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 
Common Mistakes and Fixes
Improper substrate
Proper substrates consist of tile or wood. That’s essentially it. Specific types of wood vary, but your substrate should be one or the other – BARE, with nothing installed over it. The images above depict Ditra installed over linoleum. If your thinset will not bond to the surface you are installing over it will fail – every time. If you are unsure whether you can effectively install over something, just ask. I answer all questions.
NOT fully embedding the ditra fleece into the thinset
Spreading thinset and simply laying the Ditra on top does not constitute ‘installing’ it. The fleece on the underside of the Ditra needs to be fully embedded into the thinset. This means that thinset will encapsulate each thread of the fleece and surround it, thus locking it into the cured layer.
Once you lay it down you need to use a flat…something, to push the ditra down into the thinset. I use a concrete float or a straight-edge. You can use your (clean) trowel, a float, even a flat 2/4. Anything to press the ditra into the thinset layer.
You can see whether this is happening after you get it installed. IF it is properly embedded you can see it through the plastic from the top, those areas will appear darker (the thinset is directly against the backside of the plastic, which means the fleece is embedded).
While I don’t recommend it, you CAN use white thinset to install the Ditra, you can still see the color change in the embedded areas, it just isn’t as pronounced. Gray is always better for installing Ditra to the substrate.
Improper type of thinset used for the type of substrate
When installing Ditra you should use UNMODIFIED thinset when installing over concrete, and MODIFIED thinset when installing over a wooden substrate. With this most failures are a result of using unmodified thinset to install ditra over a wooden substrate. That will eventually fail 90% of the time.
Not properly filling the cavities when installing tile
The mechanical aspect of Ditra relies on the dovetailed cavities in the top being completely filled beneath the tile. If they are not, you do not get the full support needed, nor the proper bond to the membrane, which can lead to failure.
Fill the membrane with thinset using the back (flat) side of your trowel, spreading in every direction, THEN comb the thinset out in those pretty little lines for your tile. Properly filled cavities is the only way Ditra works.
Frequently Asked Questions
What type of thinset do I use when installing Ditra to my substrate?
When installing over a wooden substrate use modified thinset. When installing over a concrete substrate use unmodified thinset.
Can I use modified thinset to install tile to Ditra?
In reality? Yes, you can. No, it isn’t necessary. Yes, it will void any warranty. And yes, you likely have access to unmodified thinsets, even if you don’t realize it. Bonus: It’s normally cheaper than modified thinsets.
Can I fill the cavities flat then come back later to install the tile over it?
Yes, you can, with a few caveats:
Do not fill it, wait a week while treating it as a regular floor you can walk all over, then decide to install tile over it. If left untouched (unwalked) you can wait a week. But it’s always better to fill it, then tile over it the next day or two. Filled Ditra IS NOT a ‘wear layer’, meaning that once cured it is not designed to endure regular foot traffic. It’s still an ‘in process’ layer, not a temporary placeholder until you FINALLY decide which tile you want.
If you fill the cavities, try using your grout float. It works much better and takes off the paper-thin layer which will sit on top after you fill it with your regular trowel, then crumble into a dusty mess when you look at it the next day. The float keeps most of the thinset just below the surface, in the cavities where it belongs.
Roger,
Just a question about your reply to Joyce’s question about substrate. You replied that drywall and cement backer board are the two, I guess I thought Ditra could be used over plywood and their own site states OSB, when used to their specs is OK, maybe I am misunderstanding what she means by substrate or are plywood and osb acceptable?
Hey Judd,
Sorry, I just corrected that. I answered the question for kerdi rather than ditra – she asked me about ditra. You can install ditra over plywood, backerboard and concrete. Schluter DOES state that it can be installed over osb – HOWEVER – in order to do that you must use a thinset approved for use over osb – you aren’t going to find one manufacturer that states their product is. You still CAN NOT install it over particle board.
Hi Joyce,
Answer redacted – I answered the question for kerdi rather than ditra. Please see answer below.
