I know there are some people out there (not my regular readers like you!) that read what I write and think to themselves ‘okay, but I’m sure that won’t happen with my installation’. So periodically I’m gonna post things like this that show exactly what happens when things aren’t built correctly. And yes, it will happen to yours, too, if the proper steps aren’t taken. If you care to see more train wrecks you can check out my ‘flawed‘ page wherein I post photos of absolutely horrible tile installations which I’ve torn out and replaced.
See that crack in the tile right there? (The line down the center is not a grout line – it’s a crack. You can click on it for a larger version) That bathroom floor is less than eight months old. It was installed with hardibacker over the subfloor and thinset. At least that part is correct, but that was about it. There was no thinset beneath the hardi and the seams between the sheets were not taped and thinsetted. To a lesser extent the correct screws were not used in the hardi – they committed the cardinal sin of using drywall screws in the backerboard. Yeah. Wrong.
So, back to the crack. (Never thought I’d ever type that!) As soon as I walked in and saw it I knew exactly what was wrong and I knew why. The crack was in an absolutely straight line – a dead giveaway that the crack is likely over a seam in the backerboard which wasn’t taped. If you read my post about how to correctly install flooring backerboards you will see that there needs to be thinset below the boards, the seams need to be taped, and the proper screws need to be used. None of which was done.
And here’s what was beneath it: 
If you click on that photo (I dare you!) you can see the crack follows the seam of the backerboard exactly. Without the tape on the seams the individual boards may move in different directions and, without the support beneath from thinset, they will move independently and eventually crack your tile or, more commonly, your grout lines first.
When you tape and thinset your backerboard seams it will lock the two separate sheets together and any movements in the substrate (seasonal micro-movements, completely normal) will all move as one and in the same direction. This won’t cause any stress on your tile.
I simply pulled up all those cracked pieces and chipped the old thinset out of there, installed proper screws along the seam, taped and mudded the seam (when I say ‘mudded’ the seams I mean thinset) and reset new tiles and grouted it up. Once that grout cures it will lighten and it will look brand new.
So all these little things like ‘tape and mud your backerboard seams’ that I throw out there may seem like it’s just overkill or taking extra precautions which aren’t really necessary – well, they are necessary. And this is why. This will also happen on a shower wall if your seams are not taped and mudded. If the boards move differently it causes uneven stress on your tile – it needs to release somewhere. Ninety seconds worth of work to tape the seam to begin with would have prevented this – just do it! (damnit)
If preventing cracked tile isn’t enough motivation for you maybe this will: all of my regular readers know what happens if your tile or grout crack – your dog will burst into flames! So if you don’t do it for your tile, do it for your pooch. Not only are flaming dogs bad for, well, the dogs, but they tend to run around and catch other stuff on fire too! You don’t want that, do you?
TAPE YOUR SEAMS! 
What mortar should i use for 8×48 wood plank tile over wood subfloor and hardi backer. U had a picture a few days ago of a mapei product. Large tile. I can’t remember if it was large tile/stone or just large tile. Recommended for moderate set according to James hardi.
Hi Mike,
Mapei has ultraflex 2 and 3, or laticrete 253 / 254, or Custom’s granite and marble.
Hi,
I purchased a house from the 1960’s 10 months ago, the tile was popping out in the shower due to rotting backboard.
I had the shower gutted, Durock installed by the contractor, then tiled professionally. There are vertical cracks appearing in the subway tile, starting about a month ago. The most visible crack is down by the tub, going up about six tiles, the crack gets less visible with each tile. It seems to me, after reading your post, the tiles are cracking along the Durock seams. The two vertical cracking lines are 3′ apart, the width of Durock.
My question is, who is responsible for correctly prepping the Durock for tiling? The contractor who puts it up, or the tile installer who does the tiling?
I am in touch with both professionals, and would like advice on how to handle the fix. And does the whole thing need to be redone?
Thank you in advance for your time.
Asya
Hi Asya,
To me it is up to the tile contractor to ensure, at least, that the backer is properly prepped for a tile installation. Anyone who is NOT a tile contractor will NEVER properly prepare it for tile. It’s always up to the tile guy to ensure it is. As for who is responsible for actually doing it – I couldn’t tell you. Around here it’s always the tile guys putting in the backer.
