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 
I’m using the Ditra-Heat membrane for a heated bathroom floor. Subfloor is 3/4″ plywood. For an interior floor with natural stone tile, Schluter recommends a second layer of at least 3/8″ which will also be plywood. The Ditra-Heat membrane is 1/4″ thick. My marble tile is 1/2″ thick. With all these layers, my floor is starting to get built up. I’m trying to prepare for the transition down to hardwood floor outside of the bathroom. The question is, how much height is added by the thinset under the Ditra-Heat and on top including the tile installation. The tile is 18″x18″ marble and will be back buttered. Thanks in advance.
Garry
DIYer here, not the elf.
As I recall, the Ditra trowel provides for about 3/32″ of mortar underneath the Ditra…I have a hard time getting good coverage / embedding with that trowel myself, so I tend to go a bit bigger.
For the tiles, it’s going to depend on what trowel you use, as well as how much you back butter the tiles. For tiles that size I probably end up with a 1/4″x3/8″ trowel, which would leave you with 3/16″under the tile, plus whatever you back butter with. But that’s just me – a relatively inexperienced DIYer…It will also depend to some extent on how flat your floor is.
NOTE: Have you verified that your joists are up to spec for natural stone. The requirement is for a deflection of L/720 – twice the requirement of ceramic tile. If not, you might be dealing with some cracks in the future…best to address it now if you can (that, or consider a ceramic tile that is made to look like marble)
Good luck.
I am setting tile in my kitchen/dining room area. It’s a new build and I have 3/4″ OSB over 16″ Ibeam joists. I’ve been back and forth about a substrate to use, but I think I’ve settled on ditra (everyone here in Utah seems to just use lath and thinset). Anyways, I’m willing to shell out the extra memory for ditra, but I’ve read conflicting views about it going on top of OSB. Shchluter says it’s ok to place it over a bed of thin set, yet no thin set company seems to warranty the use of their product over OSB. I’m very confused. What is your experience?
Hello,
Should the Ditra be used over a concrete slab in a basement? Better yet, can it be used?
Thanks.
Hi Jorge,
Yes it can be used. It’s always a good idea to use it, it’ll lead to a better installation.
Thank you Roger in advance for any help you can give me. We had ditra installed in a bathroom in August. Our general contractor was not able to determine the amount of tile needed, so the installers ran out and left the wires exposed for two months. People were walking on them for about two months. Then the tile installers came back and dug out some improperly installed tile over the wires. They also did not take any photos of the insulation, Since the general contractor did not perform any of the required electrical tests should I be concerned? Also, I found a photo I took of the orange mat with some grey material randomly spread on the floor in the area where the tile is missing. Is the grey material waterproofing? If not what is it? Also the wires appear to run under the heat radiator, is that safe? Thanks again.
Hi Ladybug,
Yes, you should be concerned. I would have an electrician come in and test the wires. The wire should be a minimum of 3″ from the radiator. I have no idea what the gray material may be, it’s likely just thinset?
Hello Floor Elf, I installed a ditra on a concrete floor (10 years old without any cracks) in my basement bathroom. Cleaned/dampened floor, used unmodified thinset, used 1/4″x3/16″ v-notched trowel spreading in all directions and leaving a notch, put ditra and pressed it using a wooden trowel. I noticed that some ditra spots/areas have uneven color. Seems like said spots did not get in contact with the thinset even though the concrete is level. If the lighter spots/areas (5″x5″ in some areas) did not get in contact w/ the thinset if that’s the case will it create problems if I put on the tiles later on? Any advise? Thanks.
Hi EJ,
It could, if that’s the case. Ideally you want uniform color from the thinset through the top, but just because it isn’t doesn’t mean it isn’t bonded. If you try to pull up on those areas it should be bonded fine – if it isn’t you’ll be able to lift it. If it is not bonded you can simply cut those areas out and reinstall them.
Thanks for the info. I’ll try a few spots & hope it’s not loose.
Hello floor elf, I’m hoping you can help.
