Photo 1
I am not writing this to tell you why your tile is cracking or why your grout is cracking – I have other posts that may tell you that. (Click on the pretty little links 
) If you happen to have Schluter Ditra as your substrate, this post will tell you why either one of the above may be happening.
While Ditra is my preferred membrane for floor tile installation (as well as countertops and tub decks) it absolutely needs to be installed correctly. The two main techniques for this are fairly simple:
- Make sure the cavities (waffles) are filled correctly
- Install it over an approved substrate (and with the correct type of thinset mortar)
Photo 2
There is a lot more to ditra than those two items but if either one is incorrect I can nearly guarantee a failure. See photos 1 and 2 there? The tile was cracked and it was a direct result of a) not getting the waffles filled correctly and b) improper coverage on the tile. Now b may be due to not backbuttering the tile, an improperly-sized trowel, letting the thinset skim over or set too long before installing the tile or simply incorrectly mixing the thinset. All three of those things will cause any tile installation to fail – whether you use ditra or not.
Not filling the waffles correctly, though, will cause the tile to not be fully supported and/or not ‘locking’ the tile into the ditra. Because it is not correctly locked into the ditra you will lose the mechanical bonding properties of ditra and you may as well install it directly to particle board at that point (That was sarcasm – don’t do that!). For more specifics about exactly how ditra works you can check out Provaflex vs. Ditra wherein I describe exactly how the mechanical bonding process works – and rant about a particular jackass. But the mechanical thing – that’s what you want to concentrate on.
You need to use the flat side of your trowel and spread thinset in every direction over the ditra to ensure that all the little waffles are full. Since the cavities are dovetailed (that means they go down and away from the opening) you need to ‘force’ thinset into the bottom corners of the cavities. Simply running the trowel over the ditra will not do this. Simply running the trowel over the ditra did that (photos 1 and 2).
Photo 3
Installing ditra over an approved substrate is much, much easier. In fact, nearly every bare substrate you find in a modern house would be considered an approved substrate – shiny linoleum is not one of them (Photo 3). While there are thinsets that ‘say’ they will bond to linoleum (and some of them will) apparently the jackass who installed that particular floor was not aware of that. 
See photo 4? I lifted that up with my pinkie – literally! It was not attached at all. He may have had correct coverage beneath the tile and all the little waffles filled – I have no idea. There was not enough stuck to get enough leverage to tear one off and find out.
Photo 4
Most any plywood (even osb 
) is an approved substrate for ditra. And if you use a thinset approved for that substrate, there are no problems at all. Photos 3 and 4 had an unapproved substrate and, apparently, incorrect thinset (and a shitty tile job, but that’s a whole other post). It was nearly guaranteed to fail.
When you buy ditra for your installation every roll comes with a handy little instruction booklet. You can go to Schluter’s Ditra Page on their website and access the instruction booklet (This link is a PDF!). They even have a flash video about the proper installation technique. You can leave a comment below and ask. You can email me. You can send up smoke signals – I’ll answer.
Given the 17 ways to acquire correct ditra installation information above there is absolutely never a reason to do it incorrectly. Ditra, in my opinion, is the best membrane for most floor tile installations. The only time I’ve seen it fail is due to incorrect installation. And that isn’t just the common BS everyone accuses failures on. Me, personally, every one I’ve seen fail is incorrectly installed.
If you use ditra, and if you have an approved substrate, and if you have the correct thinset mortar, and if you fill the waffles correctly, and if you use the proper trowel and get proper coverage it will not fail. Yes, that’s a lot of ifs – when you read it. In practice it really is not that many things to get right. It’s just common sense, mostly.
So here’s one more if: If you have any questions at all about correctly installing ditra and using it for your tile installation please, for the love of all the marble in the Sistine Chapel, ask me below in the comments. I WILL answer you. I’m just super-cool like that 
Hi Roger
How long should I wait before I hook up the power to my new ceramic flooring? The installer used the ditra-heat system
Thanks
Jim
Hi Jim,
You can hook it up right now, you just can’t turn it on for (I think) ten days. Ideally 28 days.
Roger,
Small bathroom project – @ 45sqft
I have a 3/4″ OSB subfloor supported by 2×8 , 16″ oc, span 8′.
I will use Ditra as substrate.
Floor is flat except for last 1.5-2′ which then drops 1/4″ at lowest point.
Q1 – aside from self levelers in such a small area can I use a trowled on embossing compound in that small area (approx 6sqft)? If so what do you recommend?
Q2 – is there anything I need to do to OSB prior to applying modified thinset (need recommendation here too) other than flattening and cleaning, for Ditra?
