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 
Hey Roger,
I want to put tile over tile in my kitchen. Presently have 12″X12″ sheets of 2×2,2×4 and4x4 pattern over concrete( they’re solid). Should I use Ditra before putting down 16X16 ceramic tile? What type of thinset?
Hey Dan,
Ditra would be a very good idea. You’ll need to rough up the surface of the present tile so the thinset has something to grab. You’ll also need a thinset that specifies use over existing tile – it will state that on the bag.
Sir:
I have a dilema.
I want to install a walking-in shower in my basement [new concrete floor, surrounded by 36″ high foundation walls on 3 sides] .I’ve told I need to have a waterproof membrane prior to installing tiles.
I’ve also been told, I don’t need a membrane since everything is concrete and that I’ll just need the proper slope for the drain….who is right, but most important WHY?
thank you
DA
Hi DA,
You do need a waterproofing membrane of some type. Concrete is not waterproof – think about your driveway when it rains, it soaks in water. Your foundation walls are the same way. It may lead to structural damage (depending on your particular construction) and it can lead to HUGE mold problems. A membrane will prevent water from ever reaching your walls.
thank you for your reply. It is reasonable and well founded, no doubt you are the expert!!!!
My next questions:
what sort of water proof membranes are there? and
would these membranes will readily accept tiles or mosaic?,
what’s the best kind of mortar to use to set the tiles on that will be compatible with the membrane?
I appreciate your good disposition to share your knowledge and dedicate your time to answer questions from the general public.
DA
There are a large number of membranes and a couple of different types as well. All of them will accept tile and the thinset type depends on the membrane type. If you download my shower waterproofing manual here it will explain A LOT of it to you in easily understood ways. (It’s free). Just go to that page and fill out the box on the right-hand side.
Hi Roger,
I ‘ve talked to you once and you said to use dryset mortar on my concrete bathroom floor between the floor and Ditra and between the Ditra and tile. I’ve got all the supplies but had a couple of guy come out to look at mudding and taping drywall and they said they could install the tile too. I thought OK, give me a price. I showed them the Ditra, they had no idea what it was, then said just use UltraFlex as mortar between the concrete and tile and it will give enough to keep from cracking the tile. That sounds alot easier to me than installing the Ditra but that goes against everything I’ve read or heard. I want this to be done right so I thought I would ask an expert but I couldn’t find one so I’ll ask you instead. Just kidding. Let me know what you think. Thanks alot.
Hey Sean,
I looked for an expert but I couldn’t find one either – so I’ll take a stab at it.
Ultraflex will adhere the tile to the concrete just fine – and that’s what drywall guys do with tile – adhere it. The problem is that while ultraflex will compensate for a bit of movement (normal expansion and contraction over stable substrates) concrete moves – a lot. And it cracks. Ultraflex may or may not compensate for that, it varies from slab to slab. There is no way to tell whether it will handle the movement in your particular slab or not – ditra will. Here’s a quick tip: if the people offering to install your tile have never seen the product you purchased to install your tile – it may not be a good idea.
Hi Roger,
First of all, you started a great site.
I’m installing tiles for over 30 years, in Germany, New York and Florida.
I have used Ditra a lot, but lately I’m disappointed in the quality. Kneeing down on the ditra makes the waffles crush and I’m not over weight (183 lbs/ 5’11”) at all.
You say you can pre fill the waffles. Did you know that you only fill the waffles and the rings around the waffles make up at least 60% of the area? This leaves you with 40% bond, since the thin set mortar doesn’t stick to the plastic around the waffles, especially unmodified thin set mortar.
Hi Steve,
That’s correct, and the crushing aspect is annoying. Since I’ve switched to pro-knees it’s less of a problem, but it still exists. I tend to crush more with the bottom edge of my bucket than I do with my knees.
I was told by schluter that you actually have a total of a 50% support area (bond) from the bottom of the tile to the floor since the waffles flare at the bottom. That’s normal. The thinset, modified or unmodified, does not adhere to the plastic whether you pre-fill the waffles or not. Pre-filling them does not negate any of the support your tile receives using ditra. Do you disagree with that? I see no problems with pre-filling the waffles, have you had any issues with it, or do you not do it?
