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 
Retiling bathroom floor Previous floor was tile over ditra on plywood subfloor. Question is: I removed old tile and ditra but there is a layer of papery membrane with thinnest in it that did not fully come off with the ditra. Do I need to scrape/sand all this off or will the new proper thinset and ditra adhere properly to it as long as it has been thoroughly swept/vacuumed so minimal dust?
Thanks
Hey Harley,
Follow up to above– in spite of the fact that I wish there were a magic genie answer that would let me skip getting the old fleece/thinset layer up, I realized that will not give a level consistent surface for the new modified thinset and ditra. So using an air hammer with chisel to carefully remove all the previous layers down to plywood. Then will sweep, vacuum, and wipe down with damp sponge. Time consuming but I know this will give me best results for solid lasting floor. And let me assure others on this site, that the modified thinset does its job very well in holding the ditra to a wooden subfloor.
Thanks.
Hi Giles,
Is it a ‘membrane’, or paper backing from linoleum, or cutback, or…? I can’t really give you an answer unless I know what it is. What color is it? If it’s black then it’s cutback, that needs to be removed. If it’s light gray or white it’s likely from lino, get as much of that off as you can then you can go over it. If it’s something else a picture may help.
i have a question I’m installing ceramic wood look tile Dal-Tile i have a cement floor in my basement its get wet from time to time would a ditra be recommended i have to pull up the old laminate and wood floating sub floor and se what I’m dealing with house was built 1969 some say yes I’m confused??? please help thx Harley queens ny
Hi Harley,
Yes, ditra would be a great product to use in that application. I’m unsure if you are actually asking me if the laminate will need to be removed, but yes, it will absolutely need to be removed first. Ditra is installed directly to the concrete.
thanks for the reply I’m pulling up the laminate floor to the cement i think there is mold it will be cleaned , I’m sure i have had water under the sub floor a few times will the ditra be affected if water gets under the tile will the product detach from the concrete ruining my new floor?? thx harley
No, water will not affect it at all. It will actually make the thinset stronger. I know it sounds strange, but it’s true.
thx for your help wlil visit again
Thank you this post. I am about to install Ditra and tile in my bathroom. My sewer pipe is low and level with the subfloor, so I need to get an extension. Should I do this first and then make certain the Ditra is tight around the extension? Should I then use silicone to seal it there or will that suffice?
Hi Alisa,
I assume you are speaking about the toilet flange? If so then the tile would go in first, then the extension goes on and sits on top of the tile. The extension is the last thing to go on. If that’s not what you’re talking about let me know what you mean.
I was wondering if I should buy the extension first to make sure the Ditra layer fits tightly around it. Otherwise, do I just cut a hole in the Ditra to leave room and call it good? Does the Ditra need fit as close to the extension as possible?
You can, but the ditra does not need to fit tightly against it. As long as you are within 1/2″ or so it’s fine. And the extension will be exactly the same size as the existing flange.
Roger,
I purchased Ditra to install under laminate flooring and have a couple of questions
1. I’m not sure if I need to use thinset to fill the waffles before I lay my flooring on top. Everything I see online is for tile installation where it is used. Would it be more efficient to use it?
2. Do I need to attach the mats to the floor or let it float with the floor? It’s being installed on wood flooring.
Ditra is not for laminate flooring.
From the Schluter website:
“Schluter®-DITRA and DITRA-XL are specifically designed for ceramic and stone tile installations. ”
https://www.schluter.com/schluter-us/en_US/Membranes/Uncoupling-(DITRA)/Schluter%C2%AE-DITRA-&-DITRA-XL/p/DITRA
JP is correct, ditra does not go under laminate flooring. With laminate you roll out the thin cushion underlayment and install directly over it. That’s it.
I haven’t started work on my floor, but I just removed the top layer of vinyl flooring and 1/4″ plywood to find ANOTHER layer of vinyl flooring on top of 1/4″ plywood on top of the solid 1″ plywood subfloor on 16″ joists). Vinyl is in good shape, glued and stapled down (from top layer of plywood), plan was to sand vinyl, clean, put on Mapei Prim Grip, then lay down DITRA and put 12″x24″ tile on top. OK based on Schluter installation requirements, but wanted to get an actual installer’s opinion here. Thanks!
Hi Keith,
It will work, it comes down to how comfortable you are with the bond of the layers beneath. Are you positive there are no hollow areas beneath that vinyl or subfloor which would allow the tile installation above it to move even a little? It all depends on how confident you are with what you are installing over. Prim grip is great stuff, it will bond to the vinyl.
