This post was updated on July 2023.
Typically, I encourage people to follow the manufacturer’s instructions.
Especially when the company has clear, detailed, and easy-to-understand instructions like Schluter does.
But when it comes to both Ditra Heat and Ditra Heat TB [edit: now called Ditra-Heat Duo] there are two things that I just don’t feel are good ideas.
Estimated reading time: 5 minutes
This post deals with the installation of Ditra Heat mats only and not the electric heating wire. I also have a post with some installation tips for Ditra that you may want to check out.
So what are the two things you want to avoid when installing Ditra Heat mats?
1. Pre-fill the waffles. Always. (see update below)
I feel strongly about this. Now the Ditra Heat Handbook doesn’t specifically tell you to not pre-fill the waffles.
However, it does tell you to start setting the tile right over the mat. Also, the photos show the tile being set right over the orange heat mats.
This is not a good idea, in my opinion.
First of all, what does pre-filling the waffles mean? This is where you skim-coat thinset mortar over the top of Schluter Ditra. You do this with the flat side of your trowel.
Then you let it dry before installing the tile. This skim coat layer helps to protect the wires below. This is important for two reasons.
- It helps to protect the wires from the teeth of your trowel when combing the mortar.
- If you have to pick a tile back up after it’s been set (during installation) you won’t drag the wires out with it. The wire can stick to the underside of the tile. You can prevent this by pre-filling the waffles.
An additional benefit of prefilling Ditra mats is being able to snap chalk lines and actually being able to read them.
FYI, Schluter has rather specific guidance on which thinset mortar when installing Ditra-Heat or Ditra-Heat-Duo. Additionally, the recommend using a 1/4 x 1/4 inch square notch trowel for installing these thicker membranes.
February 2022 update:
Apparently, Schluter has made an adjustment to the manufacturing process for Ditra-Heat in an effort to make it more pliable so that it lays down flatter.
However, in doing so, it makes it so that prefilling is even more problematic in that the little centers pop loose much more easily.
This is a problem because when you’re installing tile and you have to pick a tile back up you will have the a bunch of the hard little centers stuck to the back of your tile.
Consequently, if you want to use Ditra-Heat it’s best to not prefill the mat and just fill it in when you are setting your tile- all in one step.
Additional options include:
- Prefilling and installing Kerdi membrane over Ditra-Heat (I know, more time and expense)
- Using a competing product. There are several different brands and I like both Strata_Heat and Flexbone Heat for uncoupling heat membranes
- Use a completely different kind of underlayment for your tile like, for example, cement board.
- Use a self-leveling product to prefill. This is another practice that Schluter does not endorse but other manufacturers do. Be very careful which self-leveling product you use. Only certain ones are approved for this type of installation.
2. Don’t install tile the same day over the Ditra Heat mat
Schluter says this is ok. Again, I think this is a bad idea.
As mentioned, when you have to pick a tile up and re-install it (you will have to do this- more than once) the suction of the tile can pull up the Ditra mat causing it to break the bond to the plywood.
My advice: install the Ditra Heat mat one day and install the electric heat wire on a different day.
Then skim coat the wires with thinset and let that dry. You have enough to do just installing the tile properly. You don’t need additional challenges or things going wrong.
Did you have any issues getting the DITRA HEAT-TB to stick to the thinset? When I layed the pad down it didn’t seem to grab the fuzzy backing.
I have noticed some issues with getting the heat membranes to stick. Not just Ditraheat tb, but also ditra heat, prodeso heat, and suntouch heat matrix. When I’ve peeled them back to check the coverage it hasn’t been what I would like. They have all been fine the next day and well adhered.
But currently I don’t know if this is a something to be concerned about, or not. I just don’t have enough information about it.
If yourself, or anyone else, has any feedback on this I would love to hear it.
When running the lead wire from the membranes to the thermostat box, I have a lot of extra lead wire. Can I rim that and how do I deal with the cable sheathing?
Yes, you can trim it down. The sheathing just gets stripped down enough for the wire ends to show. It’s similar to wiring in a light switch or an outlet in that regard.
One cautionary note: The wire leads can be cut but the heated portion of the wire can’t be. I know this isn’t what you are asking about but just want to make it clear for anyone that may happen onto this comment.
Please help!
1. Modified or unmodified thinset to smooth over the ditra-heat mat?
2. Small mosaic marble tile going over the ditra-heat mat (with thinset smoothing coat), modified or unmodified to install this type of tile?
Unmodified. You may get away with a modified if you use very small format tile and give a long curing period, outside of that. unmodified or your thinset will never cure.
1. Schluter wants unmodified over the top unless it’s their own brand of thinset. Then it’s ok to use modified.
FYI, Schluter now has their own line of mortars and some are even modified. They say that they are “self curing”. The thing is that this self curing technology is not unique to them and has been available in other manufacturer’s mortars for some time now. This is the reason other mortar manufacturers have required modified over Schluter products. So going over Ditra with a modified mortar is probably not just ok, but could likely be a better installation. But I want to make it clear that it would void Schluter’s warranty.
2. Same answer as above with one caveat: Schluter has a 2 inch minimum tile size for going over their uncoupling membranes. The reason is because they are worried about point loads- too much pressure concentrated in one small spot. For a residential bathroom you may choose to take the risk but at least you’re informed enough to take the risk if you choose.
Good comment!
