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! 
Roger,
Regarding putting silicone in the inside corners of a Hardi wall installation:
OK, leave a gap, fill the gap with silicone, tape with ARM tape or install Kerdi–got it.
And now for the minutia:
1) How careful do you have to be with the caulk? Some will smear onto the surface of the Hardi and form a small disbonding area. Some will stay inbounds but be concave (the minor void being later filled with thinset), and some may be convex and maybe make it difficult to get a smooth seam in the corner.
a) Is this all too insignificant to matter?
b) Do you tool the caulk with your finger or just go with how it comes out of the nozzle?
2) If you wanted a belt-and-suspenders approach, could you use the ARM tape, let it cure, and then install the Kerdi? Or would that make it too difficult to smooth out the Kerdi in those areas?
1 a. Yes, it is too insignificant to matter.
b. Tool it.
2. It would make it too difficult. You’re overthinking it – again.
Hello, man am I glad i found you. My wife and I are remodeling our kitchen and are installing a ceramic tile floor for the first time. We installed hardibacker 500 over new plywood. We mudded our seams and our tape. Is it okay to let that dry overnight before we start installing our tile? I really hope it is or that you can tell us how to fix our screw up cause we just wrapped up for the night. Thanks for any help/advice you can give us.
Hi Joe,
Yes, it’s fine to leave that as long as you need to before tiling. You did put thinset beneath the backerboard, right?
Help. A tile soap dish in my son’s shower fell out. He didn’t tell and continued to shower there for a week. Because he continued to shower, the hardibacker got wet and broke. Actually, I don’t even know if it is hardibacker, it may just be dry wall. Anyway, the stuff is cracked and the insulation is exposed. It would be easy enough to replace the missing tile soap dish had the backer remained intact. However, I am not sure if I can actually complete this task with no backer behind the tile. Would it possible to get a small replacement piece of backer and install before putting the tile soap dish back?
Hi Juan,
Yes, you need to remove a tile on each side of that hole, place a piece of 2×4 or similar in there and screw into it from the exposed wall, then screw your patched piece in the hole screwing it into the 2×4.
Roger,
Is it OK to use thinset on top of already-cured thinset?
i.e. will thinset adhere to cured thinset just as well as it will adhere to Hardi?
Example—I have a depressed spot in my substrate (Hardi). Its 10″ in diameter and 1/8 to 1/4″ deep. Can I just screed that flat with thinset, let that cure, and then proceed with troweling on new (additional) thinset on top of that to actually set the tile?
Hopefully Roger will reply to you as well but I had the same issue in one spot and did exactly as you describe with no problem. You’re going to have “cured” thinset (with alkali resistant mesh tape) at all your seams over which you’ll set your tile so I can’t imagine a small spot like you describe will be a problem. I wouldn’t want to fill in a low spot any deeper than the 1/8 – 1/4″ you describe though.
Hi J,
Provided it doesn’t exceed the recommended maximum thickness of your thinset then yes, you can.
I assume you mean each layer can not exceed the recommended max thickness, right?
i.e. you could put in two 1/4″ layers of thinset (assuming 1/4″ is the recommended max for the thinset)–right?
No, total combined thickness. It does not have the compressive strength needed to go that thick.
Roger,
Thanks for the response.
1) Would the same apply for a wall application?— shear instead of compressive strength.
2) For either floor or wall application, if I went with medium bed mortar (Mapei has one good for 3/4″ thickness), then my example of 1/4″ filling of the depression (letting it cure), followed by setting tile with another 1/4″ should be OK –right? (the combined thickness of the two 1/4″ applications of mortar being less than that allowed for that medium bed mortar).
1. Yes
2. Yes, that should be fine.
Hey thanks for all the great info!
I am currently in the middle of my first ever tile work project… I’m trying to replace a cracked tile on the wall of my shower. When I removed the tile, there was hardiboard behind the tile, but when I was trying to remove the mortar from the backer board, it all basically just fell out as if the hardiboard wasn’t secured to the wall at all…
I was able to place new hardiboard (which was actually quite challenging because the cracked tile was in a recessed area for a soap dish) and I have just “mudded” and taped over the seams. My question is an odd one – is there such thing as too thin of a coat of mortar over the tape? I can still see the mesh tape after applying the thinset over the tape. Is that a problem? I have not seen this come up in any research that I’ve done. Is the consistency of the mortar too thin?
