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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  • Shannon

    Great read! Looking for a little advice – my husband installed the ditra paper for the first time. For whatever reason it appears uneven now. Thus will now cause the tiles to be uneven. What’s the best way to fix this?

  • Patric Carstens

    Hey there. After reading everything I’m a little anxious now. I just finished laying 2×2 hex tile (mesh backed) over ditra in a small bathroom. I missed in the ditra instructions and a few videos I watched about ensuring the waffles are 100% full. I’m positive a lot of mine are not full, but I mixed my thinset relatively wet and got a thick bed of it down before pressing the tile in. Assuming I used the correct mortar (recommended to me at the store), and the correct sized trowel comb, how likely would you say I am to have cracking in the near future?

  • Judd King

    I have hardibacker screwed into subfloor according to requirements. I did all of that before I learned about Ditra for heating floor.

    I have peel and stick Ditra to put on top of the hardibacker.

    Does that work?

  • Keith Wallace

    Having issues getting dita to bond to self leveler. I’ve used Schluter allset and mapei uncoupling membrain thin set which was unmodified. The thinset sticks to the self leveler but pulls off the fleece on the ditra when I check a corner the next day. What am I doing wrong? It stuck just fine to the plywood. I sponged everything with water first to make sure it’s clean. I e don’t the job twice and ground and scraped off the old thinset and now at am a loss for how to make it work.

    • thomas

      I had a similar issue. It turned out unmodified Portland Cement takes several days to develop enough strength so that it does not pull off the surface. Give it several says before testing. For me that was 2 days.

      I had a porous Flex Bond base that I set the Ditra on so I wet it 30 minutes prior to applying the unmodified mortar so that the water would not get sucked out stopping the cure.

      There is no rule you have to get it right the first time without experience. Do a sample to test your materials prior to doing a finished job.

  • Sally

    Hello! I am remodeling a small half bath.

    Ripped up linoleum and got all the glue off. It looks like there is a thin layer of thinset still left over the wood and don’t want to remove if I don’t have to. I’ve been told mixed reviews on if I can lay self leveling over the top or not (need to level due to some uneven spots. Can I put self leveling over the top of this thin layer?

    if I can self level over the top of that, I was planning to do the primer then self level.. then the ditra membrane, then penny tiles. I’ve seen others use penny tiles and this is an attractive option because I won’t have to cut anything with a cutter and I think it’s pretty. Any concerns with my approach?

    I’m a total beginner by the way

    Any advice on my planned process?

  • Martin Larsen

    Want to install Ditra heat over plywood
    Contractor wants to use self leveling concrete over plywood first since it is quite uneven. Do we need to treat the plywood before applying self leveling concrete?

  • Ray

    Roger, I enjoyed reading that article. I recently had a concrete patio poured, it is about 520 sq ft, and has four control joints cut into it. I do see a hairline crack in each of the control joints, so they did their job perfectly, there is one section of concrete that also has a hairline crack meandering across it, no control joint unfortunately, and probably should of had one.
    I do plan on covering the patio with porcelain tile.
    in my previous house I redid the kitchen floor and used ditra and porcelain tile as well, which worked out great.
    I was going to use ditra for this application as well, and go right over the control joints with it. can I span the tile over the control joint as well or should the tile stop at this joint? the other crack has no control joint, and is irregular, not sure how that would work avoiding going over the hairline crack.

    and one last question, a hot tub will eventually be placed on this patio, it will weigh in at about 4000 lbs. do you think its okay to place that much weight on the tile with the ditra product between it and the concrete, or might the ditra product compress further and cause the tiles to potentially crack? from your response above it would seem as long as the ditra squares are filled properly it shouldn’t be an issue. I would like to tile the entire patio, but could leave a square of unfinished patio for where the hot tub will eventually go. looking forward to hearing what you have to say on those issues.
    Thanks,
    Ray.

  • Paul

    Just installed Ditra on a bathroom floor. I used the proper Schluter thin set and trowel. The first piece of Ditra I installed may have a less thin set underneath than recommended because of hard to get around plumbing. However, it cannot be lifted so it appears the Ditra is bonded to the floor Should I cut out that area and reinstall Ditra before tiling Great Site,

    • Steve

      Thanks for the great information. I have tiled several times on different substrate but this is only the second time I’ve used Ditra. The first time was a bathrooom on plywood and it was amazing and went great. This time I’m using it in my kitchen. I used a self leveling cement but I’m having a terrible time getting proper coverage. I used the proper sized trowel as per instructions and that wasn’t giving me proper adhesion so I used a bigger trowel and I’m still not getting the coverage when I pull up the Ditra. I’m at a loss and don’t know what’s going on. It has made me go from thinking the product is amazing to disliking it. Your input would be appreciated