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 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 have a 10 year old home that i pulled some pergo laminate up. There is sheet vinlyn underneath. Its not linoleum. What thinset would bond the ditra? The instructions say use modified thinset. Or should I just put down bakcerboard? First time installing tile, using porcelean.



I’m installing travertine over ditra.after filling the squares completely What is the appropriate towel size?



Hi Roger,

Great site, I learned a lot about tiling and still learning more about it. I’m a new homeowner and starting to do the kitchen floor tiles. I leveled the floor by using a 19/32 plywood on top of the slanted planks. I layed down the Ditra-Heat on top of the plywood using Custom’s Flexbond Crack Prevention Mortar. After reading some of your articles I’m afraid that I might have used the wrong mortar to bond the ditra-heat to the plywood. Please let me know if the Flexbond is good enough that I won’t have to redo anything.



Hi Ferd (?), :D

The flexbond is just fine for that. You don’t have to redo anything.




Your site is amazing! I recently bought a house that I am in the process of renovating. I have become quite the DIYer, but I am a complete newbie to tiling. I am about to do my kitchen floors in 12×24 tiles and have a question about the best installation method. The kitchen has vinyl floors (4 layers of various vintage shades to be exact), and I’m sure at least one of those layers is asbestos. I know the best course of action would be to tear everything up, but that is just not an option for a host of reasons, including prohibitive cost. The floors are not exactly level, but are flat. My question is how best to go about prepping the floor for tiling. My initial thought was to do 1/2 cement board over the vinyl followed by Ditra. Is that overkill? Or would other methods be better? Any advice would be most appreciated!

Thank you for your great advice on this site!



Hi Kait,

I think you’ll be just fine using 1/2 plywood over all the vinyl, screw it down REALLY well, then use ditra over the top.


David Chapman

I just installed ditra for the first time and I am concerned I may have made an error. I checked to ensure the ditra was fully covered by peeling back a corner as suggested. However, my thinset might have been too thick. Once it is cured, is there a way of checking proper bonding before I tile? There are also a couple of small humps. I don’t think they are tall enough to cause lippage though.

If I have mixed the thinset too thick, what do I do now?



Hi David,

If you had full coverage when you peeled it back then it wasn’t too thick. If it is too thick it will not bond to the fleece and there will be no thinset on it when you peel it back. Those little lumps are easily taken care of with the thickness of the thinset beneath the tile as you set it.


doroteo arango

Sr: I want to put 13”x13” ceramic tiles on my old concrete floor in the basement. I have blast shot the entire floor and patched the cracks and voids. However, the floor is uneven and some of the “valleys” are 3/8” deep. The entire floor is 600 sq.ft.
Should I put a self-leveling compound on the entire floor or just screed the self-leveling or other compound ONLY where is needed?
Kind regards



Hi Doroteo,

You can do either. Both will work just fine.



Trying to find a definitive answer on whether we need to use Kerdi band with our ditra on our kitchen floor



Hi Lori,

Only if you want your floor to be completely waterproof. It isn’t required.



Thank you. I planned to put down 1/4 hardibacker 500 on top of the 3/4 osb subfloor not plywood. unless there was a good reason you mentioned 3/8 plywood instead of OSB…

Plywood within 3 galaxies of water gives me the heebie jeebies.

That’s what I used in the other bathroom (non ditra install) and it has held up great for14 years. (you mentioned plywood).


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