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.
We laid the ply underlayment on top of the subfloor to Schluter’s specifications.
However, one dip is measurable: Using a straightedge, a varying ¼ inch dip occurs in the middle of the straightedge span of 33 inches. The dip line runs for about 5 ft as the dip levels out.
My question concerns the best tactic to fill this gap:
1. Use a self leveling cement, or
2. Make the modified thin-set fill the gap when laying down the Ditra.
This dip occurs in a kitchen floor a few inches away from where a cement slab floor meets a joisted floor that has multiple pipe holes. (the kitchen is partially over a basement room and partially over a slab with sleepers).
Hey Ron,
Either will work. It would be easier to use slc first, then go over it with ditra. Saves the hassle of trying to get the ditra absolutely flat over a floor that isn’t. That said – I use the thinset and ditra method all the time. Just take your time with it and pay close attention to the flatness as you lay it.
Hi Elf
I just started remodeling a bathroom in my house and found out that under the linoleum there is a asbestos tile from the pre 60’s and below that is a 1/2 inch thick pine parquet . The linoleum is in good condition. Is it possible to use ditra or something similar and if so what kind of thin-set should I use to adhere to the linoleum to the ditra?
Hey Sveinn,
You need to either have that removed or go over it with a product which will make it a suitable surface for thinset to bond. Tec has a primer which can be rolled over it, I believe Mapei has one as well. Search for ’tile over tile primer’ and you should be able to come up with something suitable. I wouldn’t trust trying to bond any thinset directly to that.
Roger: I need to ask for some guidance: 5/8 plywood on floor, putting down
1/4″ hardee board, then Ditra. Installing travertine on bathroom floor and shower surround.
1) Laticrete 220 on plywood then put down hardee board. Is that ok or do I have to use a flexible additive with it ?
2) Can I use 220 on top of Hardee under Ditra ?
3) I can buy Ditra Set here so would like to use on top of ditra then onto the tile ( so far is all this acceptable or do I need to do something else ?
4) What size trowel would be best for Travertine 6×6 ( shower ) and possibly 12×12 or 16×16 for floor.
Would like to thank you for all your help. Its amazing that you would take your time to help those of us that dont know to much !!
Thanks
Hey Chuck,
1. You can use the 220, but you could also use something cheaper. It can be nearly any thinset, it’s just there to fill voids, not to bond anything.
2. Yes, but again, you can use any good thinset there as well.
3. DitraSet will work fine, it’s good stuff.
4. I normally use a 5/16″ v-notch for smaller and 5/16″ or 3/8″ for larger tile.
Roger: Travertine on shower surround…..
1) Would I use the Ditra Set or the Laticrete 220 ?
2) When waterproofing shower can you use 6 mil plastic behind Hardee, then Kerdee water proofing on top of Hardee or would that create a mold sandwich ?
Sorry for all the questions, but I dont want the dog to explode into flames !
Thanks “a lot” for your help !
Hey Chuck,
1. I would use the ditraset.
2. That may create mold. You want to use one or the other, never both.
We are tiling an open kitchen/family room 350 sq ft. The family room portion is over 12″oc sleepers over cement slab with 1/2 ply then new 5/8 ply while the kitchen is over j 16″oc joists with 3 layer of plywood but has no under the joist access. Prior tile job directly to plywood had cracks along every plywood long seam. Our carpenter put some new sleepers and shims, screw existing ply to sleepers or joists whatever to strengthen those two portions. And then laid new 5/8 plywood per ditra quidelines. (their tech said use rink shank nails not screws and 2nd layer perpendicular to first layer no glue 4″ edge nails, 6″ field nails) Now the floor seems very firm but there are a few high spots. We are planning to use ditra and 13X13 porcelain tiles but are hyperventilatiing about cracking again. A tile installer gave us an estimate and said no problem with the few high spots. We will do the tiling (save $$$) – have done tiling before on a utility room over sleepers with ply then cement board with excellent results. Should we use SLC for leveling the high low spots, or can we adjust for those with the ditra/tile installation. If you say yes to adjustments do we try to get it with the thinset below the ditra or above the ditra or in both places? We have talked this to death – hopefully you can give us your opinion of best approach.
