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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  • Sal

    Great site!
    I have a 2″ mortar slab on the second floor over reinforced joists and 3/4″ tongue and groove plywood, glued and screwed. The mortar bed sits on top of a layer of tyvek first, on the plywood, then 1/4″ extruded polystyrene, then 3.4 lb/yard galvanized diamond mesh, then the pex tubing with straps to the plywood. Thus the mortar slab has embedded 1/2″ pex, 8 ” on center, – hydronic radiant heat, to create a thermal slab.
    I want to install 10mm thick porcelain tile on the mortar bed.
    My question, I want to add a layer of crack protection. I looked at Ditra, paint ons (CBP RedGuard, Laticrete Hydroban) and aliphatic membranes, petroleum based membranes like Laticrete’s Fracture Ban.
    I want to keep a close contact between the warm mortar slab and the tile rather than defeat the effect of radiant heat. With that logic, it seems Ditra might not be the best choice. For it to work, as per their own video illustration, it must have some air space between the two surfaces to allow the 1/8″ movement to prevent cracks. This decreases the efficiency of the radiant, albeit small.
    A 40 mil aliphatic membrane worries me, possible release of odors, VOCs, noxious gases AND it decrease the efficiency of the heat transfer from the slab to the tile. It would seem to me, more so than Ditra would. A true contiguous thermal barrier.
    A roll on product, like CBP’s RedGuard, is an elastomeric product, less concern for noxious off gassing, still a contiguous break, but perhaps with a less thermal break.
    What do you think?

    Reply
  • Chris Cornilsen

    I have a question regarding bring up the height of the floor over the Ditra heat before I install the tile. I’m about 1/4” low in the bathroom from matching the height of wood in the adjoining room. (I know a threshold transition could be installed, but owner wants it level). Can I install 1/4” backer board over Ditra heat? Will there be any problems? Wouldn’t it be like having thicker thunder?

    Reply
  • AK

    I installed Ditra on a slab, used correct trowel and thinset type, methods described by Schluter, etc. and now finding many hollow sounding areas where Ditra is not attached (thinset adhered to slab well, just not Ditra). I’m removing them and replacing but wondering what I did wrong. I only did about three or four feet at a time and thought my thinset was sufficiently thin so couldn’t have skimmed over…or could it? Maybe slab was too dry? Used Keraflor unmodified thinset.

    Reply
  • DAN

    What should you do if you are not sure what the thckness of the plywood is on a bathroom floor to be tile using the ditra membrane?

    Reply
  • Paula M Bhagyam

    Help! I removed a tile about 48+ after installing over Ditra. Now in that isolated area I see that the Ditra is loose, maybe because of my removal of the tile. What do I do now, to fix the loose Ditra?

    Reply
  • Bud

    Hi Roger,
    Great info. First time tiling ever. And I’m doing a bathroom floor. I laid the Ditra down. Started tiling and about 1/4 of the way through I realized I was using the wrong trowel. I let the tiles sit overnight and some popped right up. Is it okay to remove the tiles and start over again using the proper size trowel with the same Ditra? I am laying down 6×24 tiles. I used a “V” Notch trowel ( I know, I’m a Idiot). Lesson learned.

    Reply
    • sean

      hey roger
      doing a tile floor on old plank subfloor — can i use 3/4” advantech t & g then ditra? and its a 2nd floor bathroom would you recommend the waterproof membrane under everything?

      Reply
  • Saunby

    I have a 3/4 inch plywood as a floor substrate. I have 16 oc. Joists. Can I use the Ditra right over the plywood or do I need a thicker substrate?

    Reply
  • Jon

    I am installing new ceramic tile in my living room and my contractor who I have since fired did the demolition, took out the old wood floor and put down new plywood and then immediately put down the Ditra membrane heating system on top of the plywood without any self leveller underneath the membrane…. now my membrane has the wire in it and it is stuck to the plywood….the membrane is not even in spots because the floor was not ….can I use self levelling concrete over the membrane ? I know Schluter says you cannot but I have seen it done and I think the only issue is potentially a minimal reduction in heat or longer times to warm up . What say you? I don’t want to have to rip up the membrane and take out the plywood floor and do it all over again but I will if I have to .