Thank you for your help! Nick
Hi Nick,
1. I don’t know what embossing compound it. You can put more thinset beneath that area of ditra to get it flat.
2. Nope, just make sure it’s clean and key in the thinset with the flat side of the trowel first to get a good bond.
Roger,
I removed wood tile from a concrete floor. A very thin but extremely hard to remove adhesive is left. Is ditra my miracle solution to not remove the adhesive?
Hi Jay,
No, because you still need to bond it to the concrete with thinset. You can use a primer like eco prim grip (google it) over the adhesive and go over it with ditra if you want.
I just laid ditra on a 3/4 subfloor and the next day I walked on it and near
my tub I heard cracking noise should I be concerned or is the thin set
cracking that maybe went under the gap of the tub
Hi Ed,
I don’t know, I can’t hear it from here.
Provided your ditra is still bonded to the floor correctly it likely was just thinset at the edge of the tub.
I am tiling a 7’x5′ bathroom. I am removing the 3/4″ wood floor and the rotten CDX subfloor. I am using a ceramic tile and would like the finished surface to meet the 3/4″ wood flooring of the adjoining room. As I understand it, I have three options:
1. 3/4″ subfloor + Ditra
2. 5/8″ subfloor + 2 layers of Ditra
3. 5/8″ subfloor + Ditra XL
The area of rot (leaking tub) extends beyond the tiled area, so remaining with 5/8″ subflooring would make that repair easier. I also can get Ditra XL by the foot, so I don’t need to purchase a roll. My only concern is that 5/8″ will deflect too much (16″ OC 2×8 joists). Between option 1 and 3, which would you recommend? Or am I totally mistaken regarding finished surface height?
Hi Gian,
Since the rest of your floor is 5/8″ as well that would be the easiest option. In a 5×7 bath that with xl should suffice with 16″ oc joists. 3/4″ would be better (with regular ditra), but requires replacing all the ply. Completely up to you, but either would work fine and should meet your hardwood correctly.
Roger,
I installed ditra just as you and the handbook says to (very easy). I used the mortars you suggested which luckily a local tile store had. I have mocked my pinwheel layout and it looks great. Now I’m ready to start tiling using the unmodified mortar. After this is complete, and has had the proper time to dry, how do I caulk the expansion joints of the perimeter? it’ll be ceramic tile installed on ditra which baseboard. I guess I’m just confused on what or how to caulk there perimeter. Do I leave the area that the baseboard covers without grout and instead fill it with the appropriate caulk from the grout line to the subfloor? Just confused on how to properly do this and would appreciate your help.
Thanks
Hi Antonio,
You don’t caulk the perimeter joint, it is left open and just covered with the base.
I am pulling up an existing lino floor, which is sitting atop MDF. The MDF is glued and stapled onto the OSB. As I am scraping up the MDF/lino, I am getting a bit of the OSB up with it. My question is what recommendations do you have to ensure properly adhered ditra to the OSB?
Thanks for your help,
Rob
Hi Rob,
I would float over the osb with thinset after you get everything up. Let that cure, then install your ditra.
Dear Roger,
Thanks for all your help in the past!! We are on our 4th and 5th tiling projects, and have appreciated your comments/help/encouragement. I downloaded your bundle for shower bases and tubs, since we’re going to demo out and replace the shower and floor in our basement bathroom this weekend. Question: We like your plan with the plastic, etc. How do we know where to end the Durock or Hardibacker? Once we get the base in and have a good idea where the walls are going to end up, how do we figure out where exactly to make the transition from green board to Hardibacker? Right now, we have a neo-angle shower with acrylic shower walls that are fastened to the walls. It is horrible, so we’re planning to replace it with a larger, better quality neo-angle shower base and walls, and then run white subway tile up the back shower walls, rather than go with the preformed shower walls. My husband thinks that would be easier to clean, and look better. Advice on how to figure out the break between shower walls and bathroom walls? You are the best, and we’ll do whatever you suggest.
Hi Ann,
I always cut the drywall straight up from the outside edge of the base. Once tiled you can still cover that transition with tile and it won’t be affected since it’s not in the wet area.
Hi Roger,
First off, truly appreciate your site and help. I have a new build that is now 4 years old. The bathroom floor has linoleum on it. I bought ditra because of the ease vs backer board. I read that if you thin set allows, you can put drita over the linoleum as long as it secure, but I didn’t want to chance it since i pulled the heat vent up and the linoleum around it was bent up a little by the edges. Is seems fine everywhere else but I rather nor chance it so I’m going to pull it up. Now it appears above the subfloor, the builders installed plywood to build the floor up my guess to be at the same height as the carpet in the halls that it meets. Is this extra layer of plywood acceptable for me to install ditra on (it’s on secure)? or should I pull that up as well? If not, the adhesive they used to secure the linoleum I know i should scrape up, but how far should i go with removing it? Thanks for your help and keep up the sending people down the correct path in home improvement.