In May last year I got my kitchen floor It had been done 18 months previously but the builder made some errors resulting in cracked tiles. The subfloor wasn’t secured very well. To cut a long story short we got the floor redone, this time by a professional tiler. He was fully aware of what happened previously and said he would assess the subfloor before making a call on wether him and his partner could strengthen it themselves or get a carpenter to come and do it. They did it themselves and sent me pictures to show all the additional noggins, and screws they applied. In January I got back from my holiday and noticed that where the tile meets the stairs in the hallway (which is part of the same floor) there was a crack in the grout. I’ve since established it’s likely to be because of two different materials meeting (tile and wood) and that grout should be raked out and replaced with silicone. This weekend, I noticed a sound which I can only describe as a click (or like what I hear when I walk on the wooden floors in my livingroom) when I walked in a certain area of the kitchen floor. Every time I walk in this area I can hear the sound, so far there is no evidence of cracked grout or tiles. The floor is made up of joists, 18mm ply, ditra and porcelain tile. Any insight would be greatly appreciated. I’m rather worried given the previous problems I’ve had. Thanks in advance. Nat
Ps I initially thought it could be the joists but now I’m starting to think it could somehow be the ditra not applied properly? There is a tiny amount of movement in the overall floor but not much, I’ve done the bowl of water test and the what barely ripples..
Hi Natalie,
Yes, that area at the stairs needs to be siliconed rather than grouted. The sound could be a number of things. I would call the guys who did the floor and have them come out and check it out. It may or may not lead to a larger issue over time, it depends on what is causing it.
I just laid my thinset and D mat over a cement floor and this morning noticed that a small section on a seam didn’t adhere. What should I do? Thank you for your help!!
Hi Will,
Cut out the area that isn’t bonded, scrape up the cured thinset and reinstall it. Ditra does not have to be a continuous piece, it can be pieced in.
Hello,
Thank you for all of the great info, I’m learning so much!
I had a guy time my for using a hexagonal mosaic (each tile is roughly 2 x 2). I fear he did not fill all of the square voids in the ditra because a) I can see the ditra in places (he hasn’t grouted yet) and b) a handful of the tiles are loose!
I am confident the ditra is adhered to the ply as I did this part myself (with your help!)
Should I
a) pull up individual times and replace, or b) have him rip it all out and do it again?
Thanks,
Paul
Hi Paul,
If you’re paying him for it I would have HIM tear it out and repair it properly. Whether that means removing everything and starting over, or just fixing the loose ones, that’s up to you.
Hi, I had a tile installer Kay tile over Ditra yesterday and when I just checked the bag (in the garbage) for recommended dry time before walking I noticed he used Mapei ultraflexible 2, which is polymer modified. My understanding is he should have used a non modified over Ditra. Can you tell me if this is a major problem? Should we just let it cure longer? We haven’t walked on it yet. Thanks Rachel.
Hi Rachel,
You’re fine. Mapei ultraflex 2 is actually now approved for use over ditra. This is something that manufacturers are working on getting approved, that’s why you don’t know about it yes, but it’s fine over ditra and have been approved for that application for about six months now.
Hello,
We have 2nd story home on the water we would like to have travertine installed. The current tile and carpet are on plywood. We’ve received separate opinions from two reputable installers for the underlay of the travertine installation: 1) red guard with backer board and 2) ditra. Please kindly share with us what you believe to be the best method and why?
Thank you very much!
Hi Yolanda,
I think ditra is the better option, but either one, properly installed, will work fine. Ditra allows for more in-plane movement compensation. I would be more concerned with whether or not your existing floor is a double-layer and has the proper deflection capability for a stone installation. It has to be a double layer of ply with a 1 1/8″ minimum thickness under either of those methods.
I had a so called contractor add a ceramic tile over my cement patio floor. The installer did not add any mortor under several of the tiles and left no space between the tiles. The end grout cracked and about 10 tiles have buckled up. What has to be done short of pulling the entire tile job up and redoing it.
Hi Donnis,
Sorry, nothing can be done short of a full, proper, replacement.
I have a marble floor with thermal heating on a second floor master bath. The floor has cracked in several places. I want to do a tile over to save the heated floor. No hollow spots under cracks. The sub floor is 3/4 tongue and groove ply with 1/2 concrete board. Should I use a decoupling membrane or just sand and redgard? Can I use a 6″x24″ porcelain plank tile or should I stick to 12×12? -Anthony
Hi Anthony,
Sand and redgard??? If your floor tile has cracked, you WILL NOT be able to tile over it and have it last. No substrate at all will compensate for an improper base. But you can use any tile you want, doesn’t make any difference, provided you start with a suitable substrate. What you have now is not one.
I am researching a DIY tile installation over existing vinyl. Question 1: The Ditra PDF says ” for wood substrates, nail off floor with ring shank flooring nails every 4″ o.c.”. Does this mean literally every 4 inches over the entire floor or over the floor joists or along the outside edges – I am confused!? Question 2: Can you advise specific brands of thin set for the vinyl to Ditra then the tile to Ditra. I am leary of the HD and Lowes brands after reading a lot of comments. Thank You!!!
