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 
Rodger,
I have 3/4 Advantech subfloors, 16″ o/c. I plan on using a Suntouch heat mat, which tapes down initially, then using a 3/8 notch trowel as per Suntouch instructions, modified thinset over the mat, then lay the Ditra into the thinset. I called Schluter, and the tech support person said this is an approved method. Do you agree, or should I use a different method.
Thanks
Chris
Hey Chris,
Your method is fine, but the 3/4″ subfloor should be 1 1/4″. Other than that everything else is fine. He should have pointed that out to you. Even kerdi is required to have the minimum subfloor thickness.
Hi Roger , I have had a tile floor in the kitchen for about 12 years. The last 2 years some of the 12x12s have cracked. I had 1/2″ plywood with 1/2″ wonderboard on top. When ripping it up I noticed the wonderboard was not securely down in some spots. I used 1 1/2 ” screws when I installed it. Could they have loosened from time and caused it to crack the tile? and would it be better add another layer of 1/2″ plywood instead with ditra on that, when I am installing the new tile . thanks mark
Hey Mark,
Yes, it would be better to have an additional 1/2″ layer with ditra. You didn’t have any thinset beneath your wonderboard, it wasn’t fully supported. Over time plywood will begin to compress, leaving hollow areas beneath the backer. The screws didn’t necessarily come loose, the plywood probably compressed. Thinset beneath your backer prevents that.
Roger,
second post. this time with email box checked.
Reading over my newly purchased Liquid Topical.
Project Background:
Have 1950s rancher with post and beam and 2×6 tig car deck over 2 foot crawl space with vents. Baseboard popped up and found the cause of the smell my wife had been noticing.
I removed subfloor and some wall framing due to rot from small 36×36 corner shower that extended through about half subfloor in 5’x8′ master bath. (From a previous owner remodel 6 years ago where the idiot thought backer board and tile were water proof).
So far I have:
New ABS 2″ for drain. (Plumber installed).
I Hung new joists with Simpson Ties and blocked shower and toilet. I am replacing car deck now with GRK Fasteners – R4 and subfloor glue.
Future PLANS –
Floor:
1. 1/2″ plywood over car deck.
2. Laticrete Floor Heat
3. Ditra with Laticrete Platinum Pro top and bottom. (I know this voids warranty but wife was so disgusted by mold that I want the Microban).
Pan:
1. CLEAVAGE MEMBRANE
2. Mud Deck
3. Hydroban drain
4. Hydroban
Walls:
1. Hardiboard 500
2. Hydroban
Change of Planes:
1. at least in shower – schluter Dilex EKE with the soft movement joint (wife does not want any maintenance or places for mold to grow).
Need help:
1. Is 1/2″ AC ply too thick? Do I need a vapor barrier between car deck and plywood or will this create a mold sandwich (wife will have me sleep in garage) with the Ditra on top? Could I put green glue under the plywood for sound reduction our will this add too much deflection? (Noise is a real problem with these trampoline style joist span in our entire house).
2. For the cleavage membrane under the mud deck, will moisture from the crawlspace get trapped on plastic? The Laticrete website has a video that shows the mud deck going right onto the wood. Not a good idea in my opinion. Is there a semi-permeable membrane?
3. How do I cut and glue the 2″ ABS to match the Laticrete drain. Can I do it from the top because the crawl space is only 2 feet? I could leave 1/2 the car deck off for access but risk dropping something on my new expensive plumbing.
4. Maybe hygienic overkill but have you used the Dilex EKE?
5. Can you baby sit? On top of all this, we are expecting a new baby girl in 1 week! Just kidding, your handbook has already helped me more than babysitting. Thanks sooo much. You deserve an industry award!
Hey Jerry,
1. No, 1/2″ is fine. 3/4″ would be better, but the 1/2″ will suffice. No idea what ‘green glue’ is. Laticrete does make a sound dampening thinset, you may want to check into that. It’s called laticrete 125 sound and crack adhesive.
2. I would use roofing felt for your cleavage membrane in that application.
3. Yes, you can do it from the top. Set the drain in the empty hole and measure the piece you’ll need between the drain and p-trap. Glue that in then just glue your drain on when you’re ready.
