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,
Thanks for all the great info! What’s a rule-of-thumb timeline for the unmodified thinset between the DITRA and the tile to dry/cure? How quickly can I grout and then how quickly can I set the water heater back in place? Wasn’t sure if the thinset specs account for a dryset vs. additive application or installation between two impervious materials.
Thanks.
Hey Mandy,
24 hours for the grout and three days or so for the water heater. Unmodified doesn’t care whether there is impervious materials around it or not – it cures through a chemical process called hydration. It does not require air to cure.
Hi Roger,
I really enjoy the website and your sense of humor! My first tiling job was my bathroom, which I completed thanks to your site. Since I’ve proven to myself I’m not a total klutz at remodeling, I’ve decided to tile my kitchen floor. I have 2×8 joists in good condition, 16″ o.c. with about 10′ span between supports. I believe that provides me with an acceptable level of deflection. On top of that is 1/2″ plywood subfloor and another 5/8″ plywood that had vinyl tiles stuck to it. I have removed the 5/8″ plywood, leaving me with 1/2″ that doesn’t feel like it would be sturdy enough as the only underlayment for porcelain. I have considered removing the 1/2″ ply and installing 3/4″ TNG, but ripping up the subfloor seems extreme. I’m wondering if you think a viable alternative would be to glue and screw 3/8″ BC plywood to the existing 1/2″ ply. I would use 1/8″ Ditra over top to stay as close to the hardwood transition height as possible (laying 1/4″ thick 16×16 tile). Am I out of my mind? I don’t want my dog to catch fire, so please let me know what you think is sufficient.
Thanks!
Hey Chris,
The minimum required for your floor is a double-layer totaling 1 1/8″ – you could get away with another 1/2″ layer of plywood then the ditra. Your deflection is about 480 so you’re good there, but you need the plywood height as well.
1/2″ it will be. Do you think it’s necessary for me to glue AND screw the second layer onto the sub floor or will screwing it be sufficient? After thinking about it some more, I suspect that gluing might do more harm than good since the purpose of the second layer is also to decouple any joist movement. Thanks again for your advice.
Hey Chris,
You are exactly right! Just the screws.
Hi Roger,
This info has been very helpful thank you for that
I do have one question though
I am installing tile in a batroom with exsiting vinyl. I tore the old vinyl up but there is a wooden underlayment attached to the 3/4 OSB subfloor (this is what the builders put down when they installed the vinyl). Can i put ditra in this or do i have to tear up the old underlayment as well. Id rather not tear up the underlayment since the builder used a million staples on it.
Thanks for your help
Hey Chris,
Unfortunately that underlayment does need to come up. Most builders use what is called ‘luan’ to install vinyl over – it is about 1/8″ thick and not stable at all – it has no business beneath a tile installation. I normally find it easier to pound the staples down into the subfloor rather than attempting to pull them all out after I remove the luan. Another option, if you have the height, is to install backerboard over that (with thinset beneath it) and screw it down very well. It’s still not ideal, though, and would be better to remove it.
Hi Roger!
I am about to tile a concrete floor in a basement and am using ditra. The floor is not completely level so I am using SLC to make it flat. The first pore of SLC was in the bathroom and after it set up I found that in one area near a wall, the floor was 3/32″ higher than the rest of the floor. Should I grind this area down or can I compensate with the ditra and tile?
Also, I am planing to use unmodified thin set under the ditra and under the tile. I am using 18″ x 18″ travertine tiles. Am I on the right path?
Hi, Roger,
Great website. So helpful.
I have a 45 year old 6-8 inch thick, approx. 750 square foot cement patio in Savannah, Ga. It has been painted several times with solid color concrete stain. It has quite a few cracks in it but not of them are actually separated and the patio is extremely level with no vertical differences along the cracks. I want to lay 16 inch ceramic tile all over it. I’ve considered using Ditra all over under the tile, but that is really too expensive for this much area. Someone told me I could just use foot wide strips of Ditra just over the cracks. I’m not sure that makes sense because each tile along the cracks would be only partially sitting on the Ditra and partially on thin-set alone. I also have heard I should use caulk instead of grout every 8-12 feet.