This happened to me on the first few sheets. Always peel back the first sheet to make sure that the thinset is completely “soaking into” the fleece. When the thinset is too dry, it will not be absorbed properly by the fleece and when you peel it back you will see white areas. Make sure that you use enough water to make it drip from the trowel and yet stilll hold a trowel pattern on the floor. Then when you examine the fleece it will be soaking it in, as desired. Good luck!
Not finding the info I need, and want to make sure I don’t screw up now…….help this poor sole!
1. Bathroom floor has 1/4 ” Hardiebacker attached with thin set and screws to plywood subfloor.
2. I will be putting Ditra Heat mat down to it.
3. I have 18″x18″ Porcelain Tile.
Not finding what thin set to use between Ditra and Hardiebacker. Modified or not???
I have Un-modified for the Tile to Ditra, but I may need special for the large Porcelain tiles?
I know Schluter wants unmodified between tile and Ditra, but what under Ditra to Hardiebacker?
Have both HD(for Custom products) and Lowe’s (Mapei) close by to purchase.
Any thing I am forgetting?
Thanks!
You can go with either modified or unmodified with the Hardibacker but I would push you towards modified. There’s too much riding on it with the wire and the tile to have something go wrong.
One thing about the unmodified mortars is that they tend to be the cheapest mortars available and they aren’t all created equal. I would encourage you to stay away from any thinset that is under $10. A good unmodified mortar for large tiles is what you want. I’m pretty sure Lowes carries something. If you have time to order Mapei Kerabond T from Lowes that would be what I recommend.
I am trying to tile river rock on my bathroom wall. The stones are approximately 2″ x 3″ and anywhere from 1/2″ to 2″ thick. So some are pretty heavy and some are very light. At the store, they recommended to me to use TEC large stone mortar-latex modified. I am combing it to 1/4″. However, the stones are seriously sagging. I know I should work from the bottom up, but I am working around a mirror so I really do not want that as my bottom.
Do you have any suggestions for me? I would really appreciate it. It will really save my sanity. thank you!!
A lighter weight thinset may help but probably making the thinset to a thicker consistency would work the best.
Why can’t prodeso be or ditra be glued down over hardwood?
Too much movement and too unstable. You can read Schluter’s comments about their feelings on hardwood floors here.
https://www.schluter.com/schluter-us/en_US/faq/ditra-ditraxl-over-hardwood-flooring
I am planning to install Ditra-heat-tb over concrete in a bedroom and Ditra in hallway leading to that bedroom. The difference in height is 5mm or 3/16″. Is this going to be a problem? How do I transition? Thank you.
It would depend on what you are transitioning to. But typically people will use wood or metal profile reducers to go from a higher tile surface to a lower surface.
It will be the same tile in the bedroom and in the hallway. I was hoping to get away without metal profile reducers by sloping the tile and make the transition from area with ditra-heat-tb to area with regular ditra invisible. Would sloping the tile work? Or I still should use the reducers? Thank you.
I didn’t realize that you were going to transition from Ditra-Heat TB to more Ditra. You might consider the following options:
-Running Ditra-Heat TB (now called Ditra-Heat Duo) throughout the whole installation and only heating one section of it.
-Using Ditra XL for the non-heated part. Ditra XL is the same thickness and is probably a little bit less expensive than Ditra-Heat Duo.
-Running regular Ditra-Heat mat (not Duo) in the non heated section. This is probably the most impractical of these three options.
If you still want to use 1/8 inch thick Ditra in the non heated section then you could transition with just a tile. If you were using, say wood plank tiles, then you could always run the plank a different direction at the doorway which is something often done with real wood flooring installations. You would have to angle the tile but it would still work.
I am considering skim coating over Ditra Duo heat cables over concrete substrate. It could be 3 or 4 days before I start installing the tile. Will the skim coating crack or crumble when working on it to install the tile.
Yes, there will be small cracks and crumbling. This is fairly normal because there is a small amount of movement in the plastic before the tile is installed. As long as you clean and vacuum it well prior to installing tile then you should be fine.
I am planning on installing Ditra heat in a bathroom. I wish to install a redundant heat wire(not connected at same time) in case the initial one fails at some point in the future. Can the heat wire be dual run right next to each other? Can the non powered backup wire cross over the live one? Please advise?
Unorthodox for sure but I’ll speculate: I don’t think it would be an issue to run a redundant heat wire nor cross over the real heat wire as long as only one or the other is working- and not both. However, crossing the wires could lead to an uneven floor and also leave the high wire exposed to potential damage.
That’s my speculation but this isn’t something that you should take people on the internet’s word for it. A call to Schluter’s tech line is advisable. :-)
I realize that following the manufactures specs to use the Schluter Ditra membrane is recommended and the best option. I personally dislike Schluter mats in general so is it possible to not use the membrane at all and pour a self leveling layer over my wires instead of going through a triple layering process?
Yes. If you’re going over a wood subfloor then Ardex makes a product called Liquid Backer Board that works great for this purpose.
Otherwise, your supposed to use lath for reinforcement and Mapei makes a plastic lath that won’t cut into the electric wires. Then you have more options for self levelers by using that.
If your going over concrete then the self levelers doesn’t need reinforcement.
Hi, I have installed my Ditra membrane and realized after the fact that it would be cool to have heated floor. Can I install heat cable on top of the regular Ditra membrane? Thanks for your help!
I don’t know whether Schluter would approve, or not. You would have to call their tech line to find out.