Crap, sorry Joyce. I was thinking kerdi last night when I answered your question about ditra. You can install ditra over plywood, backerboard and concrete. Schluter DOES state that it can be installed over osb – HOWEVER – in order to do that you must use a thinset approved for use over osb – you aren’t going to find one manufacturer that states their product is. You still CAN NOT install it over particle board.
Hi Roger,
Thanks for your reply to my recent question about porcelain over ditra install. I have another enquiry:
I laid some porcelain 13″ and 6.5″ tiles in a hopscotch pattern in my laundry and half bath area recently. I used ditra set on solid double plywood substrate with modified thinset and per ditra instructions set the porcelain tiles with kerabond unmodified on top of the ditra. The substrate was flat prior to laying the ditra (used SLC in areas that needed it,etc.). I had to tile different areas of the room over a period of several days to have walking areas, etc. and once each day’s work cured, I noticed that I seemed to have problems getting each day’s work to match heights with previously set day’s tiles that had cured and set. I thought I was careful and laid the tiles flat without lippage issues but it seems that after the thinset cured there was some sagging or movement of the most recen tiles or I was unable to match newly set tiles to the existing heights of previously set and cured tiles. Could this be the difference between how I mixed my thinset each day varying ( I tried to keep that very consistent)? I backbuttered all the tiles to ensure full coverage. I am wondering what the issue(s) might be and how I could avoid this problem in future when I lay tiles in another area over a period of days, not in one single session. How do you address the issue of laying tiles in the same area over a period of several days- Perhaps there something I’m missing in how I set the tiles or my installation of them? Maybe pressed some in too much or ? Shouldn’t be this complicated…. Thanks again for your expertise!
Hey Lee,
It’s mostly just practice and experience. There is no real secret to it at all. I am always pulling up tiles to add or remove thinset to get the height correct – it’s just part of setting tile. The best thing to do is have several straight edges and make sure everything is on the same plane. Do not be afraid to pull up every tile to get the correct amount of thinset beneath it. I use to start floors with the expectation of pulling every tile up at least once to correct the height.
Thanks Roger,
So does unmodified (or modified) thinset set up somewhat lower or sagging after fully drying/curing? If so, I would expect that the tiles end up setting somewhat lower than you initially planned when you initially laid them. Then when you come back on day two or three (or longer) to set more tiles (and level them to the previously set tiles), once these tiles dry, they end up lower than those previously set? Is this my theory or do I just set tiles for succeeding days to the same level as the previous days’ cured tiles? Maybe it’s just my care in setting each days’ batch of tiles that’s the issue, and I need to be more diligent like you have mentioned…
It really depends on which specific thinset and how much water you add to it. The more water the more shrinkage. The more sand in the thinset mix the less sag the thinset will have once cured. Every thinset is different. It really is more a matter of experience with both setting in general as well as with that particular thinset. The best option is always to set it all in one shot. If you pound your tile down with a rubber mallet it will considerable lessen any sagging the day after.
I wouldn’t mind chemically removing the cutback but would that affect adhesion to cement floor after???????????????
Most chemical scarifiers have instructions to neutralize or remove any residue left after using. As long as you do that it won’t be a problem.
Thank you for the reply. I hope this doen’t qualify me as a jackass but what if i just set the Ditra on the cement floor and set the tile on it?? would that give me a secure free floating tile floor???????
Hey Jeff,
It would give you a free floating floor but it would be far from secure. Any movement at all is going to create problems and unless your concrete is laser flat there will be movement.
Hello. I want to lay ceramic tile on my cellar floor. I was originally going to put down ceramic tile backerboard but read lots of posts against that. I really like what i have read about Ditra. The floor has peel and stick tiles on it now that when I take up leave a black cement floor. That would be glue put on the cement before peel and stick laid down???? I like the idea of somthing between the tile and cement floor for better adhesion. I have never done tile on cement, only backerboard. Do you think I need the barrier between the tile and cement floor or lust lay tile and what about the black material under the peel and stick if i just lay the tile on the cement floor?? thank you.