Can you set me straight on how I should plan this project? Any help you can give me will be very much appreciated!!
Hey Karen,
The idea behind the strips is crack suppression – but that is definitely not the way to do it. Ditra should not be used solely for crack suppression, it should be under the entire installation or not at all. A good option for you would be redgard, it can be painted over the cracks (about six inches onto either side of it as well) and you can tile directly to the concrete. A better option would be to cover the entire patio with redgard – but that’s gonna be kind of spendy as well. If you redgard over the cracks it will be fine – it was initially developed as a crack suppression membrane.
Yes, you need a soft joint every 8-12 feet, it compensates for movement in the installation without cracking the grout.
What would you recommend for a Ditra installation over an existing, very well set ceramic tile floor. Our Victorian home has mosaics set in 6+ inches of cement mortar bed. The tiles are in excellent shape, no cracking or loose tiles, so we don’t want to remove them. Would a good quality unmodified thinset work to adhere the Ditra to the tiles?
Hi Amy,
No, unmodified is not what you want. You want to scarify the surface of the existing tile so it isn’t shiny and use a highly modified mortar to install the ditra over it. Mapei ultraflex II I believe is approved for installation over tile, laticrete 254 works well too. I don’t know what the other ones are – I don’t go over existing tile. It will say on the bag whether it is approved for that or not.
How would you deal with the space between the two halves of a modular/mobile home where the tile needs to cross this gap to happily meet the transition between two rooms? This gap is about 0.25 inch and is about 2 inches from where the transition strip needs to be positioned.
The subfloor is 5/8 ply and I am using Ditra to minimize height and 12 inch porc. tiles. Also, one area of small bathroom is about 1/8 low. Can I deal with issue with thinset and tile placement over the 2 ft area?
A few pros have all said…no problem, just lay it and be done…seems to good to be true?
I would either have a soft joint directly above that seam, move the tile two inches back so it isn’t over that, or not tile it. Modular homes are not stable, at all. Attempting to do anything other than keeping those two halves separated (with at least a soft joint) is asking for trouble.
Yes, you can build up thinset 1/8″, but tiling over ditra on only 5/8″ is also not very stable, you need a minimum 1 1/8″, especially in a modular. If those pros have said no problem then tell them it should be no problem to warranty it and come on back and fix it WHEN it fails.
What is a soft joint exactly?
Hi Don,
What is a soft joint and when to use one.
We have put the detra down with unmodified thin set over plywood subfloor. Haven’t done the tile yet. Do we need to pull up the detra before we go any further. We got modified and unmodifed thin set but used the wrong bag under the detra!!!! Please advise. Thank you so much!
Hi Mark,
It depends on which unmodified. Yes, it should be modified under it, but depending on the particular thinset you used it may be fine. Keep in mind – if you don’t change it Schluter will not warranty it.
Hi Roger,
I am in the reno business and have installed many tile floors but have only recently installed a floor using the Ditra product. Because I was overly excited about putting the tiles down I did not take the time to fully read the products installation instructions. After thinsetting the Ditra down I layed about a half a kitchen floor and called it a day. I thought to read the instructions more thoroughly the next morning (I know, I know… one should always educate themselves before starting the job). I noticed that there was a print that read “IMPORTANT: use unmodified thinset to lay the tiles”. I’ve now made the mistake of using polymer modified for everything. Fortunately, it is ok to use the modified on my plywood subfloor to install the Ditra. I’ve been walking on the tiles that have already been laid. The installation seems to be sound and isn’t even grouted yet. Should I be concerned? Should I just continue completing the installation but switch to the unmodified thinset? Why is it so “IMPORTANT” to use unmodified thinset? Your feedback would be very much appreciated.
Thanks,
Mike (not a professional tile setter)
Hey Mike,
Don’t worry about it – I do it all the time. You will not have Schluter’s warranty backing up the installation but that’s about it. Schluter’s ‘reasoning’ is that since cement products cure through hydration and water or moisture does not dissipate quickly that the ditra may actually hinder the curing process of the polymers in modified thinset. It will to a point, but not so much as to be an issue on most installations in my opinion. Just continue on with the same thinset.