But I don’t see a reason that it wouldn’t work. I don’t think self leveling over it would be a good idea but you could probably coat it with thinset.
Here’s a little known and probably against the rules tip: before the days of Ditra-Heat some guys would slice the ridge part of the waffles on normal Ditra and stuff their wires in there.
But you didn’t hear that from here. ?
Haha great, thanks a lot for your help!
Just had this installed and the guys out down durock, then ditra heat mats, then put self leveling concrete on top of that, and finally the next day laid down stone. Is this a completely botched job? I stopped payment on their check…
Not necessarily.
I don’t think Schluter wants self leveling over the top but some self leveling companies will warranty the installation. But it depends on which brand, which product, and how it was applied.
If you can find out which product they used then you can contact the manufacturer and see what they say.
But there’s nothing wrong with Ditra Heat over cement board.
Can I do like a stair pattern with my electric wire to go around curves of a shower base ?
That is one notch each stair . So over, down, over, down over down
As long as you keep the spacing consistent you can run it how you want. Personally, I don’t care for stair-stepping and prefer to keep the lines running straight but it that’s more of a ocd thing than anything.
Hello,
Im using prodeso heat membrane and it was mentioned to use an unmodified thinset on top of the membrane – but what is recccomended to use to adhere the membrane to a concrete basement bathroom floor that has been already levelled with self leveller? Modified or unmodified? Thank you ;)
I don’t know that Prodeso requires unmodified over the top. I’m almost positive that they don’t but I can’t seem to locate their install instructions online anywhere- including on their own website- which seems quite odd to me.
However, unmodifed should be ok over concrete but I hate encouraging anyone to use unmodified mortars as there are much better modified choices out there.
edit: Nuheat sells a relabeled version of Prodeso Heat membrane and they have installation instructions on their website. They mention both modified and unmodified are ok.
https://www.nuheat.com/products/heatingsystems/cable-membrane
Hi
I have installed ditra heat with modified thinset. The heat cable was put down and the flooring guy installed unmodified thinset from mapei (kerabond) over the ditra and cable before starting the ceramic. It as been 48 hours since the thinset was installed and i notice this morning when i was walking on it that there was cracking sound. I puch down on the thinset over the round in the ditra and the thinset is caving in at mostly every round but over the chanel for the heat cable everthing seems ok. Is this normal?
I put down Ditra Heat mat in a small bathroom and it adhered great to the subfloor(plywood) except for a 6″ spot near the wall. How can I fix this bubble and make it adhere without lifting the entire mat? The thinset has hardened. Installed 40 hours ago.
This sounds normal. The crunching sounds and even thinset coming loose, especially in the centers, if something that happens with prefilling.
Working on it, kneeling on it, and putting pressure on certain areas can cause the mortar to come loose.
The loose areas should be removed prior to installing tile and should be refilled in the process of tiling.
This happens sometimes and the fix if pretty easy. Cut the bubble out with a razor knife, lift out that bubble, and replace that section.
Hi, and thank you for your wonderful blog. What is the “thinnest” heat plus uncoupling system you know of? I’m trying to stay close to adjacent floor height!
I think 1/4 inch is pretty standard and about as thin as you can get. Ditra Heat, Prodeso heat, Suntouch’s Heat Matrix (actually from MD Building products) are all about the same.
I am thinking about DIY’ing the install of Ditra Heat Duo in my basement. I’ve read everything I can find on the process and watched endless videos. My fear is that I do something that may void the warranty.
Just read your comment re: prefilling the waffles. Sounds logical to me, two questions:
1.after this pre-fill dries does it not crack when walking about tiling the floor?
2. I am tiling over concrete and plan on concrete/modified/Ditra Duo/unmodified/tile. Should you use the unmodified to fill the waffles and then another unmodified to tile?
Thanks in advance!
Trying to save $3000 :))
Yes, prefilling can crack.
I’m not sure why you would want to use two different unmods above Ditra-Heat Duo. I would use whatever you are going to use to install the tile.
If you meant that you wanted to use modified to prefill then that’s fine. At least I’ve heard that Schluter doesn’t have a problem with that.
Congrats on saving $3000. This is what’s great about DIYing.
Is it okay to combine Ditra Heat Duo and Ditra XL within the same room? I figured using XL for the unheated areas would save me around 300$ over the whole basement project. Is it worth the trouble? Thank you.
It’s fine to combine the two. I’ve done the same thing.
The floor near the wall is sloped up a little bit (starts about 6 inches from the wall). I am thinking to stop the Duo 6″ from the wall and fill the gap between Duo and the wall with regular Ditra (1/8″) and then skim coat over the Ditra to bring the level up to Duo. Will this work? Can I use polymer modified skim coat type mortar for this or unmodified thinset will be better?
Thank you very much for your advise..
That should work. I don’t think it would be recommended by the manufacturer but it’s definitely a way to solve the problem
Hey there, I’m probably a couple of months too late, but the ditra heat instructions specify unmodified thinset between the slab and membrane. Modified thinset cures by drying, and while a wood subfloor allows this, a slab does not. Hope this helps someone, anyways!
Have you ever poured leveling compound over the Ditra Duo + wires directly? Schulter says ‘no, use thinset’. But my contractor didnt level the old floors before putting Ditra down.
Thanks for the great tips!
All self levelers are not created equal so it’s a matter of using the right product for the right application.
Ardex makes a leveler called Liquid Backer Board and they approve this product over their own Flexbone uncoupling membrane.