    Reply
  • Eric

    We are planning to install 12×24 3/8″ travertine tile in our kitchen and would like to know what the thinnest underlayment we can get away with is.

    Our house is post-and-beam construction: the kitchen subfloor is 2×6 tongue-and-groove pine, which also constitutes the ceiling of the floor below (i.e., we have no enclosed joist space, so the 2F floorboards are the 1F ceiling boards). In the 2F kitchen, these subfloor boards are supported by the 1F interior walls and a single 4×6 pine beam, all parallel and about 48″ on center. I don’t notice any deflection when walking on the exposed subfloor in the kitchen, but that doesn’t mean there’s not some.

    We are looking for a solution that will get the floor and tile flat as well as reduce deflection, without raising the finished floor more than necessary. Since we want radiant heat, we could use Ditra Heat mat (1/4″ thick) which would help with horizontal movement but not vertical deflection.

    With the understanding that the “correct” solution would be to brace the joists from beneath, or glue and screw 1/2″ or 3/4″ plywood on top of the subfloor as an underlayment – in your opinion, could we get away with 1/4″ or 3/8″ ply on top of the subfloor boards? With 1/4″ ply + 1/4″ DITRA mat + 3/8″ tile, we’re already at 7/8″ or more above the subfloor, much higher than the neighboring rooms which have ~1/4″ engineered hardwood. Any suggestions?

    Reply
  • TanToes

    Another photo of shower your advice helped me do. (The counter top is quartz, and I had that made.)

    Reply
  • TanToes

    Hello from the lady in Naples, Fl who gutted and retiled her shower from concrete slab and metal studs out with your advice and info. Otherwise, all by my 122 lb self. Huge thanks. Floating bench, corner shampoo shelf. Direct drain replacing nasty divot thing. Arched niche. Window. Sliding shower bar. I did get carried away. That was besides the gutting/rebuilding rest of master bath. Can I send photos? Fun. But was what the buyer specifically lovvvved about my condo. And paid well for.
    I’m off to a full fledged house now, and it only needs fine tuning. Am I stuck with scraping up a 110 sq ft area of square tile adjoining main part of my master bath, down to slab to ditra before Arabesque (has to match tile shape in adjoining part of bath) tile over it? It’s a half inch lower as is.
    Steps to take? Options?

    Reply
  • Erin Hamilton

    Parts of our ditra heat mat is not sticking to the floor. Not in the entire installment, but around the corners of the mat. Will this cause future problems?

    Reply
  • John

    Roger,
    I have a 5’x10’ upstairs bathroom with 3/4” OSB. The problem is it has an uneven slope in both planes, but parts are level.
    My plan is to use Henry 549 Feather Finish to build up the sloped area and use Ditra for an uncoupling membrane. So part of the OSB would be skim coated with Henry 549, and part would not.
    My question is, what type thinset would I then use to put down the Ditra? Because it would be going down over two different substrates, OSB and Cement based Henry.
    Thank for your help!
    John

    Reply
  • Colin

    I am doing 12″x 12″ ceramic tile in a kitchen that buts up to a laminate flooring. Should I use the Ditra Or Ditra XL?

    Reply
  • Mark

    I used polymer additive to my unmodified mortar for on top of my ditra to lay tile. Will this hurt ot any?

    Reply
  • Dan S

    I am in the midst of a kitchen remodel. I removed the old tile and the subfloor is covered in old glue/adhesive. Can I install ditra over the old glue/adhesive with thinset or does the subfloor need to be clean? If it needs to be a clean subfloor, would it be easier just to screw concrete backerboard to the existing subfloor instead of using ditra? Thanks for any info!