If it makes you feel any better in Germany and most European countries where ditra is sold you are supposed to use the modified. I honestly believe it to be a diy marketing ploy here – as in: ‘we know it’s expensive but you don’t need to buy modified – unmodified is cheaper’. That’s a personal opinion only, however. While I love Schluter products I absolutely cannot stand the company nor their ‘customer service’ – they won’t allow their reps to post anything representing the company anywhere online – in 2012 that is an absolute abomination in my opinion.
Roger (not a professional elf…)
Dear Roger,
This is from the couple who tackled a bathroom with sandstone tile. We have followed your recommendations to the letter, and it’s turning out great. We did chicken out of using epoxy grout, and used regular grout instead. That’s where my next question lies: before grouting, we put on 2 coats of enhancer, 2 coats of sealer, and 2 coats of grout release. Still, cleaning the sandstone after grouting was a b*&%!! We had to keep at it for what seemed like hours. Wait, it was hours! Hours, and hours, and hours. And, after all that work, it appears there is still some kind of haze on the tstone. I’m wondering if we rubbed off the coats of sealer and enhancer while cleaning the grout, and we’ll have to enhance and reseal the stone. I tried a haze remover, and that didn’t seem to help, either. It is sandstone, not limestone, so should I try something else in a spot that won’t be seen? We have yet to do the floor and 1/2 of one wall (the visible part of the wall). So, another question is: Is there another product or something we haven’t tried that would work better to prepare it for grouting that wouldn’t be so much frigging work? Anxiously awaiting your elf – lee thoughts…… Ann
Hey Ann,
Sandstone isn’t any fun – no one told you that?
If your layer description is correct (enhancer, sealer, grout release) then you very well could have scrubbed off the sealer since the only one really adhering to the tile itself was the enhancer – the other two only adhered to the enhancer, if at all.
Enhancing sealer is a topical sealer – it lies on top of your tile similar to a coat of varnish on wood. Anything you place onto it after that will never get into the tile itself. It’s like trying to stain waxed wood – doesn’t work. An impregnating sealer (I’m assuming that’s what you meant by the second ‘sealer’) fills the pores of the stone and travels into and past the first layer of stone. It seals up all the little porous spaces and spots in the stone and prevents anything else from getting into it. Grout release is the same topical system as the enhancer, but is water soluble so it comes off while cleaning the grout. If there was any of that on the tile at all it came off with your first wipe-down. Don’t even bother with it – it’s not doing anything for you.
Think of the impregnating sealer as the stain and the enhancer as the varnish. Doing it the other way around doesn’t work. For the rest of it first use the impregnating sealer, then the enhancing sealer, then grout it.
It’s still not gonna be any fun, though.
Use microfiber towels to clean up the grout if you aren’t already – much easier and more effective. Then send pictures! Send me pictures damnit
Hi Roger:
Thanks for all this information. I am in need of some clarification regarding the Ditra. We are re-doing a 50 SQFT half-bath and are planning to have the new flooring be porcelain tile. The subfloor is made of two plywood boards. They meet 6 feet deep into the room and are not perfectly level, off by about 1/8th of an inch. I bought a roll of the Ditra material because I had heard so many favorable reviews of it, but after watching the installation video on the manufacturer’s website I am second-guessing whether I should be using Ditra at all.
And that’s where I need the clarification.
Can I successfully install Ditra underlayment without using the corner movement joints as shown in the installation video? I feel that these movement joints will ruin the look I was going for with a nice decorative wallbase trim.
Any insight would be much appreciated. Thank you.
Sincerely,
Justin
Hey Justin,
If you are referring to the metal trim/transition profiles then yes, you can definitely use ditra without them. That is simply another product they make – they sell stuff, it’s what they do.
No need for it if you don’t want it, it won’t affect your installation.