Hi Karen,
The best approach, and the most expensive (of course) is to use slc to level the floor. You would be raising the rest of the floor up to the level of the high spots, so it will likely require a lot of slc.
You can level it out with ditra and thinset. Use a 3/8″ x 3/8″ trowel for beneath the tile and rather than flattening out small areas at a time use a large straight-edge to flatten larger areas. Be sure to wait a day before walking on any of it. That should take care of most, if not all, of it. Any small areas remaining can be compensated for as you set the tile.
Roger, I am not sure I understand. Are you saying to put down thinset directly to the plywood without putting down the ditra and use a long level to fill in over the low spots. (sort of using the thinset in a controlled areas of leveling instead of the whole floor) Let it dry and then put down the ditra let it dry and finally the tile and while doing the tile take care of hopefully only a few minor imperfections.
No. I’m saying put down your thinset and lay the ditra on top of it then use a straight-edge to embed the ditra into the thinset. Usually people use things like floats or a block of wood to embed the ditra, that’s simply too small an area to ensure flatness over a larger area, it will tend to follow the slope of the floor, imperfections and all. If you use a straight-edge you can get larger areas flat at one time.
I listened to my friends and not the ditra dealer. I used 1/4 ply over vynil and screwed it down every 6 inch square. I was doing the project in phases and inthe middle of laying tile I noticed that I was getting flex in some of the tiles and grout was popping/cracking. Did I just cost myself a ton of work and several thousand dollars or is there a way to fix it?
Hi John,
Oops.
Don’t know about several thousand dollars yet – depends on how far along in the process you are and what the tile cost you. Unfortunately, though, it does need to be removed down to the layer beneath the vinyl (vinyl and vinyl substrate – likely luan – need to be removed) then built back up with a minimum 3/8″ layer of ply and an appropriate substrate for the tile – cement backerboard or another approved membrane.
Hello Mr. Elf
I’m tackling my first tiling project and want to get things right. We are tiling our kitchen with a 12” x 12” white/black marble (3/8” thick) checkered board pattern. We are using DITRA. I prepared the subfloor as per Shulter’s directions and we had to add some SLC to fix some issues.
The question I have is: I’ve read that black marble tiles are suceptible to warping due to moisture. Some thinset manufacturers recommend using modified thin sets or epoxy blends for black or green marble. Shulter recommends using unmodified thinsets between the DITRA and the stone tile. Which one should we use? Is there a particular thin set you would recommend for black marble tile?
thank you for your advise
Tile away
Carlos
Hey Carlos,
The warping issue is delegated to marble tiles which fall under the ‘serpentine’ classification. These are normally green marbles, although some black marbles qualify. If your marble does not contain a LOT of striations and color variations in it then it is likely not a serpentine. I would, however, test it by bonding it to a scrap piece of backerboard or something (nearly anything, really, it’s the vapor dissipation from the thinset which causes the problem) and checking it after a day to see if it warped. It will be VERY noticeable.
I prefer Laticrete 317 as my unmodified. The problem arises due to uneven moisture differential between the top (face) of the stone and the bottom. ANY thinset will warp a stone if it falls under the serpentine clarification.
Roger: How the hell do you measure a trowel ? I bought one that is 1/8 x 3/16 x 1/8 ( u notch ) but it certainly doesnt look like it would give you enough thinset spread to stick to the tile ?
Sorry for the dumb ass questions but couldnt find anything about it through the posts.
Thanks a lot, appreciate your help.
Hey Chuck,
The first number, 1/8″, is the height of the notch from the lowest point to the highest – the height of the ridges on the floor
The second number, 3/16″, is the width of the teeth, the space that will be left between the notches.
The last number, 1/8″, is the space between the teeth, the width of the ridges on the floor.
You have a trowel used for gluing carpet down.
It is normally best to have the first and last numbers 3/16″ or larger. The smaller the second number the more thinset will be on the floor.
We just installed hex tile over Ditra. This was the first tile install I’ve ever been part of. The caveat I have (and I think I’ve read Roger saying the same thing): Definitely fill in the waffle holes with the thinset and then let the thinset harden before installing the tile. I believe Roger has said elsewhere on this site that this voids the Ditra warranty. (But how would one make a warranty claim anyway? Would Schluter send a rep to the house?)