Where in Germany did you install?
Hi Roger,
I’m installing porcelain square/octagon mosaic tiles on my bathroom floor. The squares are 1″ and the octagon is probably 2″. The shop I bought it from said to put on Ditra and I was all about it. When I was looking through the Schluter installation documents, though, it said something about not using it for tile less than 2″. What are your thoughts on here? I already bought Hardi-Backer but it’s such a pain in the ass, and want to try the Ditra.
Also… I stripped the floor down to the 3/4″ thick planks and put a 1/2″ plywood over that, screwing into the joists. Assuming Ditra will work for me, will this combo work for me? And if Ditra doesn’t work, is 1/4″ Hardi on top OK?
Thanks!
Hey Rob,
I know exactly what tile you’re talking about and ditra will work just fine – I’ve done it a couple of times. It would be much easier to pre-fill the waffles, let that cure, then install your tile. That gives you a solid, flat surface to set the tile on which is always better with smaller mosaics. In a smaller bathroom the planks and plywood will be fine, not recommended procedure (planks are a source of contention for most of us) but it’ll be fine.
hey roger,
floor is finally finished turned out good – was in home depot today and seen a new item for installing back splashes called simplemat have you seen this before or ever used or know anything about it. attaches to drywall no need for thinset to set the tiles. thanks.
Hey Randy,
Yup, I’ve heard of it. Never used it – never will use it. From the people I’ve talked to that have used it the product seems to work as advertised initially. I say initially because it hasn’t been around long enough for anyone to truly know the long-term durability of it. I do know that your wall must be absolutely flat or your tile will not be – you can’t build up thinset beneath the tile to level them out. What you have for your wall is what you’ll have for your installation.
looks like i’ll be using thinset
Hello,
thanks for sharing your knowledge! We are getting ready to put tile in our bathroom. Previously there were two layers of vinyl/mystery tile. We have removed those but under the oldest one is that old tar-paper-like stuff, and we haven’t been able to get that off down to the wood. We have scraped and sanded, but that stuff is tough. We are planning to put Ditra over this… Will it bond ok to that black stuff?
thanks,
megan
Hi Meg,
That black stuff is called cutback – and it sucks! You will likely not be able to remove it and thinsets do not stick to it well long-term. The best thing to do is install another layer of plywood, even 1/4″, over that and screw it down. That will give you a clean suitable substrate for your ditra. Don’t try to stick anything to that stuff – take my word for it.
thanks, we figured out that our black stuff is loosened with hot water, so we got it all off!
Next question… how do we keep from crushing the Ditra waffles during tile installation? Is laying a piece of cardboard under the knees enough? They don’t even mention this concern in the video, but the stuff seems a little susceptible to direct pressure.
Glad to hear you got the ‘sissy’ cutback.
You can use cardboard or a piece of plywood. I have pro-knees (they look like bionic legs) and they will crush it into nothing if I don’t put something over it. Cardboard is normally just fine.
Hey Roger. This is perhaps the most informative floor tile site I have found. I have been worried about mixing the thin set despite the suggestions. I managed to make the under layer work and I am hoping with your detailed pictures I can figure out hoe to apply to the tile.
My main concern is wall gaps. I see you suggested 1/8 inch gap between the Ditra and the walls. What is the max. I mis-measured a couple spots that are about 1/2 inch from the wall. Under my cabinets there is almost a 2 inch gap. Do I need to cut a small strip for this gap? Thank you.
Hey Matthew,
The 1/2″ gaps are just fine. It would be better to cut a 2″ strip for under your cabinets, though. Without the ditra there your tile will be attached directly to the substrate in that area and won’t move the same way as the part that is attached to the ditra will. While the same thing may happen to a small degree in the 1/2″ areas, the 1/2″ of attachment will give way before negatively affecting anything – the 2″ is a bit much and places much more pressure if there were movement.