The idea of that it will last flat but doesn’t have so much strength that it grabs and curls the edges.
Other manufacturers probably have products that work similarly but this is a relatively new technology so your options may be limited.
Additionally, you’ll probably be in no man’s land as far as warranties go but it’s a way to solve a problem.
Thanks. What primer do you use for Ardex Liquid Backer Board over Ditra?
I don’t believe a primer is needed for going over uncoupling membranes but, again, this is where reading the most current and up-to-date instructions is advisable as things can change without notice.
Apparently I’m late to seeing this, but do not ever cross wires under tile. Also, have your second wire in a totally different area than the first.
Sweet baby Jesus
Please tell me you are kidding about not understanding why you do not skim out the ditra heat/duo and let it dry ahead of time (if you are going to boast about NTCA and CTEF, please stop persuading tile installers to take shortcuts) . You want ONE coat of mortar between heat wire/ditra mat and tile. That way the heat is as efficient as possible. Having one layer, letting it dry, and adding another one is asking for it. This is not correct. Basic heat, tile/masonry knowledge, and why they do not say to do this. While you should definitely skim in the ditra as you are setting it (duh), do not let it dry before installing over it.
As far as your chalk line situation, you can use sharpie or hairspray over a chalk line to preserve it.
I agree with not tiling over the ditra immediately and always apply any kind of ditra underlayment a day prior to installation.
As far as being worried about having to pick up tiles and the mat with it because of needing to add mortar, the answer is simple: you should always prep any surface you are going to tile (floors or walls) completely before you start setting tile. A rookie mistake that can lead to mistakes and headache that no one wants.
Also, I know this will sound crazy, but you don’t have to use schluter products to install a quality tile project. And honestly, chances are, if you are using schluter shower systems, you don’t really know what you are doing. Some Ditra products are convenient and make things in the right situation, but always ask if your tile installer is capable of doing the project without any Ditra products. Their reaction will tell you how much they really know.
Don’t want to sound harsh, but I hate bad practices being passed around in our industry. I’m always learning as well and hope this helps!
Cheers to you also choosing such a tedious and maticulous trade!
What about floating floors above Ditra-Duo/Nuheat. Do you thinset down the wires and float the LVP above it? Ive have read/heard so many strategies. Among them:
1) Ditra+wires then thinset then tile is the only really good combo.
2) Ditra+wires then thinset then laminate or LVP (floating?) will work but unlikely mfg will approve it.
3) Ditra+wires then thinset then only solid hardwood (floating?) because heat might delaminate engineered hardwood glue for top layer and cause similar problems with other products.
4) Ditra+wires then thinset then gemcore (floating?) or other ~70 stone product which is approved for at least hydronic heat. But need very level floor which I dont have and which is hard to level for other reasons.
From Schluter:
——–
Schluter®-Systems currently only recommends the installation of ceramic, porcelain or natural stone tile over the DITRA-HEAT system.
thx
Alan
Good tips. Yes!
I’ve heard your arguments but you haven’t changed my mind. Ditraheat will heat two layers that are the same thickness just fine.
Additionally, your comments about prepping the surface are correct but still doesn’t mean that a tile won’t have to be installed, picked back up, and reinstalled.
It’s important to keep in mind that this blog is aimed at the DIYer who is going to have a more difficult time doing perfect prep work. This would, therefore, increase the chances of having to pick tiles up after they’ve been set.
I feel it’s more important to protect the wire than to worry about any alleged heat inefficiencies.
As always, my opinion. ?
I’ve only installed tile over DitraHeat. I’ve never installed LVT or anything else.
Would it work? I think it’s conceivable but I don’t know how to accomplish it.
You might try to contact some of the other manufacturers such as Suntouch or Nuheat. They both have wire and membrane systems that compete with DitraHeat and may have guidance for non-tile floors.
You can use laticrete and you wont get the sag but its a out 45 a bag
You’ve already helped me a lot, thank you in advance for this question! I plan to prefill the ditra heat mat with a modified, then apply the tile with ditraset. My questions are:
1) when you have to pull up a 12×24″ tile to check for coverage etc., do you find that the suction pulls a lot of the dried prefilled mortar out of the mat?
2) do you feel like a highly modified mortar would be less likely to be pulled out of the mat in the above scenario, vs a lightly modified one like ultraflex 1?
2) how loose or wet do you mix your prefill mortar? Seems like wetter would be better.
Yes, pulling up tile will pull out little chunks of mortar. I haven’t found a good combination to prevent this. When prefilling, normal tile mortar probably works the best but I usually use what I have left over from sticking the mat down and that mortar is wetter than normal. Bottom line is that I don’t think it matters that much.
I’ve laid Ditra Heat membrane over plywood and OSB a couple times and was always given Mapei UltraFlex 1 by the tile store. Mapei UltraFlex 1 does meet or exceed ANSI 118.11 requirements. I’ve never had a problem securing the membrane, but I often wonder if I should be using something with more adhesion?
This product is fine. The ANSI 118.11 is the test for plywood adhesion and so it’s suitable for use over plywood. Personally, I like to work with premium products so I typically would go with UltraFlex 2 as a minimum. But there’s nothing wrong with UltraFlex 1 for the application that you are referring to.
I am installing the HeatMatrix uncoupling membrane mat by suntouch. To also use their heating wire system (Home Depot has it on Special Buy right now).