4. Yes, I have used EKE. It’s a very cool product, and they charge accordingly.
5. Sorry, have three kids of my own. I’m babysat out.
We are tiling a small laundry closet (33 x 29 inches). We know that the recommendation is to use modified thinset between the wood and Ditra and then unmodified between the Ditra and tile. The lumberyard in Poncha Springs, CO told us we could use modified between the Ditra and tile (13 x 13 inch porcelain). Can this work? We have unmodified premixed thinset. Could we use that?
Hi Sue,
Yes, modified mortar will work, although it will void your warranty. The ‘premixed thinset’ WILL NOT work. It isn’t thinset, it’s mastic with sand in it. It will never cure – ever.
Hi Roger – I am looking to install large tile over my hydro radiant floor system, there are water tubes that are in grooved channels in the wood floor. How do I install or more importantly, can I install ditra over the hydro floor?
Thanks,
Chris
Hey Chris,
Yes, you can. You need to fill in the channels with either deck mud or SLC then just install the ditra over the floor as normal.
Hi Roger,
I am currently remodeling my kitchen and am laying new tiles for my floor. I placed sister joists beside all my joists to make a stronger floor and to remove some bouncing i had in the floor. I currently have 2X8 floor joists doubled(sistered) with a 11foot 5 inch span and are 14.5″ on center with 3/4″ tongue and groove plywood screwed with 2″ floor screws every 6″ on center for my floor. I used to have vinyl floor which I scrapped up. I am planning on laying regular ditra before my tile but am wondering if the 3/4″ T&G floor is enough. I know normally the total height with the sub-floor is suppose to be 1 1/4″. Do you recommend laying down a sub-floor before the ditra or will I be okay with what i have?
Thanks
Chris
Hey Chris,
Regardless of the frame you really should have a double layer of ply beneath your ditra. I know that sounds counter-intuitive, but it does more than simply add support for the tile. Standards dictate a minimum of 1 1/8″ beneath your ditra.
That said, in all reality with the framing and joists you have in place it will likely be fine with the ditra.
Roger, we have a small bathroom floor to lay, 3/4 in OSB. sub floor and want to install 1/2 in. wonderboard, then Ditra then 6×24 in porcelain plank tiles. We are scratching our heads over what type of thinset (mortar) goes where. It might seem like overkill but we DON”T want any cracked tiles. Help ! Schluter doesn’t mention cement board as an approved substrate.
Hi Cathy,
Schluter doesn’t mention a lot of things. Backer isn’t mentioned because it is normally used in lieu of cement backerboards. But you can use it, it’ll be just fine. Under your backer use any kind of thinset you want, it’s only there for support, not to bond anything. Over the backer, under the kerdi you are supposed to use unmodified thinset, I prefer modified thinset there. Either will work. Over your kerdi under the tile use unmodified thinset.
just found this website, very informative, I have a plan to tile w/Ditra, 3 areas in a 50 yr old house, it is constructed on 2x10s 16″ oc, sub floor is t&g 1×3 nailed with flooring nails (hidden). areas to be tiled are kit. bath and front door entryway (inside). Had to gut bath down to floor joist, and reinstall 3/4 osb glued and nailed, (5×5 area) plan to use ditra right over osb here. Kitchen still has 1×3 t&g, plan to cover with plywood then ditra, question here is should any screws be used to fasten 1x3s down in addition to the exsisting nails? (cant hurt?)
they do squeak in places so sure something is moving, prior to adding the plywood for the ditra base, and what is recomended thickness 3/8 ok or 1/2 needed, what screw spacing for the plywood attachment? read the ditra lit. for not placing ply seams on the joist,assume this is important?
Entry way stripped to floor joist also, reattached, 3/4 ply here (non osb) what thinset for all these areas would be best to attach ditra? Have ditra -set thin set for tile to ditra, recomended by tile store.
Having problems getting a grip around ditra over 3/4 osb but having to cover a 3/4 plank floor with 1/2 ply, is 3/4 osb that stiff and strong, vs 3/4 planks and any thickness of plywood on top?
thanks in advance.
Hi Roger,
You should have an additional layer of ply over the osb. 3/8″ is fine, 1/2″ is better. Versabond works well for ditra over ply. I would screw down the planks to firmly attach them and get rid of the squeaks. Screws every 8″.
