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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  • Robert

    What should I cover my Ditra heat system with before I put my vinyl Looselay planks down? I have been told thin set or just a sand cement mix drypack scratch coat. Can you recommend a particular kind?
    Our Ditra floor system is glued onto cement floor.
    Thank you so much!

  • Donna Berry

    Where to begin…Re Ditra for marble floor: my handyman/friend (who has installed much tile) says:
    1. “You can read me the instructions as we go.”
    2. “Any leveling” of underlayment is not really necessary.”
    3. “I know what I’m doing.” (he’s 64)
    4. “Minimal penetration into joists” of the screws to pass through 2 layers of plywood subfloor – he says “I like to penetrate the joists.”
    5. I have a leak stain in my ceiling under this small bathroom. So re waterproofing he says. “It’s impossible. You can’t waterproof around the toilet and the door entrance.”
    6. “You don’t need movement joints for a small bathroom.”
    I could go on, but…you get the idea.
    I told him to call Schluter. “I don’t want to waste my time.” So…I’m afraid he will not install per specs. He’s stressing me out. He’s an old dog, as others have alluded to. How can I find a qualified contractor? I’ve wasted 3 hours on the phone with this guy plus hours of research on the Ditra product (which I kinda enjoyed). I’ll be doing a total master bath Reno after this one. BTW I’m the customer, a girl, not a contractor. And I have already bought DitraSet from the Internet. I got white because the store said grey would leech into my mostly white marble. Any help much appreciated. Donna B.

  • Kenn Ramage

    Hi Roger,

    Thanks for the great website! I continue to be amazed by guys like you who can conduct business during the day and then then educate others by documenting eveything in great detail at night. It’s a gift!

    I already know the answer by reading the comments on your post, but I’m going to ask again anyway hoping that maybe the planets have aligned and it won’t be a problem.

    I’m a DIY guy doing my first Schuter baths and floors. I made a mistake and used ANSI 118.1 Unmodified thinset (Schluter Set and Mapei Uncoupling membrane thinset) to attached about 200 sq ft of Ditra to a plywood subfloor. To make matters worse I used a 23/32 sanded plywood – with a very smooth finish – for my top layer of subfloor due to its superior flatness.

    I had “unmodified thinset” in my head due to its necessity for the Kerdi and didn’t reread the Schluter information before we proceeded on the Ditra.

    I have two questions:

    1) Are these floors guaranteed to fail? My assumption is the failure will be because the Ditra will simply uncouple from the plywood base since there is no later in the thinset to stick to the wood.

    2) Once we either do it over, or stick with what we have, is it better to fill the squares in the Ditra first, let it cure and them tile over it?

    Thanks in advance for you response.

    • Kenn Ramage

      “Later” was supposed to be “latex”

  • Cheryl

    Help! Installed a Ditra Heated Floor system over concrete floor and then tiled. Not feeling much heat at all. Since been told there are 2 types of Ditra (white back and grey back). I used the white back. Is there anything I can do about this? Or have I wasted a lot of money?