We also dropped the floor in the shower for a curbless/seamless entry into the show and are sloping into a linear drain. My plan was to run the uncoupling membrane into the shower for heat in the shower also (floor heat is rated/approved for shower floor application). On top of the this I was going to use a Kerdi-type membrane over the uncoupling membrane and up the shower walls as I don’t fully trust just the uncoupling membrane for water proof barrier. I would be prefilling the uncoupling membrane for ease of laying the Kerdi.
Super excited about our linear drain from [the online store] and how the kerdi is attached to the top of the drain already for seamless waterproofing.
any thoughts/concerns/words of wisdom for me? Reading your blog and comments has been very helpful so far in planning. Thanks.
You’re smart not to rely on the uncoupling membrane above for that application. Kerdi over the top is the way to do it.
Thanks for your comments
Hi,
I am installing ditra heat over the top of a self leveling compound in a bathroom and was wondering about a few things you would suggest for the process to make it go as seamless as possible? First is that I’m asssuming that i need to use the Ditra Duo since it needs to have the thermal break between the new concrete floor and the Heating, is this correct? also would I just skim coat the Compound when setting the mat onto the floor? Lastly should i use a modified thinset for the concrete to ditra mat contact to ensure that it is stable for its lifetime?
Ditra-Heat Duo would be the best membrane for that. I believe they recommend an unmodified mortar for that application but you should confirm that prior to installing.
Lowes in my area no longer carries the kerabond and hasn’t for about 3 years. I was having to special order it until I broke down and tried their Mapei uncoupling membrane mortar. This is advertised as a premium unmodified thinset mortar and costs about $15.00 per 50lb bag. I have used this now for 2 years without any issues and they also stock a latex admix if going over plywood.
Good to know. Thank you!
When ditra first came out and few people carried it we would put the tile right on the ditra without ditra cemented to a substrate so there would be plywood no cement ditra thunder tile and nothing ever cracked but nobody was walking on it and it’s uncoupling membrane so if you get 85-90% down and notmiss big areas it doesn’t seem like it’s to bad since it wants to move a little anyway but I’ve alwaysback troweled my ditra makes install so much easier and get way more coverage
That’s not the way that it’s designed but it doesn’t mean that it won’t work. Ardex does have a version of their Flexbone uncoupling membrane that is designed to be floating (not stuck to the floor) but that’s the only one that I’m aware of.
My installer put the Ditra heat down per the specifications over my existing concrete floors and filled the waffles with thin set. It turns out my floors are running downhill and are out of level by up to 1 1/2″ or more. (I did have to do a foundation repair and put in piers 3 years ago so makes sense.) The contractor poured Level Quick over the top of the Ditra Heat to level it out. Do you think the heat will come thru the top of the tiles now that it has almost 2 inches of material over the heating cable?! Thanks. May be too late, but hopefully I can sleep tonight!
I’d be concerned about this and there’s more than one reason. Firstly, while there are a couple of different self-levelers that are OK for this application, I don’t believe that Level Quick is one of them. That’s not a statement about Level Quick’s quality but simply using the right products for the right application. So that’s issue #1.
Issue #2 is just what you’ve described in that you are now having to heat up more concrete than necessary. Along with this is the fact that it’s different depths so that it will heat unevenly and, yes, it could be warmer and colder in spots because of this.
Tying into this is issue #3 which is that it doesn’t sound like there was any kind of thermal break or insulation installed so that you are heating as little of the concrete subfloor as you can while heating as much of the tile as possible. In other words, there’s nothing to stop the heat from traveling down into the ground.
The way that your floor should have been built would have been to do the leveling first, then use Ditra Heat Duo, then tile. In this scenario, Level Quick is a perfectly acceptable product. Used over Ditra Heat it isn’t.
So it doesn’t sound like your installer really understands the products that they are using and the proper way to use them. Unfortunately, this will probably not have good results.
What about routing heat side of cable thru a piece of plastic conduit in a wall to get to a shower bench. Directions say not to put heat cable through walls or it may over heat. Have u had any experiences with routing the heat cable thru a wall?
Hi Guys great site. I am Installing ditra heat in my Bathroom. I want to
Keep the floor level with the hallway as it was before. What is the thinnest mortars in each step. I have been looking online and can’t find the answer or suggestion. Basically I have my ditra heat 1/8 inch. Then what I have left is 1/2 inch to match the height in the hallway. Can i put 1/8 thinset to install the ditra heat to the plywood and then 1/8 between the tile and ditra? My tiles are 2” x 6” netted and about 1-4 inch thick, so it has about 6 to a net. Also difference between using a square notch vs a triangle notch?
With heat cables, you can tell exactly where the transition from heated cable to wire takes place. It’s critical that the heated cable INCLUDING THE TRANSITION SECTION be fully embedded in mortar. I know Suntouch makes extensions if you need more wall cable. Other manufacturer’s might have extensions as well.
I don’t think this is something that you want to do with mortar. Your Ditra-Heat should be more like 1/4 inch. If you need to add height then your best bet is to add 1/4 inch Hardibacker or cement board to the floor. If that’s too high then I think Schluter will OK 1/8 inch Ditra underneath Ditra-Heat. You’ll want to verify that with Schluter.
You might also look into Ditra-Heat Duo which should be slighly thicker than Ditra-Heat.
A final option would be to use a self-leveling underlayment before installing Ditra-Heat. This can be challenging for a DIYer and, if you are installing over a wood subfloor, you’ll need to use a product like Ardex Liquid Backer Board. If it’s a concrete floor then you have a lot more self-leveling options.