HI, this thread alone has made me learn so much, so thank you for all your shared wisdom.
I hired a pro to install my kitchen tile and obviously prepare subfloor. As I watched, he prepared my playwood sub (an old thick sandwich of ply,vynil, ply) by adding some modified thinset mix to the areas that he thought needed leveling, then place all the hardiebacker sheets and screw them to the plywood. I though he needed to add thinset all under the hardie not just some areas so next days when I was going to complain he actually had added thinset to the hardie board joints without puting tape. So, then is when I asked him to stop and I went online and spent hours on researching. My conclusion is that he did all of it wrong and that if I install my 12×24 expensive porcelain tiles on that sub they will crack for sure. He swears and stomps thru saying the floor is sound and ready and that he had never had set all the cementboard with all thinset under. Also, a Home Depot guy actually backed him up saying the tape was not required. I am very concerned as I saw the thinset on the hardie joints go in and delineate the joint again as if the thinset was going inside and (maybe under?) de hardie board.
So, I sent him on sabatical and decided to fix this mess. I thought on 3 optons:
a) demo everything and start again – not my choice as the screws will b a nightmare and t will cost me sweat, time and money
b) scrape the thinset on th joints (it’s coming off sort of easily) , put more thinset and tape.- I am still concerned by the non-thinset layer under all the hardie boards
c) install ditra on top of the installed hardiebacker boards using unmodified and then tile using unmodified (you said modified was better?)
I already bought Ditra and am ready to move with C but I think your thoughts would be very beneficial in my current state of mind.
Hence, a fast response would be super appreciated for eternity.
thxs
Hi Maggie,
Option C would be your bast bet short of demo’ing everything and starting over. While it would definitely be better to have thinset beneath the backer under the ditra you can go that route. It will not guarantee that your grout will not crack but it will be a LOT more stable than what he had planned. It will likely be fine, just want you to know that without thinset beneath your backer there are no guarantees.
You did make a good move putting a stop to it, though.
HI ROGER,
GETTING READY TO PUT UP A NEW BACKSPLASH IN THE KITCHEN. SUBSTRATE IS PLYWOOD. CAN THE DITRA BE USED AS A MEMBRANE FOR THIS APPLICATION? WILL BE TILING WITH POLISHED MARBLE MOSAIC ALONG WITH AN ACCENT TILE. WHAT TYPE OF THINSET DO YOU RECOMMEND? ANY ADVICE IS VERY MUCH APPRECIATED AS WE ARE NEW AT THIS. THANKS FOR YOUR HELP!
Hi Toni,
My advice would be to replace the plywood with drywall and tile directly to that. Plywood is going to move quite a bit in a kitchen. Drywall is more stable. Ditra will work over the plywood, but the problem you’ll run into is at the edges where it will need to cut back to drywall – you’ll have a gap to compensate for where the ditra is behind the tile.
Hello, I have a question…we just embedded the suntouch heating/wire mats in thin set. First I thought you can install Ditra while you are embedding the wires, then I saw you should embed it first, let it cure, then notch trowel thin set to install Ditra…I went with the last option. Our concern is while my husband is a concrete finisher -so he got to do the troweling- we are not so sure that we got the thin set spread in a way that it came out perfectly level. Is this a problem for installing the Ditra in our next step? The OSB floor is level, but we did not cover the whole floor with mats, that is where we feel it may not be as flat over the whole floor. Should we be worried about installing the Ditra?
Hey Pernille,
It won’t be a problem provided you pay close attention to the flatness of the ditra as you are installing it. Use a straight edge to embed it into the thinset and don’t walk or kneel on the areas that you’ve already embedded into the thinset. Make sure you get plenty of thinset beneath the areas where you don’t have the mats installed. You may want to use a larger trowel in those areas.
Thanks Roger… in your installation part 2 you mentioned you use your thin set rather thick…how thick, like peanut butter? And would I still want this thick consistency now that I already have a “dried” layer of thinset (with the embedded floorheating). I used modified thin set on the OSB. Do I continue with the same modified thinset to set the Ditra and use unmodified on top of the Ditra to set tile. Correct?