Thank you, plan to put ply over planks for sure, 1/2″, ditra not ok over the 3/4 osb only, per ditra? small area. Assume all ply should be ext. glue?
other Roger
Hey other Roger,
Regular ditra needs a double layer minimum 1 1/8″ ply. Ditra XL (they say…) can be used over a single layer 3/4. Ply should be exterior glue, but it’s not imperative.
ok making progress, lied about the 2x10s there 2×8 so added headers and supports in basement, longest span now 8 ‘ have 3/8 ply over 3/4 t&g 1x3s in small areas 1/2″ over large kit/dine/entry area 8×24 seems very solid now.
Tile store gave me ditra set for tile and laticrete 253 gold for over ply, my installer has never worked with ditra so am nervous,he laid the bath and ft entry way ditra mats, 5×5 and 3×4 seem to be stuck down ok, and can see some grey shadow showing thru, not sure what trowel was used or thinset consistancy was used any advice I can give him? he read the install and is very open to the” new stuff” he always uses cement board. Also should a control joint be used in long 8×24 area? figure right at the line between kit and dine or should it be at 12 ‘? will read up on control joint. Thanks
other roger
Hey other Roger,
You will see gray areas showing through, it sounds like he has it down correctly. I would just tell him to make sure he fills the cavities from all sides, every angle with the flat side of the trowel to ensure they are full inside the dovetails. Yes, you do need a control joint there. It would be fine there, the maximum distance is 15 feet, you can split that however you like as long as you don’t have a run of more than 15 feet without a soft joint.
ok, control joint across the 8 ‘ width at 12′ dividing it into 2 8×12 sections? like you would do in concrete or length wise 24’ length, seams (pun intended) I am reading parallel in your soft joint info,will re read.
Happy new year,
If you have a 24′ length the seam goes halfway dividing that into 12′ sections. You need to have soft joints in BOTH directions anywhere there is a span longer than 15′ – 20′ or so. With yours the single joint splitting the 24′ span is fine.
Hi Roger,
)
What a great site you have.
I’m getting ready to install 4″x24″ Porcelain tile in our laundry room in the basement.
The concrete has a seal coat on it so I know I will have to scarify it.
I found a place locally that sells Bostik Ditra-Set so I plan on using that.
Here’s my plan.
Scarify the concrete
Apply Ditra-Set
Roll out Ditra and embed it to the Ditra-Set
Let sit and cure for 24 hours
Apply a coat of Ditra-Set to fill in cavities (making sure their filled)
Let sit and cure for 24 hours (or so)
Apply more Ditra-Set and lay tiles
Let cure for almost a week ( have to go to my day job sometime)
Grout
Receive praised from the wife (yea, right
I do plan on keeping the Ditra about 1/4 to 1/2 from the stud wall (already have drywall hung and have 5/8 gap from where top of tiles will be) this gap will be filled with either spray foam or silicon to prevent any basement bugs from finding a place to build a home.
Now the issue I might have.
The laundry room also houses the furnace & water heater. I don’t want to tile up to them in case I might replace them later on and might get a different foot print. I’m going to leave the tile about 6″ away from the furnace & water heater, will this be a problem area (besides the trip hazard)? Will it start a crumble/crack area on the tiles? The tile will go on two sides so there will be a 90 degree corner involved.
Thanks
Lon
Hey Lon,
Everything sounds good. The laundry room won’t be a problem, just install it like the rest and stop it wherever you need to.
Good luck with that whole praise thing…
Just one more question (yea, like you never heard that before)
On the 4″ x 24″ tile do I use a 1/4″ x 1/4″ U/Square notch or 1/4″ x 3/8″ U/Square notch?
I plan on back buttering the tile (with the flat side of tile, is that right?).
Again Thanks
The 1/4 x 3/8 would be better. Use the flat side unless your tile has a lot of cupping (higher in the center than at the ends), in which case comb the back of the tile as well.
Thanks alot
Arghhh!!
To many choices, help.
I went to check out renting a scarifier and I got two different people (at the same place, no less) telling me which one I should rent.
