottom tiles will crack when the tub moves when filled with water? We were thinking of mortaring only to the backerboard, and having the last 1/2 of the tile not have any mortor and then fill it in with silicone, is this correct?
Hi April,
You do not need to tape that gap. And you are correct, only thinset to the backerboard. If you mortar it to the tub as well it may crack the tiles when it’s filled with water or as normal seasonal movements expand and contract the two materials at different rates. You do not need to fill that entire gap with silicone – just leave it open and make sure you install weep holes in the bottom caulk line where the tile meets the tub. (You can read about weep holes in tub surrounds here.)
Wow! Thank you for the fast reply. I read the article on weep holes and have a question. Do we only need 2 weep holes- one on each side? We dont need one on the back wall? Also for every where else that does not have a weep hole, would you use grout or silicone at the bottom of the last line of tiles?
Thank you so much.
Hey April,
You can put as many weep hole in there as you want. As long as your wall is waterproofed with a moisture barrier behind it there won’t be any problems. All the moisture will make it to the weep holes eventually. I normally only install two, I think it becomes really noticeable if you do more than that. Always use silicone at any changes of plane – there the tile meets the tub and all the corners should be siliconed rather than grouted.
I’m ninja-quick today.
Awesome- Ok Thank you for the reply. One more quick question. When you say all the corners, you mean the corners where the two walls intersect- back wall and side walls? Or do you also mean where the tile ends and the drywall begins?
You are Ninja-Quick!
Had to take my daughter to lunch – my ninja skills just went into the crapper – sorry.
Yes, where the back wall and side walls meet, where the tile meets the tub and, although not ‘necessary’ where the tile meets the drywall as well. Those are areas of either the most movement or where two different materials, which will expand and contract at different rates, meet. You want to have silicone in those areas to allow a bit of flex – grout will eventually crack.
Hi Roger –
I am tiling our bathtub walls and using Hardibacker. I have a lip on my tub that is about a 1/2″ tall. I noticed you said “You do not want to run the board over the edge of the lip because it will cause the backerboard to bow out”. I noticed this when I put the 1st pice of backer board up 1/8″ above the tub. Can I rest the backer board on top of the lip of the tub?
Hey Randy,
Yes, you can either set it up above that or shim out the wall studs above the tub lip so the backer will set flush. Make sure your moisture barrier runs over the flange and is siliconed to is so any moisture will end up in the tub.
I have a double plywood floor in my bathroom. I’m going to tile over it as I have done in the past without backerboard. Is that ok to do or not. I never seem to have had any problem in the past doing it this way. Your input would be great.
Thanks,
Mike
Hey Michael,
Tiling over plywood CAN be done IF: it is a very specific type, brand, and grade of plywood, you use a particular thinset, the plywood is installed to very exacting standards to both allow for movement in one plane without allowing excess movement in others, the plywood is installed in a specific manner with regards to overlapping the layer below and offset from the floor joists, etc, etc. And most importantly: You’re lucky.
Tiling over plywood uses a very exacting method to GUARANTEE that there will be no problems with it. Most professionals won’t do it – I won’t do it, and I know how. If you haven’t had problems with the ones you’ve done before you should consider yourself lucky. It’s not that it will definitely cause or have problems, it’s that you cannot guarantee that it won’t. And anytime you place a material made to not move over a material that will move you’re asking for problems. It would be best to install at least 1/4″ backerboard so your tile has a suitable substrate – wood is not it.
My contractor has installed cement board over studs for my shower, but did not put plastic behind it. I thought it would be no problem, I would just Redgard it. But now I’m getting concerned because the ceiling slopes down with the roofline, which we spray-foamed with closed cell foam (moisture barrier), but the studs are not sealed in any way. The remaining walls are not exterior walls, so don’t have the additional moisture barrier concerns.
I had been thinking about maybe putting up a piece of solid surface on the ceiling to make it a little less busy, so maybe that would be the way to go? Where would you recommend Regard’ing or should I take down the cement board and paint the studs/put up plastic/other?