We are installing Suntouch flooring with Heatmatrix uncoupling membrane. Is Goboard an acceptable subfloor for under Heatmatrix?
GoBoard would work fine underneath the heat wire and would make a pretty decent insulator, I would think.
When you’re prefilling you’re still using unmodified? That should be modified since it is going to air dry – not moisture cure.
You are correct to say that Schluter’s instructions want you to use unmodified on top of Ditra-Heat.
I have a job coming up that requires a heated floor in a few bathrooms. I was going to use the Ditra-Heat but realized that the tile they selected was .6 inch mosaic! What do you think might be a good solution ? Go with the Ditra-Heat and cover the whole system with thinset and 1/4 inch cbu to try to get back to a solid substrate for the mosaic? Use some kind of leveler over the Ditra-Heat to get a smooth, competent surface for that tiny mosaic? Or perhaps some other system al together. Any advice would be helpful The floors already have 1/2 inch cbu glued and screwed.
The best way to do it from here would probably be to use a premade NuHeat mat or one of the cut & turn mats installed directly over the cement board. Then coat it with a self-leveling product.
Another option would be to install 1/4 inch Wedi board, cut channels for a wire with a router, embed the wire, then install thinset and mesh tape over the wires. Wedi will approve this installation but you’ll want to read the instructions for doing so prior to the installation.
look for a medium bed unmodified thinset follow the instructions on the bag. lowes sells a mapei (large format unmodified) this is a decent medium bed motar that shouldnt slump for your install
ditra XL will match up with ditra heat
How deep can the ditra membrane and wiring be embedded in concrete / thinset? I’ve got a difference in floor levels between two rooms of about 1/4 inch. I’d planned on installing the membrane with the wire and covering it with the proper cement then, as I lat in the tiles simply add a greater thickness of mastic between the tile and the ditra-wire-cement.
Your best bet is to level the floors first then install Ditra Heat. Another option is some of the heat membrane companies will allow CERTAIN self-levelers over the top of the membrane. Ardex is one company that makes both the membrane, Ardex Flexbone Heat, and the self leveler, Liquid Backer Board.
Not all self-levelers will work in this application, in fact, most won’t so you need to be clear on which products will work with others. But, if you only have one section that is 1/4 inch lower then the heat at the tile level shouldn’t be affected.
Also, you want to be sure to use thinset mortar and not pre-mixed mastic.
I called schlutter and they said that I can simply make the layer of thinset above the mat thicker in order to reach the height needed to match the existing tile.
Great! The follow-up is appreciated.
I’m wanting to do a large area with wood look tile into kitchen/hall/laundry room. The question I have is this, can I use the detra heat may in front of my sink and stove but no where else. That being said can I use the other mats that are not for the heating wires be used in the same room? Are the two different types of matting the same height? I just don’t see the point of hearing a very large floor when I’ll only be standing in front of the sink stove and counter while making meals.
Ditra Heat mat is about 1/4 inch thick. What you can do is run that mat everywhere but only heat the parts that you want. Alternatively, you could use Ditra-Heat mat only where you want to heat but I would recommend another similar height tile underlayment to use with it. Whether you use Ditra XL, 1/4 inch Hardibacker, or whatever is up to you. But I wouldn’t switch to another thinner mat like Ditra and run it right next to it.
Hi there, what a fantastic source of very knowledgeable and generous info. Thank you! I will save your site to read at my leisure :)
Sorry if this is the wrong post to ask my question but l cannot see a search for option.
I want to grout my fireplace tiles. I rang Mapei to check if l can use what l already have, which us a bag of Mapei Flexible Wall and Floor Grout CG2WA (Black) lt says on the packet suitable for floor heating.. He said yes that’s fine for fireplaces, but having looked at their website PDF’s l cannot see it as listed for fireplaces. They have several others for moderate heat and higher heat so I’m a bit worried about using it and ruining all my hardwork.
Can you clarify or recommend a black coloured grout l can use please?
Thank you :)
Shelly
For a black grout, I would use Mapei Ultracolor if that will work for your application. Raven is their black, I believe. I’ve never heard of the product that you mention and don’t know how it would behave.
Ive installed Prodeso mat over 1/4″ Hardiboard. It is stuck well over 95% of the area. There are a few edges that are not. Can I tack these down and continue tiling? The loose areas ore only one square wide.
thanks!
If they are loose you can always cut out the loose sections and replace with new product. I suppose you could always add more adhesive underneath them and weight the edges down until the bond and dry. That would be another way to get there.
Thank you for your site! I am planning to tile over cement slab, 1200 sf, using Ditra Heat in certain areas and a Ditra membrane throughout. Was researching Ditra Duo but appreciate reading the suggestion that I might use Ditra XL in the non-heated areas to maintain the same membrane thickness at less cost. Could there be any reason to think that the thermal break on Ditra Duo might make my unheated tiles any less cold vs. installed over Ditra XL? I haven’t read that claim made anywhere, and I know the idea is reducing heat loss to the cement. Just wondering if Ditra Duo might in theory also reduce coldness from the cement to the tile vs. another Ditra product?
I suppose it could but I really think you’d be better off installing a foam board or other type of insulation. The little bit of feedback that I’ve received about Ditra Heat Duo is that it might not be as helpful as you would think as an insulator. I have no doubt that it’s better than normal Ditra Heat but I still think insulation of some sort would be a better way to go. Either foam board like Wedi, or Kerdi board, or even a foam underlayment like QEP makes.