The first one is a floor buffer on steroids. It comes with a 10″ diamond disk/blade. It has it a dust collection port built in to it. Weighs over 100 lbs. Looks like the picture in the link below.
http://www.betterrentals.com.au/wp-content/uploads/2011/10/concrete-floor-grinder-hire.jpg
The other one is an actual floor buffer. They have a disk that has what looks like paddles on it that has diamonds on the end. It has no dust collection device since “it spins so slowly that it doesn’t make dust”.
My basement floor has a seal coat on it and thats it, no paint, no old adhesive back tile, no nothing. Its a late 60’s house so I would say its oil based sealer that has discolored over the years (yellowish).
I plan on renting one of the bigger toys to do the major area and then using a hand held grinder to get the areas the bigger one couldn’t.
Which one should I rent?
I really don’t want to take to much off and then have to fill in the voids.
Hey Lon,
First – the guy that told you it won’t make dust is full of shit. Sorry, that’s the most polite way I could put that.
You never said how big your laundry room is but I would either go with the big one or find one of the ‘buffer’ types to rent that has a dust shroud on it. You don’t want to do the whole thing with no dust shroud – trust me on that.
Hey Roger,
Yeah, that’s kinda of what I thought the guy was full of.
I’m doing 150 sq.
Now here’s an interesting thing. I was figuring out how close I was going to bring the tile to the furnace and laying out some guide lines so I can make sure I don’t go to far with the scarifier. I set my beer down on the floor as I was checking things out, I came back to get a swig and once I picked up the bottle I noticed the ring it left. It wasn’t sitting on the floor but soaked in.
I grabbed a bucket and splashed water all over the place. After 5 minutes I looked around and the majority of the water was soaked in. There was a few spots that it still was sitting on top.
Does this mean I don’t need to rent a scarifier? Please say I don’t need it….and then tell me the truth.
I’m going to still get the hand held grinder (with diamond wheel) and remove the little, little, bump I found (less than 1/32). I figured if I don’t need the scarifier I will just do a quick pass with the grinder to please the power tool guy in me.
Thanks for all the advice
Lon
That means you don’t need to scarify it.
And that is the truth.
Now go buy a new power tool!
Happy New Year Roger,
I got my laundry room floor laid this holiday weekend. Thanks for the help.
Now on to my next tile project.
I’m going to be tiling a basement bathroom. The bathroom will have a sauna with an shower in it. I was planning on putting down Ditra everywhere except where the sauna was going. Then I got to thinking could I put Ditra down where the sauna is going? The floor of the sauna will be built just like a shower pan (mud, liner, etc..). Can I put Ditra down in this area and then build my sauna on top of it, that is including the walls of the sauna.
It basically will be; thinset, Ditra, 2×4 walls, mud, liner , and so on.
Thanks for reading this strange question.
Lon
Hey Lon,
You can if you want to. The only caveat would be trapping moisture between your liner and the kerdi, but if you allow the bottom mud deck to cure for about 48-72 hours before installing the liner it shouldn’t be a problem at all.
No strange questions – only wrong answers! (In my line of work, anyway…)
Hi Roger,
I am glad to have found your website. I am wondering if you may know of anyone (or maybe yourself) that is available to complete installation of 1/8″ ditra and install 20 x 20 porcelain tiles. I don’t know where you’re located. I’m located in Grundy County Illinois. We have a kitchen cabinet delivery ready to be delivered and the flooring still needs to be completed. Any help you can provided would be greatly appreciated. I look forward to hearing from you.
Thank you,
Bette
Hi Bette,
I’m in Fort Collins, CO, a bit far.
Give Jon Koessler a call, he’s around the Chicago area. He website’s here: http://www.koesslerenterprises.com/
Thanks for the referral Roger. I’ll follow up. Appreciate your quick response too, Bette
Roger,
A contractor recently installed 3/4″ OSB tongue and groove screwed down to 5/8″ plywood in preparation of ditra installation. The majority of the ditra has been installed. TEC Ultimate Large Tile Mortar 383 was used between the OSB and ditra. About (5) 40 lb. bags (which indicate coverage of a 50 lb. bag) of this mortar were used on about 450 SF. 20 x 20 porcelain tiles are to be installed.