Is it ok to place a 2nd coat of mortar over the mesh tape prior to replacing the new tile?
Thanks for any advice you can give me!
Joe
Hi Joe,
There is, but once you get the tile installed all the mortar from the tile installation will also cover the mesh. It doesn’t need to be done in stages, I often mud the tape and install the tile both at the same time.
Not sure where to start here. So I am remodeling my bathroom. The tile would NOT come up without a fight, which took out mortar and even the backer board with it in some areas. So, my floor is all dented up and 100% not a flat surface. I’ve used 5 jugs of what the store guy calls “level all” (He said just pour it in the floor, and it will level itself. That was not the case. It left marks every time I picked up my flat edge applicator. How “flat” (not talking about leveled) does the surface need to be to start applying mortar and tile while considering early prevention of future cracked tiles? Here’s a few pictures of my attempt. ANY help would be great!
Hi Heather,
I’ve never even heard of that stuff. It needs to be flatter than that! The easiest way to do it is to mix up some thinset and skim-coat over what you have there (after you remove ALL the loose stuff), then let that cure and install your tile. For the record the allowable variance is not more than 1/4″ difference in ten feet.
Hello, I am remodeling my bathroom and the only tub that I could get was a drop in to match the plumbing. so I am now going to build a base can i frame my 2×12 bottom board right on top of the hardy board. I have a 2″ sub-floor and a 1/2″ plywood on that and now a 1/4″ hardie backer that I was not going to thin set but after reading I guess i should…..but anyway can I frame right on top of the hardie baker. Thanks
Hi Mark,
Yes you can.
Hello..I am using Hardibacker 500 on a shower/tub surround and wanted to know if taping the joints with kerdi-band instead of the alkali resistant mesh tape was a good idea. I have installed a moisture barrier behind the backer board. And my thought was using the kerri-band on the joints, corners and niche would keep water out of those potential problem areas with out trapping moisture between the vapor barrier and a full waterproof membrane over the entire wall. Is there a reason I should not do this and should just stick to the traditional taping method? Thanks for your response.
Hi Jim,
Kerdi-band will work just fine.
i installed floor tile…waited the 24 hours then grouted…its a grey groute but im noticing sigificant color differences in the grout lines…my biggest concern is the extremely light spots (i assume the darker spots will lighten up). any thoughts as to why the tile is extremely light in areas? almost white…and its a grey grout
Hi Michael,
Yes, too much water was used when washing the grout. Take a drywall sanding sponge and lightly sand the white areas to see if the correct color is beneath.
Hi floor elf. I’m recently remodeling my kitchen and using concrete board and porcelain tiles. I also am doing the stairs going to outside and basement. I taped the seams and put thinset over all the tape my questions is on the stairs so you have to tape the seams and edge as in the top where the concrete board meets the face? If so what’s the best way to make the thinset stick on the top edge corner? I used fibratape also. I would post a picture of the stairs but not sure how to.
Hi Jesse,
No, you do not want to tape those. In fact, you should have a soft joint where the tile on the step meets the tile on the face.
Hi Floorelf,
Your site has been a valuable tool in my shower renovation project!
I have a question about backer board seam spacing on shower walls, (the seams have not yet been taped and thin set. ) Most of the backer boards are fit flush right up against each other. Do i need to adjust and ensure a gap between all boards, or is the flush fit an acceptable way to install?
Thanks again for your site!!
-b
Hi Brandon,
Ideally yes, there should be a gap between all the sheets, which you fill with thinset when you tape the seams. I would adjust it. You need to be able to anchor the tape between the sheets (the thinset fill) when you tape and mud it, otherwise it defeats the purpose. 1/16″-1/8″ should suffice.
Appreciate the quick reply. I will adjust them like you recommend.
Hi there! Such an informative site. My husband recently installed wonder board. He taped and mortared the seams… Well he got slightly overzealous with the mortar and made some humps at seams. When going to sand them down the tape is coming up! Where do we go from here? Sand down humps, re-tape and mortar seams?
-a concerned “uninformed” wife ?
I am ready to apply Redgard to my Hardi backer board (bathtub suround). I did a test application on a piece of clean Hardi with the Redgard and found that it could be peeled off without to much effort a day later. Am I missing something in the application process? I even primed the backer board with 4 parts water to one part Redgard (per instructions) and let that dry a couple of days before applying the full strength Redgard.