I say this because to ensure equal spacing between tiles, you most likely will shift the tile around a little after dropping it onto the thinset. This will result in thinset rising up through the spaces, where the grout is going to go. Even though we laid the thinset on thick, I’m afraid we may have some waffle holes with too little. Had we let that layer dry, we could then have applied the tile with just a thin layer of thinset. (I knew this was an option, but the warranty thing scared me. It’s weird that Ditra would discourage the best way to install its own product.)
Roger,
We have installed tile a couple times as Do it yourself-ers. But, we had always installed with on ground floors. We are getting ready to remove all of the linoleum in our upstairs bathrooms and tile the bathrooms using Ditra. However, I want to do everything correctly and I had one question. I know that the builders generally put an underlayment over the subfloor. Do I need to rip out the old underlayment and reinstall a new underlayment with 3/8″ plywood and then lay the ditra, or can I install the ditra over the existing underlayment (assuming it is clean of all old adhesives)?
Hi Bridget,
If the underlayment is luan (1/8″ – 1/4″ plywood veneer) beneath the linoleum, and it likely is, then it needs to be ripped out and replaced with AT LEAST 3/8″ plywood.
Building front deck on covered porch in Canada with -40 temps. If we put T&G 3/4 ” then Ditra (reg or XL) then porcelain tile. Will this survive the climate?
Hi Dennis,
I don’t know. You haven’t mentioned anything at all about the joist system or measurements beneath that single layer of plywood. In a freeze-thaw climate such as yours I do not like to use ditra. The problem, as I see it, is that when water does get beneath the tile (and it will) it will soak into the thinset filling the dovetails. When the temperature drops that water freezes. Not enough expansion at any single time to create problems, but continued expansion and contraction over time may cause the thinset to debond from the tile. I prefer solid layer waterproof membranes for that purpose.
If you stick with the plywood you need a minimum double layer with total 1 1/8″ thickness. Over that you can use an elastomeric membrane such as hydroban or, if you choose, a decoupling membrane such as ditra. But you do need two layers at least that thick.
Roger,
My husband and I had tile installed on our kitchen floor in April 2010. I called the flooring business Sept. 2011 to complain that 2 tiles had cracked. The grout is becoming discolored and cracking and just simply breaking up in place. The grout is very soft. Anyway, the tile was installed over ditra. The ditra over luan. (We don’t know luan from plywood) We would hope the installers would. The home is a modular, when built we initially had vinyl.
Finally got them to come take a look. They removed the 2 tiles to find out underneath the ditra they placed, was a layer of luan over plywood. They are blaming the home builders for not using the correct size staples to hold the luan down properly. Everything I’m reading points to, I believe, is that they should recognize luan when they see it. What is your opinion?
Hi Sandy,
They should absolutely know luan from regular plywood. The builder has nothing at all to do with it. Any staple over 1/2″ will hold luan down sufficiently for a vinyl installation – which is what they installed. They did everything properly.
Your tile ‘contractors’, however, should know that regardless of the staple size luan is an inadequate substrate for a tile installation. Luan could have 6 inch staples in it and it would still compress and/or come up. The luan is less than 1/8″ thick and not dense at all. Any consistent movement (as in wear patterns – where you walk) will always compress. If the staple is at the face of the luan and it compresses 1/16″ the staple will now be poking above the luan 1/16″. This 1/16″ is room for the luan to consistently bounce up and down as it’s walked over. This will cause your tile to bounce up and down as well. Which leads to cracking grout and cracked tiles – as you obviously are aware.
That is a BS line from a company looking to cover their ass. They hired incompetent or untrained installers and now want you to pay for their on-the-job training, making you foot the bill while they teach their installers why tile should not be installed over luan. Win for the company – you’re SOL. Call them on it and make them foot the bill to fix an obviously incorrect installation. If you need backup I have more letters after my name than most PhD’s – all tile related. And I’ll be right here.
Roger,
Thanks so much for your quick response! Maybe I’ll finally sleep tonight!
