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 
Can I use Kerdi-Band to seal up 1/2″ hardie backer joints for the walls of my bath area and 1/4″ hardie backer for the floor?
i think that it should work just fine.
Thanks for your help
Hi Chris,
Yes.
Hi Roger,
Have you any experience of using Ditra-Heat and, if so, am I correct that a tanking layer (e.g. Kerdi-DS) is required over the Ditra-Heat before tiling? I am curious about this since it would technically break your rule about tiling directly onto the Ditra.
Hi Richard,
The only ditra-heat product of which I am aware is heating elements incorporated directly into the ditra itself. It isn’t on the market here yet, so I’m assuming you’re not in the states? So no, I have not worked with it personally, but tile is bonded directly onto it just like regular ditra or ditra-xl.
Hi Roger,
Yes, I am in the UK. Thanks for taking the time to respond.
Hi Roger,
I have a small deck surrounding my whirlpool tub. (4 inches on all 4 sides). Should the joint where deck meets wall (which will have a 12 in splash) be water proofed with kerdi band? The four inch deck will not have a detra base but rather cement board. Can I apply kerdi band to the backer board and the verticle wall? Use unmodified? Can I place my ceramic tile on wall and deck then with unmodified thinset?
Thanks again You have been very helpful,
Jeff
Hi Jeff,
It doesn’t really need to be waterproofed, but it doesn’t hurt. Yes to all your other questions.
Hi Roger,
I just laid ditra down over a double layer wooden sub-floor. I used a dark gray rapid-set modified mortar (never again – I’m not experienced enough for such a fast mortar). I started with a 3/16″ V-notched trowel, but the first piece of ditra didn’t seem to have mortar saturation of the fleece despite my really pressing it with float, book, hands, etc. So, I stepped up to 1/4″ square notched trowel and was getting better saturation. However, the color looked a little blotchy through the ditra. I assume if I have even saturation of the fleece that it would be an even color. The last piece I tried to put down was just not saturating well. I blame the rapid-set mortar. Even though I was working as fast as I could and trying to keep it from skinning, it was probably a little over the hill. So, I tried walking on top of the ditra with bare feet to put more pressure on the mortar and squish it into the fleece. Well, no surprise it turned out uneven, but I cannot pull the ditra off the floor, and there is less than a 1/8″ height difference in places where I stepped. So…I’m just not sure if my ditra is adhered well enough to floor to prevent future tile failure or if the height difference really makes a difference. I want to say it’ll be fine, and proceed with tiling, and use my (non-rapid set) unmodified mortar over the ditra to even out the height differences (tile is 16″x16″x1/2″ slate). But the blotchy-ness of the mortar color through the ditra mat does worry me a little. Do you think I could get acceptable results with what I’ve described, or should I pull up the ditra/subfloor and start again with a regular 16hr dry time modified mortar between the new ditra and the subfloor? Once ditra has had mortar on the fleece, you can’t reuse it, right?
Thanks so much,
Andrea
Hi Andrea,
Blotchiness doesn’t necessarily mean that it’s not bonded to the fleece. Many times if you have a little too much thinset you’ll see thinset directly in contact with the back of the plastic through the fleece. You still have full contact, but in the darker spots you have thinset against the back of the plastic as well.
Sweet, thanks! Good to know the ditra is probably bonded well to the floor, but does the unevenness of the ditra matter? 1/8″ over short distances… I’m pretty sure I can even this out with the unmodified between the ditra and the tiles, but this might just be the inexperience talking.
No, you can compensate for that as you install the tile.
Thanks!
Hi Roger,
I have removed on 8″ backsplash of ceramic tile and am reinstalling a different ceramic tile backsplash…. This is on a plastered wall.
Some of the top layer of plaster came off (a few mm’s thick) and in a few areas some of the paper drywall face is exposed (no larger than an inch in diameter). Can I tile right over these areas if I use thinset mortar and if so should I use modified or unmodified? If not, what is the best product to repair these areas and do I need to prime in anyway before tiling? Mastic or mortar?
Last question….. I am using ceramic or stone as the baseboard trim and these walls were previously painted. What should I do to insure a good bond for this procedure?