Thanks for all your advice on this site, it’s great!
Hi Capitalsfn – if that is your real name.
The only concern you need to have with the ceiling in a shower is vapor permeability – that’s just water in vapor form. Unless it is a steam shower you will not have enough vapor penetrate the grout lines on the ceiling to even reach into the backerboard – it will dissipate before that. So unless you have a steam shower your ceiling will be fine without the barrier behind it – the vapor isn’t going to be doing any damage up there. Solid surface is another option, but not really necessary.
Roger,
Thanks for the advice. We’ve sorta tucked this shower in, so the “ceiling” comes down pretty low, about 5′ at the back wall. It probably won’t get a ton of water on it, but it will get some. Is the idea that gravity will force it down instead of through the grout and into the cement board?
Thanks again!
It’s a combination of gravity and the fact that it will not be bombarded with water constantly as the shower is on. The grout will soak in some moisture, the amount, however, is minimal and will likely dissipate before it even reaches the substrate. Most of the moisture that will get up there is simply condensation from water vapor (steam from your shower) so it isn’t as if you’re shooting a hose at it.
Since your ceiling is sloped you need to ensure that the wall/ceiling transition at the bottom of that slope is waterproofed well. Gravity, while helping you eliminate most of the moisture in the ceiling, will also drag every bit of moisture that condenses up the down to that point. That grout line will be constantly subjected to moisture – more so than other areas. It’s not a problem as long as it’s waterproofed well.
Hello
It is now time for me to tape the joints in my shower. I am very confused about what kind of compound to use on the tape. I know it is called thinset, but is thinset the same as tile mortar?
thanks
Hi Michelle,
Yes, it is the same as tile mortar. Thinset, mortar, mud (in one aspect) are all the same thing.
I live in a home built in 1970. All three baths have tile installed over what appears to be standard issue drywall. After 40 years, one of the showers finally gave up the ghost and we took it down to studs. My question is, why was standard issue drywall fine 40 years ago, but now, longer acceptable material?
Hey Chris,
Much of the problem stems from two things. First we began to import manufactured drywall from China. This was done simply because it was cheaper than what a builder could get it for here in the States in larger quantities. The reason, we discovered after about five years, is the product was extremely inferior in any area in which it was exposed to moisture. It simply disintegrated. The core was not as dense and the paper facing was entirely different – it would not stand up to regular moisture exposure.
The second problem is that to combat this manufacturers came out with ‘greenboard’. Greenboard itself wasn’t a bad product – for a regular wall. The problem was that it was marketed as a ‘moisture resistant’ drywall so, of course, builders somehow read that as ‘perfect for shower substrates’ – it wasn’t. Not only would it disintegrate it also contained the perfect mixture of stuff to feed mold – rampantly.
So beginning about the mid-80’s the drywall in showers was no longer solid and at least resembled something that would last a while, it was either Chinese drywall or greenboard – neither of which was suitable. By the time we got back to using drywall made in the good old USA the manufacturing process and materials for it had changed to try and compete with the Chinese garbage – it is no longer sturdy enough to be used in showers now.
So the short answer is that the product has changed – what you have in your shower there, the standard drywall from 40 years ago, is not the same stuff you can buy on the shelf now. There is no way the new stuff will last ten years, let alone 40. That’s still fairly impressive even for that stuff!
I plan on using hardi backer for my tub surround in the bathroom I am building, and I plan on extending that hardi backer about a foot past the edge of the tub. My question is how do I float the transition between the hardi and the sheet rock? I would assume I’d use thin set, but I’m not sure. I’d appreciate any advice you could offer. Thanks.
Hey Ricky,
I’m assuming since you’re taking it out that far it won’t be getting wet? If that’s the case then you can use regular drywall tape and mud. Make sure you use the powdered drywall mud – the stuff in a bucket can actually become soft from steam.
