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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Jackie

Hello,
I’ll try to keep this short… My Dad and I decided to repair and replace a bathroom floor in a rental house he has. Everything was going well, we ripped out the old flooring, fixed the subfloor and were ready to tile. We used the Ditra uncoupling membrane and laid it down with a modified mortar. It looked pretty good except for a couple small spots that might have had too much mortar (maybe you can tell me if that could be a problem too). We had all the tile cut and mapped out and started near the toilet. I tried to fill in the membrane best I could and only occasionally would some of the mortar pull up when I was troweling. Anyway, one of our tiles was cut wrong and it was almost 10pm (there are tenants), my Dad had a slight break down and we couldn’t finish the job. We had to take up the few tiles we laid and scrape up as much mortar as we could. So we called it a night and now probably ruined a good section of Ditra. My question is can we mortar over the semi filled and dry mortar over-top the Ditra, or are we S.O.L? If we cannot, how difficult will it be to rip up Ditra and scrape the modified mortar? I am going on a trip this weekend and can’t help him anymore, and because of the tenants we are on a semi time crunch. I was thinking sheet vinyl may be our next option… We tried to do too much in too little time..

Thanks for your time in reading this.

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Mark

Read the article and photos you provided, probably prevented me from not checking if I was correctly filling the voids. Thanks

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Ron

I removed tile in our bathroom and DITRA was used under the tile. The DITRA is sill attached to the floor. Some of the waffle squares are void and some still contain mortar. Can you tile over the old DITRA or is it best to remove it and start anew? If it needs to be removed what is the best way to do that? It is on a wood subfloor.

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Paul

Dear Mr. Elf
I am about to tile a covers screened in porch in northern Ohio. The base that had carpet over it is mortared stone and brick. I plan to fill low spots (not many) with vinyl concrete patch then put down Ditra then tile. What are your thoughts thanks!

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Paul

I am tiling an covered screened in porch. aproximatly 85+ years old had carpeting over it underneath is mortared stone with some brick. Oh also in northern Ohio. My plan is fill any low spots with a vinyl concrete patch cover with Ditra then tile.
Well what are your thoughts?

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Louie

Question I’m redoing my bathroom old floor tile is loose someone suggested I just retile over the old base and not rip it up to the plywood my gut says rip it all up put down ditra and lay tile your thoughts.

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Mike

Can I install 2″ hexagon mosaic tile on top of Ditra material.

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Mike

Hi I am tiling a dining room and kitchen. Floor is concrete sub floor. I pulled up old tile so concrete has some old laminar to and tile adhesive on it from the past 30 years so it’s not brand new slab concrete. I have bags of set poly modified mortar in garage. Can I use that to adhere ditra to concrete. I know u should uses unmodified but it isn’t completely clean concrete and I have the bags laying around already. I’ll use the unmodified for tile to ditra then?

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Mike

Sorry I have bags of the PM poly modified laying around. Can I use that to adhere ditra to old concrete.

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Melanie

Hi – we are replacing our bathroom floor. It had Ditra on it and we pulled it up to start fresh with new Ditra. The fuzzy membrane is still on the floor on top of the old mortar. The surface is very even and flat. Can we just apply the mortar on top of it?

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Steve

Hello Roger, love your post!! Is it mandatory to have 2 layers of plywood subfloor for marble tile? I am using Ditra for heated floor + the floor is only 5×7 with solid blocking and 23/32 plywood. If I add a layer I have a bathroom floor that will be much higher then the bedroom wood floor.

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Amanda

Roger,

My husband and I are finishing our Reno, but are having a hard time figuring out if we use Ditra or cement board for our bathroom subfloor for our porcelain tiles. Then the very confusing question would be… which thin set do we use if we do either situation?

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Thom

Ditra Failure

This is my first experience with putting down Ditra. I did 5 tests in small pieces before putting the Ditra down.

The installation is over radiant cable set in modified mortar (Flexbond). During tests that were failing I found a video (https://www.youtube.com/watch?v=UTXtd1iEV5s) that said to dampen the surface prior to setting on concrete. Damping the base and back buttering was the only test that worked.

I water misted the base with a hand sprayer and let it set while mixing mortar. I checked to make sure there was no beaded water and blotted. I mixed thin set (Ditra-set) to the proportions on the bag and then added water to get it fluid like the video indicates. I didn’t back butter the Ditra on the installation – and not sure how I could do that. When I pulled up a corner there was mortar attached to the felt.

The Ditra came off with the same adhesion as scotch tape … like my failed tests. The unmodified mortar is firmly adhered to the modified base. There is very little mortar attachment to the felt. In the test that worked the felt stuck to the mortar and tore from the waffled plastic.

Obviously something is wrong. I have set brick and quarry tile and from that I’d say the unmodified mortar is not “soaking” into the felt like mortar would act on a hard brick and/or it is drying too fast at the face of the felt.

The mortar was stuck to the Ditra at the corners I pulled up.
How wet is wet in mixing the thin-set? I had it so it would “glop” off the trowel. It was much wetter than what I would use for brick. It was most like whipped cream.
I’m thinking the felt needs to be dampened … which is nowhere suggested.

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Thom

Update:
It seems my test failures were due to believing the Ditra-set curing time instructions to be 12 hours. This was substantiated by my tests. But at 24 hours the fleece is tearing off the back of the plastic waffle sheet. So there is other chemistry happening over time.

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Cotter Sayre

Rog (too informal?),

Love your site!
As a person who knows just enough to hurt himself, I have a question. I have laid down about five tile floors directly on concrete without a problem. But while researching the installation of ceramic tile onto my concrete bathroom floor (which now, unsurprisingly, looks like a wood parquet ocean during a major storm [after a minor plumbing hot water leak], I’m only now hearing about this new “Ditra membrane” crap.
Can’t I just do as I have always done, (i.e., Pull the old tile, scrape/clean the concrete floor, trowel on the mastic, push down on the tiles, apply the grout and sealer, and walk away like a stud into the sunset? :rockon: )
Any downsides that I never noticed with my prior installations?
Thanks Roger!

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David DeMartini

We have purchased uncoupling mortar for this job as well as modified thinset. Which one goes on the bottom and which one fills the waffles and sets the tile? Or have we made a mistake somewhere along the way. The job is approximately 400 square feet and we can’t afford to do it twice. Thank you for any help!!
David

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Roger

Hi David,

If you are going over a concrete substrate you use unmodified thinset for both over and under the ditra. If you are going over a wooden substrate you will use modified thinset beneath the ditra and unmodified thinset between the ditra and tile.

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Kathy

I pulled up old linoleum….some of the paper backing is still stuck to the floor in some places….it is over plywood…..will the ditra adhere to that ok?

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Roger

Hi Kathy,

Ditra doesn’t adhere to anything, it depends on the thinset you use. It is ALWAYS best to get as much off as you can. An orbital sander normally makes quick work of that leftover paper.

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