Between pudding and peanut butter.
You want it stiff enough to hold the ridges from the trowel when you comb it out but loose enough to work with easily. Technically over the layer of thinset, which is a concrete product, you want unmodified thinset, then unmodified over the ditra as well. But you can use the modified under if you want – I would.
Roger – We live in a ranch house which we had built in 2007. It has a 5 ft “crawl” space and I’m not sure if the subfloors are OSB or plywood, but we do have infloor heat running from the rafters in the crawl space (don’t ask…that’s another story).
Anyhow, we have 12×12 ceramic tile on ditra in our kitchen that we believe was installed improperly (in November of 2007) by a “professiona.l” You can actually see the orange substrate where the grout is gone – and about 1/4 of the grout is missing right now. My husband has taken out and replaced the grout twice and it cracked and came out of the joints each time. He has laid tile (on Ditra) and grouted it himself in other rooms in the house with no problem, so we believe that the kitchen tile problem is an installation error.
We only had enough of this particular tile to cover the kitchen floor – it does not go under the cabinets or island. This is the area where the grout has cracked and come loose. My husband laid other ceramic tile under the refrigerator/freezer and stove and there are no problems there.
My question is – do we have to remove the tile in question AND the Ditra mat and start from scratch in order for grout to actually stay in place, or is there something else that can be done? By the way, there are a couple of tiles that “give” when you walk on them.
Any suggestions are appreciated. I’d really like to be done with this floor situation this year (it looks like crap!)
Missy
Hi Missy,
I’m afraid the only viable long-term solution would be to remove the tile and ditra and start over. It sounds like something somewhere in the substrate has improper coverage, which lead to an improper bond. It’s nearly impossible to tell where that happened without removing tile. It could be the ditra to osb (or ply) or improper filling of the ditra cavities, or improper coverage to the tile itself. This coupled with a single layer of wood over the joists nearly guarantees problems. Unfortunately the only solution is new installation with proper techniques.
Sorry it’s taken me so long to respond but THANK YOU for your response. I knew in my heart that we would have to start from scratch – I just needed to see it in writing.
Hi Roger,
Thank you for all the good info. I’ve read a bunch, but have a few questions on a DIY project if you get a moment:
The joists are better than L360, subfloor is Home Depot 3/4″ Home Advantage (like Advantech, I believe), and the tile is 18×18 ceramic. So…
1. What are the pros and cons of cement backerboard, Ditra or plywood (realizing that special care/techniques are needed with plywood)?
2. The tile runs 26 feet. Should the expansion joint be in the tile and the underlayment? In other words, if the tile is bonded to the underlay, what good is an expansion joint that is only in the tile? Is there a link showing how to do this?
These are no doubt common questions, so links would be great also.
Thanks,
John
Hey John,
1. Plywood shouldn’t even be on the list in my opinion. I know how to properly install it over plywood and I won’t even do it. Too many uncontrollable variables such as humidity in the joist structure over the course of the year infusing the plywood with moisture causing swelling and excess movement. Just scratch that off. Cement board is the standard, and works just fine provided it is properly installed with regards to correct screws and having thinset beneath it. It’s a pain in the ass to work with, though, heavy and difficult to cut. Ditra is my preferred membrane, it handles in-plane movement, dissipates any moisture beneath it (vapor management) between the under channels for things like the seasonal moisture I mentioned above, and it’s easy to work with, cuts with a razor knife, limits added height. The only real downsides are the requirement for unmodified thinset if you’re concerned with their warranty, and the price over backerboard.
3. The expansion joint should be in just the tile, although you can run it through the cement board if you want. The ditra will handle the movement and any modified thinsets have a limited amount of flex which will handle most normal movement. The tile itself, however, will expand and contract. This puts pressure on the entire installation and could cause tenting in the tiles where they come loose from the thinset bond and pop up. I’ve seen tiles do this, I’ve never seen underlayment do it. If you use backer and want an expansion joint in it just place the seam in the proper location and leave about 1/8″ filled with silicone to keep thinset out of it, and put your joint in the tile directly above it. If there is undue pressure on the backer the silicone will compensate for it.