Tell me, how can I copy this response and it be dated? I’m looking for as much material as possible to back us up. I have a letter from the business I would really like you to read. It was sent to us yesterday.
Sandy G.
This comment as well as my answer is dated. Just bookmark the page it’s on. Feel free to print out whatever you need as well. You can email me at Roger@FloorElf.com and I’ll take a look at anything you send.
Roger: Is installing hardee board ( 1/4″ ) on plywood, with Ditra on top of that something you would or would not do ?
Thanks
Hey Chuck,
Provided your plywood layers are correct and you have sufficient deflection the ditra can go right to the plywood. The 1/4″ isn’t normally needed. It doesn’t hurt anything, but it’s normally not needed.
I will be installing 18 x 18″ porcelain tiles over Ditra. I installed the ditra with modified thinset per Shluter’s recommendations. I am wondering if it is acceptable to use modified on top of the Ditra as well, even though they don’t recommend it. The only reason I’m considering this is that I’m having a hard time finding a QUALITY unmodified thinset. Home Depot does not carry any and Lowe’s carries TEC skill set, which is very inexpensive (this scares me) and I can’t find any reviews of it. Any advice is appreciated. Thanks.
Hi Matt,
A lot of pros do it. I’ve done it (and still do at times). I prefer to first fill the cavities to the face of the ditra and let it cure overnight before installing tile, but I haven’t had any problems with it at all. Keep in mind that if you choose to do that you lose Schluter’s warranty. No big deal, just wanted to make sure you know that.
I do have an unmodified guide, but don’t know if you have any available near you. I’ve never seen a lowes that carries TEC and I’m not familiar with the one you’ve mentioned, but you’re correct, you usually get what you pay for. The guide is here: Unmodified thinsets
I too am interested in hearing what Roger has to say on this. We used Mapei modified thinset from Lowes for under the Ditra and will use Mapei unmodified for under the tiles, unless Roger says that’s a crap product.
Hey John,
Depends on which Mapei unmodified you may be referring to. Roger has already commented on the three available here: Unmodified thinsets He may or may not have said your particular choice is crap – go see.
Roger, it’s Kerabond–so (wiping forehead) not crap! (I just read your page on these.) That said, I could return it and buy some Ditra-Set at a tile shop in my area–if it would be worth it. How much better do you think that product is than the Kerabond? Thanks as always.
It’s a little better but the kerabond is really good stuff – I wouldn’t bother changing it.
Roger, hi again. We just yesterday put down Ditra over the required modified thinset. Alas, it is not pefectly flat. The subfloor was smooth and even, so these undulations are definitely from the thinset. After we laid the Ditra down, we (as directed) pressed very hard over the whole surface with the trowel, but there are areas where you can feel a slight undulation with your hand.
Can we make up for this in the next stage, when we put the unmodified thinset over the Ditra and then lay the one-inch hex tile? Is there a trick to making sure the thinset is completely level?
Thanks a million!
Hey John,
Yes, it can be compensated for with thinset. There is no real way, short of a flat substrate, to guarantee flat thinset, but after you lay the tile on it you can use a level or straight edge to ensure that the tile is flat – the thinset will conform to the bottom of the tile.
Roger, thanks so much. (What a relief!)
BTW–in case it may help others–one thing that Schluter doesn’t seem to make clear is: When you put the first layer of thinset on, atop the subfloor and under the Ditra, are you supposed to leave ridges with the trowel, or just make it a flat surface of thinset (using the smooth edge of the trowel)? I looked at the official Schluter YouTube video, and it looked like they were doing the latter–so that’s what we did. Although it could’ve been that the computer resolution just didn’t show the ridges from the distance they shot it at. (They definitely show ridges for the thinset that goes on TOP of the Ditra.) The other thing they don’t state is how hard you’re supposed to mash the Ditra down after laying it. (We assumed we should mash the bejeezus out of it to ensure adhesion.)
Yes, you are supposed to leave ridges. The ability to collapse the ridges unevenly allows it to be flattened over a wavy floor. The bottom of the ridges will, of course, follow the floor and the top of the ridges can be flattened to whatever height you need.
Since you had a flattened layer you already had the maximum compression (relatively) of your thinset layer which is why it came out that way – it was simply following the floor. Nothing that can’t be compensated for as you set tile, though.
