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)

{ 2354 comments… add one }

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  • Mark Hawes

    I need to know if I should fill in the waffles, float flat, then let dry before tiling or fill the waffles at the time of tiling?. There seems to be an equal distribution online between the two camps and they each defend it like a religion.

    Reply
  • anny

    I would like to tile over a basement floor.
    I saw in a schluter company video that their shower product has ditra over kerdi shower trays, which are polystyrene.
    My question is:
    Can I put polystyrene or other panel insulation, then the “correct” thinset, then ditra, etc?
    Meaning will ditra allow me to tile over insulation without a hard surface to adhere to?

    Reply
  • Melanie

    What is the best way to level a concrete substrate before applying ditra?

    Reply
  • Lance Kirk

    Roger,
    Second question: I installed Ditra yesterday, and when I looked at it this morning, I noticed about 8 or 9 “pancake” lumps, about 1/16 – 1/8 inch in height, maybe about 2-4 inches in diameter. I’m laying large format tile, with 1/2-inch trowel. Should I cut out those pancakes and painstakingly insert new Ditra, or will the thin-set, with large trowel, allow me to compensate. [BTW – mistake was going in a forward direction with the installation, with a large sheet which hid the pancakes – poor troweling on my part…never had a problem wokring backwards with everything in full sight.]
    Thanks
    Lance

    Reply
  • Lance Kirk

    Hi Roger,
    Is it better to fill in the waffles with one application of thin-set, let it dry, then apply the notched layer, or is it better to do both at the same time. I’ve seen mixed recommendations. The last application for me went fine, as I did them both in ne application, but more recently, I saw a professional recommend two separate applications. Thank you !
    Lance

    Reply
  • Isabel Ryan

    Hi, I just tried putting down the Ditra, and I think I put too much thin-set (how am I supposed to know??!) it was very stressful. So since I think I had too much thinset and The Ditra looked bubbly and uneven I used my rubber float to push out as much thinset as possible. I think I pushed too hard and damaged the squares of the Ditra….is that possible?? Some are dented. I weigh 100lbs so I’m pretty small but strong, do you think it will be ok??

    Reply
  • Don

    Hello I am going to be installing prodeso mat and tile in upcoming weeks. I had done a small bathroom remodel and used 3/4 GP dryply for flooring old osb had rotted. It has some sort of wax on it for waterproofing during new builds. Will the thinset adhere to this dryply. I call GP and they said it probably wont and sanding the dryply first may help.

    Reply
  • Sabrina

    Hi Roger,
    My husband and I have recently installed Ditra on top of level plywood. We spent yesterday dry fitting the tile to install soon (12″ x 24″). However, I am concerned after spending hours dry fitting the tile over the installed Ditra, I noticed that there are lumps UNDER the Ditra. We went through great pains to install it correctly: modified mortar, 5/32″ grooved trowel, mortar sticking evenly to the Ditra, grout float over the Ditra to get it all even. I measured the spot that seems to be the worst hill–>valley and it is 6/32″, so a bit over 1/8″. My understanding is that the next layer of mortar should be about 1/8″ which would hopefully even it all out? I guess I’m worried that the mortar layer under the tile won’t be enough to even it out because I broke a tile by leaning on it when we were dry fitting….that how we discovered the bump. I would love to know what you think we should do. I’d hate to put the tile down and then have it crack, that would be heartbreaking….tiling is such hard work!

    Reply
  • Daniel Foley

    Hi Roger,

    I laid down the Ditra and I thought it was pretty level when going through it with a level but now that I have cut and dry fit the tiles (12″ X 24″) I am noticing more than 1/8 of an inch give in a couple areas. Am I able to pour SLC or a Self Leveling Underlayment over the Ditra Membrane to get it more level and then install the tile over that? Schluter says no but it seems in some of your comments below that it may be possible. Is there a best SLC or SLU to utilize? Or would it make more sense to rip up the Ditra, pour the SLC and then buy some new Ditra and reinstall?