Thanks,
Antonio
Hi Antonio,
It is likely luan (very thin plywood – 1/4″ or so), if so it needs to be removed. If it is regular ply you can go over it provided that when you splash some water on it the water soaks into it within 15 seconds or so – that indicates that the thinset will bond to it properly. Good call on tearing out the lino!
I am getting started on my first Ditra project. I have removed linoleum from my luan and there is a film of the adhesive left. I’ve scraped and scraped but I haven’t been able to remove all of the adhesive. It is very level and the luan is in very good condition. Will the thinset adhere to this adequately or do you think I should remove the luan? I’m thinking of running a test with a small piece of Ditra to see how well is sticks.
Hi Mike,
The luan needs to be removed. When the moisture from even the thinset gets to it luan tends to warp. It does not have the compressive strength necessary to be under a tile installation.
Rodger,
I installed the Ditra E heat system in a bathroom–great system by the way–so easy to run the heating cable. I got the Schluter programmable thermostat to go with the system. When I powered things up the thermostat was dead. I rechecked all the wiring with the meter and all was good there. Have you heard much about the Schluter thermostats ? I saw a few comments in other places about similar problems. I know there is a 3 yrs warranty which I will use. Do you have any knowledge about other brands of thermostats that might work with the E heat set up ?
Hi Frank,
I haven’t heard anything overwhelming about problems with them, you likely just got a bad thermostat. It happens, I’ve run across 1 or 2 bad suntouch thermos, but it’s a very good product and they were replaced immediately, I imagine schluter will do the same. I don’t know if another thermostat would work with the wire or not. I imagine so, but I AM NOT an electrician.
Rodger’
I had ordered two thermostats–one for the guest and another for the master bath. Switched them around and the second one functioned as advertised–no problem .Will contact Schluter for a replacement. Thanks for the reply.
Hey Roger. I am in the process of remodeling my bathroom. I have the floor stripped and cleaned and 7/16″ wonderboard down using thinset underneath for 100% surface contact and the backer board is screwed down every 6 square”. My wife decided after that before I tiled that she wanted floor heat installed so I purchased schluter ditra heat membrane and heating cable. My question is can I screw down the ditra heat membrane or am I going to get a better finished product if I thinset it to the cement board? And if I thinset it do I have to wait 24hours to tile over or can I start tiling immediatly?
Hi Mike,
It will be better to thinset it down, as is intended. You can tile immediately after setting it and getting the wire in.
Hi Roger, first off, great site….
I was asked to tile an outside porch (east facing/covered). Can ditra be used under the tiles? And if so, would I use modified or un modified to attach ditra to concrete? Toronto, Ontario, Canada.
Regards,
Santo
Hi Santo,
Yes, you can use ditra on that porch. Schluter wants unmodified both below and above the ditra in that application.
Hi Roger,
I’m planning to lay 3/4″ circular penny tile on a new construction (OSB) subfloor. I also want to use Ditra Heat so the floor is nice and warm. Do I need a leveling course of thinset over the ditra so my penny tile will lay flat and have the support it needs…or do I need to go with a different product for the uncoupling rather than ditra….so my tile lays flat and is supported. My contractor suggested a 1″ layer of mortar rather than the ditra. I’m not a fan of mixing that much product or having my floor an inch higher than the adjacent hall.
Thanks for your help,
Chris
Hi Chris,
The minimum size over schluter products is 2×2. That said, you can use ditra heat, install the cable, then use slc over the top of it to the top of the ditra. Once that cures you’ll have a flat substrate with uncoupling.
Hi Roger,
I’m mid-tile in my main bathroom. My buddy has been helping me out but I found your site and now I’m wondering if we are doing this right. We put warmwire over the plywood, then a layer of SLC. About a week later, we put the ditra down with thinset (Kerabond), but we didn’t wait 24 hours as you advised. We went right ahead putting the 12″ x 24″ marble tile down over the Ditra with the same Kerabond white thinset. Later, another buddy said that we should have used some liquid latex additive with the thinset, or it won’t hold. Are we doomed now? Are my floor tiles more likely to crack? When I put up the wall tile, do we need to use the liquid additive with the thinset? I’m using 3″x6″ subway tile. Thanks for all your advice!
