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 
Sometimes I come here just to read your snarky comments. Refreshing.
2nd floor bathroom. 16 inch on center 2×10 joists. 9ft x 14 ft bathroom, with the joists running with the 9 foot side (90 degrees to the 14 foot side). 3/4 OSB on top of that.
I have to remove several rotted areas around the tub and separate shower stall. At least one full 4×8 section under and in front of the shower. Possibly another to fix urine stained OSB. Will probably put blocking in just to satisfy my paranoia
My question. Would it be beneficial to install 1/4 backer board on top of the OSB prior top laying ditra? One reason I am thinking of it is I may use Zinser BIN primer to cover feline urine stains where I can’t replace the OSB. Would the thinset stick to this shellac based primer?
And if I go direct to the OSB, MODIFIED thinset under the ditra?
Yes.
Hey Bruce,
Thinset will not bond to anything shellac or urethane based. If you cover that osb with a layer of ply to bond the ditra I would use 3/8″ rather than 1/4″, the 1/4″ tends to warp when exposed to the moisture in the thinset.
I and a DIY guy and have a 24′ x 8′ outdoor porch that is exposed to sun and occasional rain in southern CA. The ceramic tile on it is cracking badly. I believe the tile was laid over plywood (circa 1980). I want to replace the floor and was planning on also replacing the plywood, overlaying it with cement fiberboard and then laying ceramic tile. Then I ran into your comments on Ditra; it sounds like I should use this product. Do I still need the layer of cement fiberboard? Any other suggestions would be much appreciated as this is new territory for me.
Hi Tom,
No, you don’t need the backer, but you do need two layers of plywood at a minimum 1 1/8″ thickness. The ditra can go directly over the plywood.
Linoleum over particle board,can I thinset and screw hardy backer over this and then tile directly over that?floor will be destroyed removing old linoleum.
Hi Martin,
You can, yes, but the particle board really should be removed. It has absolutely no place beneath a tile installation at all.
Hi Rodger,
I may have found your site a bit too late.
I started a shower remodel and installed CertainTeed Diamondback GlassRoc Tile Backer for the substrate. Sounds too good to be true. Installed according to manufacturer’s instructions: no vapor barrier, no waterproof barrier, just silicone the corners (plane change) and seal all the joints with mesh tape and latex modified thinset. Then just add tile.
Now after reading your book on waterproofing a shower, I am having doubts that I may not have made the right decision. I’ve searched your site for advice on Diamondback, but can’t find it mentioned.
What do you know about this product and what is your opinion of its use? I already have some tile up so this job is probably a done deal, but I am planning to remodel another tub enclosure and want to be sure I’m doing everything right.
Thanks!
Jim.
Hi Jim,
I don’t know much about it but from what I gather from their website it is water-resistant. What that may entail is a wide open discussion. The two key things I found (or did not find) are the word waterproof and the fact that they reference the TCNA manual as the procedure which should be followed when installing in a wet area, which requires a moisture barrier, while in the same page stating that additional barriers are not needed. However, on that page they do not state that it for use in a shower, only on floors and countertops. So they are walking that fine little line where they cover their ass – they aren’t *technically* misinforming the general public. Yeah…marketers.
You may be fine in that shower, you may have problems down the road. Truly impossible to tell. But in the next one definitely use either a barrier behind it or a membrane over it to waterproof your shower.
Roger,
Thanks for the site. I have a question for you about Ditra. I am tiling my bathroom with 24″ wood-like tiles. I put a 1/4″ layer of cement backer board over the 1″ of plywood then started reading about Ditra. So I figured I better do what the pro’s are doing these days and use Ditra (in addition to the cement backer board). Is this good, bad, or redundant? Also, I noticed the that Ditra is sticking to the cement board in most places, but there is a small area where it can be lifted(it didn’t adhere). I used non-modified mortar(from Schluter) for the entire installation. Is it OK that the Ditra didn’t adhere is some spots or should I completely lift that section up and put a thicker coat of mortar down.
Thanks again for the site!
