Improper coverage on tile / Ditra not filled correctly

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 :D ) 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)

Improper coverage on tile / Ditra not filled correctly

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. :D

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).

Improper substrate for Ditra

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. :guedo:

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.

Improper substrate for Ditra

Photo 4

Most any plywood (even osb :whistle: ) 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 8)

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  • Linette Klucas

    Replacing roll linoleum flooring in bathroom and kitchen with porcelain tile. Want to use Ditra. I have removed the linoleum and discovered cement board over, I assume, plywood. Customer purchased and wants Ditra used, height differences in flooring are not a concern. What thinset do I used to adhere the Ditra to the cement board?

  • Tammy r seed

    My dad is a carpenter and had spare plywood so he put it down for me. I bought ditra to lay next but the plywood he put down is mahogany plywood. Is that ok?

  • Paul

    Not the usual question. Is there any limit on how long you can wait after installing Ditra and kerdiband before tiling. E.G. waiting a week and then tiling while you do another job. Thanks in advance?

  • Deanna

    Hello, I did NOT do my homework when getting a contractor but ….we now have OSB subfloor (on top of plywood and OSB. The OSB was installed upside down…….we have porcelain tile…..which we were told could go right on the OSB (wrong…) tile is now off. I wanted to use Redgard two coats and then put on DiTRA. I know I need a modified thinset and Ordered the DITRA modified thinset. After we put on the Ditra…some videos recommend putting on a coat of thinset (we have mortar especially for our porcelain tile)…Can I use ANY nonmodified thinset to fill in all the holes on the Ditra….let dry and the use my porcelain mortar to put on the tiles (12 x 24 tiles)…..Does this sound like a plan? If not …PLEASE give me some guidance…….I cannot afford to but in another subfloor……

  • Justin

    I installed 5/8 plywood as an underlay over an uneven 5/8 subfloor, to eliminate any deflection issues, I noticed around the edges that it seems like the plywood isn’t getting fully sucked down to the subfloor unless you bury the screws halfway into the plywood and I’m concerned there could be voids in certain spots that would create an issue later on
    There’s already a million floor screws in this already, probably more than necessary
    Should I have used thinner plywood that would conform to the shape of the subfloor, possibly two layers, should I have self leveled before the plywood underlay, is there special slc that I can use multiple pours and go to a feather edge? I do not want to slc the entire area if I don’t have to, and over time does the slc stay attached to the plywood
    It would make sense to me to use slc after the uncoupling membrane
    I understand using modified to attach to plywood but can you use it to attach the membrane to the slc?
    In my case I am using flexbone and Ardex products, not ditra
    I appreciate your reply and advice

  • Steve

    Hello . I have installed distra xl on concrete . Everything is adhered properly coverage was good . My issue is I hadn’t noticed there was a dip in the floor – over a 12ft span i have a dip of approximately 5/8’’ in the middle .this area is roughly 12’x12’ . Could i level it out with schluter allset to keep my adhesion proper for tiling . I would really like to not have to pull up the membrane if possible .

  • Amanda Ampey

    Hello! Trying to install porcelain tile for first time in laundry room (79sq ft) and reading a lot before starting project to make sure I don’t cause bigger error. Floor Joists are 16″ oc and the subfloor is 19/32 Sturd-i-floor (20″ oc is also written on Subfloor, but I measured joists at 16??) . Is this Subfloor good to go and can I install Thinset/Ditra on top? The subfloor is so smooth I hate to have to put anything else on. Reading in Ditra manual, it seemed like Ditra can be installed over 1 layer of OSB (and Sturd-i-floor seems to be slightly better and sturdier than OSB) as long as joists are 16″ oc? Additionally:
    1) There are some parts of wood of subfloor that got ripped up. What can I fill so that the subfloor remains super smooth (AKA is there a mud for wood like there is for drywall).
    2) Does subfloor need to be treated with anything before thinset is applied


  • Chad

    Hello, I just read your article and am getting ready to install tile in my kitchen. I do not have the option of getting an “preferred” types of thin set, but have to stick with what’s available at my local Home Depot. I am putting down Ditra and was planning on using Custom’s flexbond to bond the Ditra to the OSB subfloor and Versabond-LFT for the 12×24 ceramic tiles I’m installing.

    Do you think that’ll work okay? And what do you think the dry time would be on the versabond between the Ditra and the tile?

    I had considered using Custom’s CustomBlend unmodified, but I haven’t heard a lot of good reviews for it.

    Thanks for the article and for any info you can provide. Thanks.

  • Dave Matthews

    I have a porch that is under roof, but subject to cold northern winters. ( to -30)
    I want to lay porcelain tile on it, and am wondering if that Schluter Ditra will work as plastic gets brittle when very cold. It would be on plywood, and only
    8’ X 10’. What do you think, and have you ever seen it used where temperatures get this cold?

  • Paul Bevacqua

    Excellent article. Thank you. I have a question on suitable substrates. I’m installing Victorian floor tile in a part of my front hall (approximately 7 1/2 feet x 8 1/2 feet). My home was built in 1890. Although the floor is structurally sound, the subfloor is random width planks, laid horizontal with fairly wide gaps. I’ve used Ditra many times in new construction but never over a plank floor. If I lay 3/4″ plywood over the planking and then Ditra, I’ll have a large transition to the rest of the finished floor in the hallway. What do you recommend in this situation?