Excellent, thank you!
Just to confirm: you said don’t consider plywood, so that means the 3/4 Home Advantage subfloor is adequate? I keep seeing recommendations that plywood thickness be 1-1/8″.
Thanks again,
John
I meant don’t consider plywood as the substrate for your tile – meaning do not bond the tile directly to the plywood.
Hi, Roger:
Hope you don’t mind a question from one of those Canadians! :-)
I have a handyman who is redoing our bathroom. I would like to apply new tile over the existing tile in our shower. I really do not want to take the old tile out. I have juast bought some Ditra to waterproof over the existing tile. The existing tile is shiny; there are no cracked or loose tiles. In my mind, I thought I would just get our handy guy to thinset the Ditra over the existing tile and then retile with the new subway tiles.
I have never used Ditra, nor has our handy guy, so in doing some research on the Net, I came across your site. Oh-oh, I am in way over my head, I think! Not sure what the difference is between modified and unmodified thin-set, even. Yikes
What do you think? No to Ditra bonded to existing tile?
What about putting up concrete board over the existing tile, then Ditra, and then the new tile?
I am so out of my league on this, I am not even sure that the questions I am asking make sense!! Darn those DIY shows on HGTV!!
Would appreciate any advice!
Thanks!
Sue, on the seashore in Nova Scotia!
Hi Sue, eh?,
Let me ask the obvious question – why don’t you want to remove the existing tile? You mentioned going over it with backerboard, it would actually be easier to take it out and screw the backer right to the studs. Also – ditra is not for waterproofing showers, kerdi it. Ditra is the waffled plastic used as a substrate beneath horizontal surfaces such as floors and counters, while it can be made waterproof that is not it’s main function. And you don’t want to go over existing tile with kerdi anyway.
There are a couple of different options for you. IF! your shower is currently waterproof and you have no leaks or problems with water containment you can rough up the existing tile (get the ‘shiny’ off of it) and tile directly to it using a highly modified thinset approved for that application (tile over tile). Mapei Ultraflex II is one I remember offhand – there are quite a few others. It will state on the bag that it is approved for tile installation over existing tile.
If you have concerns about the waterproofing you can go over the existing tile (after you remove the ‘shiny’) with a liquid membrane such as redgard or hydroban. Let that cure, then tile right to it. You can remove the shiny surface of the current tile with a grinding ‘cup wheel’ on a grinder (ideally) or with a belt sander.
You’re welcome, eh!
Roger, landlocked in Colorado
Hello:
We have a floor that is breaking and cracking which was laid over Ditra. The subfloor is plywood but the spacing of the joist was to far and the deflection is causing the problem. What is required to remove the tile and the Ditra?
It appears the Ditra will separate from the fiber back. Is that correct?
Hey Tom,
Getting tile and ditra up is a serious pain in the ass. The easiest it just to get in there with a crowbar and pry up the tile, a lot of the ditra will come up with it. The ditra WILL come apart at the fleece, that is what gives it the ability to compensate for in-plane movement. Once you get that up you’ll need to scrape the fleece backing off the floor.
I thought Ditra was made to withstand some effects of deflection and would eliminate problems caused by movement of the tile. I am having similar issues with a tile job that used Ditra. Doesn’t Ditra have a warranty that will cover this issue? Who has the responsibility to inspect and make sure the subfloor is structuarly sound so that the Ditra does it’s job and the floor/tile won’t have these issues? Homeowner or the florring company/installers hired to install the tile floor.
It is but nothing is going to compensate for a floor with inadequate deflection for tile installation. Ditra is not made for vertical deflection, although it does assist with that to a point. It is made for in-plane movement. The floor must have the proper deflection ratio before any substrate or tile is installed on it.
It is ultimately up to the company/installer who installs the tile. However, if you check the fine print of a lot of larger companies it states that the floor must be built to certain specifications or you are signing off that it is. It should be stated in the contract, although ultimately it rarely is.