Thanks for the response – so I have been going through the floor to sand off the sheen and been checking here and there for the adhesion of the vinyl and looking for hollow areas. Seems solid and doesn’t move. I am going to throw down some backer screws into the subfloor to make sure everything is mechanically attached. I also have been pulling up the floor under the dishwasher and stove area to see how good the bond is and to see how the top layer of plywood was installed. All looks solid.
I have a painted plywiod floor that I am going to tile. The plywood has some significantly worn spots. Can I use floor leveller to fill those spots and then ditra over them? Can I use ditra over painted floor, and if so should I use modified or unmodified thinset?
My other option is rip up the plywood and lay down a new layer; it’s a small room (8×10) and there is a subfloor underneath the painted plywood.
Your suggestion?
Thanks.
Hi Armindilo,
You can not install ditra over a painted floor. The thinset will not bond well enough to the paint. You can sand the paint off, install another layer of ply or 1/4 backer over the ply, or remove and replace it.
Hey Roger,
I am in the process of installing tile in a connected bathroom/laundry room. The bathroom portion had previously been tiled, while the laundry room was raised on 1/4″ plywood and topped with linoleum. I have completely demolished the bathroom, removed all tile and cement board down to the subfloor and have removed all linoleum from the 1/4″ plywood. I have already laid hardie board to bring the bathroom to the same level as the laundry room. I didn’t rip up the 1/4″ plywood due to my wash and dryer being stacked, heavy, and in a very inconvenient location to move out of. My question: would it be ill advised to lay ditra connecting the two substrates (hardie board and plywood) to do a continuous tile between the two rooms? Or should I put a divider between where the different substrates meet, lay ditra on both sides, and tile each room separate from one another? Sorry I don’t have a more current picture of my progress. I have removed all linoleum and nearly all the glue attached to the plywood in the laundry room aside from what is under the machines.
Thanks,
Brad
Hi Brad,
You can put continuous ditra through both of those. It’s what it’s made for. And you can use modified thinset to install it to both.
Hi Roger question I installed a ditra heat mat over a luan subfloor that I was told was glued and stapled down. Turned out not all was glued so now i have loose spots. Taking up the Luan but can I reuse the ditra mat? The thinset never fully cured but there is a coating of thinset on the mat. Thx for the tips.
Hi John,
You can. I wouldn’t. But you can. If you do make sure you use a larger trowel to ensure you get full coverage.
Thanks for any info you may be able to provide.
I recently laid ditra over a polymer modified mortar over a concrete substrate which was recommended by Lowe’s for ditra. I haven’t laid the tile yet and I seem to have good adhesion to the concrete. Should I peel it up and reapply an Unmodified mortar under the ditra. I would hate to install the tile and have any failures. Thanks
Hi Austin,
No, it’s fine.
4 years ago I installed porcelain over DITRA over advantech subfloor. I accidentally laid the DITRA over a bed of unmodified thinset (mixed the wrong bag) 4 years later about 10 of 80 tiles have cracked in various locations. Considering replacing only the cracked tiles, or will the rest likely fail over time too? If I should start from scratch, do I scrape all the way back to the wood subfloor and start over? Lastly, if I do that, I can go DITRA back over any fleece residue that is remaining securely and smoothly on the subfloor?
Hi Jeff,
Unfortunately the rest of it will end up doing the same thing. Yes, scrape it all the way back to the wood (as much as you can) and start over. You can go over some of the fleece if needed, just keep in mind that the fleece that will still be bonded is bonded there with unmodified and the new stuff will be bonded to the fleece, not the wood.
You were correct. I removed all the tile and Ditra in virtually one piece. The floor was floating on a powdered thinset floor. The fleece was properly embedded, but it did not stick to the wood. My subfloor is almost perfectly smooth now. I’ve managed to scrape away nearly all the thinset and any fleece that came off the Ditra during demo. Overall I’d say I have half of the wood subfloor visible and the other half is thinset. Since that was unmodified thinset, I’m hoping there is enough wood there for the new modified thinset to grab. Your thoughts?
You can go right over it, it’ll be fine. (With modified
)
I’ve just installed a ditra uncoupling membrane for heated flooring and one small patch seems to have not grabbed the thinset. It’s approximately 4″ by 3″. It’s right along the edge where one ditra membrane sheet meets another sheet. What do you suggest I do? Should I cut it out, dig out the thin set, and reset this patch? Or is this small of a section negligible?
I have plenty ditra left over and plenty thinset I could mix up quickly to repair and replace the section.
Hi Jen,
I would cut it out and replace it. You can cut out just the part that isn’t bonded well.
My husband and I will be installing the heat membrane ourselves and then we have a tile guy that is going to tile. My question is, when we install the membrane should we also fill the baffles with thinset and let it dry and set before the tile guy comes in. I have been given that advise and I’m not sure it’s good advise. I was told that would ensure the wires are secure and the tile person has a solid flat surface to tile.