Hi Roger I have a small bathroom to tile that has 1/2 ply over 16 on center joists ,will ditra work without adding more ply ? If I added blocking under the floor every 16″ would that make a difference ?
Hey Bruce,
Ditra XL is rated for use over a single layer of plywood. Regular ditra is not. That said – I have used ditra over single layers and haven’t had problems. Doesn’t mean you won’t – just means I haven’t.
hey roger
im almost done with the tile – im about a foot away from the wall can i change direction with my notch because its hard to get into that small area. thanks.
Yup, no problem at all.
We are putting Ditra on a bathroom floor that is 5×5. It is in a cabin in Northern Wisconsin. The subfloor is 3/4″ particle board with 1/2″ Durock bonded and screwed to it. We are going to put down 1/2″ sandstone soon. There are some slight out of level spots on the floor at this time – kind of a 1/8″ wave of sorts. I’m reluctant to use floor leveler, because I’m afraid it will crack and not do a good job. We have cracks in our porcelain kitchen tile, because we didn’t put plywood down and then the Durock. Hindsight is 20/20, and besides, Ditra wasn’t even invented, then. How would you proceed? Some one who does quite a bit of tiling looked at the floor and suggested it should be fixed with a little additional thinset on the final layer where the tile adheres. Thoughts?
Hi Ann,
Before I answer I’ll let you know that particle board has absolutely no business beneath any type of tile installation – ever. It simply has no structural stability. And if it gets wet your tile is being supported by wet, swelled sawdust. It is way too weak to support even ceramic tile, let alone sandstone which requires a sturdier floor. Ditra will not make up for that.
That said you can use a 1/2″ x 1/2″ trowel to set your tile and you will be able to compensate for that ‘wave’ without a problem.
But don’t expect it to last long-term. It simply doesn’t have enough stability. Sorry.
Thanks for the answer so quickly, and all. I am not surprised by your answer. It’s just depressing to think that for $300 and a little more work 18 years ago, we would have plywood over the particle board, and we would not have the cracking problems we do now, and we’re applying this beautful sandstone knowing it’s going to fail. Luckily, I’m pretty old, and so is my husband, so our goal is to keep it from lasting until we die. To that end, I notice you recommend Mapei Kerabond, which, of course, is a special order product taking 14 days to get here in our small, rural Minnesota town. Any other product that might do for us?
Thanks,
Ann
I just called Home Depot, and they have “custom blend”, which after reading the nightmare story about it, we won’t buy it. We have a LOWES within 50 miles, too. I’ll call there are see what they have. They have a Mapei thinset locally, but it’s not Kerabond.
Thanks,
Ann
OK – a continued saga. I called the local tile shop. They carry the “Superior” line of products (don’t you have product names that have the potential to become oxymorons?). Anyway, they have a non-modified thinset that they will sell me. AND, I had to endure a 10 minute lecture about how bad Ditra is, and that they don’t sell it because it has all kinds of problems, blah, blah, blah. BTW, I did some more thinking, and we might have OSB subfloor rather than particle board, because it isn’t compressed sawdust, it’s splintery type little pieces of wood. Would that be better? Forgot to tell you earlier – you do beautiful work! Or, you’re really good at pasting beautiful tile work done by someone else onto your web page.
Ann
Ann
Hi Ann,
Yup, run far and fast from ‘custom blend’ – it’s essentially powdered mud.
Mapei’s kera-flor will work – you just need to allow about three days to get a good cure on it. If that’s what they have I’d likely use it if I had to. I’ve heard of superior products – never used them so I really can’t speak to the quality of it. If the people at your local tile shop have had problems I’m guessing it wasn’t due to the product – it was due to the installation. I’ve been using ditra for nearly fifteen years and I have had a few problems – every single one of them my fault (sometimes my head is just in my ass – what can you do? ) The product is not going to fail.