Hello:
Greatly appreciate all of the comments and I hope I have the correct solution. It appears I need to remove the tile as best possible and then the Ditra will pull up by separating at the base fabric. Thanks to all of you.
In Christ,
Tom
Roger,
I am doing a 12×24 porcelain tile installation in a 53 sq. ft. bathroom. The subfloor is plywood but was not level. I used SLC on part of the floor to bring it up to the correct height. The manual for ditra says to level the plywood floor before installation. My question is, do I install as if over plywood (modified thin-set) or as over concrete (unmodified thin-set) as I now have a beautiful combo of a subfloor. Also I read that you suggest using modified thin-set between tile and ditra. Is this an ok option or your preferred method of installation? Thank you for any advice you can provide.
Hey! Somebody actually read the directions!
Thank you!
You should use the modified. It will adhere better to the plywood and has no problem at all adhering to SLC.
I normally use modified between tile and ditra so yes, it’s an ok option. You will, however, void your warranty from Schluter – they’re picky like that.
I’m getting ready of tile a 12’ x16’ kitchen with 12”x12” 3/8” ceramic tiles with 3mm Ditra underlayment. Floor is ¾” plywood on 16” center joists. Joists are shored up with steel beam running the length of the room. Question: what are the odds I can get away without laying down 3/8” OSB underlayment before the Ditra? Ditra+tile+OSB exceeds the threshold on the patio door, the dishwasher won’t fit and they’re will be a huge step down to the living room Pergo floor. Dealer said “no problem” put the Ditra and tile right on the plywood and be happy. But of course the Schluter manual seems to indicated min 3/8” OSB over the ¾” plywood is necessary.
Your opinion? Am I in for a cracking nightmare? -Thanks
Hi Steve,
Schluter, nor any other manufacturer I’m aware of, recommends OSB beneath anything – there is no thinset approve for use directly to it. They mean plywood. The standards require a minimum of 1 1/4″ substrate beneath your tile – that’s where the recommendations come from. That said, you’ll probably be fine. A better option would be to use ditra XL which states it can be used directly over a single-layer 3/4″ substrate.
Thanks very much for the reply!
I see you’re in Fort Collins; I’m in Louisville so I’ll recommend you to friends and co-workers, good contractors are hard to find.
Well, when all else fails, RTFI over and over (good tech writers are hard to find too). The booklet that came with my DITRA on page 23 talks about a plywood/OSB underlayment over existing subfloors for “ceramic or stone”.
Page 6 says a single layer of 5/8” OSB or plywood with 16” o.c. is fine for “ceramic or porcelain” tile.
They don’t say anything about special thinsets or not for OSB, but they do show and talk about OSB a lot.
I’m going to add 4×4 backer blocks at all the lap joints in the floor and two more shores just to make sure. With that epoxy grout you recommend I think I can get away with the ¾” subfloor.
-Thanks again!
Thanks Steve. I think the manuals with the OSB references are written by Canadians – dunno if they know the difference.
Aaaand there goes 20% of my readership – Baddum-ching!
Backer blocks never hurt.
OK, I survived the crawl space torture and the credit cards are smoking, I should be ready to lay tile.
Question: I must trim door moldings and stuff before laying DITRA & tiles. Assuming I apply the mortar and thin-set correctly (I’m an engineer so doing everything correctly is a forgone conclusion… naturally) do you have a rule of thumb for the TOTAL thickness of everything? The tile is 10mm thick with 1mm deep ¾” x¾ ” waffle grid on the back and the DITRA is 3mm thick. About how much more thickness should I add for the mortar & thin-set? I’m guessing about 1/8”, is this in the ballpark?
Thanks
-Steve
Hey Steve,
Oh, you engineers. Is the tile 10mm thick with a -1mm waffle into the z-axis or is it 10mm thick plus a 1mm waffle? Makes no difference whatsoever, I just like messing with engineers ’cause I used to be a physicist.
