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! 
I am about to duro-roc a new bathroom floor. The floor is unlevel and must be leveled with a leveling compound. Should I level the subfloor then add duro-roc or visa-versa.
Hi Marie,
Sorry for the delay, been out of town at the new Schluter facility all week.
You can either install the backer first, then slc, or just install the slc and install tile directly to it. You can not attach backer over the top of leveling cement.
We hung up cement board in our hopefully to be tiled shower and we realized that we used mastic to cover the seams, nail holes and even out to the sheetrock. Can we use thinset over this to tile, or do we need to sand all down and restart? My husband attempted to sand and within seconds we were in a dust storm. Thanks for anything helpful.
Hi Jen,
It needs to be removed, it’s normally easier to scrape it off with a razor scraper than sanding, though. You don’t need to get all of it completely off, but get as much as you can.
Elf,
Question: I have my durock up, seams taped with mesh tape, and I mixed up some thin set and skim coated the joints, & once it was semi dry I put a bullet level over each joint and there are a few areas that are not 100% level, and I am talking like a 1/16 to an 1/8. It was pretty dry and so I used some sandpaper and sanded it down as best as I could get.
Sorry I’ll cut to the chase. My questions are: How critical is it for the thin set skim coat to be dead on?. (I know I will be using thin set for tiles).
Secondly, Do you suggest sanding it until it is dead on or do you suggest skim coating all of the durock with thin set then applying the redgard?….
Thanks Roger
Hey Scott,
It’s not imperative that it be dead on. You’ll have a layer of thinset a bit less than 1/8″ behind your tile so you can make up for that difference there. I would just go ahead and install the redgard over it now then compensate for any inconsistencies as you set the tile.
You Da Man!!!!….
Thanks Roger!!!!!!…
Enjoy your Labor Day, minus the labor……
Roger
To make sure that my floor doesn’t flex to much and causes problem with cracked tiles, I am thinking of adding a 1/2 plywood underlayment layer on top of my 3/4″ subfloor. I am concerned about the transition between the wood floor and the tile. The difference between the height of the existing wood floor and new tile will be close to 1″ if I use Durock.
Is a 1″ transition just too much?
Hey Curtis,
It’s a little high, but there are several options to ramp it down so it doesn’t seem so large. Schluter has a lot of different transition ramps and you could also find a wooden threshold for it. You can also use 1/4″ durock or hardi – makes no discernible difference on a floor installation.
Thanks Roger for the quick feedback!
As far as plywood for underlayment, is CDX grade acceptable if I will using durock or hardi on top of that?
BC would be better, but yes, cdx will work fine with backer over it.
Roger,
I got a little too close to the corners when screwing the backer down and have a few cracks. I used some galvanized nails within a few inches at these corners to reinforce. Some edges cracked due to cranking down too much due to the board jacking up as I was screwing. 1) How can I prevent this jacking? Excuse me if I used the wrong term there. 2) Also, do I have to use the tape on walls where I am using kerdi. I see on Schulters website that tape is not needed when kerdi over drywall panels but was not sure if the same principle applied to hardie board. 3) should I replace the boards where there are some cracks due to my excessive cranking?
Thanks again.
Hi Joseph,
1. I don’t know what you mean when you say the board was jacking up. If you mean it was bending in some manner then the easiest thing to do is get the face of your studs all flush before installing the backer. If that’s not what you mean…???
2. No, you do not need tape and mud with kerdi
3. Unless they are completely cracked through to where it compromises significant portions of the backer it will be fine.
Roger,
sorry about the confusion. as I screwed them, the hardie board raised off the stud slightly and I had to let them screw a bit to get it to go back to the stud. sometimes i screwed too long and cracked them. Some corners pieces are cracked through but it appears to be just at the edges (half inch to an inch) near the corner. should i bother or leave them? remove broke edges and fill with mortar maybe? thanks again.
sorry if i put in wrong place.
Aaah, I gotcha. Keeping constant pressure on the screw while driving it usually keeps it firmly against the stud. I’d just leave those corners, fill them in with thinset as you install the kerdi.
Do u have to wait A while before you tape or right away. Plus how long do u have to wait to start laying tile
Hi Chrissy,
U can do either. U can start right away.
Hi Roger. My husband and I will be installing 1/2″ Hardie in our 4′ x 4′ shower then applying Kerdi membrane. I read your books but still have a few questions:
Since the Hardie is 3′ x 5′, can we run it horizontally starting from the bottom of all walls or do we need to stagger the horizontal seams (start at bottom of wall 1 and top of wall 2 etc) so that the seams don’t line up all the way around the shower?