Question: What affect could occur since 3/4″ OSB tongue and groove was “screwed down” to plywood? – I just found in schluter’s installation guide that OSB should be installed with sheets 1/8″ apart from each other.
I’ve been told some areas of the ditra installation containing dips are 3/16″, 1/4″, 1/2″. Just wondering if we’re ok to proceed with the tile installation…???
I recently left a message for your referral contact. He is a distance from me so I’ll need to find out if he’s willing to travel. Any feedback you can provide would be greatly appreciated.
Thanks,
Bette
The osb should be screwed down to the plywood. I’m not understanding exactly what you are concerned about? Did he butt the sheets of osb tightly against one another? There should be a gap left for in-plane movement of the individual sheets. If you are referring to an 1/8″ gap between the sheets of osb and the layer of 5/8″ beneath it then you are misunderstanding, there should be absolutely no space between these sheets, they should be screwed together tightly.
There are several different ways to compensate for dips in the substrate. A 1/2″ dip is HUGE! So I’m not sure whether that is going to be made up for with the ditra or thinset beneath the tile. Are the dips in the ditra surface, or were they only on the substrate surface and have been made up for with thinset beneath the ditra?
Each contractor has their own method, it may be one thing or a combination of things. Just because dips exist (they exist to some extent in EVERY installation) doesn’t mean he’s doing anything incorrectly.
No, I’m not refering to the 1/8″ gap being inbetween the OSB and plywood layers. My reference was to the OSB tongue and groove being installed – and I just read in ditra installation that there should be a 1/8″ gap between sheets of OSB for a ditra installation. So, I am wondering what affect not having the 1/8″ gap between sheets of OSB (because they are tongue and groove) will have on our tile installation since the underlayment is ditra.
The 5/8″ plywood bottom layer of subfloor had dips which the installation of OSB tongue and groove seemed to improve in some areas. In other areas, shims were added before the OSB T and G was installed. Now those areas that were raised with the shims underneath the OSB are found to be higher than floor areas near those locations and the dips that were there before the OSB was screwed down to the plywood subfloor are now deeper compared to the increased height of the shimmed OSB locations. To answer your question further, many areas that were flat once the OSB was installed are now bumpy since the ditra has been installed.
I hope this clarifies things but please let me know if you have any further questions. I appreciate your quick response too – I really need to proceed with this project and I want to be sure what direction to take. Thank you Roger.
Just to clarify what I mean by “bumpy” since the ditra was installed, its the mortar that is not level beneath the ditra.
If the t&g is butted against the wall then there could be a problem with expansion. Wood expands and contracts all the time, if there is no room for it to do that it may peak at the seams.
There should have been no shims placed beneath a plywood layer for a flooring substrate. It’s just incorrect procedure because it may lead to exactly what you have there, more dips and peaks than you began with. That said, many inconsistencies in a flooring substrate can be compensated for with proper tile installation. Simply more thinset in the lower areas, less in the higher. That, however, requires experience and attention to detail. That will depend entirely upon your contractor.
Thanks Roger.
Hi,
My guys is installing Ditra in stand-in shower base under the tiles. Do you think that is a good idea. He think it will water-proof the area. I know that installing it was very difficult as he was trying to push it in nook and crannies. Ge put cement on plywood and then thinkset and then the ditra material. What do you think?
thanks..
Mike
Hi Mike,
I think you’ll be replacing that shower in short order if it’s allowed to remain. The proper material for that is kerdi, not ditra. While the dovetails will be filled with thinset water will saturate the thinset and fill them with water. It will never be able to dissipate. And while it can be used to waterproof a flat flooring substrate, it will not be waterproof in a shower which sees regular water saturation.
Hi Roger,
Thanks for the great site, I am desperatley searching for a solution to my kitchen tiling project. We took up old vinyl to find a two layered subfloor. ( 1/4″ plywood on top 1/2″ osb).
My challenge is that I need to get the tile on with a minimum of increase in floor height or my dishwasher wont fit under the counter.
We are looking at Ditra due to its thinness, but what can I do with my subfloor? I do have access to the underside from the basement so reinforcement from underneath is possible – is that really an alternative to adding another layer of plywood?
Please help – I am getting a different story from everyone I ask -and your posts really seemed sensible so I would love to know your opinion.