Hi Roger,
Thank you so much for your quick response. Any way to fix this without having to tear the whole thing out?
Unfortunately no, there isn’t. The tiles on at least each side of the seam will have to be removed, which is a minimum of two feet, and the seams being at three feet each it would actually be easier to remove it and do it over correctly. You’ll end up removing nearly all the tile just to fix it anyway.
Thanks, Roger. I really appreciate you getting back to me.
Roger,
I have a friend that has a tile area where several tiles have cracked and many grout lines are cracked. There is 3/4 inch plywood with 1/2 inch concrete backerboard. I checked at a HVAC register cutout and confirmed that there is no thinset under the concrete backer board. The existing tile is 12 inch ceramic. They want to replace it with an octagonal mosaic. Sooo do we need to pull up all the CBB or could we leave it and run Ditra over the CBB then the tile, or what do you suggest? Also have you ever done a mosaic over ditra and if so how does it work out?
Hi Brad,
You already know the answer, right?
The backer needs to be pulled up and installed correctly. Larger mosaics (2×2 or bigger) work fine over ditra, smaller may cause problems.
Yep, I suppose I did, but it helped convince my friend when I showed him your email. Expert authorities help to convince. Thanks so much for responding to my post.
:-)
Roger,
I need advise! I had Bath works instal my shower pan, so I knew it would be done properly….I have installed the cement board about 1/4 inch above the what I guess is called the pan flange (it’s screwed into the studs. My membrane behind the CB is good, but the CB obviously won’t be flush to the flange. When I start the first row of tiles, do I put the tile to almost the very bottom of the flange the eventually caulk or do I start the tile on the bottom of the CB? If it’s the 1st option, do I try and fill that void with thicker thinset behind the tile to fill the void???? I’ve tiled floors, but this is my first shower! Help please! Cindy
Hi Cindy,
Tile will go to within 1/16″ or so of the tub arm – the horizontal portion of the base below the flange. The tile just hangs over that area, do not put thinset in there, it will crack and may cause problems.
Hi, thanks for the reply. I do only have 3/4, unfortunately. Its a bit too late at this piint to add another half inch – Ill just lat the tile and say a prayer. Thanks.
Ive just laid down 1/2″ 3×5 hardibacker over 3/4 plywood with thinset and screwed every 6 inches. I havent laid the tile yet and have walked on it over the past 2 weeks. I noticed hairline cracks running through some of the taped joints that run perpendicular to the joists. These cracks are thinner than a hair but I do notice them. There is no noticible movement between the boards, although the floor does deflect slightly and I can feel someones footsteps if they’re walking nearby. The tiles are going to be set on a diagonal. Should I be worried?
Also, on one 5′ side I only left about 1/16 of an inch from the sheetrock wall.
Thanks.
Here’s a little update. I just checked the deflection between the two hardibacker boards with my dial indicator. It showed a deflection of less than 1/1000 of an inch, which is pretty much any margin of error.
Should I still care about these hairline cracks?
No.
Hi Frank,
If it’s 1/16″ only on one side it should be fine. Floors will ALWAYS move. Hairline cracks in an uncovered substrate exposed to traffic and air are nothing to worry about provided your floor is built well enough to support a tile installation. Do you only have one layer of 3/4″ ply? It may be a problem. Backer does not add any significant flexural strength to your floor.
In your article for repairing the crack: “I simply pulled up all those cracked pieces and chipped the old thinset out of there, installed proper screws along the seam, taped and mudded the seam (when I say ‘mudded’ the seams I mean thinset) and reset new tiles and grouted it up. Once that grout cures it will lighten and it will look brand new.”
Was there thinset below the hardibacker? Did you have to remove the hardibacker and apply thinset below?
I have a repair to do on some cracked tiles with no tape and assuming no thinset below.
Your advice is greatly appreciated.
Hi Sam,
No, there was not existing thinset beneath the backer. I did not remove hardi and install thinset (what’s the point at this point?). This was a quick repair I did for a company I used to work for, they just wanted it fixed and did not want to spend money to do it correctly. The post was not to inform on how to repair a crack, it was to point out the importance of properly installing the substrate and to show what happens when you don’t. The only correct repair would have been complete removal and replacement.