Also, when you wet down the Hardie before thinsetting the Kerdi to it–how wet is wet, just short of dripping or just damp?
We’re not tiling the shower ceiling-can we use a piece of Hardie on it and texture and paint it or should we use drywall? We have an electrician coming next week to put a light in the shower ceiling and we bought a remodel style light that doesn’t install to the joists. We have Hardie board but no drywall yet.
We’re also tiling the bathroom floor. Vinyl was glued down before but came up in one piece without any real glue residue (you can see faint trowel marks but can’t feel any ridges) remaining on the floor. How do I know if there is a residue that will prevent the thinset from bonding to the floor (we’re putting Ditra down) before we install the Ditra?
Thanks for your help. Your books are great.
Hi Laurel,
You can do either. It’s normally best to stagger seams, but being as they are on different planes it really makes no difference in that scenario.
Aim for ‘SSD’ – saturated, surface dry. You want the board itself fairly wet, but you want the surface dry (not shiny with water).
Yes, hardi can be finished just like drywall.
Splash water on the substrate, if it soaks in within 30 seconds thinset will bond to it just fine. If your subfloors are wood and the vinyl underlayment is luan (1/8″ or 1/4″ thin plywood) it needs to be removed. You can not have a tile installation over luan.
Hi Roger,
Thanks for the quick answers. The substrate is concrete. I will try the 30 second test. If it doesn’t soak in, what do I use to prime or clean it?
We are thinking about having a pro install granite slabs on the shower walls instead of tiling. Would a mud shower floor that is 1 1/2″ thick at the outer edge (waterproofed with kerdi) be able to support 3/4″ thick granite slabs 4′ x 8′ on the walls? Would we need to reinforce the mud bed with anything? We were going to use the foam kerdi tray and tile the walls originally but I’m not sure the tray would be sturdy enough. What do you think?
Thanks, again.
It needs to be either chemically or physically scarified to remove any residue. Regular mud will more than support your granite. I can’t honestly say one way or the other about the kerdi pan.
Thanks, Roger. Unfortunately, these steel studs are hollow and open on one side. The way this corner was put together, the open sides are facing out from the corner, making sistering impractical at best, and at risk of coming apart later at worst. Placement of copper pipes running through the studs also would make it difficult to sister a wood stud all the way down to the tub flange. . . .
Can you put that one in first and use the backer on the back wall to hold it in place firmly?
Roger,
First, thanks so much for the fantastic resources on this site. I pulled out the disgusting looking plastic liner around my tub/shower, and I want to tile it. When pulling down the greenboard behind it to put up cement board, I found out one of the short walls had metal studs for some reason. This isn’t horrible for the middle of my cement board, but every time I try to screw in the inside corner with metal tapping screws, the edge of the backer just crumbles. Any advice on how to deal with this? Can I put a nylon corner bracket along the inside corner to hold everything in place, or will that cause problems with my thinset? Any other advice? As it is now, there’s just a bit too much play/movement in that corner than I am comfortable tiling over . . . I’m quite fond of my dogs and would feel awful if I set them on fire!!
Thanks in advance!!
Spencer
Hey Spencer,
A plastic corner may cause more problems than you currently have. Is there any way you can sister a wooden stud to the steel one in the corner and just screw the backer to that? If you get too close to the edge it’ll bust up the backer whether you’re going into wood or metal. If you can sister a stud in there it’ll give you both a more solid stud as well as being able to keep the screws further from the edge.
Roger
Thanks for all your previous answers regarding hardie backer board. I am remodeling a 150 old house. For the surround, I want to install 1/2 inch hardie on top of wet plaster for a new enameled steel bathtub because on other walls where I took out the plaster, the studs were not straight. The plastered wall are straight. Also, should I put 1/4 inch board under the tub or just put the tub on the 3/4 inch plywood. I will be putting 1/4 on the rest of the floor prior to tiling the floor.
Thanks again,
Ed
Hey Ed,
No real way to waterproof that board unless you’re using a topical membrane – you didn’t say. If so you can go over the plaster, if you’re using the traditional method the plaster should be removed and the backer shimmed to plumb. You can do either with the tub, it normally just goes on the 3/4″ ply.
Hey roger,
Tks for your reply. Sorry that my poor writing and omissions confused you. My plan was to install 1/2 hardie over 1-2 inches of wet plaster, apply Redguard, then tiles. Should I apply the Redguard membrane after I tape and sand the backer board?
Ed
Yes.
Pleeeeze help!
Can u teach me an half decent way to measure up for wall tiles. What do u do if u have different sections like in a fitted kitchen. Mine has 4 different walls
Thank u in advance!