Hope to hear from you soon,
Ron
Hey Roger,
Just realized the true thickness of my two layered subfloor is actually 1/4″ plywood on top of 5/8″ osb = total of 7/8″. I am planning to screw every 4 inches. Is this ditra approved underlayment?
Thanks,
Ron
Yes, approved by every standard of which I’m aware. (which covers most, if not all, of them in the US)
Doesn’t Schluter state that 3/8″ underlayment is the minimum for Ditra? I’m adding a thin plywood layer to my subfloor to cover remnant adhesive and also stiffen the floor bit. I was planning 3/8″, but if 1/4″ is okay I won’t have as much of a height problem.
Hi Gary,
Ron asked whether or not ditra was an approved substrate by standards. It is, that’s what I answered. TCA standards dictate minimum 3/8″ additional (actually 1 1/4″ total) but schluter says the XL can be used over 3/4″ substrate. Standards and manufacturer’s recommendations don’t always jive with one another, that’s where the experience comes in. As long as your floor is sturdy 1/4″ should be fine.
Hey Ron,
Strengthening your floor framing is actually better than simply adding more plywood. If you can get the joists rock-solid that would be fine with the 3/4″ subfloor. Alternatively you can use Ditra XL rather than just regular ditra. Schluter states that a 3/4″ substrate is suitable for that product.
Hey Roger,
We are installing a 24″ x 24″ porcelain tile on top of plywood. We already installed the ditra with a modified mortar. My installer has also skim coated the to of the ditra to fill all the pockets with an unmodified mortar and has left it to dry for 2 days before he starts to install the tiles with the same unmodified mortar. Is this method of “skim coating” the ditra first a common installation method?
Please advise.
Thanks
Daniel
Hi Daniel,
I do it all the time. It makes it much easier to get a flat installation and prevents the ditra from being damaged while working over the unfilled areas.
Hey Roger,
First class site! Glad I came across it. My question(s), Ditra over plywwood subfloor, whats the average and the best Mapei modified thinset to use? 2’X2′ porcelain on top, whats the average and then the best Mapei for this purpose and the trowel size for 24″X24″ tiles. I restructured underneath, double beamed and the span is just 10″ with small cross support in between those so its really rigid.
Hi James,
Ultraflex 2 for your modified and kerabond for the unmodified – 2×2 and 24×24’s. 3/8″ u-notch or larger trowel on those 24’s.
What about Ditra over OSB?
What about it?
Technically you need to use a thinset specifically approved for use over osb. Realistically I’ve never found one that actually stated that. Also realistically, ultraflex 2, 3 or versabond works.
Thanks Roger!
Hi Roger another question if I may; My house was involved in a home reno show recently and they laid 12X12 porcelain tiles that are basically dumb looking. Regular ditra was used. (originally a yellow substitute was used called supertest that actually failed underneath, the fuzzy layer delaminated and the tile floor literally was floating) What is the removal method? Could I pry up and knock away the tiles and attempt to preserve the ditra intact? Could I rebond to the filled ditra properly or it all has to go? The ditra is laid on self levelling cement over floor boards. Thanks so much for your time.
Hi James,
There is no way at all to save kerdi after the tile has been installed to it. You will completely destroy it getting the tile off. The best thing to do is remove the tile and kerdi, scrape the remainder of the ditra off, and start all over.
I wouldn’t trust a product with the word ‘test’ right in the name.
I guess it failed the test, eh?
Thanks for all of your help. We installed the ditra with modified thinset and are now installing 3/8″ through body porcelain tile with unmodified thinset. However, I am finding so much conflicting information regarding the series of events for grouting, ceiling, caulking. According to the manufacturer, the tile does not need to be sealed, according to the guy at Lowes, it needs to be sealed before grouting. Who would you trust? How long do you have to wait to grout, and then how long do you have to wait to seal the grout and/or tile? And how long do I have to wait to install the toilet. Trying to get it done by Friday but I don’t want to rush it and do something wrong. Thanks!
Hey Rita,
If it is glazed through-body porcelain (shiny on top with a pattern or solid color) then it doesn’t need to be sealed at all. Always listen to the manufacturer, they want their product to last and will tell you the steps necessary to accomplish that. The guy at lowes is just waiting for lunch and trying to sell as much product as he can.