    Thanks and really appreciate the content for DIY!

    Reply
  • Peggy

    I have a 14x 14 screened porch with a concrete base. I’m using 24” square tiles. The floor is relatively level but there is an area that has a slight dip in it. Is it possible to use a floor leveler under ditra? Thanks!

    Reply
  • Kosta Stavrianeas

    I used Ditra for first time and unfortunately had a hard time putting it down. I think my trowel is too big and too much thinset. It left me with some bumps on the first sheet. I realized the problem later and started using a roller to get the excess out but I’m wondering if I should take the first sheet out. I’m putting down 24 x 24 tiles so maybe I can get away with it with sufficient thinset and those levelers, but wondering what you would do in this case. Thank you kindly!

    Reply
    • Isabel Ryan

      I had the same problem! It was so stressful. I pushed out so much thin-set I think I damaged the little squares. I just payed one sheet and let it for now for my dad to inspect because I’m afraid I ruined it. I hope yours turned out ok!

      Reply
      • Kosta Stavrianeas

        I took it out completely and put it down with the right trowel and it was perfect. Because the mortar had not dried, I was able to get it out fairly easily. I also power washed the Ditra and it became like new. Just make sure to let it dry well if you do that.

        Reply
  • Daniel L Whatley

    Hey Roger, I’m putting .59″ porcelain tiles in my kitchen. There is a 1×8 plank subfloor in generally solid shape perpendicular to joists spaced 24″ apart. I will patch with plywood where it’s needed and reinforce the rest with ring shanks. I’d like to keep the overall thickness as close to 3/4″ as possible, so what I was thinking after that was 3/8″ plywood and Ditra. After tiles, that would put me at about an inch. Does this seem like a good plan or would you suggest any alternatives landing at a similar thickness?

    Reply
  • Peter Edwards

    Before putting down ditra do I need to scrape the latex paint overspray off the concrete subfloor?

    Reply
  • Christopher

    Can I reuse Ditra if it pulls up ok ? I used the wrong thinset and would like to redo it but it’s already cured

    Reply
  • Don Bell

    Liked you analysis/diagnosis of failed installations.
    About to tile a concrete floor in the basement of a home. Plan to use Ditra mat which I’ve laid several times before. My only question is do I need to necessarily ‘prime’ the concrete, before then using Thinset into which to embed the Ditra mat. Or, is priming of the concrete substrate unnecessary

    Thanks.
    Don Bell
    Denver, Co.

    Reply
    • Nickolyn ritz

      I have a bathroom that is 4×9 give or take a couple inches my sub floor is 1/2 inch real wood with plywood on top screwed and glued I am going to put down ditra long ways because plywood is running the other way so no one will be walking on the seam so do I have to tape the seam.

      Reply
  • Kevin Caldwell

    Hi,

    I am installing ditra and have attached it to the sub floor and half of the kitchen floor is tiled. However, when I finished for the day I spread thin set mortor onto the top of the remaining ditra and its now dry. So when I lay the remaining tile in two days will the wet thin set mortor back buttered on the tiles adhere to the dry thins set mortor that is already on the ditra? Could there be an adhesion issue?

    Reply
  • Josh

    Hello Roger, i am laying ditra over an bathroom osb floor , then tile. Should i use wonderboard or just modified thinset the ditra to subfloor then unmodofied the tile?

    Reply
    • Roger

      Hi Josh,

      Just a good modified over the osb then an unmodified over the ditra under the tile.

      Reply
  • Kelly

    I know this is an old thread but wondering why premixed mortar is not recommended? Also wondering if after installing the membrane , should I wait 24 hrs before installing the tile.

    Reply
    • Roger

      Hi Kelly,

      Because premixed ‘mortar’ is not actually mortar at all, it’s mastic with sand in it (to diminish shrinking). It CAN NOT be used over a membrane. The premixed products ALL require air to fully cure. Placing it between a membrane and a large tile, or between a subfloor or slab and the membrane, is just like placing the lid back on the bucket – it will never fully cure. You HAVE to use a powdered mortar that you mix with water.