Chris
Hi Chris,
It’s redundant, but it won’t hurt anything at all. If the area lifting up is larger than about 6″ x 6″ then you can cut around the perimeter of it, install thinset, and reinstall the patch you just cut out.
Hi!
Reading your blog really helped me with my Ditra installation. Originally I had taken out the vinyl flooring, but did not go the extra yard to also scrape off the paper backing… because I read somewhere else that it was not necessary. Encountered sticking issue early on and turned it you for help. Thanks!!! I used a hammer drill and a mortising chisel and it helped with the removal of the thin set and paper backing. However, the dust is real bad. My partner had this idea to put water on top and let it soak for a bit horn we returned to removing the old materials. It worked wonders!!! No dust at all AND it was easier to remove. Thought this tip could help others as well.
-C
Hello Roger,
I am ultra new to this and probably as smart as a new born child with terminology…so please bear with me.
I had Linoleum in my kitchen which i have removed on my hands and knees with a hand scraper (not realizing that you can get power scrapers). the floor underneath has a lot gouges in it, which I have now learned will have to be leveled. (Thank you). i am not sure what the flooring in here is called…looks like saw dust packed together?
Anyway, I had a guy come in and price out the installation of 20×20 tiles (which I already have). He states in my quote (which to me is outrageously priced hence my DIY effort) that my sub floor is NOT good enough to support the tile, and Ditra Sub floor is required. I am a little confused here… i am not sure if he is implying that there needs to be more sub floor put on top of the existing floor and then Ditra, or just the Ditra on top of the existing? Also i am not sure if i am further ahead to just put another sub floor on top of this one to save floating (?) it. Just a FYI (that i am not sure if it makes a difference or not), I have 3 small children that i will have to wrangle while I do all of this, so that is part of the reason i am trying to decide about waiting for the float to dry or just re-sub flooring it.
I have a small space about 435 sq ft (give or take) to tile. I have never done this before, but I have googled and watched countless hours of DIY videos to learn the process, it is the prep work i am lost on.
Hi Angela,
I think the easiest thing for you to do is to place cement backerboard over it, with thinset beneath it, then just tile directly to that. Whatever wooden subfloor you had under the vinyl will not be sufficient for a tile installation, you need a proper substrate to bond the tile to. Cement backerboard would be the cheapest. Ditra would work, but you would need to first either level the existing or place an additional layer of plywood over it.
Hi Roger,
We are in the middle of replacing the flooring in our bathroom and have just laid down the Ditra over plywood. It worked beautifully. We were taking a day off before laying our tile and had an incident where a good amount of water leaked onto the floor, and you could see that the thin set again became wet. We pulled up the Ditra where we could see this, and the plywood lifted a bit. My questions are, can we screw down the plywood where it lifted once it is well dried? and can we reuse the piece of the Ditra that we removed from the floor if the cloth backing appears to be intact? Any info you have would be appreciated. Thanks.
Hi Carol,
Yes, you can screw down the plywood, yes you can reuse the ditra if the backing is intact. If that happens again just leave it, water will not affect thinset after it’s cured (unless it happened before it cured, I’m assuming not). It will get darker, but that’s all it does.
We were going to use self leveling compound on top of our plywood before mod thinset, ditra, unmodufied thinset, etc. since we have time constraints we decided not to use the self leveler , but we already applied “pro-primer” for pro-level mortar system to our plywood. My question us, now that we are applying thinset directly to the plywood which now has the pro-primer, will we have and adhesion problems from plywood to thinset or thinset to ditra. http://answers.tileshop.com/answers/1812-en_us/product/5020975/superior-adhesives-chemicals-pro-primer-gallon-questions-answers/questions.htm
Hi Mike,
Nope, it’ll actually bond better with the primer. You’re fine.