If you have osb it’s still not ideal – but it’s a hell of a lot better than particle board. (We call osb ‘beaver barf’) You do need to use a good modified thinset to adhere the ditra to the osb. Here’s a little secret that’ll solve all your problems – go to home depot and get versabond (they’ll have it). It’s a modified thinset and you can use it for everything – under and over the ditra. Just give the floor two full days to cure before you walk on it or grout and you’ll be just fine. Schluter will void your warranty if you do this! But I used to do it all the time and I still use a modified thinset over ditra – A LOT. (don’t tell anyone). It works just fine.
I copied and pasted every one of those photos on both my websites – I actually mow lawns for a living.
Just kidding – thank you very much for the kind words.
I removed a formica backsplash, to install subway tile, but after removing there is a lost of hard black glue or thinset on the walls. Do I need to remove it, if so how, or replace the wall? I was told to use a leveling compond. I think this would extend the wall over the countertop of which I am also installing tile. Would like to fix the backsplash problem, before installing tile on the countertop usind the dritra. Help.
Hi Gwen,
You should be able to scrape that off of there with a putty knife or drywall knife. You can also remove and replace the drywall in that particular area. All a leveling compound will do for a backsplash is extend it over the counter like you’ve mentioned and force you do buy a $50 bag of leveling compound rather than a $7.00 sheet of drywall.
My walls are plaster, house builded in 1946. The hardened thinset is not bugging. Is there any other way to remove it or level it for the tile. Had a tile man over last week, said it was ok to thinset over the hardened thinset, but I don’t feel to good about that application. To have the plaster wall removed and replaced is more than I can afford at this time. Had i known that was behind the formica I never would have removed it. This is a DIY PROJECT for me and I think I’ve made a mess of things.
In that case a hammer and wide chisel are likely your best option. You don’t need to worry about removing a little extra plaster – any gouges or small voids can be filled with thinset as you install your tile. That’s the only thing I can think of short of replacing the wall. If the ridges aren’t very high on the old thinset you can probably just skim over all of it to level it out. On a backsplash that would actually be fine – especially if the thinset won’t budge.
roger,
im going to lowes on saturday to get the megabond to finish the floor. the only modified thinset i seen there was laticrete multipurpose thinset – will this be good thinset to use for the backsplash tile. was going to use the ultraflex 2 but its gray and im putting in white stone mosiac travertine tile did not want it to bleed through the stone. thanks.
Hey Randy,
Yes, the multipurpose will work great. It’s good stuff. If Lowes only has keraflor – some of them do – you can use it but you need to allow an extra day for it to cure fully and bond well before installing or working on it.
roger,
what if they do not have the keraflor – is the multipurpose a modified thinset when mixed with water if so cant i just mix it and put on wall and set the tile. not sure on this never used laticrete products. thanks. just to make sure is the megabond a unmodified thinset when mixed with water.
Oh, didn’t know the megabond was unmodified. (Laticrete professional products use numbers). I see what it is you’re talking about now. Forget the keraflor, go with the megabond for all your unmodified needs. (THAT sounded like a commercial) The multipurpose is a modified so yes, you can just mix it up and put it on the wall and set tile.
Hi Roger,
This was my first time with Ditra and I did use the (now I know!) cheap unmodified thinset from HD (custom blend) over concrete. I now have what looks like a bubble in one place and I know it did not bond in some other places to the substrate as you can knock on it and hear the empty echo. Any chance to repair these areas before I start tiling? I wouldn’t want to redo all the work as it is a huge area (all basement floor). Any advice s appreciated. Also, what is a good unmodified and where to buy it? HD does not seem to carry anything but custom blend…
Thank you.
Hey Tino,
You can simply cut out any areas that are not adhered correctly and reinstall them. Ditra doesn’t need to be in one large, continuous piece to work correctly – you can have patches.
With that typed, I honestly, really wouldn’t trust that thinset beneath your ditra. I would redo the entire thing, although I know that isn’t ideal it’s better to do it now than when you have thousands of dollars worth of tile over it and it fails. Mapei makes kera-bond and laticrete makes 317 – they are both very good unmodified mortars which, unfortunately, are not readily available. Find a flooring supply shop near you and they should either have something there or at least be able to order it for you.