Hi Dee,
Just separate it into squares and rectangles. For instance: most backsplashes are 18″ high, so measure the length of your countertop and multiply that by 1.5 and you will have the square footage needed. If there are areas that go above or below the cabinets or countertop line measure those as a separate spot, like the area above the stove for a microwave. Add that amount to the original square footage.
Measure each wall like that then add them all together.
Roger,
I’m in the process of my tub/shower install and I’m feeling a little thick when trying to process some of the information I’ve been reading. I know it’s just me over analyzing, but I’ve reached project paralysis and am afraid to take the next step for fear of making a big mistake.
I installed a new tub with flanges approximately 1″ on three sides. They dip down in the corners and also don’t reach the curve on the open end of the tub by about 2″. Per installation instructions I also had to secure the tub by using fender washers overlapping the flanges and screwed into my metal studs on the short sides and furring strip on the long side. It was necessary otherwise the tub creaked and flexed.
Next, I installed my 1/2″ Kerdi-board and overlapped the flanges, but that led to the issue that Shelly G. from an earlier post ran into with the bulge over the flange.
Reading your response to her and some of your other posts “Shower Tile 101 – Shower-Tub transitions it seems as though I should have just butted the Kerdi-board to the top of the flange. Is this correct? No silicone between the bottom edge of the Kerdi-board and flange? That would also leave about 1″ of tile with no backing
Also if I rest the Kerdi-Board on the top of the flange, what do I do with the flange corners that dip down at the transition between the short and long ends of the tub? And, what do I do with the gap where the flange ends 2″ before the rounded front of the tub? Those are substantial gaps that are causing my angst. I can’t see how to make the transition. I have about a 1-1/2” gap between the front of the tub and the beginning of the wall stud which is already aligned like your post in “Drywall to Backerboard transition in tiled showers.”
I have not taped the Kerdi-board yet, but that is my next step and I know something is wrong. Please give me some advice so I can stop staring at my orange walls and take some action.
Roger, to be more specific, when I say “flange corners that dip down” I’m saying that there is basically a “V” notch at the right angle where the short and long ends of the tub meet which comes down level with the horizontal plane of the tub. This would allow water to pour out if it ever reached it.
I know. I’ve seen ’em. I don’t like them either.
Hey Tom,
Yes, butt the kerdi board to the top of the flanges and use either silicone or kerdi-fix (best) at that seam. For all the areas that dip down you can tape and mud them with thinset, then go over that with liquid waterproofing or kerdi-band. The tile does not need backing over the face of the flange at the bottom 1″ – it just hangs there.
Hi Roger,
About backerboards… I am about to build a shower using Kerdi, and it’s my first time so I got your guide to Kerdi showers. In the guide, you mention that drywall or CBU may be used, but you recommend CBU. Is there a specific reason? For my shower install, I will be tiling with travertine, so is that even more reason to recommend CBU over drywall?
One other really quick question… I need to replace the shower ceiling… what material would you recommend? I won’t be tiling it, just priming & painting it.
Thanks!
Nathan
Hi Nathan,
The main reason I recommend cbu is simply that if you make a mistake or there is one very tiny area where a bit of water may get through it won’t affect the substrate. If it’s drywall it will. That’s it. If it’s installed correctly either one will work equally. If you’re just building a regular shower, and it doesn’t have a header, regular drywall will work fine on the ceiling.
Mr. Elf
Thank you for your advice and offerings it is much appreciated.
Regarding a kerdi tile shower installation. In your membrane book speaking of how to deal with changes of elevation and seams you discuss to silicon caulk the changes in plane and all other seams will be taken care of during the kerdi install with the thinnest. I thought I had read a comment recently to a poster (which I cannot seem to find now) stating that you now felt it unnecessary to caulk the corners in a kerdi instll and that the thinnest is acceptable. Please feel free to reprimand correct me if I misread.
I have some seams (more like gaps) pushing a good bit beyond 1/8″ in the corners and wondering if the caulk would prohibit proper adhesion of the kerdi.
Thank you, you da elf!
Hey Freeman,
The only thing I’ve changed recently is the method of whether or not to tape and mud the corners rather than just silicone. I recommend taping and mudding them over the silicone now. With kerdi it is not necessary to tape and mud them, but I still recommend siliconing that gap so it does not get filled with thinset. It isn’t absolutely necessary, just an extra step to prevent possible problems with expansion. If your gap is that large I wouldn’t worry about doing anything with them, just install your kerdi.