Hi Roger,
Cant imagine how you keep up, but grateful for the wisdom:
I am about to lay 1′ x 2′ porcelain tile in a 65sf unheated porch in New England. My magical thinking is weeks past debunked (once again), in terms of time to completion. I removed tongue-in-groove floor, replaced/ sistered joists, put down 3/4 ply and 1/4 Durock, thumbing my nose at a membrane. Now I think I should put down Ditra (what do you think of Permat?) over the cement board. I have Laticrete medium build thin-set (for tile), and will revisit your Ditra installation pointers as per thinset. The porch is sandwiched between garage and Kitchen entry, 6 ft off the ground, uninsulated old-fashioned walls/doors with glass window inserts front and back in winter. The tile will begin and end inside the porch. I can insulate below (vapor barrier?). In your opinion, will I regret omitting the membrane? I suppose I should have omitted the cement board, but here I am. Any light you can shed much appreciated.
Hey Zach,
If it were me I would definitely use a membrane (permat is fine). Being that it is not heated and it is part of the structure (not on the ground) you will have movement. Better to bite the bullet now than have it fail and have to replace everything.
Hi Roger, I was helping my son-in-law with a tile floor in his bathroom. When we pulled up the old vinyl part of the backer remained so I suggested we put down 1/4″ Luan plywood to smooth it out. We then put down Ditra heat mat with modified thin set and 12 x 12 tiles on top with unmodified thinset. My son-in-law discovered online that Luan should never be used as a substrate. Should we tear up the floor or wait and see if it fails? Thanks for your help.
-Mark
Hi Mark,
You may as well wait until it fails at this point. Once the grout lines begin to crack it would be the time to take it up. It may be fine for several years, or it may not. Strictly a crapshoot at this point.
Hi Roger,
Thanks for all the great info here on FloorElf. I am in the middle of a bathroom renovation, getting ready to tile the floor with a combination of 16in square tiles and 6in square tiles. The bathroom is on a concrete slab with some height variation as you approach the edges of the room (as if the floor was originally intended to drain to the center of the room). I’ll be using DitraHeat with Ditra-set to install.
I have two questions:
1. How level does my floor really need to be? Is it more important that it be smooth than level? Can I take up some minor imperfections in the process of applying the Ditra? (meaning, will the thinset fill in small dips or chips and level it out as I install the Ditra-heat)
2. How difficult is it to install 16in square tiles than say a 12in square tile? I have read some people online saying that they are much more difficult to work with. The design I WANT requires 16in, but I have a design I can settle for using only 12in if I’d be getting in over my head.
Thanks in advance for your time! Mike
Hi Mike,
Flat is imperative, level is relative. As long as your floor is FLAT, it doesn’t have to be level. You can install the ditra-mat with a larger trowel, embed it into the thinset with a straight-edge to keep it flat, and let it cure before walking on it. This will flatten out your floor and give you a good substrate to begin with.
12’s and 16’s are the same to me, one is not considerably more difficult to install. Do the pattern you want even if it takes a bit more time, if you don’t you’ll hate yourself forever.
OK, NOW I am confused. I thought that modified thinset was NEVER to be used in conjunction with Kerdi or Ditra. I am doing my granddaughter’s playhouse floor, 12 inch tiles over Ditra over OSB. Floor is 8×12 and runs out the door to a 4 by 8 covered porch. Should I have a 2nd layer of OSB? Is the unmodified correct for this application or should I take it back? 2nd question – I had some professionals do my bathroom despite wanting to do it myself (a concession to the man in my life) and they used some sort of thinset on the floor that didn’t look special to me but is supposed to be flexy, maybe versabond. I am not inspired with confidence. The pallet sof 8 by 48 porcelain for the remainder of the house are sitting outside and I want to do it myself. Should I buy the Ditra and allow the transitions to be uneven or is this flexible thinset OK? I am grinding my teeth. Eva
I read a comment above regarding the use of modified thinset to adhere tiles to the top side of the Ditra but Schluter would not warranty the job. Why is that? If the modified is better thinset, why is it not recommended? I have had several customers ask me this and I don’t have an answer.
Hi Gary,
It is schluter’s position that, because thinset cures through hydration and the whole reason for adding polymers to it to make it modified is so it can retain moisture, the thinset in the ditra cavities allows the unmodified to retain that moisture without additives. Adding polymers to the mix, which require air to cure, makes the full cure of the thinset inconsistent and unreliable. Read through this to understand how it works: Brief history of modified thinset
Very simple question. I have a plywood subfloor in the living room/dining room where I want to install 16″ x 16″ tiles.. Besides making the floor as clean and level as possible, what do I need to do before installing the tile. Dicta? That hardy board stuff? both? This is for my home which I am renting (to help pay the mortgage…) but hope to move back into! Very helpful site, thank you!
