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 
) 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)
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.
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).
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. 
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.
Photo 4
Most any plywood (even osb 
) 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 
Hello Roger,
I think you may have answered this already but my anxiety compels me to check…
I have plywood substrate with Ditra25 applied 4 days ago and ceramic tiles due to be fitted. The tiler used up the excess adhesive (sorry, not sure of type) to fill the waffles in part of the matting. From what I read above, this is fine and will not cause a problem. Am I right? It seems to me that it must weaken the mechanical bond function of dovetailed waffles. Am I wrong? Please advise.
Great site by the way.
Hi John,
It’s completely fine. I don’t understand why you would think it would weaken the mechanical bond. The only thing a mechanical bond is is the thinset cured into the shape of the dovetail. No way at all to weaken that unless the dovetail is not filled.
I was also wondering what the height of Ditra and thin set would be. My tile is 1/4 ” so what would my total finished height be. I have to match it with a wood floor 3/4″.
Ditra with thinset beneath the tile averages about 5/16″ – 3/8″.
Can I install Ditra over the 3/4″ sub floor or do I need additional plywood.
Hi Mary,
Technically you need a minimum of 1 1/8″ double layer of ply. Realistically you’ll likely be just fine over the 3/4 provided your floor framing is solid.
Hi Roger –
Where can I see the video of your building jumping?
Also a tile question – – I’m using Ditra on the floor and the center of the floor is great. However, along the wall behind where the toilet will go, the floor was a bit off and so the Ditra layer back there is not level – it sinks down a 1/4″ – 1/2″. So being the newby that I am – I used a layer of the Kerabond back there to level it off. Now that it is cured, I’m now wondering will the new layer of the Kerabond adhere to the cured layer?
Thanks,
Michael
Hi Michael,
Yes it will bond just fine.
My wife won’t tell me where she put the video. She says people will think it’s funny and will just encourage me to do more stupid shit like jump off 110 story towers – whatever! I’ll find it and post it up and let everyone know. May take a bit, though, she’s pretty damn stubborn.
Hi Roger
I just had 6×24 plank tile “professionally” installed in my kitchen and have quite a few places where the grout is cracking and there is movement of the tile after less than 3 months. The flooring business is supposed to come back and fix this but I would like to know what the proper procedure is to fix it. I am pretty sure from what I have read here that it must be an installation issue-but I don’t know what products they used. Any suggestions? Also, I am guessing they will want to fix the areas we have problems with now- is that reasonable or will I just have problems with the rest later?
Thank you!
Diane
Hi Diane,
I imagine they just plan on regrouting it. That WILL NOT work. There is likely excess movement in your substrate causing the cracking grout. The only proper fix for that is to remove it and build it on top of a properly prepared substrate.
Roger,
We have 3/4″ plywood that’s generally level for our kitchen and dining area except for a noticeable incline in a hall area. To make matters difficult, we are going with 12 x 24″ porcelain tile. The existing 12 x 12 ceramic had been laid over cement board and was probably there at least 5 years without any cracking in tile or grout. But we’re worried about these longer tiles and using ditra (instead of poured cement? ).
1. Should We use ditra with that hump in the floor? Or go with poured cement?
2. If ditra, Should We add more plywood? And/or should we use a self leveler to reduce the incline?
3. Are you very familiar with the ditra heat system? Opinions?
Thanks
Nina
Hi Nina,
1. Yes, you can. With slc first, let it cure, then install the ditra. I don’t know what you mean by poured cement. If it’s simply poured cement then no, if you mean slc then yes.
2. See answer one.
(slc is self-leveling cement)
3. Yes. It’s extremely awesome! The easiest way yet to do in-floor heat.
Hey Rodger!
So just to make sure I was clear in question 1. It is okay to use the existing particle board in the hall as a substrate for ditra?
Thanks again!
Curtis
Hi Curtis,
No. You never want particle board beneath a tile installation. Anywhere.
Great site!!
I tried searching through the thread to find my answer but couldn’t find it, so I hope you haven’t answered already. (It may just be a horrible question that I should already know!)
Two years ago I put tile down in the downstairs bathroom and adjacent hallway. I knowingly installed it incorrectly over vinyl flooring using flex-bond. The reason for this was because I knew the beast that was beneath, particle board. Nailed, stapled hundreds over and glued! I dealt with this before in my kitchen and resorted to ripping through the particle board and plywood TG subfloor in spots.
Okay so back to present day, bathroom has been gutted because I improperly installed toilet and water got to particle board. So my dilemma now is where to go from here. I have 48 sq feet of bathroom down to the plywood subfloor but another 200 sq feet in the hallway/laundry room to pull up(side note the tile is in fine shape but I want to upgrade tile while I do the bathroom).
