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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  • Greg Hammock

    As part of a bathroom demo I’m tiling the floor – I’ve removed the old tile down to the 1-inch OSB subfloor which is level and secured. The tile needs to meet up with a wood floor which is approx 3/4 inch above the OSB subfloor. I’ll be putting down mosaic square tile boards and the height of the tile is ~3/16 inch. What do you recommend to raise the subfloor the add’l ~1/2 inch … plywood, backer board? I want to use Ditra for my underlayment which will eat up 1/8 to 3/16 of the gap. Thanks in advance.

  • Rick

    Hello, I’m new yo using Ditra. I was originally going to use wonderboard but got talked into Ditra. Kind of regretting it now. My problem is this, I laid the Ditra down and now there are waves in spots on the Ditra. I’ll admit the mortar was a tad thick, but I made sure to press hard with a wooden float to squeeze it down & out.
    What can I do now? When I place the tile down to check the placement, some hace a slight wobble. Will the tile mortar make up for the wobble if I make sure to back butter the tiles? The tiles are 18×18.
    Thank you

  • Leah

    Hi! First time working with ditra and I noticed today after it dried there are a few spots that move up and down when I step on them? What should I do? I’m using a large format slate tile on top of the ditra.

    I used versabond modified mortar, what did I do wrong?

    Thank you for any advice!!

  • Finley

    Hi, we have a kitchen floor we pulled up that revealed flooring leveler that was spread on top of small tiles possibly asbestos. The tiles came up fine. The Plywood that is left is covered in a black mastic glue we believe. We have tried chemicals, scrappers, a heat gun, and searched all over but made little progress. What’s the easiest way to go about getting it off to lay the ditra? Does it matter?

  • Steve Spenceley

    I am installing 12 x 12 light green marble tile over ditra. What are the acceptable non-modified thinsets to use? I have a home depot 45 miles away, also some flooring stores that sell Schuter Set, I think. What would you recommend?

  • Evan

    My old tile floor isn’t removable as it was installed in an inch of concrete (70s). Can I put ditra heat above the old tiles then retile?

  • Joel

    The subfloors in my home appear to be particle board except in kitchen and bathrooms the used plywood. Can Ditra work over top particle board?

  • Eric Smith

    Hi, had another question. I have a heat vent coming up thru the floor how would you waterproof around it?


  • Eric Smith

    Hi. I am doing a bathroom reno. Replacing vinyl flooring with tile. I want to use Ditra for waterproofing. Found K3/particle board under the flooring. It has been removed and what is remaining is 3/4 OSB. The K3/particle board was glued and over stapled. When removing the K3/particle board some of the top layer of the OSB came off so the floor is not 100% level. How or when should you level the floor? Use self leveling on top of the Ditra? Also there seems to be some adhesive from the K3/particleboard on the OSB does it need to be removed and if so how?

    Thanks Eric

  • William D Parsons

    Nice presentation regarding Ditra, thanks.

  • John Z.

    I plan to install Ditra Heat in a room with wood floors that were covered with asbestos tiles. Can I attach the Ditra Heat mat directly to the asbestos tiles with quick setting modified mortar, or do I need to install plywood first? Thanks!

  • Mark

    after installing ditra on floor, can you fill all the waffle holes on top, and allow to dry before installing tiles. I feel this would be better than to try to do it in conjunction with laying the tile, given the shorter open time of the mortar

  • LaNell

    Tiling over pre existing tile over slab.
    Attaching Ditra to tile.