The total height of your installation depends entirely on how big your trowel is. If you use a 3/16″ x 3/16″ trowel you need to add 3/32″ for each layer of thinset (under ditra, over ditra) so a total of 3/16″ plus your tile plus the ditra. Keep in mind it doesn’t need to be EXACT! We aren’t building a particle accelerator here – we’re setting tile. It can be adjusted as you go along. Particle accelerators – not so much.
Hi Roger!
.
I am about to install 500 sq ft of tile on my main floor. To give you an idea of whats going on, (floor joist 2×10 on 16″ center) with the old house substrate 1×6 board with 3/8 ply on top. Now I have heard so many different ways to prepare my floors for tile, some being: min 1 1/4″ of plywood and cement board, or 3/4″ ply on top of the existing 3/8 ply with dirtra. I don’t want anything to happen to my dog or my 18×18 tile (could be stone or ceramic)
Thanks.
Mark
Hey Mark,
Standards require a 1 1/4″ thick substrate. Your best bet would likely be the 3/4″ layer of plywood with ditra on top – that will make it essentially bullet-proof. Do that and your dog will be fine.
(Tile too…)
Thanks Roger!
but what would be the case for cement board (like 1/4 hardi)?
I don’t want to bug you too much
And for both those applications (ditra or cement) would I use 3/4 t and g (glued and screwed to the existing 3/8 ) or 3/4 ply spaced 1/8 apart (glued and screwed)? Thanks for clearing the grey areas for me.
Mark.
You can use the 1/4″ backer as well as long as you place thinset between it and the plywood so it is fully supported. (It isn’t there to stick or adhere anything – only support). Regular 3/4″ ply spaced 1/8″ apart. No need to glue it, but it won’t hurt anything.
So with the backer you want plywood, thinset, 1/4″ backerboard, thinset, tile.
Would you recommend the SpectraLock grout over Opticolor for ease of installation for DIY? Because we can get SpectraLock, it’s just a bit more difficult to obtain (ie. 25 miles one way car ride – but, of course, it’s the holiday season so we shop near there anyway).
Thanks!!
Ann
Yes I would. The spectralock is much easier to work with in my opinion.
Well, in the continuing saga of the sandstone being installed over ditra, we haven’t yet done grout, because, well, we aren’t done installing the tile. However, we’re getting close! We were going to use Mapei regular grout, but our son (who sets tile on the side and is very good at it) suggested we’d be happier with Opticolor epoxy grout, being that it’s in the bathroom, and because we’re amateurs, the color would end up better. We’re worried about getting different shades of grout from wiping too much, since the sandstone is h&% for getting grout out from the cracks and crevices. What are your thoughts? What would you recommend?Thanks!!!! (it is turning out great – thanks again!!)
Ann
Hey Ann,
The opticolor epoxy will definitely give you consistent coloring but it is fairly difficult to work with for people without experience. It is very good grout, though.
Hey, Can you install Ditra over Luan flooring?
Hey, nope.
Luan is not stable enough to be anywhere beneath a tile installation at all. It should be removed.
Hi Roger!
What a site! I have a question about DITRA (actually, I have many but I’ll try to stay focused here): I’ve been hearing about unmodified thin set and on the HD review site many people have been hard pressed to find the stuff (I haven’t actually looked to verify the claim…I’m still in the planning stage); could you recommend a good unmodified thin set to use with DITRA? Oh, and does the “unmodified” part just mean there’s no fancy goop added to it, making it more like good ‘ol cement or something?
Thanks,
Tony
Hey Tony,
Unmodified thinset has no fancy goop in it – that’s correct.
Modified thinset has powdered polymers added to it. These normally require air to cure, that’s why Schluter doesn’t want you to use it. I normally use Laticrete 317 unmodified. You’ll likely need to go to a tile supplier to get a hold of id.
Right on Roger!
I really appreciate your input! Hey, now that I’m on the fast track to DITRA and beyond, I hope you don’t mind me poppin’ around for more advice, ya know, in case I stray too far off the Yellow Brick (tiled) Road. I’m satisfied with a full plate of theory, but sometimes applications rip the menu.
Cheers Roger