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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  • Carson

    Great story. I have used Ditra for all my amateur and have had no fails.

    I am building an additon and there will be OSB to tile over. In my past projects I have screwed down a layer of 1/4 or 3/8 plywood just to give a clean surface to start because I was always doing a reno and the floors were old.

    Would it be of value to add even a thin layer of plywood over the osb to have a better ditra bond or might I be risking adding a moving part to the floor.

    Your opinion would be greatly appreciated.

    • Roger

      Hi Carson,

      3/8″ ply would be the minimum you should put under any tile installation. In my opinion a really good modified thinset is going to bond to the osb as well as it will to a thin layer of ply. I would just go over the osb provided it meets the minimum criteria for your subfloor.

      • Carson

        Thank you very much. I had in the back of my mind an easier tear up as well if anyone ever wanted to change the flooring… but I would rather not add to the floor height and get out of synch with the laminate. So over OSB it is. Thank you.

        • Carson

          A bit more to ask. The addition is a 30 x 30 ft box with full foundation. The joists are 19.2 oc, supported up the middle by one of those multi-lam beams. So the span is actually 15′ between supports.

          The contractor specs 5/8″ OSB, over which 3/8″ plywood would be added, then ditra and 12 x 24″ tile. On schluter’s website for 24″ oc it says use 3/4″ for double layer floors. Do you think I should go that extra bit thicker. I am getting joist specs as well.

          Sorry for my multi pronged questions.. just trying to be smarter than I am now before any work starts.

          • Roger

            With 19.2 joists I would probably use 1/2″ over the osb with a 15′ span. I wouldn’t think you would need the 3/4″, although it never hurts to go thicker. I know it can screw with doors and transitions, though.

            • Carson

              Well luckily we can play with the basement ceiling height to balance transitions to match floor height… so just looking to do the best possible. I am more concerned than my contractor and I am going to tile it… so being a hawk on the floor and substrate.
              So better to put 1/2 instead of 3/8 plywood and leave 5/8 osb instead of 3/4″. I had just read Schluter for multi layer floor (they only show on 24 oc).. and they said 3/4.

              Appreciate the advice.. wasn’t sure what gave the best value under Ditra for my tile.

              • Roger

                Yes, the 5/8″ osb plus the 1/2″ ply will work just fine.

  • Dorothy

    I ve used ditra before on Plywood but this time around Im installing it on concrete. The floor had black asbestos mastic on it which I used bean a doo to remove. I ve removed over 98% of it as some got into divots and cracks. I then used a de-greaser to clean up the bean a do. How do I know if the concrete is clean or de-greased enough for me to begin laying the mortar/ditra/mortar/tiles. I dont want to have the unmodified thinset not adhere bc of any of the cleaners. thanks for any help !

    • Roger

      Hi Dorothy,

      Splash some water on it. If it beads up and sits there you need to scarify the surface. If it soaks into the concrete then the mortar will bond to it correctly.

  • Marlene

    Hi I’m trying to getdrued mortar off of mortar. I’m chiselling away but it’s such a slow process

    Is there an easier way?

    Thank you.


    • Roger

      Hi Marlene,

      A grinder with a cup wheel is the fastest way to remove cured thinset off of anything. But it is dusty and messy. But easy! :)

  • Diane Marzec

    Our contractor installed part of the orange Ditra mat in pieces – like islands! In front of the closet door, a piece about 6X8 inches is sitting in a bed of mortar at least 2 inches wide before the next piece of Ditra on the floor. I don’t think that’s right, but after contacting Schluter customer service with a photo, I was sent the installation manual!
    The photos I have are too large to upload for you to see, but the mat also is about 6 inches away from any surface – tub, vanity, and walls. If I can send to you another way – like email – I will do so.
    Many thanks for your input!
    Diane Marzec

    • Roger

      Hi Diane,

      All of it should be connected. It can be installed in pieces (it doesn’t all need to be a solid piece), but the pieces should be next to each other without gaps. If you want to you can send them to and I’ll take a look at them.

  • Paul O'Loughlin

    Years ago I put down some DecRez on my concrete slab because of moisture issues. Subsequently I installed carpet, but now 11 years later my wife would like tile. How would you treat the Deco-Rez surface prior to thinset? I’m leaning toward scuff/remove and replace with Red Gard? Thanks!