Set the tile. The next day you can grout the tile. The next day you can seal the tile. That gives you two days to drink.
I’m installing a heating element on a concrete slab, under my tile. Should I use Ditra for this to avoid cracking from slab movement? If so, does the heating element go under or over the Ditra? Thanks
Hi Aaron,
Ditra is always a good idea, especially over a bare slab with heating. You’ll have all sorts of differential temperatures in that floor, any compensation you can have for that helps tremendously. Yes, the heating element goes below the ditra.
Thanks for all the great posts! I have one question for you. I am in the process of installing those 1″ x 1″ hexagonal white and black tiles in a bathroom floor. The homeowner wants to install that sun touch warming system and I was following your other post about that. You say you like to use ditra embedded in thinset over the wires, which is what I was planning on doing until I read Ditra’s installation instructions. It says not to use any tiles smaller than 2″ x 2″. What’s your take on this?
Hey Dan,
My take is that schluter doesn’t want you to do it. I’d do it anyway, I’m a rebel like that, though.
It’ll work. It works better (easier to set) if you pre-fill the ditra and let it cure overnight, then set the tile.
When you pre-fill, do you use modified? Then unmodified for tiling?
Sometimes, depends on the tile. With the smaller tiles I would use modified for both.
I’m about to start laying tiles on a terras and use ditra on top of concrete. Do you know whether it is important to immediately put the tiles on ditra after cementing it to the substrate or first let it dry and start tiling the day after? The reason I ask is that I probably will not manage to finish the whole work in 1 day.
Hi,
I’m trying to understand the total thickness of my tile installation. My starting substrate is plywood.
How thick is the modified thinset-ditra-unmodified thinset stack-up?
Thanks.
Hi Gary,
Normally about 1/8″. It, of course, depends on the size of trowel you use, but that’s average.
So the total (for 3/8″ thick tile) would only be 1/2″ ?
Approximately. Again, depends on what size trowel you use. If you use a larger trowel then it will be higher.
Dear Sir,
First, thanks for all of the great info on your page. We want to put tile down in our kitchen but we have hot water radiant floor heat underneath and thus don’t want to put down hardibacker and risk puncturing the pex w/ a screw. So… ditra seems perfect. Linoleum tiles are on the floor now and I’m afraid that they might be really difficult to get up. They’re pretty dull w/ age and the guy at the local tile store told me that we could use ditra on top of it if we used modified thinset under the ditra. I’d like to know if you think we can leave the linoleum tiles and if not, what the best way would be to get them up.
Thanks,
Steve
Hey Steve,
The easiest way to get them up is simply to scrape them up. And it isn’t simple.
You can go over it if you use a thinset specifically recommended for use over vinyl and linoleum. I know mapei ultraflex 3 is one such thinset. You may need to rough up the face of the linoleum first.
Hi,
We plan to install ditra over our wood subfloor in our bathroom. A couple of questions. We pulled up the laminate floor to find that there is a plywood layer (not sure of the thickness, perhaps 3/4″) over a sub floor (not sure of that thickness either, thinking they were 1″x6″ beams). The plywood floor has some areas that have water damage and is kind of peeling up or chipping. Do we need to replace that floor or can we just chip off the loose areas and level with the thinset? Also, the floor squeaks in some spots, if we can not easily fix that, will it cause damge to our tile in any way? Also, the store recommended modified thinset for porcelain tile for under and ontop of the ditra, soes that sound appropriate? Last question, we are also re-tiling the wall, do we need any kind of “expansion joint” at the corner where the 2 meet? I don’t have the time or money to do this project twice so i want to try to do it right the first time…thanks for your help!
Hi Rita,
You need a second layer of plywood over that first. If you do that you can chip off the soft areas and place thinset there before you install your second layer. If you don’t do that then you’ll need to replace the entire area that has water damage – every layer you remove is going to weaken the substrate. If the floor squeaks it is a sign of movement. Movement may end up cracking your grout of damaging your tile. Another reason to install a second layer of plywood.
Schluter requires modified thinset between the ditra and wooden substrate and unmodified between the ditra and tile.