IF you aren’t concerned with the warranty you can use versabond. I’ve done it – a LOT – and haven’t had issues. Doesn’t mean you won’t, just means I haven’t. It will void your warranty from Schluter but it’s right there at HD and works just fine. Entirely up to you.
Thank you Roger. Couple of questions though.. I did reapply one smaller patch of Ditra and it is now a bit higher than the rest (old thinset is making it high, it bonded really well to the slab, I could not easily scrape it). I guess this is okay, as I can level with a bit more thinset later on adjacent tiles. The other question is regarding versabond. I think HD only has it with added latex polymers…is that what you mean? I know this is not recommended by Schluter and I guess this is what you mean by losing the warranty. Correct? It’s a shame HD does not carry any other….I have not checked at Lowe’s though..
Yes, you can level that out as you set the tile if need be. And yes, I mean the one with polymers – that is what I mean when I mention the warranty. Lowe’s usually has mapei products – look for the kera-bond.
roger when i do my back splash im using 12×12 mesh back tiles (mosiac different size tiles in 12×12 size) going on drywall forgot what thinset to use modified or un-modified. can i use mastic. thanks
Hey Randy,
You want to use modified thinset. You can use mastic provided your tile is porcelain or ceramic and not any type of natural stone.
roger,
these are travertine mosaics not sure if there stone, ceramic or porcelain also do i use the 1/4″ square notch. thanks also if i cant get more kerabond for the floor can i use latcrete megabond. thanks
Megabond is fine. Travertine is a natural stone so you do not want to use mastic on them. The organic oils in most mastics may leach into the stone and leave what looks like an oil stain on the front. Use a modified thinset for your backsplash.
Hi Rogers, first off thanks for the site and answering all the questions. It really helps out new guys like me who are attempting to do things the right way.
Just a quick question. I have a small 5×7 bathroom I am planning on using Ditra this weekend. I watched their video online and they reccomend putting the Ditra down and then tiling immediately afterwards. Is this a requirement or can you put Ditra down and then tile the following day? Since im pretty new to this it seems like it takes me 3x as long to do anything so I just wanted to see if you really needed to tile immediately after ditra installation.
This is the video i am speaking of right around the 6:20-6:30 mark.
http://www.youtube.com/watch?v=f6FyWs2WZ1k
Thanks
Hey Joe,
It’s not necessary at all, simply possible. They point that out because with some membranes you need to wait for something to cure before installing tile. It’s not required, you can install it and install your tile next week if you want.
Hey Roger,
Working on a bathroom floor. I stripped the old floor down to the two 5/8 layers of plywood, all good and solid. I installed 3″ strips of 5/16″ Durock around the perimeter (thinset and screwed) of the room and around the toilet hole, leaving a cavity in the walking area for WarmTiles wire heat. I installed the WarmTiles wire per instructions onto the plywood in the cavity. I tested my ohm readings and all is good. I filled the cavity with Ultraflex 2, encasing the WarmTiles wire, and used my 4′ metal level as a screet (my dad would have killed me for treating my tools like that). The Ultraflex is probably about 3/8″ thick. I let it dry for 24 hours and then put a very thin second coat of Ultraflex 2 over that just to fill any voids that sunk or weren’t quite perfect. Now for the 40 million dollar questions…I read too much on this new fangled Internet thing where everyone and their red-headed stepchild has an opinion. Was Ultraflex 2 the right choice for encasing the WarmTiles wire? Should I install Ditra over this before tile or is it not necessary? Do I use modified or unmodified thinset between my Ultraflex 2 bed and Ditra? And always unmodified thinset from Ditra to tile, right? (13×13 porcelain tiles 3/8″ thick going on top).
Hey Rob,
Ultraflex II will work just fine for that. The best option would likely have been a self-leveling cement, but a good thinset works just fine provided it has enough time to cure. Use Ultraflex beneath your ditra and unmodified on top under the tile.
I’ll keep an eye on the mail for that 40 million dollar check.