Schluter has a Technical Bulletin published that describes how they poured a self leveller over the ditra heat to a level of approximately 1/4” above the waffles and the they installed either wpc, lvt, lvp, and spc . They list the heat ranges that can be used with each as well as surface temperatures that can be expected.
I am caught between two tile contractor experts, regarding installation of DITRA on a sunroom’s concrete slab floor with in-floor heating (in the slab, not on top). One says use DITRA to avoid cracking tile if the slab moves (hard for me to imagine that happening). The other says to not use it because it will interfere with the floors ability to heat. Thoughts?
I noticed in your picture you run a two lug gap instead of three. Any reason when schluter recommends a three lug gap?
1,000 SF on concrete slab. A couple questions:
1. DITRA Heat Membrane is expensive!!!! For areas not heated can I use backer board or durock instead of the membrane… it’s a lot cheaper. Or bite the bullet and go with XL?
2. I have the option of going 240 or 120… seems like I can cover a lot more area and eliminate a couple thermostats to help reduce cost.
3. Plan was to cover walkways and room centers – how far does the heat radiate from the normal pattern?
I’m not sure why Schluter recommends the spacing they do. I use a Suntouch wire and they are OK with spacing down to 2-inch.
These are good questions. With a concrete subfloor you won’t be able to install cement board or Hardibacker over it as it’s not an approved substrate for that application. You can use Ditra XL where it’s not heated. You can also use 1/4 inch foam board like Wedi board, or you can use a self-leveler. The self-leveler might be a good bet but they can be tricky to use.
I would go with 240 over concrete if you can. Heat does not radiate very far. Maybe 1-inch?
Here’s something to consider: with a concrete subfloor, you want the heat to travel up rather than down. But if the wires are installed directly on top of the concrete then there really is nothing stopping the wire from heating downward. So you are then heating up the entire slab and the tile floor and that takes a lot of energy.
Schluter has a membrane called Ditra-Heat Duo that is supposed to address this. The one floor that I used it on, a small bathroom floor, the results weren’t overwhelming.
In the future, when I run into this, I’ll figure on installing a 1/4 inch foam board over the concrete with heating wires on top or maybe think about using a cork insulation under the wires. I believe QEP makes cork underlayment for this purpose.
I’ve seen some comments and feedback about the Ditra Heat Duo (TB) creating a hollow sound upon finishing an install. Any thoughts or comments on that topic? I don’t know if they prefilled waffles and let it dry or not.
Thanks!
It can sound a little bit hollow.
Electrical questions for DITRA Heat. Each of my rooms already has wiring from electric baseboard heating that I have not used in years. Each room is connected to a Two Pole 20A breaker. Voltage reading is 247V. My concern is it appears that the wire size is 12 gauge, not 10 gauge as I thought it would be. I thought I saw someplace else that 12 gauge would be sufficient. I believe I would rather use the 230 option versus the 120V option due to less “current”.
So… with 12 gauge wiring… should I replace the breakers with 20A single pole and use the 120V system, or do you think I would be okay using he existing two pole 20A breakers on the 230V system. Gut tells me that the 20A rating is the key.
I don’t know the answer to this. I always lean on the electrical contractors that I use to make sure the wiring is sufficient. Sorry.
Just wondering, what mortar consistency do you recommend for the waffle prefill coat? The base coat adhering the Ditra to the substrate should be rather thin and the tile setting mortar should be much thicker – more like the former or the latter?
If I had done more research first, I would have the right products for the job, but…
I have the Suntouch TapeMat and Ditra XL and 6″ x 24″ wood look tiles for my 30 sq ft bathroom floor. will be on a plywood substrate. In the Schluter handbook, it says to use All-set then the TapeMat, then all-set, then dirtra xl then all-set then tile. I want to confirm a few things. First, the floor is not level, by only about 1/4″. Do I need to use a leveling compound first? I already purchased Level-Quick (which seems to be the wrong choice from the things I’ve read) Second, from what I understand, I should level the floor, let it set up. Next day, put down the TapeMat, and skim coat All-Set (also, already purchased) and then lay down the Ditra XL, then let that set-up?? or keep going with All-Set over the Ditra XL and Tile right away?
If I don’t need to level out that 1/4″, do I Still need a cured Mortar base under the TapeMat? If I do use the LevelQuick first, there would be a section that would still be plywood….
also , I need to match all this up to my 3/4″ hardwood flooring at the entryway/door.
any advice is much appreciated!
I have acquired a ton a respect for anyone in the Tiling Trade, it may be one of the most meticulous. with far too many ways of doing the same thing.
I use whatever is left from installing the mat. If I make up more then I would mix it thicker like normal thinset mortar would be
I’d say you have some decisions to make.
I don’t think you can do it the way you want and have it match up with the hardwood. So, something has to give.
The floor should be leveled up before installing the mat. Don’t use Levelquick to do that. I would take a look at Planipatch which can be purchased from Lowes, or other retailers that sell Mapei products. I think Home Depot has a version from Henry’s but I don’t have any experience with it.
Then you can install the rest of it like you said. Personally, I’d rather see you use Ditra-Heat instead XL and the tape mat.
But I think, no matter what, you’ll have to change it out to regular Ditra to have a shot at matching heights with the hardwood
I have a 1800s house. I am about to pull up the 3 layers of flooring. I know there is a subfloor over the pumpkin pine that i will keep. I don’t think it is 100% level, but close. Do i need to use a Hardie board first with this ditra mats when installing heating and using 8″x36″ tile?