Thanks much,
Jeff
Hi Jeff,
Already answered your question. Best to just ask once, if I have to read every question twice it takes more time. I get to it, but, you know, day job and all…
Hi Floor Elf
I’m a DIY putting in 18″ Travertine in a entry way, hall way, and bath. I have 5/8 OSB on 16″ center joists and 3/8 inch plywood on top of that. Two novice questions.
First the schuter installation pdf talks about a 6″ maximum on-center fastener spacing in the field. Are they really asking for 6″ spacing between each screw used to hold the plywood to the OSB?
Second, how close does the Detra need to be to the edges and where they are butted together? I have some long runs that because of poor cutting and wall straightness have about an inch gap at wall edge. Will this be OK
Thanks
Hey Tim,
Yes, 6″ between each screw. An inch is a little large, but should be fine along the wall.
I have to level 1/2 of my bathroom floor (approx. 5’x10′) so 1/2 will be plywood and the other 1/2 will be a self leveling compound. Can i apply Ditra over this and what type of thin set do I use ? The floor slopes from 0 to -9/16 over a 5′ span. Also what can I use to keep SLC from going over my toilet flange? Thank you.
Hi Grady,
Yes, you can install ditra over that. I would use modified thinset for it. Wrap your toilet flange with perimeter foam (concrete section of big box stores) and wrap a piece of duct tape around it to keep it in place. After the slc cures just pull it out.
Thank you for this info. No one else has said you can lay ditra over both ply and floor leveler. I would assume it would take the modified thinset longer to dry over the leveler.Great site
Hi John,
Yes, it does take a bit longer, but it works just fine.
Grady you can also use the spray foam insulation to protect the drain
Roger,
I’m wondering about using Ditra over 1/4″ hardiebacker. The existing floor has two layers of plywood, then a modified thinset and then the hardiebacker. (All of that prep was done 2 or 3 months ago.) The Ditra would be for mostly for gaining some height (and movement isolation) before installing granite 12×12 tiles…
Several questions occur:
Most fundamentally, would this be okay?
If so, would you recommend modified or un-modified thinset under the Ditra?
Also, should the hardiebacker be dampened just prior to the thinsetting?
Also, the hardiebacker seams have not yet been taped, should they be?
Also, looking ahead, wondering if I should seal the granite before grouting or after?
Thanks for the fantastic job you’re doing with this site!
Cheers!
Hi Harley,
No problem with that at all. Schluter want’s unmodified between ditra and backer. Yes, absolutely dampen the hardi first. Doesn’t matter if the seams are taped or not. They don’t need to be, but if they already are it won’t hurt anything. Unless you have light granite and dark grout there’s no real reason to seal it first. It won’t hurt, though, and may help with cleanup of the grout.
Roger,
Thank you for fielding my many questions so quickly. Can’t wait to get started and feeling much more confident now.
Harley
Dear Roger,
I am redoing a bath that currently has ceramic 12×12 tiles. I am replacing it with 12×24 travertine stone tiles. Tell me if I have this correct:
Plywood subfloor should be a minimum of 1 1/4 inch
modified thinset for installing detra over plywood
unmodified thinset to install stone over detra
can let detra set before installing stone, but may also do tile install at the same time
can use kerdi-band to waterproof seams (should I?) and if I use and want to let detra set first, do I install band at stone install step?
What substrate do I need for stone on vertical surfaces? (18″ wall enclosing tub)
Want to replace base board with 4″ travertine. Any tips?
Thanks in advance,
Jeff
Hi Jeff,
It is correct. Do the kerdi-band as you set the tile. Substrate for the shower depends on your waterproofing method. Usually cement backerboard. You can use a hand sander on the edges of the travertine to shine them up so they don’t look so dull.
Hi Rodger,
I have removed on 8″ backsplash of ceramic tile and am reinstalling a different ceramic tile backsplash…. This is on a plastered wall.
Some of the top layer of plaster came off (a few mm’s thick) and in a few areas some of the paper drywall face is exposed (no larger than an inch in diameter). Can I tile right over these areas if I use thinset mortar and if so should I use modified or unmodified? If not, what is the best product to repair these areas and do I need to prime in anyway before tiling? Mastic or mortar?
Last question….. I am using ceramic or stone as the baseboard trim and these walls were previously painted. What should I do to insure a good bond for this procedure?
Thanks much,
Jeff
Hi Jeff,
You can use modified thinset for your backsplash. You can also skim over the whole thing first to get it flat, then let it cure and install your tile. That’s normally the easiest way. Just rough up the paint behind where your base will be and it’ll bond just fine.