    • Roger

      Hi Paul,

      Yes, it will need to be abraded off the concrete to the point that the concrete will soak in water when splashed on it. (This ensures that tile installation products will bond well). Redgard can be used over the concrete, as can any other flooring membrane like ditra, which has cavities below it to dissipate moisture in the concrete if negative hydrostatic pressure is one of the issues with your slab.

  • Beverly Wright

    After my custom sized river rock shower floor had to be removed because the rubber underlayment was improperly installed, I decided to go with Ditra. However, like your article says, some of the grout began breaking away almost immediately and some of the tiles (inexpensive 12″ octagonal tile sheets from Home Depot) began chipping, and I could hear the floor creaking. I told the contractor and they picked up the broken tile and regrouted. Problem recurred. Clearly, there are gaps under the tile causing the grout to break off. I have forwarded your article to my contractor, who put Ditra in his own house so he should have known how to install it. However, his “guy” did the work, so I now need the solution and I don’t think or want it to be done piecemeal again, although most of the chipping is only around the drain. If I were to remove this flooring, what else do I need to know? Is it just a matter of properly refilling the existing cavities? Do I need more waterproofing material? Should I use larger tiles or is that not relevant? I have attached some photos, the darker areas between the tiles are where the grout came up. Thanks.

    • Beverly Wright

      I used a Schluter-Kerdi shower kit. Is that the same as Ditra?

      • Roger

        Hi Beverly,

        No, it is not the same as ditra. And ditra is not what should be used in a shower floor, kerdi is. Ditra is a flooring membrane, kerdi is a shower membrane. Ditra is not waterproof (although it can be made so) and it does not conform to slopes well. Whatever ‘guy’ installed this in your shower floor had no idea what the hell he was doing. The shower kit floor should have been covered with kerdi, if he covered it with ditra instead then your shower is not waterproof and it is likely leaking around the drain.

        • Beverly Wright

          Roger, thanks for your reply. My contractor used the kerdi floor shower membrane so I think we’re OK with that part. I was mistaken and thought it was ditra and only realized there was a difference reading one of your other posts that talked about ditra and cracking grout. So the shower is waterproof but there is still a problem if the grout is cracking and the floor creaking. So I’m guessing that the installation issue may be the same with kerdi as with ditra? I’ll respond to your second reply separately. Thanks for the clarification!

    • Beverly Wright

      Roger, I’ve read all the other posts but still don’t see a reply that seems to fit my situation. My floor is creaking and grout and tiles nearest the drain are chipping, clearly installed improperly, even after initial repair to pull up chipped tiles. (1) If the grout is not cracking in some areas, are those areas OK? (2) if the entire tile floor is pulled up to start again, do I need another roll of waterproofing paper or can thinset be reapplied over existing paper to ensure a better waffle fill with the correct tool? (3) my original tiles are small 1″ octagons – would larger tiles be subject to less movement or is that irrelevant if installed correctly?

      • Roger

        Hi Beverly,

        I answered your question above. Sorry for the delay on the initial answer, but it remains the same. Also, not mentioned (I don’t think) in your last comment is that the octagons are 1″, the minimum allowable tile size over ditra (even in a proper installation application, which this is not) is 2″ square. So it’s obvious whoever installed this has no idea what he’s doing.

        • Beverly Wright

          Roger – since kerdi was installed as it should have been and not ditra ( my error), does the minimum tile size apply to kerdi as well? I think that he knew how to install the membrane because he installed it in his own house, but he may not have known that the tiles I selected were too small. I don’t recall anything in the kerdi literature about tile size, but maybe I missed it. I’m just glad to know that a larger tile may solve the problem. Do I need to buy a new roll of membrane if we pull up the small tiles?

          • Roger

            No, the size limitation does not exist for kerdi. The issue is likely the bond of the pan itself to the substrate. Around the drain a lot of times the subfloor is cut out in a very large circle. This needs to be repaired before the pan is installed, otherwise for about 4-5 inches around the drain there is no substrate supporting the pan. That is also the thinnest part of the pan (since it’s the lowest part of the pan). That could be the issue. Or simply improper bonding of the pan to the substrate. It has to be a modified mortar, he may have used an unmodified.