Thanks
I’m starring at the same issue. I used Hydroguard. I actually vacuumed mine before applying, but have discovered lots of dust between Water batrier and hardibacker.I too want to know where I went wrong.
Hi, great info.
I have an interesting situation. A large steel beam pushing up the subfloor by almost 1/2 inch. I had already started putting down backerboard before noticing the bump (I know I should have checked first!) I have pulled up the subfloor just over the beam and my idea was to remove my already laid backer board and lay a 2nd layer of 3/4 subfloor on top of the existing and then re-lay backer board. BUT, the backer is very hard to remove and coming off in tiny pieces! Could I lay the 2nd 3/4 subfloor over the existing backer board? And then re-lay backer board on top? It’s only adding 1/4 inch extra.
Hi Chris,
Yes you can.
Hi Floor Elf
Last night I taped and mudded the seams in my 3′ x 3′ stall shower project. Since it’s small, I have 1 horizontal seam on each shower wall and then seams around the 12″ x 12″ nook. I also have vertical seams where the hardiebacker meets the drywall. After returning from a nice dinner with my wife and a couple of adult beverages, I found to my horror that when I started yesterday afternoon I had grabbed a roll of regular mesh drywall tape and NOT the backerboard mesh tape that I had purchased for this project. I’ve beat myself up pretty good for being so careless but now need to figure out what to do. My understanding is that the alkilinity in the thinset will cause the “regular” drywall mesh tape to fail over time? Do I have no choice but to chip/grind/chisel the bad stuff out and start over with the correct tape? Also, my 12″x12″ nook is one of those preformed foam products so I’m concerned about damaging that if I try to remove the thinset at those seams. Time to get some chocolate milk to drown my sorrows.
Thanks for your assistance.
I had my bathroom recently tiled, they tiled the floor and grouted the floor right after, now the grout looks dirty, is there anyway to fix it without removing all of the grout and starting over?
Hi Laurie,
Yes, you can figure out why the grout looks dirty. It is actually dirty? As in there is dirt and grime on the surface of the grout? Or did it cure a different color or shade than it was supposed to? Grouting the floor right after does not normally cause any type of problem.
Hi Roger, great information. My wife and I bought a fixer upper almost 3 years ago and there was some cracking in the living room tile when we moved in. Now I know the cause of it. I can actually measure my living room (to the inch) using the cracks as a guide. Every five feet in one direction and every 3 feet in the other direction. They did stagger the boards in some places but I think that was just an accident as the fire place sticks out 2 feet from the wall.
Hi Chris,
Sorry for the issues, but the line ‘I think that was just an accident’ made me spit beer all over my computer. Thanks! I really needed that laugh tonight.
Regarding outside corners in a tiled shower (for a niche, or bench, or, window frame), using Hardi as a substrate and Kerdi for waterproofing—–
Please help me understand the philosophy of how to handle that joint. From reading other posts, it seems that the concerns for inside corners don’t apply to outside corners. My confusion centers around the expansion issue.
Specifically, for outside Hardi corners:
1) Do you need the 1/8 expansion gap? Why not?
2) Do you fill that gap with silicone (to keep the expansion space open/active), and then apply ARM tape and thinset? Why not?
3) I understand that Schluter doesn’t require the taping, so if you don’t go with a belts and suspenders philosophy, do you still need the silicone (in the gap) for Kerdi directly over Hardi (with thinset)?
4) The Kerdi has to be pressed down into thinset and screeded out really flat or it will leak–right? So, it would seem that the corner would need to be
formed to accommodate that—like not uneven. Is this an issue for the tiny ledges that might form due to a bad mismatch of the two Hardi pieces at the corner?
For outside tile corners—–similar expansion related questions—
1) Do you need the 1/8 gap for expansion? Why not?
2) Why is it OK to use grout here instead of caulk?
Hi John,
1. No, because it’s an outside corner, the two pieces are not pressing against each other, one has space to swell or expand.
2. No, because when using kerdi it does the same thing that taping and mudding does when being installed.
3. No
4. Yes it does, and no, that doesn’t create any problems unless you’re using 1×1 mosaics.
1. You need a grout line
2. Because the two tiles are not pressing against one another.
Roger,
Regarding expansion in a 90 degree outside Hardi corner—
I believe you, and I can’t argue with success, but I don’t understand it.