Hey Jeff,
The black stuff is called cutback, and it’s a pain in the ass. It will need to be removed, thinset will not adhere to it over the long-term. You can try to soak it down and scrape it. If that doesn’t work you’ll need to mechanically or chemically scrarify the surface of the concrete enough so it will soak in water. If the surface soaks in water when you splash it on there then thinset will adhere to it properly. You don’t need a membrane over the concrete, but it is always advantageous because concrete actually moves quite a bit. Ditra is the better option.
Alright, first off, this is the most helpful site just about ever. Great job!
Now, here is my question: Will it work to apply slate tile directly over a plastered brick chimney if the plaster is skim-coated to be flat? I have one that juts out into my kitchen that my cats (the jerks!) have decided makes a great scratching post. It was covered with tattered wallpaper until about fifteen minutes ago when I took it down. The plaster is OLD (80+), but completely solid. I don’t see any reason why it wouldn’t work, but then, I’m usually wrong!
Thanks for the advice!
Hi Renee,
You’re right. You can install the slate directly to the plaster with a good modified thinset.
Thanks Roger!
I’m glad to discover I’m right for once!
-Renee
Hello
i am dealing with new construction. my contractor opted to fiberglass the shower stall floor and 2 feet up the wall instead of using a rubber pad. the fiberglass job is great , all plywood and drain are very well sealed.
i am now wondering the next step in this process, if i am not using a rubber membrane, should i now lay a bed of thin-set on the fiberglass let that set and then use mortar to set the tiles? I am installing a river pebble tile floor .
the drain is in the center of the shower, i assume i should be setting a thin-set base on the fiberglass in an effort to build a little pitch towards the center of the stall , is that accurate?
if i am to use thin set prior to mortar to set the stone tiles, can you suggest , modified , unmodified etc for both layers?
any advice is greatly appreciated as start tis work.
OK, we’re getting down to the wire. I have looked up some grouting information, because that’s the next step. I noticed you’re not a big fan of sanded grout with polymer. I just bought Mapei Keracolor sanded grout with polymer. We really, really, really don’t want ugly, discolored grout. Are we in for trouble, here?
Thanks!!
Hey Ann,
Regular sanded grout with polymer is just fine – I use it all the time. What I am not a fan of is the liquid polymer additives which are mixed with grout in lieu of just water. Can’t stand them because they drastically skew the working time and cleanup ability of regular grout. You’ll be just fine with keracolor – it’s good grout.
I wish I read your posts before! I have just installed ditra, unmodified thinset and slate tile. I have not grouted yet. Two tiles have just popped out. There is full coverage on the ditra, a nice looking set, but no thin set stuck to the tile. Not all the tile backs were buttered. Should I chip out the thinset from the ditra where the tile popped and reapply? or can I epoxy the tiles back and move on?
Hey Erin,
They all should have been buttered – but you know that now. You can just reinstall them with thinset, it will work just fine. No need for epoxy at all.
Hey Roger, great website – thanks for sharing your knowledge. We are wanting to install Ditra in a hallway. We are in the process of removing some peel n stick vinyl tiles on the existing floor. The tiles have left a sticky residue on the subfloor. Do we need to be concerned about whether the modified thinset will bond the Ditra to the subfloor properly with this residue on it? Of course we would prefer not to add another layer of subfloor or remove the existing subfloor but I also don’t want to have to redo this job in 2 or 3 years.
Hey Dave,
It likely will not stick well. That residue needs to be removed. Try soaking it with water then using a razor scraper to take it up. The glue for those tiles usually comes up fairly easily with water – although it is messy.
Hey Roger, where can I get that great tapered square trowel that the Schluter pro uses so effortlessly to install Kerdi-Band?
Hey J.C.
You talkin’ about these? You can get ’em right there.
Help please just tell me the brand of modified thinset to use to bond ditra to OSB. I’m so confused.
Thank you! cindy
No manufacturer will recommend their product for installation over osb. That said, you can use a good modified thinset such as laticrete 253 gold or even versabond from HD or Mapei ultraflex II from lowes.