(and never listen to red-headed step children – they grow up to be politicians!)
Thanks, Roger. I put the ultraflex 2 down on Saturday eve 6 pm. I put the extremely thin leveling coat of ultraflex 2 down at 8 pm on Sunday. The bath is over a finished basement (with a drop ceiling where I removed the tiles). I’m in Wisconsin…75-80 degrees, but we keep the central air on at 73 to keep the dampness out of the air. Dehumidifier running in the basement. Would Tuesday night be enough cure time to put the Ditra down?
I’m totally a paranoid schizo when it comes to this stuff. I don’t plan on energizing the floor until October 1…just to be darn sure everything is cured. Thoughts?
This just gets richer. Not that I didn’t trust your elfly opinion, but thought I would check with WarmTiles and Schluter.
WarmTiles rep says Ultraflex 2 was good to encase the wires (like you said), which makes me feel better. He confirmed Ultaflex 2 between current bed and Ditra and then unmodified on top…but he also offered his opinion that he would think modified is better on top with porcelain tiles.
Schluter rep says bond the Ditra to the Ultraflex 2 bed with UNMODIFIED and then use unmodified again to bond tiles to Ditra. I’m so confused!
Hey Rob,
Did the Schluter rep know that the entire floor does not have ultraflex on it? Ditra is supposed to be used with the type of thinset ‘appropriate for the substrate’ – that’s a bit vague for non-professionals but a modified is what should be used since you do have areas without the floated-over wires. He likely thought your ultraflex bed was incorporated over the entire substrate. And October is fine for your heating wires.
OK, Roger…the Schluter rep (a girl, unless Shawna is a guy) was given a full explanation of exactly what I did…3″ Durock perimeter border with cavity filled with Ultraflex 2 and WarmTiles wire.
She confirmed that unmodified was the way to go, not because of movement, but because modified would NOT cure between existing modified and Ditra.
So, we’re back to the big question…unmodified below and save the email correspondence with Schluter so they can pay for a new floor when it fails? Do the modified below and risk an incomplete cure? Or go with what the Home Depot guy said, “Sh*t, you got so much crap on that floor already with the two layers of 5/8 and 3/8 inch of Ultraflex 2…you don’t need that Ditra crap! Lay the tile right on what you’ve got.” (I didn’t even tell him I was doing a bathroom, but with all his fecal references, apparently he already knew!)
By the way, we have to be walking on this floor in less than a week. Knee surgery next Thursday and two foreign exchange students showing up a few days after that.
Hell I dunno. I’ve never, ever had a problem sticking anything to modified thinset with more modified thinset – including the inside of my buckets.
If you’re concerned with the warranty I’d do what Shawna says, and keep the email. It won’t fail provided you use a good unmodified – not the 5.00 bag of crap HD sells. The guy at HD obviously doesn’t know that all that shit (you can type shit on my website 
) in your floor is gonna move – a lot – when you fire up that heating element. Ditra compensates for that.
Knee surgery AND foreign exchange students??? Sounds like a bad week I had in college.
hey roger,
started installing the ditra – i used gray ultraflex 2 – after pushing the ditra into the thinset i can notice gray areas and then no gray areas on the ditra – i hope i got the full coverage or i am probably screwed. also alot of thinset came out from the edges by me using the wood float pressing firmly on the ditra – help. thanks
Hey Randy,
It’s probably fine. When you get big splotches like that it is indicative of too much thinset in those areas actually soaking through the webbing and up into the channels on the underside of the ditra. Not ideal for utilization of vapor management, but it isn’t going anywhere.
roger,
just got home from work floor seems to be solid – will set the rest of the ditra in today – also do you think im pushing to hard on the wood float causing it to squeeze out the edges of the seem. should i make the thinset thinner. not sure on how much pressure to use first time installing this product. thanks.