– John
Hi John,
You guys are doing it correctly, whoever told you about using the additive is incorrect. The ‘waiting 24 hours’ is due to having wet thinset beneath the ditra when you’re crawling around on it (like a LOT of thinset). Since you used slc you have a solid base, you’re fine. Use the additive unless you are tiling walls over kerdi.
Roger – you are the best
. Thanks for the quick reply! What a relief that the marble will be OK. (My dog will not catch on fire!) For that wall subway tile, we are putting kerdi over the seams and screws, and in the shower niche/shelf, so should we use latex additive in the thinset with the wall tile? I am planning to use the Kerabond (that’s what was at my local hardware store).
It’s not necessary, but it won’t hurt anything.
I am adding onto our house and am now in the process of finishing the bathroom. I’ve chosen Ditra Heat as my underlayment. I am now in the process of preparing the floor for the installation and was wondering if a cement board underlayment or backerboard is necessary? I have 2×8 floor joist 16″ OC with 5/8″ OSB as my subfloor. I can’t feel any flex in the floor, but was told by a contractor friend that it would be a good idea in any case. He’s not familiar with Ditra Heat and was just giving blanket advice. Should I only use plywood or osb backerboard? Or is cement or fiber cement board ok to use?
Hi Jeremy,
The backer is not required. An additional layer of ply or osb would be a good idea, but if you are installing ceramic or porcelain it’s not really necessary, if you are installing natural stone you need the additional layer beneath the ditra heat.
Hey Roger I am installing a tile floor using Ditra. I mixed the thinset with too much water to stick down the Ditra. Should i tear out and stert over?
Hi Chris,
It should be fine. If the thinset held a notch it’s fine.
Roger,
I am renovating our master bathroom. I just installed Schluter Ditra on the floor over plywood. To my horror, I just realized that I used unmodified thinset under the Ditra! The bathroom is on the second floor, is fairly small, and does not get much traffic. The plywood floor is very solid and it meets all Schluter specifications. I plan to install 12 x 12 tile over the Ditra. Tearing out the Ditra and using a modified mortar would be a real pain. Should I tear out the Ditra and use modified mortar, or will I probably be ok with the unmodified mortar?
Dave C.
Hi Dave,
You should, yes. It may be fine, but it may not. No real way to tell. If you want to take the chance that’s completely up to you, but I probably wouldn’t.
Hey Roger,
In the past I always went with backer board using thin set and screws to adhere to the subfloor. Then I discovered Ditra. I have successfully used Ditra for a floor tile project and a countertop project in the past. Both were installed over plywood. The countertop was over 3/4 sanded ply and the floor over plywood subfloor(after removing linoleum and Luan). I was careful to scrape the loose adhesive off the subfloor concerned that the Adhesive may interfere with the Ditra adhering properly (being my first time using Ditra). I am now on my third project using ditra for a bath floor. After removing the carpet(yes ,carpet in a bath, not my doing), the floor has quite a bit of latex primer from when sprayed during construction. My question is, how much effort should I put into removing the primer? I scraped what was loose and sanded a little. Worried that the moisture from the thin set will break down the primer and cause the Ditra to break bond with the plywood. Should I use backer board that is screwed and adhered to subfloor with thinset or stick with Ditra? Am I over analyzing this? Love the info and help you share, it’s much appreciated!
Hi Anthony,
If it’s primer then you’re fine, it’s porous enough that the thinset will bond through it. If it’s any type of latex paint it needs to be removed or sanded down. If there is a lot of it you may be better off with backerboard. I know – that sucks.
Roger,
Great site. Extremely informative and always an entertaining read.
It’s my first time working with ditra, and while I read all the Schluter material, I need your guidance. I applied modified thinset using the specified trowel to the plywood, then rolled out the ditra. When I pulled back the corner, the underside of the ditra wasn’t completely covered, so I added additional thinset. It seemed to fix the coverage problem, but now it appears there is too much thinset resulting in minor lumps on the surface of the ditra. After researching this scenario online, it appears I mixed the thinset too thick, despite following the thinset manufacturers instructions. A few questions:
1. Assuming the lumps are less than 1/8″, can the unmodified thinset above the ditra be used to level them out (laying 18″x18″ ceramic tile)?
2. Is there a risk that the ditra did not adhere properly due to the thinset being too thick, and if so, is there a way to check without pulling it up?
3. Is Versabond by Custom an acceptable thinset, or should I have gone with a Latacrete thinset?
4. On a separate note, is modified thinset acceptable for filling the expansion joints in the plywood, or is something else preferable?