Just ripped out the vinyl/luan underlayment in my 10-year-old bathroom. I have 3/8″ plywood subfloor, and it is sturdy. Can I put ditra right over the plywood or do I have to do another 1/2″ plywood underlayment? I don’t want to get too high with the floor as I am laying slate and its fairly thick to begin with. What kind of thinset do I use under the ditra to adhere to the plywood? Also, the reason I took the vinyl out to begin with (besides it being ugly!), my kiddos have a tendency to splash an inch of water out of the tub when they bathe. The vinyl got kinda wet. So, I want to make sure that doesn’t happen again. I have a plain old acrylic tub/shower combo. What kind of transition do I put between the tile and the tub from to waterproof it (besides caulk, which didn’t work the first time)?
Hey Niki,
You need to put 1/2″ plywood over that. The required minimum thickness per standards is 1 1/8″ double layer. To be up to standards you technically need to add 3/4″ plywood. Use modified thinset to adhere the ditra to plywood. Use silicone between the tub and tile. The combination of ditra and silicone will keep water problems from arising.
Can I install the ditra one day let it set up and then lay my slate the next or following day? Or is it better to do it all at the same time.
Hi Judd,
Yes, you can do it either way.
Hello
i am in the process of installing a bathroom tile floor, its new construction so plywood substrate. i have installed an electric heating system as per specs, i have covered the electric coils with thinset as per the instruction as well, however there are some spots where the heating coil was not fully covered by thins set. i have applied ditra over this thinset using the correct trowel (which i why i think some of the heating cable is not fully covered. My question is this, do i have anything to worry about where the ditra felt material may be in contact with a a heating coil and there is not enuf thinset? I am wondering if it would be or could be a fire hazard as that material is warmed by the element. Other than that installation went well, but concerned about the contact issue before i install the tile. Thanks for any insight.
Hey Bill,
Absolutely nothing to worry about at all. The ditra can be laid directly against the coils without creating a problem.
Hello Roger,
Thanks for your very informative site. I’ve learned a lot here!
I have a substrate question. I’m wanting to put ceramic tile in the kitchen of my home which was built in 1970. The current floor has one layer of sheet vinyl over 1/2″ particle board which is over a sub-floor of 1×6’s over joists @ 16″o.c. According to page 9 of the Ditra Handbook, I *could* install Ditra over the existing vinyl. The vinyl seems to be generally well-adhered but is worn through in a few places and curls up at some place along the perimeter.
Would you recommend:
1. Patching the worn places in the vinyl with thin-set or embossing leveler, skimming the rest, and then installing Ditri over it? OR
2. Tearing out the vinyl and particle board, add a layer of plywood or OSB, and then installing the Ditri?
For #1 it’s a little hard to know how “well-adhered” the vinyl is to the particle board. But #2 is a lot more work. I’d either have to remove cabinets or figure out how to cut around them. Also, if I went with #2 would 3/8″ material be sufficient or would you go back with 1/2″? Do you have a preference between plywood and OSB?
I would really appreciate your thoughts on this,
Steve
Hey Steve,
A very expensive lesson early in my tile career taught me to choose #2 – EVERY TIME.
You don’t want to learn that the way I did. Find someplace nearby where you can rent a ‘toe-kick’ saw which will allow you to cut the particle board out up to the bottom of the cabinet base. I would use a layer of 1/2″ plywood, then ditra. OSB has a debonding effect on a lot of thinsets – they won’t hold long-term. I know it’s cheaper – I have to pay for plywood too, but osb just doesn’t work.
Thanks for the quick reply Roger. Now that I’ve started to remove the particle board, I have a couple follow-up questions:
1. It turns out it is 3/8″ particle board I’m removing. So would it be OK to replace with 3/8″ plywood rather than 1/2″? I’m not sure I have extra height at my two exterior door thresholds. With the 3/4″ 1×6 sub-floor adding 3/8″ plywood would give me a total 1-1/8″ substrate between the 16″ o.c. joints.