I’m finishing a new master bathroom with heating mat, Ditra and porcelain tile over plywood, in that order. The heating mat is approx 1/8″ thick but will not extend all the way to the walls or under the vanity and toilet. Does it make sense to use the regular (1/8″) Ditra over the heating mat and the Ditra XL (5/16) in areas where there is no heating mat to try and keep the tile flat/level? Or… is there a better way to keep the transition between areas where there is heating mat and the areas where there isn’t level?
Hi Tom,
Ditra and xl will work. This will show you how to do it another way. Installing suntouch
You mentioned the comparible Ditra modified thinset will bond to Kilz primer. I am tiling a bathroom with 19.2″ O.C. 23/32″ plywood substrate with a ton of overspray on the plywood from the contractor painting the doors and baseboards. It’s impractical and very difficult to sand off. I have no issue with adding 3/8″ plywood except that the transition would be (3/8″ + 5/16″ + 1/4″) 15/16″ or roughly 1 inch to a 12mm laminate plus pad or 1/2″. Will the modified thinset bond to painted plywood? Should I just paint over it with Kilz? Also what are my options with regard to transitions and where is the ideal location for a transition at the door way threshhold?
Hi Paul,
Modified thinset will not bond well to paint over plywood. Painting over it with killz will not solve the problem either, you still have a sealed plywood substrate under a thin layer of primer, it won’t bond well. There are several different reducing transitions available for tile, schluter makes several. The ideal location for the transition is under the center of the door when closed.
Ditra GURU,
I am doing a remod in my bathroom. I have the schluter-Ditra down and am now looking to lay the tile to the ditra. I have been reading a lot and am somewhat confused on what to use for this part of the application. I have a bag of polymer modified bed mortar. I am not sure if this is an acceptable material after reading all of the different posts. I could really use some of your insight on this matter so my wife doesn’t kill me if I do this wrong.
Thank you
Hi Fred,
Schluter always wants unmodified mortar between ditra and tile. The stuff you have is not the right stuff. Read through this to see what you can use: Unmodified thinset
my husband installed ditra last night in our bathroom and didn’t read the instructions as carefully as needed.. he used modified thinset as needed between ditra and wood but then also used modified (he had mixed up a whole bag and why not use it was the thinking) between the ditra and the tile (limestone). the ditra site says modified between ditra and tile may take 14 to 60 days to dry/cure. other sites say it will take longer than normal but not nearly that long…. .my question.. how do we know when it is dry/set without ripping up the tiles.
Hi Becky,
You don’t, really. Without taking up a tile there’s no real way to know. You will get an initial cure in about 24 hours, which means light traffic is fine. I do use quite a bit of modified over ditra, I think it’ll be just fine.
great. now… next question.. .how long before i grout or seal the limestone tiles (and if you want to weigh in on order of grout/seal… i think it is seal first with limestone, grout, seal again or on the type of sealer… limestone tiles on bathroom floor).. this is a great help and i am quite relieved not to have to pull it up again.
thanks
You want to seal it first, makes clean-up much easier. You can seal it again once grouted if you want the grout sealed. No need to seal it again for the stone, but it doesn’t hurt.
I am in the process of taking up a practically new engineered wood floor on a concrete slab and replacing it with tile over ditra. The wood is up, but the installller is now struggling with removing the adhesive (which is still sticky) and remnants of blue pad. I think he is thinking of just covering the mess with the ditra and tile calling it a day. This makes me very nervous. What do you think?
Hi Hilary,
Thinset will normally not bond to any excess adhesive left on the substrate. If it won’t soak in water when splashed on it then thinset won’t bond well to it. Don’t let him do that.
Roger, can I use Laticrete 317 to lay down Ditra on a OSB subfloor.
Hi Bill,
No, you need modified mortar to install ditra over any type of wooden substrate.
i currently have linoleum(20 years old but in great condition) over 1/4″ underlayment over 3/4″ osb over 2×10 joist 16″ oc…. can i put ditra over the lino??
Hi Dan,
Sorry, no. You can put 1/4″ backer over it with thinset beneath it, but thinset will not bond the ditra to linoleum well enough to last.