You can float it out with thinset as well if you want. In that case you need to get alkali resistant mesh tape for the seam – which you should have anyway for the shower walls – right?
You can use that with thinset and simply paint over the thinset if you aren’t tiling over that area.
Hi,
I recently installed and taped hardiebacker in my bathroom remodel. I had put in a 4 mil vapor barrior over the studs, but then not thinking opened up a section of the backer to install a prefab niche and cut the vapor barrier to get the niche in. Now I have a section of one wall with a messed up vapor barrier. My question is can I apply a waterproofing membrane around and above the niche to keep the water out? I also put the backerboard about 1/4 of an inch above the pan liner. I had heard that you are supposed to do this and then apply a silcone caulk between the liner and backerboard to prevent wicking of water. I know it’s probably to late to ask, but will this work?
Thanks for your help.
Hi Josh,
Yes, you can install a moisture barrier around the niche. This barrier must be placed beneath the wall barrier above the niche and in front of the wall barrier beneath the niche. The niche barrier should be beneath the wall barrier along the sides of the niche. Silicone the niche barrier to the wall barrier all the way around.
No real need for the silicone at the bottom of the backerboard. As long as the bottom of it is not in contact with the membrane it will not wick up enough water to get above your membrane before gravity sucks it back down. It won’t hurt anything, though.
Ok that makes sense, but I’ve already installed the niche and thinsetted it onto the backerboard. I was wondering if I could paint on redgaurd or some other paintable waterproofing agent onto the backerboard. If I go above the niche then any water that may get behind the backerboard won’t get to the studs via the cut vapor barrier behind the niche. Since the vapor barrier is still intact under the niche then I was thinking of not applying redgaurd as any water that gets back there would eventually flow down the vapor barrier and into the pan.
Hey Josh,
Sorry, I missed the ‘prefab’ part of the niche in your previous comment – sun got in my eyes.
Any prefabbed niche is going to be waterproof and the main concern with niches is the fact that they have a horizontal surface sitting inside your wall cavity – that’s never good for water. However, since it is prefab and already waterproofed all those worries are eliminated. It would have been better had you siliconed the moisture barrier to the niche (inside the wall) but you should be fine. Provided it’s in a normal spot there will not be a lot, if any, water getting behind your tile from above the niche.
Thanks Roger, I appreciate the help. One last question. Would the same hold true for the vapor barrier around the faucet valve? I have 2 of them, one on each side of the 5’X37″ shower. When putting on the vapor barrier I simply cut the plastic and pushed it over the valve.
Josh
Hey Josh,
Yup, same thing. Just silicone the backside of the moisture barrier to the valves and pipes so that no water can creep up behind them.
Hi,
We’re in the process of renovating our 20 year old house. So far, we’ve already done somewhere in the ballpark of 500 sq ft of floor tiling (over Ditra). Now we are working on to a shower/tub surround. We’re demolishing a bathroom that has the tub surround done breaking MOST of the rules – but fortunately the water damage in behind is minimal. We want to do a better job!
My question regards vapour barrier. I totally get that it needs to come down to and over the lip of the tub. Makes perfect sense. The question comes on the wall that is an outside wall (also the back(long) wall of the tub). If we do only one layer of vapour barrier, what about vapour barrier over the insulation that is in the wall behind the tub? I understand why multiple layers of vapour barrier (on either side of the backer board, for example) is bad – but what about the idea of floor to ceiling plastic vapour barrier over the insulation & then tub to ceiling tar paper vapour barrier over that (& only that on the interior walls).
I’d appreciate your thoughts.
Hi Sharon,
Placing another barrier directly over the one currently in place for the insulation is not going to hurt anything. The problem arises when trapping your substrate between two barriers such as a plastic barrier and a topical membrane such as kerdi. You can put the tar paper right over the current vapor barrier without any problems.
Thanks
My Engineer brain figured it should be fine, but a second opinion is appreciated!