Hi Deb,
You need to ensure your floor framing is adequate and have a double layer of plywood totaling a minimum of 1 1/8″. After that any suitable tile substrate can be installed over your plywood, ditra is one of the best in my opinion.
Roger,
Great site! I plan to use Ditra in my bathroom floor install with 2″ Hex mosaic Carrara Bianco marble tile. Tile has a grid backer to make the sqft sheets. I have a plywood subfloor, then plan to use a modified thinset to attach the Ditra. Ditra says to use an unmodified thinset to attach the tile. My question is: Can I use a modified thinset on top of the Ditra to give the stone a little more flex assistance? Additional question: Have you tried Laticrete uncoupling membrane? I believe you can use modified on it.
Hi Ben,
Yes, you can use modified (no warranty from schluter)
Yes, I have used strata-mat.
Yes, you can use modified on it.
Yes, it is a better product in my opinion.
Yes, I just answered all your questions (plus one you didn’t ask) with a ‘yes’.
I plan on tiling an 8′ wide exterior covered deck (partially over a garage – 3 foot overhang) with 6″ porcelain tiles (PEI rating of 5). The deck currently has 3/4″ plywood on it which is sealed at the seam and has a 1/4″ per foot slope away from the building. Please provide your thoughts on proper stepd to take with this project. Thnx
Hi Bill,
A LOT of different factors go into an outdoor deck over living space (garage included). I don’t know what type of climate you live in or any of that. Your best bet is a complete system from a manufacturer, Nobel and Schluter both have very good deck systems.
I installed ditra for a bath floor. I had not noticed that 2″x2″ min tile size note. I want to install the clasic white and black basket weave (marble) mosaic in the vast portion of the field. Do I need to tear out the ditra and go with a cement backer? sub floor is 2 layers of 3/4″ Can I pre fill the square cells and several days later install the tile?
Hi David,
Yes, you can install that tile on ditra (just don’t tell schluter I said that…) No need to pre-fill, but you do need to make absolutely sure you get the cavities completely filled.
Just another thought regarding the heat-e system. Other than voiding warranty issues can other than Ditra heating wires ( ie-warm wire ) be used with the heat-e substrate ?
Hi Frank,
Yes, but some don’t fit very well. Suntouch works fairly well.
Roger,
I’m back again with another question–I’m looking at a floor that has a layer of 1/8in tempered hardwood. Can ditra be installed over that material ?
Hi Frank,
It can be, but it definitely should not be. Tile should NEVER be installed over any layer of wood thinner than AT LEAST 3/8″, tempered hardwood or not. It is all moisture-sensitive, the thinset will inject moisture into the wood as you lay the ditra. 3/8″ is the minimum thickness at which the wood layers are not affected enough to conform due to the moisture content in thinset. It should really be removed.
Roger,
Thanks–removal it is.
Hi Roger! Great info! We’re getting ready to use ditra over our concrete subfloor that had to be repaired due to cracking. We are going to grind down and level it, but I was wondering if we can seal the concrete with a water sealant/crack prevention sealer first. Also per ditra site, we need to use an unmodified thinset on a concrete subfloor. Is that correct? And will the sealant cause any issues with the thinset bonding to the subfloor? thanks!!
Hi Dee,
Any sealer you put on your concrete will hinder the thinset bond. Concrete with open pores is best for thinset adhesion. Yes, unmodified thinset over concrete.
Have you had any experience with the Ditra heat-e product? If so–any problems ?
Hi Frank,
Yes I have, and no, no problems at all except for handing them the check.
It is, by far, the best way yet to install in-floor heating.
I have some OSB that I want to install ditra over. Thing is; the osb is in less than ideal shape I cannot imagine that a bit of loose osb strands would kill the polymer modified thinset adhesive, however I could be wrong. Your thoughts? I need help.