1. Can I match the height of the PB from the hallway to bathroom and use Ditra?
2. Can I pull up the tile leave the vinyl over PB than use Ditra.
3. Is there any reasonable way to pull up PB that is nailed, stapled and Glued?
Thanks for all your help!!
Curtis
P.S. The PB around the tile was fairly easier to pull up. Would you recommend flooding the floor for a day to loosen up glue? Seriously, I am desperate for help!!!
Hi Curtis,
1. Yes
2. No
3. Unfortunately not really. It’s a pain in the ass. Flooding it would help if you want to do that, I would be leery of it, though, you don’t know where all the water will go if it doesn’t get into the pb.
Thanks for your great site !
I want to tile my outdoor patio. I wasn’t happy with it’s slope, and I decided to resurface the concrete with a mud mix (also often used in shower installations). Since the mud mix was thin I used an acrylic fortifier to improve bonding to existing concrete and itself.
Unfortunately the mud mix is not as smooth as I wanted (it’s quite rough actually). I am thinking to make sure there’s no loose gravel, but I fear differences of 1/8″ or so may be present. Do you think this will form a problem installing the Schluter Ditra layer ?
By the way since my budget is limited I decided to try DIY for this project.
Hi Arne,
It’s supposed to be rough. You can skim over it with a layer of thinset if you want it smooth first, but the ditra will bond to it just fine.
Great, Thanks man !
Arne.
Hi Roger,
Thanks for answering my other question regarding Ditra-Set or Laticrite 317. I am now the proud owner of some 317.
I have ripped up all the linoleum and the particle board it was attached to. Now I have a possible issue.
First, there was water damage and mold on the particle board. The subfloor (3/4 TG OSB) was not damaged, but did have some surface mold in a small 2 sq foot area.
Second, when the house was built (in 2006) the tape and texture guys REALLY loved spraying mud (beadex, not mortar) everywhere, so under the particle board there is texture and paint.
According to Schluter installation instructions, I can go with modified thinset on top of the OSB, under the Ditra, but that is based on new construction.. ie, not painted. I am concerned that my modified thinset (versabond) will not adhere to the texture and paint.
My initial solution was going to be to lay down ¼ inch plywood then the Ditra and tile. After some forum reading, I understand that is not accepted practice and that ½ inch ply is minimum. The problem is that ½ would bring me up too far (3/8) in comparison to the hardwood at the perimeter. I would rather be 1/8 low than 3/8 high, but I am not sure about the thinset adhering to the not-so-new, beat up and abused OSB.
I could scrape/sand the crap off the OSB, but then I would likely have gouges that would need to be filled. Right now the subfloor is flat according to my 4 ft level. I am a proficient DIYer and an engineer by trade, so I am looking for the ‘right’ way to address it as well as the ‘most economical’. What are your thoughts?
Thanks,
Elf-in-training (still)
Hi Jon,
I would just go over it with a sander to remove surface debris. That will give it plenty of bond for the ditra.
Hi Roger,
Thanks for all the tips – I love the site!
I’m setting my tile on Thursday (my weekend) and just read something that I want to confirm with you first.
I am going to put down the Ditra on Wednesday afternoon using Versabond. Then on Thursday – around noonish – I will begin setting tile over the Ditra using 317.
I read that you can pre-fill the Ditra waffles with the leftover thinset used under the Ditra (Versabond in my case.) I like the idea of not wasting thinset, but I really like the idea of having a proper bond between the tile and subfloor. What are your thoughts?
Also, if you recommend NOT prefilling the waffles, is there any advantage to letting the Ditra set on the versabond overnight? other than not having two different thinsets open at the same time.
Thanks,
Elf-in-training
Hi Jon,
Yes, you can prefill it with versabond. I do it often. No real advantage to having it set overnight, but it definitely doesn’t hurt.
Ceramic tile over ceramic tile (in a mud bed).
I’m redoing a small bathroom and the floor is very well adhered mosaic tile in a 1″ mud bed. There are no cracks. I was going to use Ditra but I Don’t know whether to use unmodified thinset between the Ditra and the existing floor. Ditra doesn’t cover ceramic tile as a substrate. Do I even need Ditra?
Hi Bill,
You can use ditra with a modified thinset approved for use of tile over tile (like mapei ultraflex 3) or you can just use the thinset approved for that use.
Roger,
Thanks for the speedy response. I’ve got versabond and that says its okay over ceramic tile.