            • Beverly Wright

              Roger, OK re no tile size limitation for kerdi. Thanks for your explanation of the pan and substrate. I’m attaching a photo of the plywood substrate after the old river rock was removed, the floor cleaned and before the kerdi was installed. It looks to be cut as close to the drain as possible. I am also sending a photo of the kerdi laid down before the membrane was put on and it looks like it should be ok. I don’t know about the mortar used. I appreciate you sticking with me on this. Maybe you’ll see something in the photos.

              • Beverly Wright

                a second photo of the kerdi in place before the membrane installed.

                • Beverly Wright

                  not sure if the second photo got sent – kerdi pan in place before membrane installed.

                  • Roger

                    I don’t see any photos at all. Can you send them to and I’ll take a look.

                    • Roger

                      In the second group of photos in the pdf, the photos entitled ‘fitting the new drain to existing pipe’, you can see the hole cut for the drain. It is EASILY 10″ round. The hole in the subfloor for the pipe should be a maximum of 3″ or so. You can see in the first photo you sent me the 2×4 under the far side of the pan at the drain hole, not even a joist since it’s oriented incorrectly, and it is sitting 3/4″ below your pan. This means that there is zero support beneath the pan at the drain for at least the size of that hole.
                      I also see no mortar beneath the pan, although there may simply not be a photo of the pan actually being installed. There is no support beneath your drain, that is obvious by the first photo in addition to the photo of the cut subfloor in the pdf. There needs to be full support beneath that drain – you have none.

  • Leandra

    Dear Roger
    I am trying to lay tile on my own in a bathroom on top of a ditra waffle membrane that a contractor has laid down. There are some things that I have noticed and do not know what to do about. Here is the list: 1) There is a pretty large gap around the entire floor where the walls meet the floor. I am assuming this is because the house was built in 1950 and the old tile was on the floor and walls, knocked out of the walls by the contractor [about 1″ thick] to install new sheet rock. The ditra is attached to the ground only and the gap around this Ditra flooring and this wall is pretty wide and deep, causing the ditra to curl a bit. Is this standard practice and how would a tile setting pro deal with it? 2) The contractor who laid the ditra didn’t make it flat leading up to where the toilet will sit. Is that standard practice? If not, how should this be corrected? Also, in the area surrounding the place where the toilet should sit, the Ditra seems to be unattached to the thinset underneath…3) The whole floor has slight undulations in it. Am I supposed to even these out somehow while laying the tile? I’m wondering how to do it since all the troweling videos I watch seem to be on floors that look like they are level. 4) Finally, the tile I am using is a square of very small black and white tiles that look like a weave you might see in a basket [spaces between the tiny pieces]. While researching what to do with the problems above I discovered that this type of tile is not ideal for ditra. Should I just take this Ditra layer off and set the tile on what is underneath it [thinset over concrete]?. Now that the concrete has this thinset on it….Is there any way to get the thinset off this concrete if I need to remove the ditra? WHAT A NIGHTMARE, AHHHH! Thank you so much for your time and for considering my question. Sincerely, Leandra in Memphis, TN

    • Roger

      Hi Leandra,

      Not sure what type of ‘contractor’ installed your ditra, but none of the things you’ve mentioned is correct, except that you can not use that tile over ditra. The minimum allowable size over ditra is 2″ square. Your best bet is to remove the ditra. The thinset can be scraped or abraded off the concrete. Yes, you can install that directly to the concrete.

  • Bob Kuntz

    Hi – I’ve just installed Ditra Heat in my kitchen…approx 150 square feet…using the 39″ x 31″ panels. I followed all instructions after watching videos and reading the install manual several times. My project was 1/2 over cement and 1/2 over 1.5″ of plywood (two 3/4 inch sheets). I used unmodified mortar over the cement and modified over the plywood, per the instructions. (Keraflor and Ultraflex 1). There are several sections near the corners and edges where the Ditra has not bonded to the subfloor, in spite of checking coverage during install, rolling it and “walking” on it to embed it.

    At this point I am planning to go ahead and run the heat cables and tile over it because I have no clue how I would go about trying to “spot” fix places or pull up and re-do while keeping a level surface.