      Reply
      • Kelly

        Thank you so much for your response. I have all my Ditra pieces cut n was getting ready to start. I’m assuming that I have to wait 24hrs for it to dry before doing the tiles? Sorry I’m new at this , I have only done a bathroom floor before.

        Reply
        • Roger

          Sorry, missed that part. You can tile over it immediately, no need to wait.

          Reply
          • Kelly

            Thank you for your help Roger

            Reply
  • Al

    What is a good way to level a concrete floor prior to installing Ditra? Previously the room had carpet.

    Reply
    • Roger

      Hi Al,

      Self-leveing cement, or SLC is the fastest and easiest. Depending on how out-of-level it is you may be able to do it with thinset beneath the ditra by using a large enough trowel and smoothing the ditra out with your level, once cured it should be level.

      Reply
      • Al

        Thanks. Is SLC something you can use over an entire house? Also would you recut the sawed in control joints after using a leveling cement?

        Reply
        • Roger

          Yes, and yes.

          Reply
  • David

    Hi Roger

    If I prefill dita cells, should I use modified or unmodified mortar to set tiles?

    Reply
    • Roger

      Hi David,

      If you’re concerned about the warranty you need to use unmodified for both. If you aren’t concerned about the warranty you can use either. I normally use modified (don’t tell schluter…). If you use modified give it an extra day to cure before grouting.

      Reply
  • Scott

    Roger, I just finished a recessed (curbless) Kerdiboard shower with Kerdi tray that slopes down from the entrance to a Kerdi-line linear drain at the wall. Next up is a waterproof bathroom floor using Ditra. The question I hope you can help with is about the transition from Ditra to the Kerdi shower tray.

    Are there issues overlapping the Ditra floor membrane a few inches onto the top of the shower tray?

    Kerdi instructions show butting the Ditra right to the edge of the tray and overlapping both with Kerdi-band. With that, it seems to me that the Kerdi band is decoupling the subfloor from the tray, not the Ditra.

    I will run the same 12×24 tiles from the floor, into the shower, The finished tray is about 1/8” lower than the subfloor where they meet at the entrance.

    Reply
    • Roger

      Hey Scott,

      There is no issue at all running it into the pan. For clarification, though, the kerdi-band is placed there in order to waterproof the transition only, it doesn’t uncouple anything.

      Reply
      • Scott

        Thanks for reply Roger!

        I understand your point about waterproofing with the Kerdi-band at the shower entrance transition. I was thinking that with large format tile running over the transition, using ditra to decouple possible movement between the subfloor and the Kerdi tray would be important.

        I will go ahead and overlap the Ditra over the transition joint. If I overlap the Ditra 2 or 3 inches onto Kerdi tray with thinset, would it still be best to also use Kerdi band on top?

        Reply
        • Roger

          I would, just to have a completely waterproof transition. Ditra is waterproof, but the cavities filled with thinset will absorb and hold water. I like to eliminate that where I can.

          Reply
  • Tau

    Hi Roger,

    Ditra install question… nuHeat may has been installed and now requires a skim coat of thinset over it before tiling. I will be installing Ditra, and wonder 1) if the thinset to install the Ditra is sufficient as also the skim coat to protect the heat may; and 2) to avoid nicking a wire with a trowel, is it possible to apply thinset to the back of the Ditra, then lay it over the dry heat may? (of course weight is an issue the consider). Thanks.

    Reply
    • Roger

      Hi Tau,

      Yes, the thinset you use for ditra will be fine. Trowelling the thinset to the back of the ditra is not a good idea, it’ll be a mess! They make plastic trowels you can use over the wires that will not nick them. If you pay attention while you’re doing it the metal trowels work fine – those cables are a LOT tougher than you may think.

      Reply