Hopefully all this keeps our mouldy sheathing (outside the insulation) from getting worse. My husband just finished treating it with bleach (yuck!) and we’ll let it dry all week before sealing the wall back up again.
I need clarification on your response to steve on 5/19/09 @ 1:40 PM. Is the 1/8″ that you talk about above the shower floor(tile) or the material in the shower base pan? Sorry if this is a really stupid question.
Hi Michelle,
Keep the backerboard 1/8″ above the material in the base pan – the deck mud. This is to prevent the backerboard from wicking water up from the shower floor. No question is a stupid question if you need the answer to do something correctly, right?
is there a reason i can’t put the durock all the way down to the floor behind the shower floor and then start the tile about a sixteenth inch above the shower lip? also if i did this should i screw the lip through the backer board and into the studs? the way i look at it if i put the backer board above the lip and then 1/4 inch tile over that i would have 3/4 inch sticking out from the shower base. thanks
Hey Steve,
I’m not sure I understand what your asking. Or, more specifically, why you are concerned with 3/4″ sticking ‘out’ from the shower base.
You can do it in the manner you’ve described if you are using a topical waterproofing membrane. However, if your shower base is going to have more than two walls (it is surrounded by three walls and not a corner shower) then you need to ensure that once you get the durock installed that your shower base will still fit. Most are made specifically to fit inside spaces from stud to stud, if that’s the case then the space for your shower base is going to be one inch too small.
If you are not using a topical membrane on your durock, such as kerdi or redgard, then there is no way to run your vapor (moisture) barrier down behind the durock and into the shower – it will drain behind and under the shower base and, more than likely, into your wall framing.
When you say shower ‘lip’ I’m assuming you mean the flange around the base which curves up and is meant to be screwed to the studs? If you stop your tile above that you will have an open area which can not be waterproofed. Shower bases are built to accommodate this thickness. They are made in that manner so that your shower can be properly waterproofed.
We are tiling our bathtub walls. We are down to the studs and I am trying to figure out what to do next. We had a lot of mold which has been sprayed with bleach and water and vinegar and water. I know I need to let this all dry before I put up my vapor barrier. After I put this up should I put “green board” up then backerboard or am I ok just using backerboard? This forum has been really really helpful. Thanks, Dan
Hey Dan,
After that dries out hang your barrier (make sure it overlaps your tub flange and is siliconed along the back) then just install the backerboard. Do not use greenboard for anything.
Hi Roger-
Can I use Redgard as a watrerproofing agent on my cement backerboard vs. plastic sheeting on the studs?
Hey James,
Absolutely you can. Just make sure you have only one or the other – not both. If you want redgard make sure you read through this post: Properly installing Redgard on shower walls for some basic info like how and why you need to ‘prime’ cement backerboards first.
Hope that helps.
Roger,
I’m re-tiling the walls above my tub as well as the floor in my bathroom. I’ve ripped out the walls above the tub down to the studs. I’ve read much of your blog…so I was going to do the vapor barrier over the studs and then attach the hardiebacker (1/2″) to the studs. When I went to home depot, I had multiple people tell me I needed to attach plywood (1/4″) to the studs and then attach the hardiebacker to the plywood. Is the plywood necessary? If so, I will have plywood, hardibacker, and then tile and this extra plywood will make the tile stick out further from the drywall outside the shower. What would you recommend to help make the transition from the tile to the drywall more seamless? The tile I’m using is a subway tile (if that makes any difference).
For my floor, I have a subfloor (not sure what it is ) and then 5/8 plywood on top of that. HD told me I would only need to add the 1/4″ hardiebacker board on top of the plywood without any thinset. i see that you sometimes recommend using thinset. can I get away with not doing the thinset? on top of the hardiebacker i’m doing a heated suntouch wire kit and then marble tile (1″ hex shape). any advice here is greatly appreciated.
Thanks for your help!