I’m using long tiles (wood plank look, 6′ x24″) and I’m a little worried about cracking Is Ditra or no Ditra going to reduce the chance of cracking the tile?
what sort of prep should I do to the old tile? If heard of using a belt sander to scuff the surface.
Bill
Yes, ditra will help prevent cracking by providing in-plane movement compensation. I WOULD NOT use versabond, I would use flexbond. The surface of the old tile will need to be scarified. Scuffing (to my understanding of the word) is not sufficient, the surface of the tile needs to be removed to get to the base layer of the tile beneath to provide open pores.
I got a diamond cup wheel to scarify the surface. That should do a pretty good job.
I can get flexbond for under the Ditra but I haven’t been able to find unmodified thinset for on top of the ditra. I’ve been to the big box stores and to two tile stores. Can you give me a couple of brand names so I can find a local retailer.
Unmodified thinset
Roger,
I’ve installed ditra xl with unmodified thin set over a concrete basement floor. I am now ready to install porcelain tile. What is the best type of thin set to use? I believe schluter recommends unmodified but the tile manufacturer recommends modified.
Hi Tim,
Unmodified thinset works just fine provided the tile is installed correctly (backbuttered, proper coverage, etc.). Porcelain manufacturers always recommend modified, as do the specs. So you’re in la-la land just like we are. If you want schluter’s warranty use unmodified. It really does work fine. If you use modified make sure to give it a couple extra days (at least) to fully cure.
A few years ago we did a three tiled bathrooms and a kitchen where we used ditra over plywood and all the tiles have movement. I insisted on using ditra as I have installed tile in older homes and have seen it crack due to issues with the older subfloor and joist spacing. My contractor never used ditra before but read the info and watched the installation videos. He used a modified thinset under and over the ditra but the tiles still came loose. It is worse in the high traffic areas, kitchen and first floor bath. He has come back several times and removed the loose tiles, stapled down metal lathe over the ditra and reinstalled the tiles. We have also sistered up all the floor joist and added a steel I beam for additional support under the kitchen and the tiles are still coming loose in there and first floor bath. I have noticed the the tiles tend to become more loose during the summer months. I have also noticed that when the contractor has removed the loose tiles there is no adhesion between the tile and thinset. It also appears that the thinset has spider cracks. It’s been almost three years now and my contractor can’t seem to solve the issue. I am ready to have him rip out everything not under the kitchen cabinets and start over. Any suggestions?
Hi Jack,
If there is no adhesion between the tile and thinset then the tile was improperly installed, not back-buttered, etc. It is not the ditra. The thinset has spider cracks because it is simply a layer of thinset over ditra, with tile laid on top (not properly bonded) which allows the thinset to shrink without anything to stop it. Are there expansion joints? Are there perimeter joints? Stresses caused in a tile installation (especially in summer months when stuff swells) can sheer tile from the substrate, but properly bonded tile would at least have thinset bonded to them.
Roger, Thanks for the info. Do you have any ideas on how to fix the problem?
You already know
Have him remove it and begin again. Actually, have someone else remove it and begin again. There is no other way to fix improper installation with lack of bonding.
Roger,
The contractor that i hired used Mapei Ultraflex 2 – a polymer modified thinset between plywood subfloor and ditra as well as between ditra and the porcelain tile. I’ve read that you need extended cure times for modified thinsets when installed between ditra and tile. How long is extended? Or do I get the contractor to rip out the tiles and redo it again?
Hi Roshni,
Anywhere from two days to six months. It depends on a LOT of factors. However, let the contractor do his work, he’s likely experienced with this method and knows what is required before he tells you it’s a finished product. His method obviously relies on his warranty, not schluter’s.
I am getting ready to install Ditra on my Kitchen floor. The floor has vinyl flooring on it now which is tightly glued down. Rather than using a thin set mortar that claims to bond to vinyl I covered the floor with a layer of concrete backer board. Will I be ok if I use an unmodified thinset mortal to install the Ditra with.
John
Hi John,
Yes, ditra will bond to backer just fine with unmodified. That’s actually what they require. You did put thinset beneath your backerboard, right?
Ditra and Kerdi both say to use “unmodified” thinset below and above their product. I have not really found an unmodified thinset nearly as good as Versabond. That crap will outlive the house you install the tile in. I recently remodeled and enlarged my master shower with a ton of travertine. I went by the Kerdi instructions but I am really nervous about using the unmodified thinset instead of Versabond that I normally use. I understand the curing thing but I will die if that thinset ever fails. I am now about to use the Ditra system over a plywood sub-floor and I am leaning toward the Versabond. I would love to know what you think as I have several more tile jobs around the house.