2. There was roofing felt underneath the particle board. Do I need to replace it when I install the plywood or can I leave it out since the Ditra serves as a vapor barrier? (This floor is over a ventilated crawl space).
3. When installing plywood underlayment, do you prefer nails or screws?
Thanks again,
Steve
Hey Steve,
Yes, you can use the 3/8″ instead. 1/2″ would be better, but if you don’t have the room, you don’t have the room.
No, you do not need the felt beneath the plywood. The ditra will work perfectly in that application.
I always use screws – for everything. I’m an ass like that. But they don’t ever come out. Ever.
Hi there,
We just ripped up old layers down to the subfloor in our kitchen. What we had left was 5/8″ original subfloor – house was built in 1965 so no tounge and groove.
I have to be honest…the subfloor does not feel all that sturdy but part of the nails came up with the rest of the tear up so we def need to screw.nail back down…however some parts of the wood got holes in it from the crobar, etc. I called a few tile co’s who sell Ditra that we want to use and they advised to glue and nail/screw a 1/4″ plywood on top of the existing subflloor to make it more sturdy. Then lay the modified thinset, lay Ditra then tile.
Thoughts? What are our other options? We can’t remove the original subfloor as counters are not removeable. I don’t want to comprimise the tile install and don’t want the added height of using plywood and then duraboard, etc.
Thanks!
Hey Kay,
You NEED two layers of plywood (the 5/8″ being one) and an additional 1/2″ minimum for a total of 1 1/8″ plywood, then your ditra. 1/4″ plywood is not going to shore up your floor significantly enough for a tile installation. A layer of 1/2″ then ditra should be fine.
I have flexbond for porcelain tile to ditra to 5/8 + 1/2 plywood – will that work on both sides of the ditra? What is the difference between fortified, modified and polymer modified?
http://www.homedepot.com/webapp/wcs/stores/servlet/ProductDisplay?langId=-1&storeId=10051&catalogId=10053&productId=202243461&R=202243461
Hey Dana,
Yes, you can use that for both sides of the ditra, although you’ll lose your warranty from Schluter. The only difference in all those thinsets is the particular polymer with which it is modified. They are all, for all intents and purposes, simply modified thinsets. The ones with greater polymer content normally allow more flexibility, and are more expensive.
Hope this isn’t extreme jackassery (maybe just run-of-the-mill jackassery) but can I install Ditra over luan plywood? After ripping out the old linoleum I put a layer of luan over the 3/4″ subfloor (anything thicker wouldn’t have left room for tile). Reading the Versabond bag I noted with horror that it says “do not bond directly to luan plywood”. Do they mean don’t put the tile right on the plywood, or are they saying that luan ahouldn’t be in the equation anyplace. (I hope not, because the toilet flange is in and the luan is screwed down about every 4″!) Thanks!
Hi J.T., don’t shoot the messenger.
Luan has no business anywhere beneath a tile installation at all. It is simply too unstable and unpredictable to stand up to a tile installation. If it sees one ounce of moisture at all it swells to about double the size – that cracks stuff. Sorry but that luan really needs to be removed. It would be much, much better to simply install the ditra directly to the layer beneath the luan if you don’t have any room for height.
Good Morning – Thanks for the reply! I’d rather do it right than do it again, and knowing that the removal is a must takes some of the sting out. Thanks again!
Here I am again! We’re the ones with the natural sandstone bathroom floor and wall tiling job (wainscotting-type walls. We LOVE your tile tips, and are emailing you a couple of questions about the actual application of the tile floor. We figure your tile tips might eventually cover these questions, but, on the other hand, we might not be able to wait that long.
Question #1: First off, we replaced the durock on the 25 square foot, dinky little bathroom, and replaced it with 1/2″ plywood. It feels much more solid! Plus, the “wave” we asked you about earlier is gone….yipee!! So, now we have 3/4″ OSB/1/2″ plywood subfloor that’s very level. Next, we’ll put the Ditra down, followed by the tile.