Roger,
Can you explain reason for “ditra or strata-mat rather than backer?”
Thanks,
Anthony
They provide uncoupling from your substrate so any movement doesn’t transfer up through your tile installation, as well as moisture and vapor management beneath the tile.
I am adding additional framing to my tub surround before backer installation since I have 24″ centers. My concern is that the new lumber seems at least 1/16 wider than the existing framing. I suspect that it’s moisture content is many times that of the existing Arizona bone dry ones and it is swollen. How long should I wait before leveling the walls to avoid any problems from later shrinkage? Thanks!
Hi Jimmy,
More often than not a piece of lumber will acclimate to the existing environment within a week. It may still lose moisture or shrink a bit after that time, but not significantly so.
Thanks. I took off the high points with a plane and will use construction adhesive to act as a continuous shim on the studs. Brilliant!
My husband installed 1/4 haribacker boards and two areas are spaced farther than 1/8 inch apart it’s about an 1″ as long as we use thinset and the tape between will this be an issue?
Hi Lindsey,
No issue at all, unless you run out of beer. That would be an issue.
Roger,
We bought a new home 7 years ago and the 18×18, diagonal travertine tile floor started slowly cracking about 9 months ago. It started with one short, straight hairline crack 2 feet in length and grew to some 20 feet over 3 months. Over the last 6 months hairline cracks formed perpendicular to the first crack making several 3’x5′ patterns over the entire floor. Hardibacker was likely used, but need to confirm. The cracks are inverted (not tented) and difficult to see unless seen from an oblique angle. You can run your hand over the cracks and can hardly feel them since there isn’t any separation. There are three such floors with these same hairline cracks in rectangular pattern, spanning from 5 feet to 18 feet. The joist/subfloor system likely meets L/720 requirement for stone (to be confirmed). Any insight as to why the floor took some 6 years to fail? Are the inverted cracks signs that hardibacker seams weren’t taped or tape joints deteriorated over time? Builder is in denial about workmanship given the 6 year period to fail.
Please help!
Thanks,
Anthony
Hi Anthony,
It’s simply lack of traffic (the reason it took so long). It is either seams not taped, lack of thinset beneath the backer, or a combination of both. I guarantee it is one or the other, probably both. Vertical movement causes the boards to move independently at the seams, walking on it causes the vertical movement. If it was in a hotel lobby it would have failed in 30 days, in a residence it can take a long time. But that’s the reason it’s doing that.
Roger,
Thank you for your insight, it’s extremely helpful! Before the travertine cracks were visible (even with close inspection), inverted stress lines appeared in the tile as though the tile was being pulled down at points directly over the cement board seams. The tile gradually cracked along these stress lines and still appears inverted as opposed to tented. Any thoughts on why the cracks are inverted instead of being tented?
Anthony
I would guess that your backer seams are located between joists, are not taped and there is no thinset beneath it. Walking on it caused differential movement, cracking the thinset beneath those areas causing a weak point then the tile gave out without full support beneath them.
Roger,
The plot thickens. Subfloor is 23/32″ thick, joists are 16″OC with support every 6-9ft so if my calcs are correct it meets or exceeds L/720. I carefully mapped out all the tile cracks and found they form 4ft x 8ft patterns (not 3×5) throughout the tiled floor areas. I then verified that the subfloor panels are located EXACTLY beneath the cracks. The travertine tile is 3/8″ thick with an underlayment (can’t tell if its’ backer and thinset or just mortar) that is 11/16″ thick for a total thickness of 1and 1/16″. Would appreciate your perspective.
Thanks,
Anthony
Then is sounds like:
1. The seams of the backer (if there is indeed backer) are not offset from the plywood panels
2. You only have a single layer of plywood beneath the tile over the joists
3. If there is backer the seams are not taped and there is no thinset beneath it.
Roger,
The crawl space was extremely damp during construction and I doubt that the OSB subfloor panels (and travertine tile for that matter) were allowed to acclimate or dry out appreciably. I know this because some sections of the hardwood floor developed significant cracks between planks two years after installation – yes, it’s the house from hell ! It was determined that the 3/4″ oak planks were not properly acclimated and the crawl space below the failed sections was extremely damp during construction. The builder tore out these hardwood sections and replaced them and also installed a moisture barrier in the crawlspace. The hardwood floor restoration turned out extremely well and has remained so the last 4 years. If the OSB and tile were installed with a high moisture content and slowly dried out and shrank, particularly after the moisture barrier was installed, would it likely be a contributor to tile cracking?