Hey Kurt,
And I ALWAYS recommend thinset beneath your backerboard on floors – always. 1/4″ hardi is fine since it lends no deflection value but it does need to have thinset beneath it. It is not only in the TCNA guidelines but the only way to have an absolutely fully supported backerboard for your tile. My advice, with marble that small, is to install your suntouch then use SLC (Self-Leveling Cement) over the top of that to give yourself a flat substrate. Ditra won’t work there – your tile is too small.
If, when you go back to HD to get your supplies, anyone of them continues to try and feed you that line of absolute crap please feel free to give them my website, email, and/or phone number. I’ll be more than happy to properly educate them since their training department has obviously failed miserably.
First I’d like to say that I’m delighted I found your site. You explain things well, seem like you really do know what you’re talking about, and also seem quick to respond to questions. There’s a lot of contradicting information out there that you’re clearing up for me.
I’m in the middle of a nightmarish bathroom remodel where I gutted down to the studs (or lack of studs, see below). The reasons why it’s nightmarish are because my house is relatively old made of brick and stone (no framing on exterior walls), there was a “wet bed” tile job chest high around the entire bathroom as well as the tub surround, as mentioned the exterior wall had no framing just furring strips attached to cinder block with cut nails, and nothing is quite square or plumb so everything I do is slightly “custom.”
I thought ripping out 1 5/8″ of tile, cement, more cement, and wire mesh, not to mention the upper plaster portion of the walls was the hard part. No, the hard part is re-doing the furring strips on the cinder block exterior wall and trying to get everything to match up and be level, plumb, straight, etc. I’m almost done with all of that and will probably be putting up drywall and hardiebacker soon. Drywall is for most of the room and hardiebacker will be the three walls surrounding my tub. Tile will go from the tub to the ceiling on those three walls.
I’m relieved that you suggest that the hardiebacker can stop about 1/8′ above the tub lip. I thought for sure it should go past the lip which would bulge it out. Then I thought I could just sit it on top of the lip but in a reply to someone else you suggest that the tub could move when filled and that the hardiebacker shouldn’t sit right on it for that reason.
I have 3.5 mil plastic that I’ll put up behind the hardiebacker. I know you suggest 4 mil but I’m hoping 3.5 is still acceptible. Won’t using staples to attach it to the studs compromise the waterproof barrier? Also, if water does get behind the hardiebacker wouldn’t the staples eventually rust? I’d like to use silicone to attach the plastic for that reason but I know it’ll be a little tougher to use than staples.
I’ll run the plastic past the lip of the tub under the bottom edge of the hardiebacker. I know this is so any water back there will run into the tub. Once the tile is installed to overlap the tub lip and I caulk the joint between the tub and the tile won’t this stop any water that runs down the plastic from entering the tub though?
I understand that a small gap should be left in between the hardiebacker boards that will then be taped with thinset and mesh so that you have a monolithic wall. You then mention that a gap should be left at changes of plain like the two inside corners I have to allow for movement. Should those corners be taped and if so wouldn’t that remove the ability for the corners to allow for movement?
Since I liked what you had to say about Spectralock I read more about it at laticrete.com and spectralock.com and I think that’s the way to go. Even though Laticrete has a calculator for coverage I’m still not understanding just how far a mini kit will go. I don’t have any stores that carry it near me so I can’t check the package. I guess I’ll be ordering it online. My tiles are 9″x12″ for the wall and 12″x12″ for the floor. I know grout joint size is personal preference but what would you use for those tiles and can you give me an idea how far a mini kit would go based on those joints? I’ve done sanded grout on a floor before. I’m hoping the installation isn’t too much harder than that.
Also it looks like Laticrete has two color matching caulk products, one is a silicone caulk and the other is acrylic. I’ve had bad experiences with acrylic in bathrooms in the past. Do you have experience with either of these and would you recommend one over the other for the tub?
I know that was a lot to read. Thanks in advance for any help you can give.
Hey Tom,
The 3.5 mil plastic will be fine. The staples actually create little ‘dimples’ as they go in which essentially create little dams for the moisture. The water will not get into the holes created by the staples – they are basically self-sealing in terms of water penetration. They will rust if you use steel staples – they won’t if you use aluminum or stainless.