I think I have read the installation instruction for Ditra quite carefully. One thing I’m unclear about is time. In my application (bottom to top) I plan to have 2 layers of plywood, electric heating mat, unmodified thinset, Ditra, unmodified thinset, tile. I would like to lay down my heating mat, cover it with thinset and Ditra and then be able to leave it for a couple of days. Then I would like to come back with the next layer of thinset and tile. Can I do that, or do I have to do it all in “one shot”??? Thanks a bunch!
Hi Todd,
You need modified thinset under ditra when going over plywood, not unmodified. You can install the heating and ditra and leave it for as long as you need to before tiling.
Hi Roger,
Thank you VERY much.
-Todd
Hey Roger:
I know you are the GOD of tile but was wondering if you could answer a question for me? Can you use Kerdi to place down on a concrete floor before
installing a “wood floor” over the concrete ? Brother lives at the beach and water table is high and installers have told him to put 6 mil plastic down then the wood. I thought kerdi might work ?????
Thanks for answering a question that really isnt tile related, I just figured you might know…….
Thanks
Chuck
Hi Chuck,
You can, but it’s not really a cost-effective alternative. I actually believe that roofing felt would be a better option in that scenario. The pores of it actually swell shut when exposed to moisture. But yes, you can use kerdi if you want to.
Thanks for that. I am installing tile on a concrete floor ( small bathroom)
wondering if:
1) I need to use a “primer” on the floor before putting thin set down ?
2) What would be the best thin set to use in this situation ?
Thank you so much for your expeditiously reply, your the Bomb !
I’m assuming you mean for the Kerdi…
1. No. Just make sure that the slab will absorb water when you splash some on there. If it does then thinset will bond to it just fine. If it does not then you’ll need to mechanically or chemically scarify the surface to open the pores of the concrete.
2. Schluter wants unmodified thinset over concrete with ditra and kerdi. Laticrete 317 is a very good one. There are others also: Unmodified thinsets.
Actually the Kerdi question was for installation of a wood floor, but you answered my question, Laticrete 317 onto the concrete after making sure the concrete will absorb H20……….Thanks for the expeditious reply, as usual you have the answer, nobody better than the floor elf !
PETA must love you as you have probably saved more dogs than anyone on the planet.
Well, sorry for the editorial but after re reading, I actually “think” I understand !! Laticrete 317 would be used over the Kerdi (?)
but reading posts on the thinsets, I think Laticrete 253 would be the way to go on tile onto concrete, making sure concrete will
absorb H20………..?
If you are installing tile directly to the concrete then use 253. If you are installing kerdi or ditra over the concrete first then use the 317. 317 is used to install tile to all schluter products.
Dear Tile God: what is the difference between the colors of thinset? I ran out of white thinset and mistakenly bought grey which I used for the last three pieces. Is there a real reason for the difference in color ? Thanks for your expeditious reply. If I have to I will take the last three pieces I installed and rip them up and put white underneath them..
Thanks for all your help, we couldnt do it without you and there wouldnt be any dogs on the planet if you werent helping !!
Hi Chuck,
The difference in concrete colors is the color. That’s it. The white is made with a bit purer ingredients, but it’s only to make it white. There is no discernible strength difference between the two.
First, good job on the “kerdi waterproofing bundle” I purchased from you the other day. Not only is it filled with a lot of great info (of course…you knew that…), but is also very entertaining.
So…I have been directed to remodel our master bath (you know by whom…), and I have gutted the entire area as well as the adjoining master walk-in closet. We are tossing the tub entirely in favor of a larger walk-in shower. Of course, I’m planning to use schluter products throughout, but a few things regarding the product and installation still perplex (always wanted to use that word…)…me. 1. Is DITRA-XL the correct choice on the entire floor since we are using travertine tile over 3/4 inch plywood, with electric floor heat, embedded in pro-leveler cement. I was planning to use KERDI-BAND around the perimeter of the floor and walls to aid in water proofing, as well as on the ditra seams…but not certain it is necessary.
2. I know I can use regular sheet rock on the shower walls, but I prefer to use the hardi-cement board as you state in your writings…however, what do you feel about the kerdi board (besides being expensive…).
3. Using KERDI in shower area, including ceiling, butting the KERDI, and use KERDI-BAND over the seams. Do you prefer the “butting” method, or overlap?