Thanks!
Hi Sean,
1. Yes it can.
2. If you got full coverage as you were installing it then it will bond properly – no need to check. The thinset, if embedded in the fleece, will cure with a full bond.
3. Yes, versabond is fine.
4. The expansion joints in the plywood should not be filled, they should be left open. They are expansion joints.
very informative although I think it’s important to state in both of your pictures showing failures both of them looked as though to me it wasn’t so much of a proper installation on the teacher is it was somebody spread out too much thinset the thin set skinned before the back of the new tiles made contact with it there for failure to bond occurs I’ve been a professional tile setter for 22 years anyways other than that very informative thanks for the site
Hi Chris,
Nor were they backbuttered, which they ALWAYS should be unless using one of the new full-contact mortars, which doesn’t require it.
Hi roger! My wife found these great slate tiles and fell nose over tail for them and decided that they will look amazing in our master bath! They aren’t square they are cut like stones on a 2’x3′ matt. I chipped up all the ceramic tile and found that there is a crak running through my house, the same crack I found when I installed my laminate flooring in my bedroom, it goes from one end of the house to the other, through the garage and down the driveway, I sealed the crack with a mastic silicone (Dow Corning 795 to be exact) on my friends recommendation. My question is, before installing the slate should I install dirta xl? Or would red guard be sufficient? Or is the tile guy I talked to correct when he said not to worry about the crack and just lay it down without any protection as the crack won’t get any bigger? I’ve got many other steps before the slate, but I’m trying to plan ahead. Any help you could give would be awesome! Thanks, phillip
Hi Phillip,
I think you’d be just fine with regular ditra. It likely requires more than just redgard if it goes all the way through your house. You definitely need something under there, you shouldn’t go over it bare.
Roger,
My dogs nearly exploded, i’ve got some thinset on dirta but i didnt get the tile down due to my slowness laying tile and the pot life of the thinset being expired (over 45 minutes). I scrapped as much of the thinset out of the dirta as possible, i hate to ask, do i need to rip up the dirta? and start over again in those areas? Awesome site!
James
Hi James,
No, as long as you only have it in the cavities and don’t have big cured stripes on top of it from your trowel.
Roger,
Worms. I just love them. The can I opened the other day is still lingering around. Let me describe the can. I purchased a new toilet Thursday. Went to install Saturday. Broke 4 tiles while removing because the knuckhead DA$$ who installed the tile was a novice and butted the tile and hardie backer board upto the toilet. So since I didn’t have any of the same tile to replace the 4, I decided to remove the tile and replace with new. Simple enough…. Upon removing toilet there was Vinyl underneath and since the hardie BB butted upto the toilet there was a void in the shape of the toilet. My original thought was to install the new tile over HBB.While I am removing tile (25% complete), I noticed two small cracks in the tile running parallel to the joints in the HBB. The bathroom is only 5×9 and the area where the cracks are is only 4′ wide. So in my infinite wisdom I determined that something was improper with the HBB install since I didn’t see any signs of thinset underneath therefore I removed the HBB and Vinyl to install Ditra. There is OSB under the Luan. I do not know if it is glued or not; however, I’m confident that it is since it seems solid sounding when you walk on upon the sheet. My concern is when / if I remove the Luan it will remove pcs of the OSB leaving a undesirable surface for the Ditra to be properly installed. What do you suggest to be the most cost effective, expeditious and CORRECT process to install the Ditra and 18″x18″ tiles?
Thanks
Hi Shane,
You can install 1/2″ ply over the osb, use slc to level out the osb, or you can level the osb out with thinset, let it cure, then install your ditra.
Hi Roger,
Thanks for this site. We have old asbestos 9×9 tile over concrete in our basement. There is a bath down there with a raised shower base out of concrete. The bathroom floor has old 12×12 linoleum squares. We put hardie backer board on the walls in the shower and bath, and were going to put ditra down before tiling.
1. Is there any way to go over the asbestos tile without removing it?
2. Do we have to remove the old linoleum, it is not shiny and is glued in.
3. Should we use ditra in the shower only, or the bathroom floor as well?
4. What do we do about the wall to floor seams in the shower? (Hardie meets ditra)
5. Type of thin set for each?
Hi Pamela,
1. Yes, but you need to use a thinset approved for use like that. I believe mapei ultrafles 3 and laticrete 255 both do, but you should confirm that.
2. No, but you will be relying on the bond of the lino to the underlying substrate for your tile installation.
3. You should not use ditra in the shower at all.
4. See above.
5. see above.
What type of waterproofing do you have on your shower walls?