If one sheet is butted to another (at 90 degrees), it seems that one sheet will expand into the other, whether you are looking at the inside part of the corner or the outside part of the corner. i.e. it’s the same corner, it’s just being viewed from opposite sides (inside or outside).
Yes, one sheet has space to swell and expand, but the other sheet doesn’t.
What am I missing?
On outside corners the pieces have other places to expand into (the corner on the shower side – the corner around the outside corner, etc.) When one begins to expand that excess will expand into the areas left specifically for that. For instance, if the sheet inside the shower from the outside corner to the inside corner begins to expand it will meet the outside corner and get resistance, it will continue to expand, but the inside corner of the shower has the silicone space created specifically for that.
You’re an engineer, aren’t you?
Guilty, and thanks for the explanation— it’s OK as long as the Hardi is free to expand in at least one direction.
Hi there, I’m looking at an upstairs apartment that has carpet and vinyl, and the customer wants a simple tile throughout. It has an OSB T&G subfloor (don’t know joist spacing as of yet, guessing 16″?), and the areas with vinyl has 1/2″ particle board underlayment, so the vinyl and top of carpet are somewhat at the same level. I’m thinking of ripping out the particle board / vinyl, and laying 1/2″ hardibacker (with thinset under and taping seams) and then tiling to that. Thoughts? the other option would be to LEAVE the particle board / vinyl there and add 1/2″ OSB where the carpet was, then go with 1/4″ hardi, then tile.. any thoughts on which one is best? thanks!
I should add that I am leaning toward the option of removing the particle board / vinyl , and adding the 1/2″ hardi because this keeps the floor from getting too high. I suppose I could skip the hardi altogether and apply Ditra over the OSB, then tile to the Ditra, which would eliminate a lot of weight, and keep the floor even lower, close to what the vinyl is now. But with that I worry that the OSB alone may not be enough and tiles may come loose??
Ditra over osb is actually what I would do given the choice. osb works fine.
Hi Steve,
You want to get rid of that particle board. No reason at all you can’t use backer over that floor once you remove the pb.
My installer was suppose to tear out my old ceramic tiles, lay down backer boards and then install my 3/4″ marble. He insisted it was not necessary to tear out my tiles and started to lay the marble 12×24″ directly on the marble. I am really weary of this and had them stop the project until I get a few tile experts opinion. Please let me know your professional opinion.
Hi Jen,
It can be done if it’s done correctly. I don’t do it, but it is an acceptable method if the conditions are correct. I would not do it with marble under any circumstance.
So far this is the best post I have found about this topic to ask my question.
What about thinset under Durock (or similar) on concrete? I just can’t find much info on laying tile on existing concrete or how to prepare the concrete for accepting tile. I am new to your site so maybe it is covered, my apologies if that is the case, please point me to that post.
I am installing 9×24 wood plank looking porcelain tile on a slab-on-grade at my back door in a 4’5″ x 6’7″ area and am worried that the tile will be too low after carpet + pad is installed next to it.
Carpet pad at 1/2″ + carpet 3/4″ = 1 1/4″. Tile is 9 mm thick (~.35 or 1/3″) and using 1/2 x 1/2 x 1/2″ trowel at 45 degree angle yields approx .35″ depth of thinset (about 1/3″) for a total of .7 or just shy of 3/4″. I am concerned the carpet will be too high at 1 1/4″ so am strongly considering how to add a bit of height to the tile. I do not want to use any SLU here, I had to do that in an uneven section of the same floor area by the garage entry (my “new” house was built in 1964 and has some cupage around door threshold). Can I (or should I) use 1/4″ Durock or other backerboard to bring the height up a bit? Dealers choice? Just leave it and install tile on floor as is?
Using Durock I would have a nominal amount of thinset to fill voids and adhere it (hopefully? or fail?) to concrete floor plus 1/4″ Durock/cement/backer board + the 3/4″ of thinset and tile on top to make 1.1″ which would seem a better fit and only 1/4″ shy of carpet height. I am not sure screwing Durock down to concrete as is done on plywood is a good idea.
I have researched plenty of Schluter products for transitions but it seems that if I can just have the carpet tucked right next to tile that is a nice clean transition.