Anthony
It always can be. That coupled with regular seasonal movement and load weights on the floor. It’s normally a number of factors rather than one single reason.
Hi Roger,
What would be your recommended installation method for Travertine Stone Tiles (3/8″ thick, 18″ on diagonal)? Please include cement board type and thickness, thinset type and thickness – below and above backer. Assume OSB subfloor meets L/720 deflection rating.
Regards,
Anthony
Hi Anthony,
OSB, 1/2″ ply, 1/4″ hardi with thinset beneath it (I would use ditra or strata-mat rather than backer), medium-bed mortar with a minimum 3/8″ notched trowel. Grout, sealer, beer.
And yes, 1/2″ ply is still required even if a single layer of osb meets L/720. Because I knew that was gonna be your next question.
I used the Buildex Backer-On screws on my HardieBacker but some of them aren’t 100% flush… close, but not all the way (not a measurable amount, but I can feel a slight bump with my finger). Is this going to be an issue when I lay my tile? Would it help if I put some of my fiberglass tape over them? Your input would be greatly appreciated.
Hi Terry,
It will be fine. The thickness of the thinset will more than compensate for a ‘slight bump’. If it doesn’t you aren’t using enough thinset or a large enough trowel.
Thanks for the quick reply. I’m using 1/4 inch trowel, will that be good enough or should I consider 1/2 inch?
The 1/4″ should be more than enough to go over the heads of the screws. Depending on what size tile you have and the flatness of it you may want to consider a larger trowel. 1/4″ is fine for smaller tiles, maybe up to 12″ square if they’re flat enough, otherwise you may want to try a 5/16″ or 3/8″. The correct trowel is the one that gives you complete coverage.
One more question if you don’t mind. I just ripped up some old tile in my foyer and it was laid directly on the subfloor. The carpet that was in the hallway was over some old laminate tile that is on the subfloor. I’m doing tile on all of it now. There is about a 1/16 inch difference (the laminate tile is very thin) between the two areas. Will the thinset under the hardiebacker compensate for that difference or will I need to do something else?
You can definitely make up for that with thinset beneath the backer.
Hi Floor Elf,
I came across this post while trying to research hardibacker installation. I was wondering if it is necessary to level the floor before installing as you as described?
Thanks!
Hi Caitlin,
It does not necessarily need to be level, but it does need to be flat. Flat floors
Hey home are you I was reading your post and am interest. I have the worst tile install I think ever in my home 4yrs old. At this point not only grout popping out and tiles cracking but I can lift out full pieces of tile. I have noticed that when I have looked under some of the pieces even the concrete backer board is cracked. I’m not sure what this means. The home inspector came out and stated no evidence of foundation issues. Any ideas I’m at a loss. Thank you in advance
Hi Wiley,
You have movement in your substrate (backer has not thinset beneath it, it’s not screwed down well) or you simply don’t have a proper bond between the tile and backer (the tile will come up with little, if any, thinset on the bottom of it – or it will come up with no bond to the backer).
Roger
I came across this forum as I was searching for info. Since I know all these answers from my past extensive research it is nice to get confirmation I have done everything I’m supposed to.
You are a great person for taking the time to answer everyones questions.
Hi Scott,
Normally easier to confirm before doing, but I do stuff backwards too!
Hi Roger, thanks for the quick answers. We have the walls and ceiling done with kerdi board and all of the seams and washers covered in kerdi band. We bought the shower kit and will do the floor this weekend. It’s a 4′ x 4′ foam pan. The concrete floor is out of level by 1/4″ to 3/8″. The Schluter site just says the floor must be level prior to installing the foam pan.
1. Can we add more thinset to one side of the floor to level it or do we need to scrap the pan and do a mud bed? I’m afraid if we try to level it with thinset as we’re laying it, we’ll break the foam trying to pull it up if we don’t get it level or we’ll end up with air pockets under the tray.
2. Can we level the floor with thinset and let it dry then thinset the tray down?
3. Can we thinset a 1/4″ piece of cement backer to one side of the shower floor, let it dry then thinset the floor and set the tray?