I’ll need to take a look at the video again – something I never really think about since I do it every day. If it does look like a flattened layer I’ll bring it to the attention of the people who can fix it. Thanks for the heads-up.
Thanks, Roger. Happy to help. Here’s the link to the video, btw. The part that shows the installation of Ditra over what appears to be non-ridged thinset is at 3:48. http://www.youtube.com/watch?v=f6FyWs2WZ1k
Hmm, that does look like they’re installing it into a flat layer. I’ll need to raise hell about that! Thanks.
Hi Roger,
Thanks for your reply to my last question regarding what to do with different sized tiles. It helped tremendously. I now have another question if you don’t mind. In the same bathroom that I tore out all of the walls/ materials down to the joists, I also tore out the old tile, but left the cement underlayment that was found underneath them. Figuring this stuff was pretty solid, I wanted to keep it. I have now noticed after cleaning up all of the debris that there is about an inch all the way around the floor that is not cement, but a gap down to the floor joists (that used to hold the dry wall and cement board for the walls). What should I fill this gap in with so I can tile over top of the cement underlayment? Or do you think I should just remove the cement underlayment (not looking forward to that).
To add to my dismay, it looks like I’m going to have to chisel at least some of this cement underlayment away to fit the new tub in, which seems to be a few inches wider than the one the house came with. Do you think that will compromise the integrity of the cement floor making me have to tear it up anyway?
Sorry for all of the questions, I’m a newbie learning as I go.
Granted, I should add, I guess it will only be about 1/2 inch all the way around when the new drywall gets put in.
Hi Jessica,
That is likely an old-school mud bed, which means it’s solid. The perimeter gap is completely normal, just tile right over that 1/2″. You won’t be walking on that portion and any baseboard or anything you use there will likely fully cover it anyway – the tile does not need full support there.
Chipping away any of that mud bed will not compromise it at all. You’ll be fine taking out whatever you need to.
In our master bathroom, we have laid down 1/2″ plywood and are planning to put in heated floor wiring before we lay down ditra. The floor wiring is not in a mat configuration, just bare wire you lay out. I want to use slc but see mixed reviews that the slc might not adhere very well to the smoother plywood. Do you have any input? If I don’t use slc, it sure looks like it might be one heck of a job to even out the thinset to level the rest of the floor.
Hey Mike,
It’ll adhere just fine if you use the primer for the SLC. Each company makes a specific primer for their SLC for that purpose. Coat the plywood with the primer BEFORE INSTALLING THE WIRE. Then install the wire and pour your slc. You can do the primer after the wire, but you may get incomplete coverage and have bonding problems. As long as you do it in the correct order it’ll be fine.
Glad to hear that! Next step after that….I believe I read that you would then use unmodified thinset to adhere the ditra to the slc instead of modified since we’ve changed substrate types from wood to mortar? What type/size trowel do you recommend? Schluter confuses me with all the trowel sizes!
Yes, unmodified over the slc.
I normally use a 3/16″ x 3/16″ u-notch trowel for the ditra.
Hi Roger,
Great information, thank you. My question relates to the 2″ x 2″ min. tile size requirement for Ditra…assuming correct installation, would it be a stupid thing to go with 1″ hex on 12″ x 12″ mesh? Unfortunately, I’ve already cut up the Ditra rolls and can’t return them. What could go wrong?
Thanks much,
Scott
Hey Scott,
Well, your grout, and possibly your tile, can become cracked, debonded or both. The cavities of the ditra when filled with thinset and cured become essentially a little ‘foot’ for your tile. When using ditra your tile is not technically attached to anything except the little dovetailed pillar of thinset formed by the cavity. The top of that pillar is about 3/4″. If you have a smaller than 2″ tile centered directly over them then there may be up to 1/4″ of unsupported tile around the perimeter of any given mosaic piece. If you place a 2″ tile atop a piece of ditra you will notice that there is no spot on which you can place it that will leave opposite sides both unsupported. If the tile is less than 2″ that is not the case. Measure the distance between two cavities – little less than 2″, yes?
