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)

{ 2293 comments… add one }

Leave a Comment

  • Sherri

    Hi there, I realize this is an old discussion but your advice seems to be rock solid and we’ll respected. So I hope you don’t mind another question.
    I’m looking to install a few15X25 porcelain tiles at my front door. I’ll be removing some hardwood flooring from that area. Here is what I’ve come up with as a plan, but I’d appreciate a second opinion because I don’t want a DIY disaster.
    My subfloor is 3/4 inch plywood.
    Here is what I am thinking happens next:
    -Ultraflex 2 spread with 1/4 inch square notched trowel.
    -1/2 in Durock board embedded in that, then screwed.
    -Ultraflex 2 applied again, then orange Ditra decoupling membrane.
    -Then more Ultraflex 2 applied with a 1/2 inch square notched trowel.
    -Then the Porcelain tiles.

    Am I way off base?

    I found the shelf of mortars at the hardware store confusing. Should I be buying a different type of mortar for the tiles? I didn’t even see anything called unmodified.

    Thank you.

  • Anthony

    Can you use ready to use Mapei premium mortar to set tile over ditra If so what happens

  • Marby

    Hi Roger,
    I don’t know how old this post is, but have a question – redoing one of our baths, pulled up sheet vinyl to find 1/2″ particleboard over 3/4″ plywood. Planning to install Ditra then 10mm porcelain tile. We removed the particleboard because all info I read was that shouldn’t come anywhere near Ditra. Wondering if we need to add any additional underlayment. We didn’t think so but one friend thought we should put down a layer of Hardie backer. Just thinking with that, Ditra, thinset, then tile would make the floor SO much higher than the floor outside the bath and that it’s probably not needed, but wanted to get another opinion.

  • Joe

    Pulled up my very old kitchen tile and there’s a layer of mortar (trowel marks and all) left behind on the subfloor. Can i lay Ditra over that or do I have to start with a new subfloor? I’d have to rip it all up and install new subflooring if I can’t lay Ditra over it. Thanks!

  • Brian Looney

    Not a contractor, but a customer. Initial Ditra lay down is “bubbling” or buckling in spots, leaving an uneven surface for thin set and tile. Possibilities?