No such thing as pushing too hard unless you’re crushing the waffles. And if it’s splotching like that your thinset is fine. The trowel you’re using is probably just a little too big, but it isn’t a problem. Carry on.
roger,
one more question about the stairnose transistion strip from schluter (rondec-step) from the kitchen floor goes to carpet steps – i have 1/4″ thick porcelin tile the transistion is 3/8 in height for tile- don’t know what size trowel to use to lay the tile because if i use the 3/8″ knotch the tile will never be flush with the top of the transistion strip – 1/4″ might work by the time i push the tile into the thinset – need help so confused with this one thanks
If you’re using ditra as your substrate you can install the ditra and the tile on the transition strip – it comes out perfectly. My standard trowel is a 3/8″ x 3/8″ which leaves 3/16″ thinset beneath the tile – that may work if you build up the tile a bit more with thinset at the transition.
roger,
ditra is already installed – i just installed the transistion strip on top of the ditra which is 3/8″ so if i install a 1/4″ thick tile and have it flush with the top of the strip that only leaves 1/8″ under the tile. so will a 1/4″ notch be ok by the time i push the tile into the thinset it should be flush – or do you have any other susgestions – just thinking a 3/8″ notch might be to much thinset but im not sure on that. thanks
Nope, that’s fine. If you can get it flush with a 1/4″ go for it. A 3/8″ trowel only leaves an additional 1/16″ of thinset under your tile after installation than does a 1/4 – too much is relative.
Either will work just fine.
roger i set the first tile went good – im filling the cavities in the ditra before hand – did not want to use all my kerabond up any other unmodified thinset i can use for this i have a local home depot that carries versabond – they have like 3 different kinds do you which one is unmodified mixed with water. thanks.
think i found the unmodified thinset (custom blend) is this a good thinset to use for filling the ditra cavities. thanks.
hey roger,
laying tiles finnaly – i couldnt find any stores that carry a 3/8″ x 3/8″ trowel so i have to use 1/4″ x 3/8″ x 1/4″ will this be good enough for the 12×12 tiles. also whats a good un-modified thinset made by laticrete to fill the ditra squares did not want to use all my kerabond up. i know hd has the custom blend but is it any good. thanks.
That trowel will be fine. Laticrete’s standard unmodified is Laticrete 317, it’s good stuff. I like it better than the kerabond. The custom blend is not a good unmodified, it is a very weak unmodified thinset. In my opinion it has no place whatsoever in a tile installation. If you can’t get the 317 get more kerabond and use it throughout. It is always better to stay with the same brand at least all the way through.
roger,
thanks for the advice also how thick should the mix be – one mix i made had slight water on top of the notch ridge but still held the notch – should i make it thicker. im only doing small batches at a time. i am getting good tile coverage thow just don’t know how thick to make the mix. any advice on small batches for laying 3 tiles thanks. i will get more kerabond i have to drive 45 minutes away to get it.
The thinset should be roughly the texture of pudding. It should not have any water on top of it. By the way – it does not taste like pudding, it just looks like it.
Roger,
After tons of research, and wanting to do it exactly right, we installed tile in our bathroom floor this weekend. However, an oversight hit us after it was too late.
We put unmodified thinset underneath the ditra, and modified on top. How grave of an error is this? Should we tear it all up and do it over again?
This is above 2 5/8 ply layers and topped off with with 6×13 porcelain tile.
Hey Jason,
Holy crap! Has your dog burst into flames yet???
Just kidding. It will be fine. If you haven’t grouted it yet give it an extra day or so. If you have just try to not place too much traffic on it for about a week – no dancing! It will be fine, really. 
Ok I did it! Got the Ditra down and it looks good. Laid my tiles out to decide on pattern and noticed an area is a tiny bit unlevel, one tile wobbles ever so slightly. Is this going to be a problem or will the thinset under the tile accommodate that? These are 18×18 tiles. And do I leave 1/8 inch space from the wall as well?
Starting to set the tile tomorrow!
Hi Jodi,
It depends on how much it wiggles.
If it isn’t much then yes, thinset will take care of it. Yes, leave 1/8″ around the perimeter for expansion purposes.