We’re planning to place the tile on the diagonal. Unfortunately, none of the dinky little walls are square, so we end up (in dry fitting it) with a little bit off on the tub wall, or a little bit off on the towel warmer wall. Plus, chalk lines on the Ditra are going to be tough, so what we have come up with is to nail a board to the floor of the bathroom at a 45 degree angle that works for the tub, and doesn’t get too kitty-wampus on the other wall. (maybe I saw this in a magazine, maybe I dreamt it, I don’t know…..) Then, we’ll butt the first row of tile to that, and work from there. The next day, we’ll remove the board and work into the corner that we couldn’t get to because of the board. I’m certain you have some better way to do this. BTW, we found out that the water balloon method of blocking the toilet drain with a water balloon is a way better approach than the paper towel method, particularly when the neighbor’s Cairn terrier puppy visits, trots into the bathroom, and pulls it out and tears it up, allowing sewer gas to escape everywhere. As we say in Minnesota, uffda!!
Question #2: Besides the diagonal floor, we are also planning a diagonal pattern on the wall inset where a towel warmer is going to be placed. My husband, who is a tile saw junkie, is planning to cut 1/4 tiles from the 12″ x 12″ sandstone we bought. Is there a way, besides carefully measuring, to insure that each tile is uniform? We’re planning to use the little “swirly” technique with the thinset on the ceiling part of the inset so it stays put. Thanks!!
Ann
Hi Ann,
Here I am still!
1. The board method is likely your best bet, it actually works very well. I actually do it so much that my method relies more on my eye than anything else. I normally start at the tub because that’s usually the first thing noticed – so you’re right about having the unsquare area at the wall.
2. I normally cut each tile at 1/8″ less than half a tile. Most 12×12’s aren’t uniform so if you cut it a bit smaller than half you can cut every tile the exact same size and not have to worry about different sizes. That said, natural stones are usually very uniform. So you can measure carefully, set your saw up and go to town.
The swirly works well – I just put 24×24 tiles up on a ceiling today and nothing fell on my head!
Dear Roger,
OK, two more things. One, any idea what we’ll find when we take out the Durock to change it out for 1/2″ plywood? Will we have to sand out the thinset that’s left over, or can we just put down adhesive and the new layer of plywood? Also, your reply to Chester also has me thinking. We have unmodified thinset right now, but if we switch our application from Durock to plywood, should we also switch to modified thinset for the Ditra to plywood part of the application?
Thanks,
Ann
Hey Ann,
If it is in fact particle board rather than plywood beneath there it will likely come up in pieces. If you can get the backer off without tearing the floor up you will need to remove as much thinset from the substrate as possible. Yes, you need modified thinset to adhere ditra to plywood.
Hi there. I have a installation problem and I am looking for some much needed help with Ditra!
I have a double layered plywood floor I am installing Ditra on. It is about 1 inch thick or so. The tile I am using is 13×13 porcelain tile. My questions are:
– What trowel do I need to lay the Ditra?
– What trowel do I need to lay tile onto the Ditra?
– What thinset do I need for Ditra to Plywood application?
– What thinset do I need for tiles to Ditra?
– How do I correctly mix the thinset for Ditra to plywood application?
I am looking for exact answers, simple terms, so I can go to the store and say this is what I need.
I know this stuff is listed in the manual they give you, but it does not say a specific kind to get. I know nothing about tiling and this is my first try at it, it is a very small bathroom I am tiling so it is a trial, but I want it to last. My only place to purchase materials is Home Depot.
Thank you.
Hi Chester,
You can use a 1/4 x 1/4 or 3/16 x 3/16 inch trowel for you ditra. Use the 3/16″ for your tile. Ditra to plywood needs modified thinset. Porcelain to ditra – Schluter wants unmodified, TCNA specs want modified – I use modified. You will void your warranty from Schluter if you use modified.
About the consistency of pancake batter. Versabond modified thinset is what you want to get from HD – use it for everything. It’ll work – really. 
Hello Roger.
Thank you for your speedy reply!