My husband installed hardy backer over our garage floor then tiled, I don’t think he used the seem tape on all the joints, reason he used the hbb, was the concrete had been previously coated with stains, paints, epoxy and clear coated. Nothing stuck to that floor no matter what stripping, scraping washing, power scraping,etc! He used about 45 tapcon flat heat screws, per 3×5 sheet ,1 1/4″ long and 1 3/4″. Dewalt rotary hammer drill did the job like wood, Bosch bits, then drove them home with impact driver. Not many hollow areas, can’t wait to here your comments, please be kind!!
Don’t really have much to say at all. The proper method is to scarify the surface of the concrete. Installing a secondary product over concrete – one not made for such an installation – is risky at best. Hopefully he at least has thinset beneath it. I have no idea whether it will last or not. Concrete moves A LOT, that’s why they are built with expansion joints – to control where it will crack. He’s eliminated that feature.
Good luck?
We recently had a new tub installed and all new drywall installed around it. Being completely new to renovating I naively trusted that they knew what they were doing and have since laid a ceramic tile floor around it. The problem is that one end of the tub (the end the fauwcetts are on) doesn’t line up properly with the drywall. The front corner is out from the wall by about an 1/8-1/4 inch at the widest spot which if tiled over would push out the bottom of the tile considerably. When I orginially pointed this out to my drywallers, they said “oh, things never line up perfectly, as rooms are never perfect squares, just build up the mud in that spot when you tile.” …But I don’t see how I can build up mud that much on a spot that is on the side of the tile facing out to the rest of the bathroom. It’s not an option financially to start over, pulling apart walls to move the tub…Can I tile effectively tile this area?? If so, is there a trick to making it work? I considered giving up on the tiling and going to a tub surround, but there is a window that would have to be cut out and apparently that is a no no too. Any advice appreciated.
Hi Shelly,
Your tub has a flange at he back of the perimeter which turns up vertically about 1 1/2″. When they drywalled I’m sure the drywall is over the front of that flange (the vertical portion of the flange is up behind the bottom of the drywall). If you cut the bottom inch or so off of the installed drywall (to right above the top of the flange) you’ll be able to screw the drywall to the stud and it shouldn’t bulge out at the bottom after you do that, it should be a flat plane.
As to whether or not you can tile it – yes, as long as you waterproof it first. If you simply bond tile directly to the drywall you will end up rebuilding that shower after a couple of years, and possibly repairing framing around it. Tile and grout are not waterproof, your drywall will fall apart and disintegrate. You did not mention how you are waterproofing it, the only approved waterproofing method for drywall is schluter kerdi. Otherwise you’ll need either backerboard or another substrate in place of the drywall.
I wish I could say yes the drywall (when I say drywall, it’s a cement board that Home Depot told us to use around the shower) is over the flange..but that’s the part that’s sticking out that they told me to build up the mud around. The board stops right above the flange, and the flange is sticking out the 1/8-1/4 inch further. (Whereas, on the other end, the flange is slightly more inset behind the board.)
I appreciate the tips on the water proofing!! The home depot guys told us to tile right on top of the cement dent board!!
Oh, crap.
Can you remove that board and shim it out so the surface is flush with the surface of the flange?
Hi Roger thanks so much for all the great info. I’m working a new shower into a remodel using a whatadrain hidden trench drain, and since the shower floor will all slope toward the wall (the drain will be where the floor meets the wall with the showerhead is) I was wondering if I can use a single layer mudbed coated with redguard or a bed of some type with a backerboard coated with redguard since that would be perfectly flat? im using 12×6 porcelain tiles. I have 3/4 tongue and groove covered by 1/2 bc plywood. Right now my plan is to put down backerboard, then build a single layer mudbed coated in redguard (3-4 coats). I haven’t been able to find much info building a single slope floor to a trenchdrain that is mounted from below. Any input would be really appreciated, you are the single best source of info I have found.
Hey Cliff,
A single layer mudbed sloped flat to the drain is the way to do it. Install that, let it cure, then install your redgard. It still goes 1/4″ / foot so however far the opposite wall is determines your slope.
Thanks for the articles. I’ve layed a lot of floor tile over the years but doing my first shower on my new personal home. I installed 1/2″ Durock on my walls. I know you should tape the seams before waterproofing(Redguard in my case). I put a thin bead of silicone between the sheets of Durock and also along all corners, basically at every seem and used my finger to smooth and clean all extra silicone. Now I’m wondering if the Redguard and tape will stick well at the seams or if I should remove all the silicone I put in and just thinset, tape and waterproof. Your thoughts?
Hey Clint,
At the changes of plane, corners, etc. the silicone will be fine. At any in-plane seams you should remove the silicone and just tape and mud them with thinset and alkali-resistant tape, then waterproof everything.
