Effects of Improper Ditra Installation

by Roger

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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I recently moved into a block foundation house (~1930s) in London, Ontario. The walls are lined with Ditra, which diverts moisture from the block foundation into a weeping tile system below the concrete floor that goes to the sump pump. From what I can tell, the system works decently well, though I am noticing in a few places around the basement that there are moist areas (sometimes a small amount of actual water accumulation, as well) where the concrete floor meets the Ditra. I am guessing this is a result of times when the water accumulation is too much for the weeping tile to handle? Regardless, what can I do about this? Put some sort of sealant where the the Ditra meets the floor? Is this bound to fail? Thanks!



I’m wanting to install porcelain tile in my bathroom and the current subfloor is gypcrete. Can I still use ditra? Will thinset adhere?

Side note (not at important at question 1) I’ve heard of people tiling over Mapei Mapelastic AquaDefense membrane. Do you have insight into this product?


Bill V

I have a question, my contractor used unmodified thinset between my plywood subfloor and the Ditra membrane. I noticed prior to tile inttallation and had him pull up the Ditra and scrape off the thinset. Hewould of course like to reuse the Ditra membrane. The felt is intact although feels stiffer then new. Our tile will be natural stone in sizes from 24×16 16×16, 8×16 and 8×8. Can I allow reuse or must I insist on new Ditra? We are doing a kitchen, a out 300 sq ft so the membrane cost would be significant.



Hi Bill,

It can be reused.


Joe P.

I plan to put Porcelain Tile in a 40 ft. Diesel Pusher Motorhome over plywood after installing Ditra Heat. What should I use for thinset to apply the Ditra pad to the plywood and what should I use between the Ditra and the Porcelain tile. I plan to use Reflective Premix Urethane grout.




Hi Joe,

A good modified thinset like Mapei ultraflex 2 or laticrete 253 for the mat to the ply, then a good unmodified like Laticrete 317 between the mat and the tile and you’ll be good to go. I would call the tech line and make sure their urethane grout can be used over heated floors – some can’t.


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