You do need to leave an expansion at all changes of plane (corners) and they should be filled with silicone.
Thanks for the quick response and great information! Worked on the floor today and was able to stop the squeaking by screwing the plywood underlayment and subfloor into the joists. If I add a 2nd layer of plywood, I will end up with about a 1″ lip between my bathroom and hallway which is why we went with the ditra in the 1st place, to minimize the lip. Is it possible since the damage is not too terribly bad, to fill in the chipped areas with a floor patch and then thinset on top of that once it dries or is that not sufficient? Also, upon further investigation today, I found that the floor has a slope of appx 1/2″ across an 8′ span. will that make it impossible to lay 18″ tile?
Standards dictate no more than 1/4″ in ten feet for flatness. Yours is double that. You may be able to get away with filling those in with floor patch depending on where they are in regards to traffic areas, it won’t take regular traffic and last. Another option is to place down thinset, then install 1/4″ backerboard, then you can put the ditra on top of that. If you get the backer flat and let it sit overnight, then screw it down you’ll be able to flatten the floor.
Hi Roger,
I am tiling a basement concrete floor, 5″ slab with hydronic heat, and I was wondering what thinset do I use with the ditra to bond to the concrete floor? Two tile places told me different things. Thanks.
Hey Tim,
Schluter requires unmodified thinset to bond ditra to concrete.
I have a manufactured home with OSB underlayment. I want to put in tile and I understand the DITRA is okay for that application. My problem is this: When we removed the carpet there were some large (1/4″ – 1/2″) cracks – mostly in doorways between rooms. There might be a small height difference between the two adjoining sheets of OSB. What do you recommend? Should I sand down the high side of the crack/opening? Put a thinner underlayment over it to span the cracks? What filler should I use to span the cracks if you recommend that? Thanks for your help and insight. It really is helpful.
Hi Cindy,
Your best bet would be a crack isolation membrane which would span the cracks between those sheets of osb. If there is a significant height difference you can sand it down, but it would be better to simply use a larger trowel for your ditra then in those areas you can install a bit less thinset and use a straight-edge to flatten it all out.
Thanks Roger,
Whatever it is (mastic or not), it is gray in color. It is original, which mean 1964 vintage. I’d rather not increase the height, for the usual reasons, but may have little choice.
Gary
Hi Elfy,
My boyfriend and I are thinking about tiling the master bath floor ourselves using 18 inch travertine tiles. The subfloor is 3/4 inch plywood over 16 inch oc joists. Do you think we could use the schluter ditra xl directly over the plywood or do we have to put down another layer of plywood to provide the necessary strength to the floors? We have to transition to a wood floor and I am concerned about the height.
Thanks,
Carol
Hi Carol,
You and he are thinking about doing it? Or you are thinking about him doing it?
Schluter says you can, so as long as you use the required thinsets it should be fine – according to schluter.
That’s what I’m supposed to tell you – so I did. In all reality it will likely be fine, but there’s always a (rare) chance it won’t be. Do you know how far the unsupported span of your joists are? That dictates the amount of deflection in your floor. Provided you have a good, solid floor then it should be fine.
And I’ll say it again, I say it a LOT: Do not let the height of your transition dictate the required substrate beneath your tile. It’ll look pretty and flat – until it fails.
Hi Roger,
Thanks for your reply. We have decided to add a 3/8 inch second layer of plywood with the 1/8 inch ditra on top – just to be safe.
I have another question for you. We would like to use the schluter drain and kerdi membrane for our shower pan installation. Since we are new at this, we would like to use a schluter pre-sloped shower tray. It just seems easier. The problem is that our shower base is 44 inches wide by 60 inches long. If we cut the tray to fit, won’t it hit the shower wall at different heights? Does that matter?
Thanks,
Carol
Yes, that does matter. When you cut the pan you need to cut equal amounts off of each side. For instance, if you need to remove six inches you’ll need to cut three inches off each opposite side rather than six inches off of one end. It will then be consistent.
Hi Roger,
So I guess a pre-sloped base is out of the question. What do you recommend? We would like to use the Schluter products.
Carol
You can just create a regular mud bed and use kerdi over it with the kerdi drain. It’s how I build most of my showers.