Hi Debbie,
Ditra actually requires a modified thinset over plywood. You need modified between the plywood and ditra and unmodified between the ditra and tile.
I had a tile installer install Ditra Mat on my deck over an occupied space. He did not install a waterproof membrane underneath the Ditra. I am in need of the Schluter Installation Handbook that was in effect in 2006-2007. Schluter has not responded to my request. Can anyone help?
I should clarify I did not direct the installation. He took it upon himself to install it as he saw fit.
Hi Mike,
I seriously doubt you’ll be able to find that, it’s not really something people keep. I’m curious why you would need it, though. There never was a requirement for a waterproof membrane beneath the ditra, with the use of kerdi-band the ditra becomes the waterproof membrane. It’s always been that way. The 2008 version is online here: http://www.schluter.ca/media/brochures/DitraHandbook-2008-ENG.pdf?v=201401311614 It’s identical to the 2006/2007 version.
I installed detria over plywood with unmodified thinset. Will this fail without a doubt
Hi Richard,
Not necessarily. If your floor is built well enough you should be fine.
I will be installing tile on my basement concrete substrate. I will be using Ditra Uncoupling membrane. After pulling up the existing carpet, there are many areas of either glue or carpet material left stuck to the concrete. How thorough do I need to be in getting rid of this residue?
Most of it comes off really nicely . . . in sheets sometimes. But there are many stubborn areas where it is really quite stubborn.
Do I need to clear this stuff off completely to the substrate concrete? Or will roughing these stubborn areas be enough?
Thanks,
JK
Hi Joe,
Roughing it up may be enough. If you splash water on it and it soaks in pretty quickly it means that thinset can bond to it. If it just sits on the surface then it needs more work.
Roger,
I love all the information you have here. I just installed Ditra on an old concrete basement floor. I had to strip all the old paint off and then etched the concrete, There were some areas where the paint wouldn’t come off and the tile rep I used said I should use modified thin-set. So thats what I said, Now I’m reading that I should of used un-modified. Am I in major trouble or do I just have to wait longer for it to dry?
Thank you,
Shawn
Hi Shawn,
Not sure where you’re reading unmodified. The only requirement for that over concrete is under ditra. Modified is just fine.
What is your opinion of Prospec Permaset 275 as a “premium” dryset mortar for use with ditra. I did not see it listed in your Unmodified mortar article. It is what one of my local tile stores provides. Big Box Stores have nothing “Premium”.
Thanks
John
Hi John,
The permaset is a good thinset. There are a lot I didn’t include because they are either limited to very specific areas or hard to get a hold of.
Can I not install ditra on top of glue down hardwoods ? Maybe prime first or light sanding ?
Hi Brian,
No, you can not. The tile would only be as durable as your bond of the wood to the substrate.
Need to install porcelain tile over 3/4″ T&G hardwood flooring. 16″ on centers solid w/no noticeable deflection. Intend to use Ditra. Is it advisable to add a plywood substrate layer as well?
Thanks
Hi B,
Yes, you need to add a layer of ply. Ditra can not be installed over hardwood or planks.
Looking to tile a dry basement floor that has been previously painted. Can I use ditra xl directly on cement floor if I rent a machine that ruffs up the paint?
Hi Cinzia,
Provided once you rough it up the floor will soak in water almost immediately when you splash it on there. If it doesn’t you need to rough it up some more. If it soaks in water it will allow thinset to bond.
Roger,
Ditra: I filled the waffles, let it dry (36-48 hours)…It occurred to me (after I walked all over it) that maybe I shouldn’t walk on it until I have tile down. It seems fine, but I figured I’d check before I install the tile.
Kerdi drain: I installed the collar / tube part of the drain and then installed the tile on the shower floor.
1. What keeps the drain height (collar position) fixed? I gather from your eBook that the thinset does, somehow…but it’s not totally obvious to me how. Does the thinset fill the gap between the dovetail collar part and the underside of the tube flange. If so, I’m not sure I put enough thinset down to support that part. When I step on the drain, it feels supported but I can hear some sandy scratching.
2. How does the water that gets beneath the grout get into the drain? Does it have to wick through the thinset under / around the dovetail collar piece? Does it go through the holes between the collar and the tube? My floor drains fine, but some water collects in the grout lines near the drain and takes a long time to disappear (hours). Is this OK?
Kittos!
Steve
Hi Steve,
Walking over the filled waffles is fine.
1. Once it’s installed and the thinset cures it’s the thinset locked around the little tabs in the collar that lock the height in place. As the thinset cures the tabs will tighten up, the surrounding thinset locks them in place against the tube.
2. Water will wick through that thinset and down the drain. It may take a little while, that’s completely normal.