Hi Diane,
I install my wires then fill the mat with thinset and let it cure before installing tile the next day. The method is just fine.
But I would not let you install the wires and prepare my substrate. It’s a liability issue. But the method is completely acceptable.
installing Ditra over self leveling cement. We are struggling getting the mortar to apply thru the mesh side of the ditra giving us poor adhesion from Ditra to cement.. Any advice?? Thinner thin set?? More pressure??
Thanks, mark
Hi Mark,
You want to mix the thinset a little thinner. Just enough to hold a notch. And good pressure will allow the mesh to be saturated.
Roger thanks for the forum it has helped me on many jobs. I would like to piggy back of Marks post. I have a large format tile 12.5 x 40 that i am laying on the floor. I got cement brd on the floor now and the floor is fairly level( maximum dip is 2mm) would u put ditra on it due to the size of the tiles or do u believe with a good thinset that should due it
Hi Jorge,
Provided you have the backer down with thinset beneath it then a good LFT mortar (medium bed mortar – large format tile) will be just fine. Ditra never hurts, but it’s not really necessary at this point.
Hi Roger! I am planning to use ditra heat on a floor. I understand it is 1/4″ thick. How much height does the thinset under the ditra heat add? I will be using a 1/2 x 1/2″ trowel to apply 12×24″ tile to the ditra heat. How much height will that layer of thinset add? I’m figuring that it “squishes down” but am clueless how much of that to expect. Thanks in advance for your help!
Hi Pam,
Total height of ditra heat using a 3/16″ trowel to install it is 3/8″. A 1/2×1/2 trowel will give you a 1/4″ bed of thinset beneath your tile.
Greetings and thanks for the great article on Ditra,,,,, Our 1st install did not go well – the Membrane did not stick to the Thin set – we are using an Un- modified thinset Mortar. Do I need to mix that Thinset to a “Soupier” consistency so that it gets thru the small holes in the backside of the Ditra membrane ?>>
TY – Mark
Hi Mark,
Yes, you want to mix it a bit thin, then take a 2×4 or your trowel and smooth it down to embed the ditra into the thinset.
I’m assuming that you are installing the ditra over concrete or cement backerboard, right? Because if you are installing it over wood you need to use modified thinset. You probably are, but if I don’t ask…you know.
Hi Roger. I have 12 yr old tile installed over ditra and want to update by removing the tile and installing new. Is it possible to remove the tile from the ditra and install new tile over it? If so what are the steps / products to make the old ditra ready for new tile? What should I look for to be sure the ditra is still good. The old floor looks great no cracks and solid grout
Hi John,
You’ll never be able to get the tile off the ditra without destroying it (provided it was installed correctly). You’ll need to replace the ditra.
Hello! Thank you for your tips on proper installation, and the affects of not doing it properly!! We ar about to lay it down for the first time. But before we do, My question is: can we use it under marble tile?? The booklet says for “ceramic and porcelain”. Help!
Thanks!
Hi Donna,
Absolutely you can. Ditra is an approved tile substrate for any tile larger than 2″ square.
(I just sounded like a schluter representative there, didn’t I? Damnit, I hate it when I do that..).
I think i messed up i used tile adhesive for walls and floors to lay down membrane is this okay area is 5×5????
Hi Jim,
By ’tile adhesive’ do you mean mastic? As in it was premixed in a bucket? Because if so that absolutely needs to be removed.
That’s what i figured just finished taking it all out got lucky peelrd right up and easy to scrape off floor…thanks again
Hello
I am in need of some advice. I am planning on replanning my kitchen floors with 8X8 1/2″ cement tiles. My house is from 1910 and has subfloor consistenting of 1″X 6″s, 1″ of pine floors topped with a 1/4 of plywood covered by old vinyl floors. I had planned on removing the everything down to the subfloor and adding 1/4 cement backerboard and/or a layer of ditra. Is it advisable to use both layer or would neither one work on their own? Ideally I would only add an inch total to the subfloor to keep it flush with the original hardwood floors that are in the rest of the house but if doing it correctly brings it a little higher I would rather do that.
Any advice is appreciated.
Matt
Hi Matt,
You need plywood over those 1×6’s. I would use 1/2″ ply over them, screwed to the planks (no glue), then ditra over that.
Thanks
I read through enough posts to figure it out. Already have the 1/2 inch ply and ditra down and am currently putting in the tile.
Ditra over Hardibacker? OK or not OK?
Hi Gary,
Completely fine.
