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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Victoria

I have an embarrassing question…. i’ve tiled before but this is my first floor. It’s a powder room, 8’x3′, on a wood sub floor. I’ve removed the linoleum, but there is a little paper/glue still remaining on the 5/8′ plywood. The linoleum was glued evenly under the whole floor (not just the perimeter). I have a heat gun and a floor scraper, but I don’t want to accidentally “eat into” the plywood. I don’t own the tools to cut plywood, so I was hoping to clean up the plywood. I’ve had read that the old glue absolutely has to be removed as it can ruin future flooring installations. After all that, here’s my stupid question: can you confirm that I must remove all old glue before using Schluter?? Thanks!

Reply

Roger

Hi Victoria,

Unfortunately yes, you must remove it. Try laying a really wet towel over those spots overnight, then it should just scrape right up fairly easily the next morning. Most of that glue is water-soluble.

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Joe

We are planning on converting a living area with old hardwood flooring into a bedroom and bath, and want to tile the bathroom. We also want to use radiant heat under the tile. Can Ditra be placed on top of the hardwood flooring and radiant heat mat, or should we consider another base for the tile?

Reply

Roger

Hi Joe,

It can not go over the hardwood. You need to either remove the hardwood or go over the hardwood with plywood or backer first.

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mom of 2

Hello. We purchased a home from the 1980’s and it has k-3 particle boards covered by linoleum in the bathrooms as well as the kitchen. In that situation, are you able to put Ditra over top of the linoleum (some sites say that is ok), or must it be ripped up and a new subfloor installed?

Reply

Roger

Hi Mom (mom…is that you? :D ),

ALL particle board needs to be removed and a proper plywood substrate needs to be installed. Sorry, I know that’s not what you wanted to read. Put those kids to work!

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Leah

We just installed Ditra over plywood in the kitchen and have tiled half of that area as of today. We also installed Ditra in the bathroom over a combination of existing tile and plywood that we leveled with floor stone but have not installed tile in there yet. For both areas, we used UNmodified mortar to set the Ditra in. I read the manual again because of some conflicting advice we received from two different stores, and I am really concerned that the mortar was not the right kind in at least the kitchen, if not both areas. Please tell me we don’t have to pull it up…. or that we can salvage it somehow. What are the consequences of leaving it down? Modified is suggested for plywood, but is it absolutely required? It says nothing about existing tile as the substrate. Thanks!

Reply

Roger

Hi Leah,

According to schluter yes, modified is required over plywood. In reality you should be fine provided you have a sturdy enough floor and the proper deflection ratio. Over tile you should have used a modified thinset approved for use of tile over tile. IF you scarified the surface of the existing tile you should be just fine there as well. I have no idea what ‘leveled with floor stone’ means?

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joshua

I am about to lay Ditra heat in a bathroom 5 x 6 that has a small hump in the center of the room approx 1/4 inch. what is your suggestion for how to level this and is leveling needed. it has a 3/4 plywood subfloor and I’m going to lay 13 x 13 tile.

Reply

Roger

Hi Joshua,

Yes, it needs to be flattened. You can either sand down that area, use self-leveling cement, or use a larger trowel on the rest of the area when you install backerboard. If you do the latter comb out your thinset, leaving it nearly non-existent over that area, lay the backer into it and flatten with a straight-edge, let the thinset cure, then screw it down. You can do the same with ditra (no screws :D ).

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Brent

Thanks for sharing your vast knowledge with the DIY’ers. I have installed ditra heat as my substrate and put my heating wire in. Do you recommend filling the waffles with thin set, “in every direction”, one day then laying tile or doing both steps at once? Your tiling guides are worth every penny. Thanks again.

Reply

Roger

Hi Brent,

Whichever works best for your timeline it fine. If you aren’t going to be able to install all the tile in one day I would fill the waffles first, then you can walk and work over it without worrying about damaging anything.

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Ed

Tile on a covered porch: my installer doesn’t want to use schluter saying that tiles are more likely to break vs backer board. Is this true?

Reply

Roger

Hi Ed,

It depends on your freeze/thaw conditions. Water can get into the cavities of the ditra and, if it freezes, may compromise the bond. So he is correct depending on your climate. Backer would work better in that situation.

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Dave

I have a small hall bath, approx 5’x8′, just torn down to the subfloor after uncovering a water leak. Subfloor is 3/4 plywood, and still in good shape. What is benefit to using Ditra vs. Hardiboard as underlayment for 12×24 porcelain tiles in this setting? Thanks for being super cool!

Reply

Roger

Hey Dave,

Ditra is less height, gives a better separation between structure movement and the tile, allows vapor dissipation under the channels below the membrane (more for installation over concrete than wood). There are other minor ones, but those are the main points.

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Adriane

What are your thoughts on mosaic penny tile with Ditra? I am doing a tiny bathroom reno myself and although I told them what I was using, the tile store guys didn’t mention the size of my tile being a bad choice for Ditra. I hate to return it but I don’t want to replace this floor in a year… Thank you so much for such an amazing site!

Reply

Roger

Hi Adriane,

I would not use penny rounds on ditra, it could definitely cause a problem. Schluter doesn’t want anything under 2″ square over it. I would change to a backerboard or change your tile.

And I know that isn’t what you wanted to hear. Sorry.

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Lance

I am the owner of an old house with 2 layers of 5/8 OSB and a layer of 1/2 cement board. The cement board has been painted over (that is another story) i can rough it up some with a sander if necessary. What type of thin-set should I use from that to the ditra? Any advice would be welcomed.

Reply

Roger

Hey Lance,

You can rough it up with a belt sander and use a good modified thinset to install the ditra to it.

Reply

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