4. We want to use the KERDI-LINE linear drain, against the back wall of the shower, and I assume the easiest way to do it is to get a linear drain which is almost the entire length of the shower (ours is 4′ X 5’6″). I assume it will be prudent to use the Schluter-SHOWERPROFILE-S and -R, but not sure how they are used exactly with our application.
5. I am not sure whether to build a sloped mudd bed, or use KERDI-SR ramp. Since the shower floor is large, one KERDI-SR will not be big enough, so if I go that route, I will have to bond two (or more) ramps together.
6. For the curb, I was going to use 2×4’s and cover in hardi cement board and kerdi…I know Schluter has the polystyrene curbs as well, but since we are putting glass panels on top of the curb, thought the 2×4’s would be a better choice…your thoughts?
Apologies…you probably rolled your eyes a couple of times at all my questions…but I want to do this right (of course…), and although I have installed tile in several homes, schluter is new to me. Appreciate any advice, and thanks again for the great reading.
Cameron
Hey Cameron,
1. If you are installing travertine you REALLY should have two layers of ply – another 1/2″. However, schluter says XL is acceptable in that scenario, so your choice. Waterproofing the floor with kerdi-band isn’t necessary, but definitely doesn’t hurt anything.
2. 90% of my showers are now built with kerdi-board. It’s worth every penny.
3. If I have kerdi-band in the truck I’ll butt it. If I don’t I’ll overlap it.
They work equally well.
4. showerprofile-S is for drains on one side or the other of a shower – not yours. Showerprofile R is for the bottom of the walls so you have a stainless trim there which tapers rather than tiles which are cut to the taper. Here is a pdf to describe how they work: http://www.schluter.co.uk/media_produkte/schlueter_db_14_1_showerprofile_s_r_uk_1010.pdf
5. I would use mud. I would always use mud.
6. The polystyrene curbs work just fine with glass panels, but I prefer the 2×4’s as well.
We are remodeling a home. We have done tile in the past, but this is our first exposure to Ditra. When we tore out the old tile, my wife felt there was a bad smell stuck in the flooring. I took out the hardy-board along with the tile, but she still felt there was a smell in the wood. She painted the floor with KILZ. Does this mean the thinset will not stick as well as if it was applied to bare wood? Should i rough sand the floor (belt sander) prior to installing the Ditra?
Any experience with this problem?
Keith
Hi Keith,
The thinset will bond just fine to the killz. I’ve installed over it, it gets a great grab to the thinset.
What are the limitations, if any, for installing elect radiant heating mats over the ditra?
Hi Chris,
In regards to what? Any currently available electric heating products (of which I am currently aware) are acceptable for use with Schluter Ditra. The heating, however, is placed beneath the ditra, not on top of it.
Hi Roger,
I plan on using Ditra for my floor tile installation. I read the online manual and Ditra says to use modified thinset between Ditra and OSB. My question is what to use between Ditra and porcelain tile. Tile installation instructions say to use modified, but Ditra manual says to use unmodified.
What do you do/recommend?
Thank you in advance for the help!
Hi Amy,
If you can get a decent unmodified use it. If you can’t use a good modified like versabond. If you use modified you’ll lose your warranty (but you knew that).
Is Ker 121 polymer mortar a good choice for laying 1’x2′ porcelain tiles over my ditra ? If not what then? And what size trowel spaces do you recommend .
I found that the biggest issue with the Ditra was the term “thinset” most places I went refer to Thinset as a self leveller. 2
Hi Patsy,
Thinset is not self-leveler. It’s two completely different products. If they tell you it is self-leveler you need to find somewhere else to buy your stuff.
Ker 121 is a modified mortar – you want unmodified. Read through this: Unmodified mortars
And this: Proper trowel sizes
Hi!! I’m using ditra to re tile my bathroom floor. If I am using natural stone, before I put down the thinset do I have to add another layer of plywood?? The substrate is now 3/4 inch plywood. The previous tiles were porcelain.
Thank you soooo much!!
Tina
Hi Tina,
Yes, with natural stone you want a minimum of 1 1/4″, so another 1/2″ of plywood is needed.
can Ditra be used as a base for vinyl flooring? If so, would it be possible to, later, pull up the vinyl and put down travertine?
I wouldn’t recommend it. It’s not made as a substrate for any type of glued adhesive, or as one with loose-laying flooring over it. It simply won’t stand up long-term. The compression strength derives from having the product filled with thinset.