    Reply
    • Paula M Bhagyam

      I have very little experience, but I was able to remove most of the adhesive on my floor with a steam wall-paper remover and a scraper. I sanded it a bit, too. I wouldn’t use chemicals to remove the adhesive.

      Reply
  • Patricia

    Hi!
    We live in a modular home that sits on a crawl space. At the present time, we have vinyl flooring in our baths and laminate flooring in our laundry room. A DIY er told us that because we are on a crawlspace there will be to much give in the foor for ceramic tile. Can this ditra system be used in this type of home?
    Do most professionals know how to use this?

    Reply
    • Roger

      Hi Patricia,

      Yes it can be used, but it will not compensate for the lack of deflection ratio in your substrate. Your floor will need added bracing to meet the minimum deflection ratio (‘stiffness’) before you can set tile, ditra will not make up for that.

      Reply
  • Tye Jakobs

    Hi Roger,

    I’ve run into an issue with my Tiler’s installation of Ditra 25. It is being laid externally on a concrete slab with Keraquick (grey) underneath and the same on top with the latex additive.

    I’ve specifically asked for this as we will be laying large format (1.2m x 1.2m x 6.5mm) porcelain tiles. They are very high spec (and expensive) Italian tiles and we have laid these internally with the same process but different tilers 2 years ago and so far all is great!

    The issue lies in the laying of the Ditra into the concrete. Yesterday the Tiler’s mixed up the adhesive very soupy and in a rush poured it into the floor, spread it evenly and then rolled out the mat. They won’t agree to that but I watched this happen all very close to quitting time. I believe they were rushing to beat traffic.

    It was obvious to me that the fleece backing had not adhered to the adhesive as I could see light patches through (about 75%) and darker patches where the matt was pressed into the adhesive. I could even loft the mat on the lighter areas and if I pushed down I could see the fleece make contact with the adhesive and darken. After I did this tonseceral of the lighter areas it was immediately evident that it was then stuck down as I could no longer lift the matting.

    Needless to say when the tilers arrived this morning I went through this with them and they were not happy and said, “that is how it is installed” along with their reasoning behind it and a bunch of other filler that made no sense.

    I simply lifted the Ditra up and showed them the back of it and as they say, “the proof is in the pudding!” large sections of it was still white.

    They reluctantly proceeded to take it all up and afternoon I explain the installation instructions to them they sort of followed suit only to find that the results were equally similar.

    The thing I noticed them not do was float the matting properly. They used a trowel and pressed down but it can’t imagine that a trowel has the same evenly dissipated pressure as a float would. Thin metal bends and the only area properly pushing down on the mat would be the handle.

    I know that is a long story for what is a simple question but I do think it needs to be explained first.

    If the fleece side of the mat is not completely adhered to the adhesive will this create a problem down the road?

    -Tye

    Reply
    • Roger

      Hi Tye,

      Yes, it will create issues. It needs to be 100% bonded to the substrate.

      Reply
      • Tye Jakobs

        Thanks for that.

        I was pretty sure that was the case but it’s hard standing up to bullying builders at times.

        Best,

        Tye

        Reply
  • Rex

    I am installing Ditra heat over my bathroom floor and schluter foam shower pan over OSB. I had to patch parts of the floor with 23/32 osb and the result is some uneven seams (not necessary unlevel) where the new osb meets the new osb boards. I think the old osb is 3/4” so literally a fraction of an inch off. Since this is a fraction of an inch would All Set mortar fill the voids enough to ensure an even and secure bond between the osb and Ditra heat? I would rather not cover the entire floor w/ a second layer of plywood/osb and most patching compounds are not recommended for osb. Would a belt sander do the trick? What would you recommend?

    A representative from LevelQuick suggested using RedGard on the osb shower floor between the shower curbs and walls, then metal lathe, and then LevelQuick before installing Schluter shower pan to ensure the shower is completely level. What would you recommend?