I’ve read your book on how to build a mud base and am sure we can do it but thought I’d run the above by you first as they sound a bit quicker for DIYers. But, I want to do it right. Thanks for your help.
Hi Laurie,
Number 2 would be your best option. You can level it first, let it cure, then install the pan. If you do need to remove the pan from thinset do not pull straight up on it, slide it as you are pulling it up. It makes a mess, but it won’t harm the pan.
Thanks Roger, we leveled the floor with thinset and will install the tray this week. Here’s a dumb question. Do we install the finished shower head pipe and pipe for the handheld showerhead before we tile or after? There are plain galvanized pipes with caps on them sticking out of the wall now. We haven’t installed the kerdi pipe seals yet. Thanks for your help.
Normally after.
Hi Roger,
The shower is waterproofed and we did a 72 hour flood test with no leaks. I bought porcelain mosaic sheets of 1″ x 2″ subway tiles for the floor. Is there a 2″ x 2″ minimum tile size for use with the foam floor or is that just for Ditra? I can’t find a minimum tile size limitation on the Schluter site except for use with Ditra. Thanks for all your help. We wouldn’t have gotten this far without you sharing your experience and advice.
Hi Laurie,
Technically yes, 2×2 minimum over the foam pans. Realistically, though, you can install those 1×2’s over it and you’ll be just fine. You won’t have your warranty, but you weren’t concerned with that anyway.
Hi Roger. I read your kerdi shower book but you don’t mention using kerdi board so I thought I’d ask you about it. We are getting ready to tile a 4′ x 4′ x 8′ tall shower that has 4 framed walls and a glass door that will be hinged to the jamb. We’re going to use 1/2″ kerdi board over wood stud framing (after straightening the studs per your book). We’re also tiling the ceiling. Here’s my questions:
1. The kerdi boards seem a little flimsy, have you used them? They’re very expensive but seem like they’d be a lot easier and faster than cement or drywall backer with kerdi membrane for waterproofing. Just waterproof the seems of the kerdi board with kerdi and thinset and it’s done.
2. Should we install kerdi screws with washers 12″ apart or closer than that? Our framing is 13″-16″ on center but in a couple of spots is 19″ (where original plumbing was and where it was rerouted to).
3. Should we use kerdi fix at the corners and ceiling (changes of plane) and where the horizontal sheets meet before waterproofing the joints with kerdi and thinset?
4. I’m assuming that we need to attach kerdi board to the wood door jambs using the same screws and washers. Since we don’t know where the hinges will be installed, I’m concerned that the placement of the washer could interfere with the door hinges on a frameless shower door. Should we just use cement backerboard and kerdi membrane on the jamb where the hinges will be located or would placing the washers as close to each side of the jamb as possible leave enough room for the hinges? The door is on a 2 x4 stud wall.
Thanks for your time.
Hi Laurie,
1. Yes, 90% of my showers now get kerdi-board. It is faster, easier and cleaner than backer or regular kerdi. Once tiled they are just as durable and stiff and any backer.
2. 12″ apart is just fine.
3. It’s not required, but I do.
4. Use kerdi-fix to attach the board to the studs then put a screw three inches from the bottom, one in the center and one at the very top. Your hinges won’t hit them.
Any suggestions for seam cracks on properly taped and thinsetted seams?
I’ve got a floor with cracks showing up around one particular piece of backer….literally up both sides…tiles in center all fine of course….but I did tape and put thinset on very tight backer formation….
The previous sub-floor was of the old metal mesh screening variety thus very thick….nearly 2 inches….I had my frame guy go under the floor in the crawl and reinforce crosswise on the joists….
I’ve got a bag of ultra-flex and am planning of re-taping and mudding then using the flex bond thinset….but since I’ve never had this happen I’m still a bit gun-shy about going ahead without more information.
Advice or thoughts….?
Thanks
TF
Hi Tom,
You said “a very tight backer formation”, does that mean they were butted to one another? And do you have perimeter expansion gaps in your backer and tile?
Oh, also.. i’m tiling around a bullnosed window jamb.
Can I stop the backerboard before the curve, bridge the edge of backerb and jamb with thinset, and wrap the tile around the curved jamb, applying tile directly to block?