Hi Roger,
I’m planning to install a kitchen backsplash, and I was wondering whether I need a backerboard. What’s there right now is a flat painted wall with very little texture. I’m concerned that thin-set won’t be sticky enough directly against the wall, but I’d like to avoid using backerboard because it will eat up valuable counter space.
Is there a way to get thin-set to stick directly to drywall? If I do use a backerboard, should I use thin-set between the backerboard and drywall? Is this the one case in which mastic is acceptable (and does it depend on tile size)?
Thanks,
Stan
Hi Stan,
Yes, mastic is acceptable, but the tile needs to be 4 square inches or smaller. Thinset will bond very well to drywall. It helps if you rough up any paint a little with sandpaper, but it’ll bond. It won’t necessarily be ‘sticky’ as you set the tile, though.
Hi Roger,
I just pulled up a few tiles in my shower where the grout had cracked and noticed that the cement backing board is also cracked. What is the best/Easyiest way to repair. I am planning a full remodel soon so don’t really want rip everything out.
Thanks in advance
Hey Eric,
There isn’t really much you can do at this point. You likely have no waterproof barrier behind your backer and water has wicked behind it causing the underlying structure to swell, thus moving the tile and cracking the grout. You can use something very water resistant, like urethane or epoxy, and that may hold a large part of the water back for a little while.
Contractor removed vinyl floor in bathroom to put down ceramic floor. Don’t think backer board was put down. Thin set Mortor put right on top of subfloor, then tile on top of that. Problem?
Hi Terry,
Yes, it’s a problem. If there isn’t a proper substrate beneath it then it will likely not last long before the grout begins to crack. Ask him what he used as his substrate.
They used VersaBond fortified thin-set mortar on top of the wood sub-floor. Contractor told me that backboard would only be needed if the floor was in bad condition or in a high moisture room. This is a bathroom however, it’s on a southern exposure, has cathedral ceiling and I always use exhaust fan.
Well, that’s bullshit. A proper substrate is needed beneath EVERY tile installation. Southern exposure simply means more temperature variations throughout the day, more movement. Moisture is not the only thing that will cause problems in a tile installation. While the exhaust fan is good, it doesn’t solve everything. It may be fine, it may not be. There is no way to tell. The best you can do is eliminate any chance of problems arising, the first step being using a proper substrate.
Found the answer in your section….Installing Cement Backerboard for Tile in a Shower. Sorry, overlooked that section the first time.
Why does backerboard come in 3×5 size so doesn’t line up on wall studs? Do we have to cut them to line up with the wall studs?
Hi Kathie,
Because regular tub walls have a five foot back wall (59 1/2″ – two sheets horizontally) and two 2 1/2 foot (30″ – almost one sheet vertically or two half sheet horizontally) side walls. Other than that – I have no idea.
I am at the point of tape and thinset the seams in my cement board on a bathtub surround (wall). Everything I read seems so vague when they say the process is like mudding and taping drywall. When you thinset the joint and add the mesh tape how do you keep the seam from protruding making the flat plane uneven. In drywall you just add multiple layers till it looks flat across the wall. On cement board you will be adhering tile which could cause excessive lippage or high point due to the bulit up in the seam. Can you please be a little more descriptive on how to do a proper joint on cement board. Thanks.
Hey Michael,
You use the flat side of your trowel and skim over the joint, lay your mesh in there and go over it again with the flat side of the trowel. You only do this once, not multiple times like drywall. If your particular backer does not have indentations along the edges (like drywall) then you will have some unevenness there, it’s unavoidable. However (!) any build-up is going to be minimal (like 1/16″) that you can compensate for it as you set your tile. If 1/16″ causes lippage in your tile installation you need to use a larger trowel because there’s no way you’re getting enough coverage on the back of the tile.
Roger: I have searched and searched but can’t find an answer to my question of how to handle the joint between the Hardibacker on the countertop and the Hardibacker on the backsplash. I assume there should there be a 1/8″ gap at the joint but should the joint be taped and embedded with thinset or left open to allow for expansion and contraction? I plan on using mastic behind the splash hardibacker since the stud layouts vary between 16″ and 24″ so screwing or nailing doesn’t seem appropriate. I am using granite tile on both the top and splash and will use a matching caulked joint between the two in lieu of grout.
Hey Norman,
You can’t find an answer because it really makes no difference. If you ask 100 guys that question 50 will answer each. As long as you have silicone between the tiles there it’s fine. I prefer to tape and mud it. The expansion along there will normally be negligible and taping it will solidify it.