That’s the technical reason. Now, my personal opinion is that yes, you can use smaller mosaics over ditra in some instances. I normally base this decision on the size of the room and amount of traffic it will have. In a small bathroom it will likely be fine – and with hex mosaics you should be fine as well due to the shape (smaller footprint, less cantilever ability). So I will tell you that it should be fine. But I will also tell you that the decision is entirely yours because I’m not the one installing it. And no one has ever successfully sued an elf.
Roger,
Thank you for the detailed explanation! I’ve been researching more, and I do want to do this right after so much effort so far. It’s a 90 sq. foot bath on a 1924 basement slab (not very thick I believe). What concerned me was the micro fissures that appeared on the self-leveling concrete after 3 pours. I’ll try to source this Nobelseal TS product. Thanks for the quick reply!
Scott
Hi
We had the Ditra mat put down over plywood with Mapei Keraset only the Keraply wasn’t added to the mixture. Will this be ok for the flexibility? Or will this fail?
Hi H,
Maybe. I can’t guarantee a failure, I can only recommend and instruct on methods and products guaranteed not to fail. Keraset is the lowest rung on mapei’s unmodified ladder. Above that (better) is the keraflor, then the kerabond. Schluter instructs that Ditra be put down over plywood with modified mortar (which it would have been had the keraply been added). I’m sure you already knew that.
What I can tell you is that the plain keraset will not flex one little bit. It will be hard and brittle and any flex at all is likely to cause it to crack or debond over time. While I can’t guarantee it, I can bet on it. If it were mine I would take it up and redo it with modified. And get rid of the keraset.
I was afraid you were going to say that. The contractor said he had never used the Ditra before and we had purchased the Keraset and Keraply. He did not read the instructions. He was placing tile over tile in another bathroom and used the Keraply on that. I told him we bought 2 different things as instructed at the store. Now I don’t know what to do! They just put down the new plywood as this was a total bathroom redo. Any suggestion on how we should approach this with him? Thanks
Just tell him you’re concerned with your warranty from Schluter. They blame us all the time – may as well lay some blame on them once in a while.
If it is not installed over plywood with modified thinset your warranty is void. As I said, I can’t guarantee it’ll fail, but that is the lowest quality thinset that mapei manufactures. It’s fine for some installations, under ditra over plywood is not one of those. It cures very brittle and any movement may cause cracking.
Mr. Elf:
What size trowel do I use for spreading thinset under the hardee board onto the plywood which will then have ditra on top of that?
Thanks
Hi Chuck,
I use a 3/16″ x 3/16″ U-notch.
Mr. Elf: In reading these posts about Ditra, I`m worrying about “bumps”, air pockets AND not getting thinset “into the cavities” properly. Can you tell us how to do it correctly the first time, so I dont make any mistakes.
Thanks partner
Hey Chuck,
Take the flat side of your trowel and fill the cavities by spreading it at a 45 degree angle to the cavities (corner to corner) in all four directions. If you do that they will be completely filled without a doubt.
Thanks for the expeditious reply about Ditra cavities……. NOW, I have another question, I know, I know, you dont have time for this crap, but lets face it ” you da man ” !!! so here goes, I just put hardee bd 500 up in the shower, took my 6 foot level and put it from the top ( ceiling ) to the bottom (tub) and there are areas that are 1/4″ or so away from the level, do I need to take the board off and shim the edges out 1/4″ or does this matter? Sorry, but this is my first time and I want it done to “your standards”…….
Thanks again
Hey Chuck,
1/4″ is pretty large. I would probably take it down and shim it out flush. 1/4″ is normally the upper limit of accepted thickness to which thinset can be built up under tile. If you want your tile flat (you do) then it will be much easier, and literally half the time, to shim those out to a flat plane before beginning tile.
Roger,
well- trying to save some cash and attempting the project ourselves–I think we may have used a too big notched trowel for the thin set underneath the ditra which resulted in some bumps (a lot of them!). There aren’t any air pockets as far as I can tell. Is this very bad? Will it all even out with the next coat of thin set we put on top when we install the tiles?
Thank you!
Annya
Hi Annya,
You can compensate for the bumps with thinset as you install your tile. If you have bumps and/or dips that exceed 1/4″ difference you should use a medium-bed mortar rather than regular thinset.