There is not much clearance for material between the window hardware and block jamb.
You can paint redgard directly onto the block. Provided you have redgard over it yes, you can bridge the edge with thinset.
Hi Elf,
I am putting mosaic tile in my tub surround, and the long wall is cinderblock, which I have removed most of the paint from. The plan is to use 1/4 wonder board over said wall. Should I use Redguard on the wall before fastening cement board?
My husband wants to use contractors glue to hang the wonderboard; I say thinset, and then a few of those expensive blue cement screws.
Any thoughts?
Thanks,
Kellie
Hi Lauren,
Thinset and tapcons would be the best way. Install the redgard over the backer after you get it installed.
I am very new to tiling. I used Simple Set Thinset Mortar underneath my hardibacker 1/4″ boards. Now I am reading that Simple Set thinset is really mastic and not thinset mortar! Am I ok? It’s a floor installation in my entryway. I live in Wisconsin, so we will get snow tracked in. (Which is why we are tiling that area!)
I have not laid the tiles yet.
No, it’s not ok. You need powdered thinset that is mixed with water. You can try it, but you may end up taking it up and repairing it. Better to do it now.
Thanks for the answer. Not what I was hoping to hear, but I want to get it done right and cracked tiles will drive me crazy if it comes to that….
So, I need to remove the hardibacker screws and pull up the hardibacker, remove the (stupid) simple set pre-mixed thinset which is really mastic and put down real thinset, put the hardibacker on again and re-screw it in….. do I have that right? And I will be able to re-use my hardibacker right?
Yes. To both.
I have this exact problem!! Hardie backer 1/4″ was laid over top of linoleum and screwed down, (no thinset between) he did tape and thin set seams, but that did not stop movement.. I have approx. 20 tiles with straight line cracks through them. The tile is 6 months old.. Can this be repaired as well?? Or does it all need to be ripped out?
Hey Darren,
The problem lies with lack of thinset beneath the backer. Backer can be installed successfully over vinyl, but it absolutely needs thinset to fill any voids. The only way to fix it permanently is to remove it and use backer with thinset beneath it. The good news is that the backer will come up easily.
Also the same guy installed hardwood for me, an it’s tight! I’ve read a 3/4″ gap is fairly standard, do you think the hardwood is playing a partial cause in the tile cracking? Or separate issue?
Thanks
It could be part of the problem, but no thinset is your main problem. There should be a 1/8″ gap (NOT 3/4″) between your hardwood and tile and it should have silicone in it.
Can I run Hardi backer into the mud bed of the shower? You have mentioned on the site that you can. However, the Hardi installation manual states you are supposed to run it 1/4″ above the bed and caulk.
It would be much easier to run it into the bed, above the pre-slope. The bed will hold it against the studs, it is easier to mark the level line on the backer board, and I am concerned about the mud pushing out into the stud areas.
Hi John,
Yes.
First off – This site has been very helpful to me on my shower rebuild project – so thank you – I do have a question related to this article above. I just put up and patched the hardibacker seams and screw heads using thin set and the required tape in the new shower I am building. All the screw heads are counter sunk. After the thin set dried its kind of sandy and If I rub my hand on it it kind of sands off. Im not sure if this is how it should be or if something is wrong with it. I plan on putting redguard over everything but IM wondering if I should be concerned about the thin set issue.
Thanks for any help
Charley
Hey Charley,
It will be a little sandy, it’s normal. As long as it isn’t falling off the wall it’s not a problem.
We decided to go with tile for the shower. We’re looking at a limestone basketweave for the floor and porcelain on the walls. Is limestone a bad choice for a shower floor, I’ve heard it is porous and requires a lot of maintenance and special cleaners? Is there anything different about installing limestone correctly over kerdi? And my final question, do you have an opinion on the kerdi trays since you just spent some time at the Schluter facility? Thanks for your help.
Hi Laurel,
The particular limestone you choose has a lot to do with it. You need to contact the manufacturer to ensure the limestone is not water sensitive. They should be able to tell you.
My opinion of the trays hasn’t changed. They are a good product and work well, I just don’t use them. I’ve even seen someone drive a forklift over one with tile installed on it (true story), They just aren’t a product that fit with most of my projects.