I have the opposite problem with SLU pad (4’x9′) mentioned by garage door – I added 3/8″-1/2″ of variable depth to level floor area. After tons of internet searches for carpet-tile height transitions I finally stumbled across an informercial video for carpet shims. I think these will work very well for bringing the carpet up to the tile. Unfortunately this tile does not have edge pieces so I need to either have the carpet right there to be tucked tightly against it or finish with an add on edge piece.
This also same area transitions into a powder room that is on a different poor (And still about 1/8″ higher – which I am hoping to transition with thinset and will be using ATR to “level” tiles and avoid lippage.) After reading about soft joints I am now concerned that this transition should have a soft joint even though it is not a large run. Four feet to joint from edge of pad then into powder room for another 4ish feet.
Can an underlayment such as RedGard or ditre solve that for such a short run or it nothing to worry about? (ha ha watch out dog!) I am planning on using RedGard for both locations for crack prevention (likely one coat vs. 2+ for waterproofing). Realizing I can do whatever I want, just trying to avoid tile installation failure.
Whew – that is a lot of questions.
Thanks for any advice, answers or suggestions on any of the above!
– Steve M
Hi Steve,
Backerboard is not used over concrete. You can either install directly to the concrete, or use a membrane such as ditra or ditra-xl. Either of which will give you height if you need it. The carpet height is not going to be that much. It will be the height of the tack strip, which is about 3/8″. Why do you want a flush transition from carpet to tile? That’s almost never done, and never done with regular carpet, only with flat, low-cut berber. The transition into the existing tile should have a soft joint, you’re likely going to have different products below the tile in both, which likely means differential movement.
Thanks Roger. I read your reply right away but haven’t had a chance to write back. I did install directly to the concrete after troweling on RedgGard (I def recommend using roller vs. trowel for DIYers).
In my other section installation is still a work in progress. I am not quite sure how I am going to work in a soft joint yet, the slabs have been there for 50 years or so and with the offset pattern I am using I am not sure what I am going to do yet. I will use carpet shims to to bring the carpet up a bit for that transition as this tile is sitting on a 1/2″ or so leveled pad. I will work on pics for the upload section once I have something to show.
For both sections I have opted not to use any edge products from the tile to the carpet. I am using Schluter RONDEC-STEP for the tile floor to the basement stair transition, which will also have carpet.
Hi,
I am about to begin a project that is a little more on the artsy side. I want to create a strip of mosaic flooring between my living and dining room. I will be using small river stones, and metal gears. The problem I am facing, is that the backer board will lift this section of flooring up higher than what is on the sides. This will be a high traffic area, so I want to do it right. The transition will be from carpet, to the mosaic, and then hard wood. Is there a thinner backer that I could use, or will I just have to pick and choose the thinnest rocks I can possibly find? Also, when I tape and mud the seams, do I do this the same way as fixing drywall?
Thank you for your time!
Hi Jessica,
Yes, it’s the same as drywall (the taping). You can also use 1/8″ WEDI, 3/16″ kerdi board, ditra, stratamat, or 1/4″ backerboard. If you want the absolute thinnest – google ‘greenskin’.
Hi! Thank you for your blogs.
When laying the backerboard down onto the thin set – do I aim to have the seams as close together as possible? Or does it not really matter since I WILL tape and thin set the seams?
Do I screw in the hardie backer screws while the thin set is hardening beneath the backer board? Or wait until the thin set is completely dry?
Thank you.
Hi Aimee,
You want the seams offset by at least 1/3 of the board. You normally screw it down while the thinset is wet, but you can do it after it cures.
Hey I laid hardieboard (1/2″) in my bathroom without thin setting it down. Will I be okay with just taping and mudding the seams and gaps? Or should I pull it up piece by piece and thin set each board and re-screw each board back down?
I want it to last
Hi Zach,
If you want it to last you need to pull it up and put thinset under it.
And yes, I know that isn’t what you wanted to hear. Sorry.
Hi, great forum. I am tiling my bathroom with 6×24 wood look plank tile. I have read that a medium bed mortar is recommended for the larger tiles. Do you know if this is the case and if so, can I also use the medium bed thinset under the durock as well so I don’t have to buy two separate bags? Also, what size of trowel do I use for the thinset under the backer board?
Thanks
Hi Eddie,
Medium bed mortar is always a better choice. And yes, you can use it beneath the backer as well. The size of trowel depends on how wonky your floor is. Normally a 3/16″ square notch will do just fine.