I have an installer in my house now. He laid down Ditra, Filled the waffles with thinset.. But now he is letting the thinset dry (ontop of the ditra) before he backbutters the 24×48″ tile?? I just cracked open one of the bathrooms and there is ditra, and thinset covering the top of it.. with no tiles
This makes no sense to me, he said, “Don’t worry, it’ll be fine”
Hi Mike,
It was completely fine. I prefill my ditra all the time.
And yes, I realize this reply is likely too late, but the info will be here for others in the future. Sorry for the delay.
Thanks, this was just the information I was looking for. I’m using Laticrete Strata Mat but don’t have the tile on site yet and was wondering about prefilling the waffles.
As a side note does the Ditra/Strata Mat have to have the tiles installed or waffle prefilled within a set time? I saw mention in the comments on some youtube video the tiles had to be installed within 72 hours after Strata Mat was put down. There’s no mention of that in the instructions I have. I can’t see any reason for that except to protect it from damage.
Not true. It can set there for a year unfilled if you want it to.
What should I cover my Ditra heat system with before I put my vinyl Looselay planks down? I have been told thin set or just a sand cement mix drypack scratch coat. Can you recommend a particular kind?
Our Ditra floor system is glued onto cement floor.
Thank you so much!
Hi Robert,
If you are using LVT it needs to be SLC.
And yes, I realize this reply is likely too late, but the info will be here for others in the future. Sorry for the delay.
Where to begin…Re Ditra for marble floor: my handyman/friend (who has installed much tile) says:
1. “You can read me the instructions as we go.”
2. “Any leveling” of underlayment is not really necessary.”
3. “I know what I’m doing.” (he’s 64)
4. “Minimal penetration into joists” of the screws to pass through 2 layers of plywood subfloor – he says “I like to penetrate the joists.”
5. I have a leak stain in my ceiling under this small bathroom. So re waterproofing he says. “It’s impossible. You can’t waterproof around the toilet and the door entrance.”
6. “You don’t need movement joints for a small bathroom.”
I could go on, but…you get the idea.
I told him to call Schluter. “I don’t want to waste my time.” So…I’m afraid he will not install per specs. He’s stressing me out. He’s an old dog, as others have alluded to. How can I find a qualified contractor? I’ve wasted 3 hours on the phone with this guy plus hours of research on the Ditra product (which I kinda enjoyed). I’ll be doing a total master bath Reno after this one. BTW I’m the customer, a girl, not a contractor. And I have already bought DitraSet from the Internet. I got white because the store said grey would leech into my mostly white marble. Any help much appreciated. Donna B.
Hi Donna,
I realize this is likely too late, sorry for the delay. You are correct about the white thinset, but everything he says is bs. If you google either CTEF (ceramic tile education foundation) or NTCA (national tile contractor’s association) you can input your zip code into their site to find a qualified contractor.
Hi Roger,
Thanks for the great website! I continue to be amazed by guys like you who can conduct business during the day and then then educate others by documenting eveything in great detail at night. It’s a gift!
I already know the answer by reading the comments on your post, but I’m going to ask again anyway hoping that maybe the planets have aligned and it won’t be a problem.
I’m a DIY guy doing my first Schuter baths and floors. I made a mistake and used ANSI 118.1 Unmodified thinset (Schluter Set and Mapei Uncoupling membrane thinset) to attached about 200 sq ft of Ditra to a plywood subfloor. To make matters worse I used a 23/32 sanded plywood – with a very smooth finish – for my top layer of subfloor due to its superior flatness.
I had “unmodified thinset” in my head due to its necessity for the Kerdi and didn’t reread the Schluter information before we proceeded on the Ditra.
I have two questions:
1) Are these floors guaranteed to fail? My assumption is the failure will be because the Ditra will simply uncouple from the plywood base since there is no later in the thinset to stick to the wood.
2) Once we either do it over, or stick with what we have, is it better to fill the squares in the Ditra first, let it cure and them tile over it?
Thanks in advance for you response.
“Later” was supposed to be “latex”
Hi Kenn,
1. (Nearly) nothing is ‘guaranteed’ to fail. The best we can do is maximize the correct methods and steps to minimize the possibility of failure. It may be fine, or it may fall apart in two weeks. No guarantees anywhere.
2. I always prefill my ditra, makes everything much easier.
And yes, I realize this reply is likely too late, but the info will be here for others in the future. Sorry for the delay. Sometimes I’m unable to do all the stuff that allows me to do this stuff at night after work.
Help! Installed a Ditra Heated Floor system over concrete floor and then tiled. Not feeling much heat at all. Since been told there are 2 types of Ditra (white back and grey back). I used the white back. Is there anything I can do about this? Or have I wasted a lot of money?
I have the same problem!