Made the mistake of using Pre mixed thin set from home depot for ditra heat.. Pulled up the tiles and now waffles are filled. I plan to get as much out as I can. Will this be ok or do I have to rip up the membrane and start over. Thanks.
Carl,
I’m no tile guy, but schluter does not list partcle board as a suitable substrate for ditra. If you meant oriented strand board (osb), then yes you can install ditra on osb, but not on particle board. Keep in mind tha schluter has some subfloor requirements for dita (thickness, joist spacing, etc). You can download their installation manual to see their requirments.
Peter
I just tore up the tiles in my bathroom and most of the ditra either ripped or corners came up so I removed it all. The backing stayed stuck to the floor. What is the best way to remove the backing,or can I leave it. I plan on putting a new layer of ditra on the floor. Thanks Al
Hi Roder,
Just finished installing ditra heat mat over new plywood using custom’s versabond. I can not get Ditraset locally, and customs uncoupling mat mortar would have to be ordered. I know you suggest other unmodified thinsets to bond tile to Ditra, but I am installing 6×39 inch tiles and have read that medium set mortar should be used for my application, since I may need to use a1/2″ notch trowel (Ditraset and custom uncoupling mortar qualify as I understand). I picked up Mapei uncoupling mat motar. Any thoughts on this product?
Thanks
Peter
The Kerdi corners are garbage, they come with a hard fold in the area that needs to be flat and can’t be sealed down flat. Maybe you could iron them ahead of time but what a pain in the ass!! I already had all the thinset mixed before I realized the problem. I suppose I can cut them so I can flatten them and then patch it but that kind of defeats the purpose of paying high dollar for corners only to cut and patch later. Can you sense my frustration?
What is the procedure for stopping a job laying tile, due to time constraints, and restarting the job the next day when using “Ditra”?
Hi,
Is hardwood floor a suitable substrate on which to put ditra, then tile?
Thanks,
Paul
installing ditra and ditra heat in a new construction home, lowes now sells a uncoupling thin set mirtar. Do you use this for membrane or setting tile in.
Hi Matt,
It will always be used between the tile and membrane. If you’re going over concrete it will also be used under the mat. If you are going over wood you need to use modified thinset under the mat.
Hi. Can I use ditra on top of old tile? We have a terracotta tile on our bathroom floor and want to use the ditra heat system. Can we just aply to top of old tile with thunder?
Please advise.
Thanks
Nick
Hi Nick,
No. You can, but you need to prep the surface of the existing tile with either a primer or scarification. And I don’t believe that installation would be warrantied.
Hi. Installer put down ditra heat membrane and ditra heating wires with thin set (hopefully correctly). He installed about 140 ft2 tile. We noted the height difference between tiles was up to 1/2 inch (it was gauged slate from Home Depot) latter that evening when inspecting floor. One of the offending tiles was popped up and we found less than 10 % mortar coverage. Barely had any mortar around perimeter of tile only. More tiles were popped up, same story on coverage. All tiles were removed that evening and the mortar on top of ditra sheet scraped off smooth with the top of the raised ditra discs (used to put wire between). So now i have thin set embedded on top of ditra heat membrane, smooth with the top. It is now dried. We decided to find another installer and let this guy go. Please tell me we can install tile on top of the area where we removed tile from. Please don’t tell me we have to remove ditra and mortar and start over. I have $4,500 of ditra sheet and heat wire – large fraction of heat wire is imbedded in mortar on top of the ditra sheet. Please help me!!!!!!
Hi Dave,
You can go over it just fine.
Sir,
It was recommended to me by the Lowes flooring person that I use “TEC Premium Tile adhesive for floors” when applying the porcelain tile to the DITRA. I used the unmodified thinset to adhere the DITRA to the plywood.
After completing the project, I noticed a prolonged drying time for the tile to the DITRA and then (of course)further read the instructions for the DITRA. While the instructions state it is not recommend as does every person who uses this stuff….what is bound to happen to the tile?
Thanks
Hi Bri,
It is highly likely that the grout will begin to crack, if the floor gets wet there is a high chance of mold developing between the membrane and tile and the ditra will probably eventually become debonded from the wooden substrate. You’ve used mastic to set tile over an impervious membrane, it will never fully cure beneath your tile and it has essentially zero compressive strength (it can not support the tile in the manner needed). It will not bond to the membrane, which isn’t an issue – thinset doesn’t either, but thinset will cure rock hard and be able to support your tile.
We have a new house with ditra professionally installed in 2 bathrooms. The controls both make popping noises randomly. Very annoying at night. What would cause this?
Hi Eric,
What controls are you speaking of?