    Any comments or suggestions are apprciated.


    • Roger

      Hi Bob,

      You can cut out any sections that are not fully bonded and reinstall them. The sheets do not have to be full, they can be pieced in as needed.

  • Kim

    This is a great thread! Hoping you’ll have an answer for me. We have MDF in our house as a subflooring. Its 3/4 inch thick, very solid, level and in good condition. Can Ditra be installed on it? I’m concerned about the bond of the thinset to the MDF…
    Thanks much,

    • Roger

      Hi Kim,

      Thinset will not bond to mdf. Well, it will for a couple of weeks…

      You need to put a layer of plywood over that mdf in order to install ditra.

  • Steve


    Putting 6×24 ceramic tile in kitchen and family room and dining room…total of 700 Square Feet. 2x10s with 13′ span and 16″ OC. Subfloor is only 5/8 and has lots of staple holes from hardwood flooring that was removed. Want to beef up the subfloor with a plywood underlayment.

    Initial plan was to add 5/8″ underlayment…then the 1/4″ Durock and then the tile. Worried about height which is why I am leaning towards 5/8″ verse 3/4″.

    1. Do you think the 5/8″ on top of the current 5/8” subfloor is sufficient as the underlayment. I’ve read the article about underlayment that talks about the proper placing of plywood underlayment over plywood subfloor (e.g., don’t attach to joists, etc.).

    2. If I went with Ditra…do I still need Cement Board. If not, is it better to do 3/4″ Underlayment (Plytanium or Sturd-i-floor) over the 5/8” subfloor and then Ditra and then tile? I’m assuming Ditra is the roll of orange underlayment…is that correct?

    Cost is a factor (it’s my daughter’s house)…but still want to do a job that will look professional and last. If you can answer in 2 ways: what will work….and what would you do if this was your house?

    Thank you.

    • Roger

      Hi Steve,

      1. Actually 1/2″ would be sufficient.

      2. If you use ditra then no, the cement board is not necessary. It would be better to do 3/4″, but again – 1/2″ should be sufficient. Yes, it’s the orange underlayment.

      If it were mine I would likely just do 1/2″ ply over the existing 5/8″, then go over that with ditra.

  • Gordon Paul Kipp

    Had a friend put down ditra membrane for me. He has gone home now and I went and lifted a corner of the membrane with one finger about four hours after he set it.
    I don’t want to keep pulling it but I also don’t want to lay any tiles til I am sure the ditra membrane is installed well.

    My questions – can I just pull and see what happens?
    What is the best way to take up the base if it is not adhering to the ditra?
    I have two of your ebooks by the way…good stuff…

    • Roger

      Hi Gordon,

      You need to let the thinset cure. Give it 24 hours, then see how easily it comes up (it should not – at all). Four hours after it’s set it will absolutely peel up because the cement crystals haven’t had enough time to solidify the bond. I don’t understand your question about ‘taking up the base’?

  • Phil

    I had what I thought was a successful Ditra Heat installation. Ditra was adhered to plywood floor using Versabond, then TEC unmodified Thinset (I don’t remember which) to set 24 x 24 inch Crossfield tiles to the Ditra. A year later the floor crunches in a couple of spots. What I suspect is that the Ditra has become unbonded (or perhaps never strongly bonded) with the plywood underneath. There doesn’t seem to be any indication that the tile to Ditra isn’t anything but solid. I suspect the mortar just wasn’t wet enough and got past the “lift test” shown in the install guide.

    Do you know if anyone has tried any remedial actions that don’t involve tearing out the installations? For example I was considering opening a hole in the ceiling below, carefully drilling through the plywood into the bonding layer, and then using concrete crack epoxy injection to bond the back cloth of the Ditra to the substrate.

    Has anyone tried this and is this a valid approach?

    • Roger

      Hi Phil,

      I wouldn’t trust that ‘fix’ at all. If your ditra has indeed become unbonded then replacing it is really the only way to repair it.

  • Bill Neelin

    The subfloor in my bathroom is partially plywood and partially Denshield. I can’t find any info about what thinset to use when attaching ditra heat membrane to the Denshield. Can I use the same thinset over both the plywood and Denshield?

    • Roger

      Hi Bill,

      Yes, you can use modified thinset over both.