Some guys do tape the corners and some don’t. I do sometimes and sometimes I don’t
Helpful, huh? More often than not I will not tape and mud the corners specifically for the reason you stated – no movement. And the corners should be caulked, not grouted, for the same reason.
For tile that size a mini-unit would do about 40-45 square feet. You can download the coverage information for Spectralock here. That’s using a 1/8″ grout line, which is probably what I would use.
I have used both the acrylic and silicone laticrete products. For a shower I always prefer the silicone variety.
Hope I answered them all.
Thanks so much for the info and the professional opinions. I have some follow up questions and I promise I’ll make it shorter than before.
You say that inside corners should be caulked but I believe you mentioned somewhere that you can grout the inside corners if you use Spectralock. Is that true and do you prefer one over the other for corners?
Can Spectralock be divided into portions or do you have to mix it all at once?
You may have missed one question from my previous post. No big deal but I’m still curious: If the hardiebacker stops 1/8″ from the top of the tub lip and the plastic goes under the hardiebacker edge and overlaps the tub lip for water to drain in the tub, after tile goes up and overlaps the tub lip and you caulk the joint between the tub and tile doesn’t that caulk impede drainage for anything running down the plastic toward the tub?
I’ll also be tiling the floor. The existing floor is mosaic tile with an inch or two of cement underneath. It’s solid, flat, not cracked and otherwise in good shape. My plan is to tile over it so I don’t have to worry about ripping it up and putting down a new level floor. I’ve read elsewhere that this should be fine if I scuff it up beforehand. What do you think? Also there’s an inch or so gap around the perimeter of the floor between it and the wall because of how thick the old wall tile was. What do you think I should use to fill that in? I was thinking either laticrete floor leveler or floor patch but I’m afraid that if I pour the leveler in there it might leak through to my finished basement.
Finally, the linen closet was never tiled. It was covered with an old piece of vinyl. When I pulled it up I actually found hardwood flooring in decent condition but it’s about 3/4″ lower than the mosaic tile. I thought about just leaving the hardwood and using a piece of 1/4 round or cove base as a transition not caring about the height difference since it’s not a walk in closet. I don’t know if that’ll look right though and may want to tile it. If I do that I assumed I’d have to put a piece of plywood in then cement board over it to be level with the mosaic. I’m concerned that there will be a joint between the mosaic and cement board that could be a weak spot. What’s your thought? If I do that do I mud and tape that joint as if it were a regular cement board joint?
Thanks again! I’ve already told friends about the great information on your site.
Hey Tom,
If you use spectalock you can grout the corners. The grout is actually stronger than most tile.
Spectralock can be divided into portions. I usually get full units and divide it into four separate parts – this creates mini-units. It’s cheaper that way and I always have it on-hand and don’t need to waste it. You need to divide everything including the liquids by weight, not volume.
Yes, it will impede the drainage of moisture behind your tile. That is why you need to leave what are called ‘weep holes’ in your caulk (or, in this case, grout)lines. This is simply a run of about an inch along the back of each side wall that you do not caulk or grout – just leave it open. I usually put them on the side walls about an inch from the corners but you can put them wherever you want.
I’m the wrong person to ask about tiling over existing tile – I never do it. Doesn’t matter how solid I or anyone else thinks it may be – I always tear it down to the studs or concrete – always. It’s the only way I can give my insane warranty. If I build it all I know it will last. Not saying you can’t do it – just that I don’t. If you do you need to use a very highly modified (read expensive) thinset to ensure it will adhere. The space around the wall can be filled in with caulking ‘backer-rod’, that’s just a stiff piece of styrofoam to fill empty spaces before you caulk them, it can be used there and just fill in the rest with thinset. You can find it at any big box store.
If you do tile that closet then yes, use plywood and backerboard to build it up and tape and mud that seam. It shouldn’t be a problem.