So your saying go against what Schluter says and use modified for both adhering to the plywood, and for adhering tiles to the Ditra?
This is the thinset I have, is this what your suggesting?
http://www.homedepot.com/buy/flooring/flooring-tools-accessories/custom-building-products/versabond-fortified-thin-set-mortar-white-50-lb-50340.html
Yes, use the modified for all of it. Yes, that is the thinset I’m talking about.
Ok, one last question, I think?!
The surface of the Plywood had tiles laid directly to it before this. I have removed all of those and sanded down the old thinset so it is smooth and level. I will wash it off with a damp sponge to pick up the dust before I lay my thinset for the Ditra.
Does this change things at all? Will the thinset bond to this surface just as well as if it was clean plywood?
Thank you very much for all of your help!
I was just reading, modified thinset will not allow the thinset to dry completely between the Ditra and the tiles. If so, it will take a long time to cure, and the tiles may shift.
I have unmodified Versabond, and modified, should I just use the unmodified on the tiles to make sure there is no evaporation issues with modified?
I’m not sure where you got unmodified versabond – no such thing exists. If you got it from home depot then what you have is custom blend – and it is absolute garbage. Seriously – I wouldn’t use it to weigh down my truck in a snowstorm.
Use the versabond for all of it, it works fine. The tiles will not ‘shift’ unless you’re walking on them before 24 hours or so. You can also fill all the waffles, let that cure, then install your tile. That ensures the thinset in the dovetails is cured – that’s where it has problems beneath large format tile.
The thinset will adhere to it just fine. No problems with that.
Dear Roger,
I’m the person who recently sent an email regarding sandstone application on a bathroom with 3/4″ OSB and 1/2″ Durock with Ditra on top of that. Well, presently we have purchased the Ditra and the unmodified thinset, but we haven’t installed the Ditra or the stone as of yet. Your response to the woman with the loft got me to thinking (dangerous, I know….just ask my husband). The Ditra manual suggests two layers of 3/4″ plywood, followed by Ditra, before laying natural stone. You stated that Durock doesn’t add any structural value. So, would it be advantageous to us to remove the Durock (which would be fairly easy at this time), and replace it with 1/2″ plywood? I know that 3/4″ would be better, but then the stone wouldn’t match up to the threshhold. Actually, the threshhold isn’t fastened down, yet, so maybe we could shim it up or raise it up. Anyway, my question is, would it be a BIG advantage to rip out the Durock and replace it with 1/2″ plywood, or would it be a little advantage, or no advantage? And, if that’s the case, would 1/2″ be better than nothing, or should we try to do 3/4″ plywood?
Thanks,
Ann in Minnesota working on a cabin in Wisconsin
BTW, I love your tile tips, and have shared your web site with my son, who occasionally moonlights as a tile setter, and is very meticulous in his work.(We’re using his tile saw.) He offered to do this for us, but we would rather do it ourselves, even if we screw it up. Go figure…….
Hey Ann,
You need a minimum of 1 1/8″ double-layer plywood substrate beneath your ditra. If you remove the durock and install 1/2″ plywood, then ditra, then stone you’ll be right where you need it. That will give you plenty of support for your installation.
We want to install 18″ porcelain tile on a second floor that has 3/4″OSB with floor trusses that are 2′ apart. Some are telling us that only ditra needs to be installed, while others say a 1/2″ cement backboard is required with the ditra. Do we need the 1/2″ backerboard?
Also, it’s 16 x 15.5′ open area (loft) that we will use as a gaming room and a library.
Sorry, didn’t see this until I answered the other – same answer applies, though.
Hi Amber,
Neither.
Sorry. Ditra XL says it can be used over a single-layer of 3/4″ with 16″ o.c. but not with the 2′ you have there. You need at minimum an additional layer of 3/8″ plywood, then your ditra to have an installation that meets minimum requirements. Cement board adds absolutely no structural support at all, it is simply a suitable substrate to adhere the tile to. (Wow, that was horrible sentence structure – sorry)