  • scott

    I recently had a bathroom floor installed using porcelain tile. The contractor used the Ditra membrane over the wood subfloor. The job was completed in September 2017. At first everything was fine but in the past few weeks I noticed some snapping sounds when I walk on one side of the floor. The tile is intact, the grout is not cracking, but every time I walk in this section you get snapping sounds. Is that movement in the subfloor or is the tile not bonded correctly to the Ditra or is the Ditra not bonded correctly to the sub floor. This does not seem normal to me. Wondering what you think?

    • Roger

      Hi Scott,

      I’m not sure, I’ve never heard a ‘snapping’ sound. It may be your structure. If something in the tile installation were not bonded correctly the grout will eventually begin cracking. Keep an eye on that, it’ll begin coming away from the sides of the tile first.

      • scott

        The sub floor is not plywood. It is plank boards that are typically found in older homes. Does this make a difference?

        • Roger

          He installed the ditra directly over the planks??? Yes, absolutely that is the problem. You can not do that, there needs to be a layer of plywood installed over those planks before the ditra is installed.

  • Hunter Knight

    I am new to tile laying and decided to go with ditra. I found a corner in my laundry room that was not adhered to the plywood floor because I don’t think used enough mortar on that spot. I had used too much the time before, so I think under shoot it. Everything else is sealed tightly to the floor. Should I try to rip it up and start over? I was hoping the weight of the stone and motor would be enough to hold it in place, but I wanted to be sure before I started laying tile.

    • Roger

      Hi Hunter,

      You can just cut that piece out and thinset it down. Ditra can be cut up however you like, it doesn’t need to be a single piece.

  • Angie

    Thank you for the fantastic thread!! I just layed down my first tile job and fairly confident it has failed. I installed ditra over a plywood subfloor with a high quality modified thinset, and prefilled the voids with unmodified thinset. Layed 1 inch mosaic tile sheets ( approved by rep) and let it cure for 2 days. Walked on it for the first time and a whole lot of cracking noises were going on. The floor is quiet now, but I’m worried that it has failed as I’m assuming that’s not normal. Would you recommend grouting and seeing what happens, or ripping out and starting over? So dissapointed!!

    • Angie

      I will also note that the tiles don’t appear to be loose and the floor seems solid.

    • Roger

      Hi Angie,

      If you don’t have any loose tiles I have no idea what the cracking may have been. May as well go ahead and grout it and see what it does, at this point it won’t take any more to rip it out if it’s grouted than it would before it’s grouted.

  • Jeannine


    We have put down Ditra over an OSB subfloor. We checked the subfloor for flatness using a level prior to install. We used the correct size v-notched trowel and Schluter All-Set to put down the Ditra. We also used Kerdiband to seal the joints and the tub. Now that we are prepping for the tile install by first laying the tile to make sure all the cuts are correct. Some of the tiles are wobbly and not completely flat against others. What are our options to make sure we get a proper tile install. Do we need to rip up the whole Ditra? I would be worried then about damaging the subfloor. Most of the tiles that are uneven are on the Kerdiband.

    • Roger

      Hi Jeannine,

      Once you get thinset under that you will be able to level them with one another easily. In the high spots there will be less thinset than the lower spots once you push the tile back and forth to embed it.

  • Peggy Milhous

    We’re remodeling a 3500 sq ft house and using Schluter-Ditra over concrete slab foundation throughout the entire house. The floors had several large cracks as well as cut expansion joints that had also cracked at the bottom of the joints. We pulled out the old membranes that were put in the cracks when we pulled up the old tiles. We also grinded the floors level which increased some of the cracks. We are laying expensive Calacutta marbles throughout the house. Should any of these cracks be filled with anything prior to the Schluter SET unmodified mortar which is going under the Schluter-DITRA? Thx!

    • Roger

      Hi Peggy,

      It would be best to keep the thinset out of those cracks, or it’ll just crack again. Guys use all sorts of things to do that – silicone, expanding foam, tape over them, etc. Doesn’t really matter too much what you use as long as it doesn’t solidify and essentially fill in the cracks with something else that will crack. You absolutely HAVE to run those expansion joints up through the tile with soft joints or all of your expensive marble will crack – right above them.