  • TC1

    I have a ditra heat application. One small section of one of the ditra heat squares seems to have popped up from the thinset. Almost as if there is a small bubble between the ditra and subfloor/thinset. Will this cause tile failure and can it be fixed before tiles are put down?

  • TC

    I have a ditra heat application. One small section of one of the ditra heat squares seems to have popped up from the thinset. Almost as if there is a small bubble between the ditra and subfloor/thinset. Will this cause tile failure and can it be fixed before tiles are put down?

  • Dave

    Hey Elf,
    I’m laying 12″x24″ travertine tiles over Ditra. The original OSB is 3/4″ and I have added an addition 3/8″ underlayment screwed 4″ on boarder and 6″ in field per Schluter installation. The floor at an exterior wall has a slope that extends into the room about 3′; I did not cover with the 3/8ths underlayment.

    I was considering using SLC from the edge of my 3/8ths to the wall to flatten this area within 1/8 of the room. Will laying Ditra and natural stone over this 3′ span create an issue?

  • Jean Hartke

    We had a ceramic tile floor installed in the kitchen five years ago. I love the floor; however the grout will not stay in the traffic areas. We have had this regrouted twice and this still continues to happen. Ditra was used. I lifted the vents and it looks like a layer of something was put down before and after the ditra. I am a loss as to what to do. Everyone says put in this new luxury vinal flooring. I don’t like it. To me it looks like a big piece of plastic. HELP PLEASE


    So i am installing ditra heat on a bath floor. i am using an Schluter all set. i used the recommended 1/4 x 1/4 trowel. Used the flat end over clean ply then raked it out. put the ditra down and smoothed over as recommended with a wooden float.. all is good. im just curious bc i went back to an area after about 15 minutes just to see how good it bonds and was able to list it off relatively easily. Is this proper because its an uncoupeling membrane that hasnt cured or should it be difficult to lift and well bonded? i will check again after 24 hrs but it just seemed pretty easy to lift off.

  • Ogre

    Hi! I appreciate your time and expertise. I started an installation with my son-in-law, who convinced me that he knew tile installation because he works at a “Tile Shop”. Well… after witnessing the tear up and a few other things, I realized that he’s not the expert he claimed to be. Now I have a few problems. We tore out particle board in my 18×14 living room and replaced it with 3/4″ plywood, using about 40 billion screws– I’m convinced that the subfloor and underlayment is now strong. However, he recommended (and bought) Dural Backer Lite as the uncoupling membrane and installed it over the plywood. To me, it still seems a little “wavy” after pressing it flat, with a few minor high points under the membrane, which is now solid as concrete. I’ll be using a porcelain 12×24 tile. Should I be concerned about the waves, or is this common? We are also planning an epoxy grout. Any advice here? I’m panicking…

  • Scott Gorman

    Hey man, your site is a great resource! What are your thoughts about installing ditra underneath a kerdi shower pan (36×72 with linear drain) to decouple it from a squeaky subfloor? Hoping to stop any movement to avoid cracked floor tiles in the shower. Is that crazy? Will it work? The new sub is a layer of 1/2 ply glued and screwed to the old diagonal subfloor. Cheers.

  • rb

    Do you need to fill knots or gaps in plywood before installing Ditra?

  • Harold

    Can you use Masonite siding on floor then use Ditra over it?

  • Fred

    Quick question…is it necessary to tape the joints of ditra if we are not seeking the floor to be 100% water proof?

  • JP

    Hi Roger, All,

    Remodeling my bathroom. Demo’d old ceramic tile floor which had been installed directly on 11/32″ plywood underlayment over 3/4″ plywood subfloor (some of the tiles in the main field were cracked, where foot traffic heaviest.) I pulled up the plywood underlayment. There was probably 3 or 4 spots where the floor squeaked (small bath ~45 sf), I screwed down subfloor into joist and eliminated all the squeaks, though this took a while as eliminating one squeak sometimes seemed to spring another mini one elsewhere. I just had a tile contractor install 6″ x 38″ porcelain wood look tiles on Ditra Mat on the floor about 2 weeks ago, and after about a week my floor which was quiet as could be…is now squeaking and squawking. Most of the squeaks seem to be coming from the corner of the alcove wall (alcove tub/shower) next to the tub apron.

    My question – would improper ditra mat installation cause this? I understand you need to fully fill the waffles etc. Or is it likely that something else caused this, perhaps the weight of the new tiles?

    I’m considering trying to fix the squeaks from below (unfinished basement below), as Ive done this sucesffully in the past (sister blocking to joist up against subfloor), but I wonder if rather than fix the squeaking it might intensify the issue, cause cracking etc?

    Thanks in advance

  • Anna

    Hi! Does the ditra getninstalled flush with the wall? Or is there 1/4” expansion gap used for both the ditra and the tile?

  • Dave

    Hello, how much gap is acceptable between the Ditra Heat mats? I just had some installed recently and some of the mats have a fairly large gap between them (almost an inch). Is this a problem? Will it affect the support of the tiles or cause an issue when passing the heating cable?


  • Dave Austin

    Hi, I have an exterior balcony above an exterior patio. The balcony is ceramic tiled with ditra but must have been installed incorrectly as it leaks to the patio below.
    Can ditra be installed directly over the existing exterior tile, with the proper thinset, and new tile installed over the ditra?