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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  • David

    I’m in the process of replacing a tub with a walk in shower (no curb in doorway)..I want the shower entrance flush with the main bath floor. The subfloor is 1″osb..I was thinking of cutting out the osb in the proposed shower area and then recess it even with the top of the joists giving me 1″ to play with to get the proper slope. If I use the “goof proof” pre-slope sticks and the usual mortar fill, couldn’t I then use Ditra instead of the second customary mortar fill? It would let me line the floors up without having to drop the joists.
    Seems to me if the Ditra is installed properly and is as waterproof as claimed, my plan should work…?? Thanks for any advice you can offer!

  • Steven Giessler

    I have a new unheated glass enclosed porch over an elevated deck (2 years old) with floor boards of 5/4” pressure treated lumber. Will Ditra work as an underlayment for porcelain tile?

  • Thomas

    I watch your videos all the time and appreciate your work. I have a question before I get started on redoing a bad shower install. There was an area of minor rot on the plywood (OSB) floor in the shower where I plan on installing the Schluter Tray. Specifically. where the curb will meet the tray. When I came across the rot, I dug it out and then filled it with bondo. Now I am worried that this bondo will undermine the thinset from properly adhering to the plywood and Schluter Tray and Ditra floor? I asked another professional and he advised he would dig it out/remove it if I planned on using ditra. I have since removed it and am left with some depressions and gouges that I want to fill but want to use the right products (primer like mapai prim grip, floor patch, self leveling, etc.) that will be compatible with Schlutter All Set. However, no I’m hearing that if I intend on installing marble, I need another layer of at least 3/8 ply on top of the OSB, which would negate repairing the gauges. Do I really need the second layer of ply? I attached a picture so you can see what I am talking about. Please let me know your thoughts. Thanks very much for your time!

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  • Brian

    Hi Roger,

    I am doing a tile install with ditra over plywood sub floor. The plywood sub floor has two coats of KILZ 2 Primer. Can I still use modified thin set to install the ditra?


  • Jeremy

    Just out of curiosity, I have a very old home with original 3″ wide 3/4″ thick T&G wood flooring. I was considering screwing down each piece of flooring into the joists they span, and then using Ditra over the top of that. Is this ill advised? As this home is 110 years old, this is the only flooring, and there is no subfloor beneath. The flooring itself is in decent shape when it comes to bearing loads, but I would prefer tile in the bathrooms and kitchen for obvious reasons. Is ripping up all the old flooring needed, or cement board as opposed to Ditra?

  • 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.