Hi Tim,
It could or it could not. You willing to take that risk? I would likely replace it or put 1/2 ply over it. I am, however, an anal-retentive bastard. So keep that in mind when making your decision.
Roger,
Thanks for this site.
I am in the middle of a bathroom renovation for a bathroom that was built back in the early 80’s and particle board was used as the subfloor. Over that, linoleum was directly glued and installed.
When I began to remove the linoleum, a great deal of that paper back could not be removed from the subfloor without totally tearing the subfloor to pieces.
I am going to be installing the ceramic tile on the Ditra. My question is this: can I install the Ditra on the current subfloor in it’s current “mostly covered by linoleum paper backing”, or should I bite the bullet and completely tear out the subfloor and install a new one?
I would really appreciate your opinion.
Thanks!
Eddie
Hi Eddie,
Unfortunately you’ll need to remove that backing. I speak from bad experience on that one. I went over it once under a bathroom floor and they had a toilet leak. The glue used for linoleum is water soluble. The tile and ditra became a floating floor and everything cracked to shit. I know it sucks, but it sucks less than replacing a floor.
Roger,
Man, thank you so much for letting me know! I was SO CLOSE to doing it, and then thought, “you know, is there someone out there who might have an answer?” You gave me more information than my local Big-Box Home Improvement Store with the Blue Sign EVER did!
So, goodbye particle board…hello PLYWOOD!
Thanks again…I am now one of your biggest fans. :-)
Eddie
Excellent choice!
Good Morning….
We used the wrong Thinset under our Ditra, and plan to lay Porcelain tiles….
Should we take up the Ditra ? How do we get the thinset off the plywood?
Any other suggestions for us?
Thank you
Dianne
Hi Dianne,
What thinset did you use? If it is an unmodified then yes, you should take it up. And it will be destroyed in the process. A scraper can take thinset off of plywood, as can a belt sander (and a dust mask).
Thank you Roger…
Yes, it was unmodified, and was scheduled to be use for tiles on Ditra in another area, and was picked up by mistake…
Thanks for your help, we’re off to our cottage with the belt sander in tow….
Dianne
Hi Roger,
Love the site.
We’re in the middle of replacing the floor in our bathroom (eventually tiling with 13×13 porcelain). The old tile was in rough shape, due to it being applied directly to a sad excuse for a ‘subfloor’. There were also some soft/rotten parts around the tub. It was quite a job, but I now have a level and sturdy new plywood subfloor in place, with reinforced joists and all.
Anyway, I’m planning on using Ditra between the plywood and the new tile, mostly for its uncoupling properties. But I am also intrigued by Ditra’s water resistant properties.
My question is, do you recommend using the Kerdi-Band product on the seams to make the whole thing waterproof? What about where edges where the floor meets the walls? Our bathroom walls are drywall since my wife doesn’t want any wall tile, not even bullnose trim. So we will be using regular baseboard trim.
And a related question, how can I best make the joint between the tile and the bathtub waterproof? That seems to be the place where most of the water ingress happened to make the previous floor in such bad shape. I was thinking at the very least to put a thick bead of silicone between the Ditra and the tub, then lay the tile, then put another bead of silicone between the tile and the tub. Is there anything more I can do? I suppose the Kerdi-bands are useless in this case since my wife probably wouldn’t appreciate a bright orange strip at the base of her tub.
Thanks!
Brad
P.S. I have a 50 pound bag of VersaBond that I’ll use to anchor the Ditra to the subfloor. The floor of the bathroom is less than 50 square feet so this will be way more than enough. Should I just mix up the whole bag and put the remainder into the waffles? Or, should I make up just half a bag and dispose of the rest? (If it matters, I will be using Ditra-Set to set the tiles to the Ditra).
Hi Brad,
If you want your floor waterproof you can use it. No real need to, but some people want it. If you do you can flash kerdi-band up the wall behind the base. And yes, nails will poke holes in it, but if it gets that high I imagine it’ll run out of the bathroom door first, no?
Put kerdi-band right up against your tub over the ditra then kerdi-fix it to the tub. Silicone between the tile and tub. Since you have ditra-set for your floor I would just use enough versabond to install the ditra.