We are currently building a new house, tiling the bathroom ourselves. Our builder put down radiant heat, and then put schluter ditra over it. Now when we look at the ditra, it doesn’t look level at all, there are obvious bumps in it. Is there any way we can lay our carrara marble over it without having to rip it all up and start fresh? Can we use slc over the ditra to help or would that completely negate the effects of the radiant heat. So Frustrated!
Hey Bre,
SLC would actually be your best bet. It will not interfere with either the heating or uncoupling of the membrane. Your next best bet would be a medium-bed mortar for your marble – and a lot of patience.
Hi Roger,
Five yrs ago removed linoleum in kitchen, and tile in hall & powder rm. The subfloor is 3/4″ T&G with 2″ x 8″ on 16″ centres. I drove in no. 8 screws every 6″- 8″. Then I used Ditra and laid the tile dia. to hide builders inconsistencies. Recently moved front door out 3 1/2′ now need to tile new area. What is best way to remove thinset and fiberglass mat left from Ditra. I had a couple of pictures but couldn’t figure out how to put them in dialogue box.
Hey Scott,
Either a razor scraper, grinder with a scarifying wheel or a regular sander – belt or orbital, your choice. Any of those should take it off.
I Went with the scraper, less free floating dust but more labour (I’m thick that way). I used Versabond (subfloor to Ditra) and Flexbond (Ditra to tile) for the first 300 sq. ft. 5 yrs ago. I’m glad I found the post below.
“Technically (according to schluter) unmodified should be used both beneath the ditra over slc and between the ditra and tile. I use modified, as you’ve stated, most of the time. As far as under the durock and for the seams it doesn’t matter whether it is modified or not – beneath it the thinset only fills in voids, either will work for the seams.”
I have 50 year old octagon tile floors. They DO NOT want to come up and i dont have the time, this is a surprise job for my girlfriend, or the money to remove the tile and relevel the floor. The tiles are directly on concrete foundation. Can i lay ditra, or another bonder, over the tile and then put the new tile over that?
Hi Brett,
If you use a thinset which is approved for use to install tile over tile (it will say so on the bag – mapei ultraflex 3 is one of them) then you can bond the new tile right to the existing tile provided you scarify the surface of the existing tile first. That just means sand or grind it down to remove the shiny surface.
Roger,
if I use versa bond how long will i need to wait to do grouting and most of all how long will I have to wait to be safe to walk on it my floor is concret has had lanolium scaped of it extreamly small amount of resadue that I even used sveral different products trying to remove concret shows well this has been over great period on time has been moped , I guess I am being paranoid cause my samples I did for hieght adjwere on backer board and around here can’t find un modified this is a small 5’x7′ area in bathroom with tub/shower and wayne coting foot up on1/2″ hardie backer tube surround will be red gaurded will I be able to useversabond or mapie 2 all this is a bitconfusing i am 61 and do not want to have to do this over again.extra long wait traffic wise would be problem ihavecumode inhall bathoperable no bath and visaversa .makes me feel like ineed to give up and just use to slope the trasition cause i laterwill be doig a largekitchen area involvin much bigger transition area I really wantedthem to all be same.
Thanks Carol dawson
You can use versabond – I do it a lot. (Don’t tell the tile police…) The best way to use it with ditra is to install the ditra and fill all the waffles flat to the top with thinset and let that cure for 24 hours. The next day you can install your tile and you’ll be fine to walk on it the next day.
Roger ,you are so funny promise I won’t tell the tile police .I haveseveral mapie bags of ultrflex 2 do ineed to exchangethem out or willthey work onwalls with redgard same 12″glazed porcelin tub area?
Thanks a million you are great
carol dawson
Ultraflex 2 will work fine. It’s good stuff.
I am putting down the rapid set self leveler and will be using the suntouch heated flooring mat. Is there a specific thin set you would recommend to set the Ditra with? and also a brand of unmortified thinset for setting the porcelian tiles?
Hi Jenn,
If you are installing ditra over slc Schluter recommends an unmodified thinset – so you can use the same thinset for all of it. I prefer Laticrete 317. Mapei makes kerabond, it may be more readily available for you.