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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  • Craig Bugden

    Hi Jay, I have just removed the linoleum from the bathroom floor, in prep for putting down Ditra. The lino was old and did not come away cleanly (from the 3/4″ plywood subfloor), so there is a fair bit of the cardboard backing left on the floor. I was planning to sand it down a good deal, then deal with any patches of adhesive by using Ecoprim (great product with which I’m quite familiar) over the whole subfloor. My question is — will I use the same unmodified mortar over the Ecoprim, to attach the Ditra, as if I were attaching straight to clean subfloor?
    Thanks in advance for your help. Cheers, Craig

    Reply
  • Demian Ginther

    I’m installing Ditra-heat in my bathroom, the floor _was_ 3/4 planking diagonally over 16 OC joists. Part of the floor was damaged so those areas have been replaced with 23/32 ply. There is a slight difference in height between the ply and the planks and I am concerned about that. My other question is can I install the ditra-heat over the planking, or am I going to need to put another layer of ply over the entire room, and if so, what thickness should I lay down? Thanks!

    Reply
  • alan Shearer

    Hello Elf
    Putting down 12x 12 ceramic tile in a customers kitchen floor with Ditra and wanted to get consistent tile level close to adjoining hardwood floor so I pulled off floating click floor then pulled up 3/4″ underlayment with 2-3 layers of linoleum and found flimsy 1/2″ subfloor. That’s a first. Thinking of troweling subfloor adhesive onto the subfloor, underneath a nailed off new layer of 1/4″ plywood then Ditra (Ditra XL might add strength but I’ll be losing my height minimization which is why I started this in first place). Or maybe I should do 3/8 approved underlayment ply and just glue it down with tubes and caulk gun and nail it off then use standard Ditra and sacrifice a little bit of height. What do you think?

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