    Reply
    • Roger

      Hi Rex,

      Yes, the mortar can fill that void when you install the mats. No need to use the levelquick for your shower pan unless your floor is WAY out of level, you can normally level the pan up with just the mortar beneath it as well.

      Reply
  • Tim

    Hi,

    With 3/4″ plank sub-floor, and going to install Ditra for Tiling. Joists at 16 oc.
    I see the wood screw instructions for installing plywood underlayment to subfloor. Should I glue as well? I see different opinions on line. If the membrane provides de-coupling then why not make the sub-floor and plywood as stiff as possible with screws and glue?

    Thoughts?
    Thanks

    Reply
    • Roger

      Hi Tim,

      No glue. The glue will actually leave voids between the beads of glue – you are creating empty space under your tile when you glue the ply. Just use screws.

      Reply
  • MAZ

    Hi. I am installing tile over vinyl. After days of research and not finding a real “tile over vinyl” solutions, I got a reply email from MAPEI saying that I can use their MAPEI Uncoupling Membrane Thinset mixed with polymer additive to lay tile directly on vinyl (with light sanding on vinyl). I can not imagine thinset adhering to vinyl. Would it really work? will it last? I am willing to give it a try.

    Reply
    • Roger

      Hi Maz,

      Will it work? Yes. Will it last? No, not if water gets on the floor. I learned that lesson the expensive way (as I do with most). Vinyl glue is water-soluble. When water hits it the bond will release. Since your tile is bonded to the vinyl – the tile releases as well. Toilet leaked and ruined the entire floor. The thing is Mapei is correct – it bonded ridiculously well to the vinyl – every piece of tile was bonded to ditra – the ditra was bonded to vinyl. The vinyl released from the floor. Best option without removing the vinyl is to go over the vinyl with 1/4″ backerboard.

      Reply
      • MAZ

        Thanks. But I am not using Ditra .. this is direct tile to vinyl installation using MAPEI. I can’t use backerboard because firstly the floor is concrete so can’t screw backers to it, also combines with the tile, we are talking .75″ to 1″ rise in floor. what to do, what to do!!!

        Reply
        • Roger

          You need to remove the vinyl.

          Reply
  • Tim

    Hi – I’m looking to use Ditra in my bathroom floor (25 sqft).
    The subfloor is 3/4″ planks (5″3/8″ wide) with 1/4″ gap between planks. Joists are 16″ o.c.

    My interpretation of ditra instructions is to put 1/2″ plywood ontop of planks. Is that correct?
    What type of plywood should I use?
    What length/type of screws should I use and space at 6″ along joist with 1/8″ gap between plywood sheets?
    Do I need to use that level-up product ontop of plywood prior to installing Ditra? (the floor seems pretty level to me but maybe I don’t understand the need).
    Thanks for your help!

    Reply
    • Roger

      Hi Tim,

      You want to use a minimum of AB grade ply, I would also opt for 3/4″, but 1/2″ will work. Use screws that are 1/2″-3/4″ longer than the plywood thickness. You do not want the screws to penetrate the joists – only the plank. No, you do not need to use a leveler if your floor is fairly flat.

      Reply
  • Amy

    Hi,
    I just installed Ditra in our kitchen; we’re still in the 24hr curing window for the thinset, but I can already see that the Ditra mat isn’t flat. I think the thinset was mixed correctly, we used a 1/4”notch trowel to apply in a linear direction…I’m not sure where these raised bumps would have come from. Should we pull it up and redo the thinset, or is it ok to even out the flooring with thinset when we tile? Thanks

    Reply
    • Roger

      Hi Amy,

      It depends on how ‘unflat’ it is. If it’s significant – over about 1/4″, then you really shouldn’t try to compensate for that with thinset. Pulling it up, however, normally causes more issues than initially existed.

      Reply
    • Luke

      Hey, I am seeing the same thing. We know we had great coverage becuase we checked it repeatedly but now I have a couple waves. What did you decide to do?
      Thank you for any reply

      Reply