Lots of Ditra Questions:
1. Had 1/2″ subfloor (50 yr old house) Replaced bad sections and put 5/8th ply over it. Would like to use Ditra to keep the height down. Heard somewhere that the second plywood should have 1/8th seams caulked – True??? Also need to use floor leveler – don’t know if that makes a difference.
2. Do I need to apply some other waterproofing or will Ditra alone suffice?
3. I watched the Ditra video and saw their wall joints – I will not be using tile mopboards (wainscoat), do I still use the 90 degree joints and put the Wainscoat over it or do I need something else?
4. Does the same thin set get applied under both the fleece and the tile? And lastly, what type of thin set works best? Thanks for your help.
Hi Debbie,
The seams in the plywood need to be protected to keep the thinset out of them. They are for expansion and filling them with concrete defeats the purpose. You can do it with caulk, silicone, even thin strips of tape. Whatever works.
Ditra can be waterproofed with kerdi-band installed over the seams.
You do not need the 90 degree joints. If you want a totally waterproofed floor you should use kerdi-band at that joint run up the wall a couple of inches and your baseboard can be placed over that. You don’t need the full wainscot.
Over a plywood substrate you want a modified thinset beneath the ditra (fleece) and unmodified above it (under the tile). Over concrete you want unmodified for both. I like Laticrete thinsets – 317 for unmodified and normally 253 gold for modified. Whichever brand you choose to use make sure you get the best unmodified they have available. Should be about 15-20 dollars / 50lb. bag.
roger
can i use a silicone caulk to fill the 1/8″ gap in the plywood if so do i fill it so its even with the top of the wood and will thinset adhere to it when i set the ditra in place. also will the caulk allow movement (dumb question)
Hey Randy,
You can use silicone. Yes it will allow movement. No, thinset will not stick to it, but if you keep it only in the gaps you won’t need to worry about it.
hey roger,
i already put silicone in the gap got some on the outside of the gap though will this be a big deal for the thinset and ditra – its approx 1/2″ on each side of the gap because i filled the gap flush with the top of the plywood then used a putty knife to smooth it hope it will be ok. let me know thanks.
Hey Randy,
It will be fine. Small strips of silicone aren’t anything to worry about. Much better than not allowing your substrate to expand and contract.
I have a small bathroom to tile. I pulled up the old carpet / tile and found 2 pieces of sub-floor bowing up where they meet. I think they got wet and warped some. i tried pulling down with screws ans washers – no luck.
A floor installer came by and recommended the Ditra product. Will it solve my problem? The valley on either side of the joint is almost 1/2 inch.
Hey Mike,
If your floor is bowed the ditra will not solve that. The floor needs to be flat before ditra is installed. If those pieces of plywood are ‘squishy’ then they need to be removed and replaced – tile won’t last over them. If they are not then you can probably sand them down flat then install the ditra. With any option that area needs to be flattened before anything else is installed over it.
hello again roger,
underlayment installed with 1/8 gap – my question do i fill the gap with the thinset when i install the ditra – probably a dumb question. will the wood still expand if needed to. thanks
Hey Randy,
It is better not to. That will allow expansion and contraction in the layers of ply itself. That said, if you get some in there it isn’t the end of the world. Make sure you get full coverage first and foremost.
Just about to install my first tile floor, it is in a bathroom. Using Ditra. Before I cut the roll, do I leave any gap between it and the edge of the wall?
Like I said, first time doing this.
Thanks for the guidance.
Jodi
Hey Jodi,
I usually leave about an 1/8″ around the perimeter. The exact measurement isn’t imperative as long it isn’t touching the wall.
I used Ditra for the first time this week. Sticks fine to Sturd-I-Board with Flexbond. I plan to prefill the waffles, mostly because my tile setter is working alone and I think this will make it quicker and easier for him. I really don’t care about the warranty. I was planning on filling with Versabond. Which of the Laticrete products is appropriate for setting ceramic to the top of Versabond filled Ditra XL? Or something else?
Hey TG,
I like the 254 Gold as my go-to thinset in most applications. It’s a very good all around thinset.