A home built in the 1800’s likely won’t be straightforward like a more modern home would be. You’ll need to familiarize yourself with the Ditra Handbook which is an excellent tool because it contains so many different subfloor scenarios.
But for a home that is that old, you’ll have to start with “Are my joists strong enough to support a tile floor?”. I would start with the deflection calculator over on the John Bridge forum to figure that out. After that, the Ditra Handbook should be able to guide you the rest of the way.
What is your opinion on running the heat on steps? I am using the HeatMatrix for a entry way that then drops down two steps into a short hallway.
Thanks
Thumbs up!
Can you take the wire out of the heat mat and embed it in the Ditra Heat? Any issues with that? LOVE reading these comments. I’m learning so much!
I would think so. Especially if it’s one of the cut & turn types. If it’s in a mat, like some of the Nuheat ones are, then you might call and check with them and see if the matting has any function besides just holding the wires in place. But I don’t think that it does.
Hot glue gun to hold heat cable in place, so when you lay down the thinset, and pick up the tile to check surface contact, the wires will remain in place.
That’s one way around it!
I placed my Ditra heat wire 2 studs a part. After reading all the directions I’m not sure how I missed that Ditra Heat wire must be placed 3 studs – I placed them 2 studs (probably should have had my wife read the directions). Can you advise what problems this is going to cause and have I just destroyed my chances of having heated floors? The tile job is finished so it is what it is but I’m looking for some info on whether I shouldn’t use it now.
I think you’re fine. You’ll forego the warranty from Schluter for not following their instructions but you’ll also have a nice warm floor. I don’t know why Schluter insists on 3 lugs but they’re the only ones that do, to my knowledge.
hi
I need your advice. I filled the waffles of my ditra heat membrane with unmodified thinset, and directly installed a kerdi membrane onto it, then let it dry a week. Is is nicely bond on the ditra, but I notice some voids when I push my finger on some areas.
what Do you advice among those solutions :
1/ to peel off the kerdi, refill all the voids with unmodified thinset then glue a new kerdi on it with liquid form thinset
2/ peel off the kerdi, refill all the voids with unmodified thinset, let it dry, and aftewards paint liquid membrane on it.
3/ do nothing, let it so, it will be ok
I can show you a photo of my problem.
some precision : I installed a Schluter heating wire on the ditra Heat membrane, and why did I install a kerdi on the ditra, it’s because I read that Schluter recommends it for a shower area. The ditra heat membrane is glued on a concrete, with modified thinset.
thanks a lot
If the waterproofing is essential, and not simply something that’s overkill, then I would do #1 in your options.
Thanks for the clarification.
great, thanks for your comment. I’ll try it.
Does it help if the smaller tile (mine are 1.5”x1.5”) are in a connected matrix (total is 10”x12”).
I installed some plywood sheets over my bath subfloor in hope of a cleaner DITRA-HEAT install. I noticed a low spot ‘valley’ so I tried to screed some unmodified thin-set left over from the KERDI shower install on the low spot to try and build it up. After reading the Schluter guide again and realizing I now have to use Modified thin-set to install the mat, can I put the modified over the are where I used unmodified?
Most of the small tiles are connected on some sort of mesh and that doesn’t sway Schluter from relaxing their requirements.
I think the unmodified is going to be trouble. You want a A118.11 mortar for going over plywood. It should have that number on the label for the bag.
I have mapei ultraflex 2 for the DITRA mat but I had feared the worst. I initially wanted to put down the self-leveler on the subfloor under the plywood, but when I put the primer down it leaked through some unseen nail holes and joints, so I got discouraged. My ‘low spot’ is only about an 1/8-3/16″ low, so I think I will pull up the plywood, either flip it over or replace and may be try the leveler again on the subfloor beneath the plywood. Thanks for the prompt reply and keep up the good work, this is a great resource and I will be on to your tiling section next!
Thanks! You’ve got to plug the holes in plywood otherwise it will leak through. I just published a post on self-leveling if you are interested. It’s right on the front page and it’s a long one.
Hi,
I’ve done several DItra heat systems over concrete but this particular job is a mess. The floor is so bad that 6 bags of floor leveler (for 165 SF) didn’t fix it all. I set the mesh and cable but when I started tiling there were still huge (1/4″ +) gaps under the 6×36 plank tiles. I was worried about cracking so I pulled them up and tried to level with thinset. The client didnt like it and asked if there was another type of flooring that could be placed over the heat system? Of course, Schluter says no.
Just curious is you know of anyone who has tried this? TIA
I’ve only installed tile over heat but I’m pretty sure that other manufacturers will allow for other materials over the heat. You might look up some of their instructions and try to follow them.
Hi again,
You may have already posted this but I just want to be clear. I redid all my mistakes and now have ‘flat’ plywood. I plan to lay DITRA-HEAT over this plywood, using modified Mapei UltraFlex 2 for the DITRA-HEAT mat. Did say that I can fill the mat cavities (with heat wire) with my leftover modified thin-set? And if so, after it dries, I can then use unmodified thin-set for my oversized porcelain tile on top of the cavities filled with modified?
thanks,
Yes, it’s fine to do it that way.
Hello
I bought ⅝” honed marble tiles on a mesh background several months ago and decided I wanted heated floors under them. I was told that the tiles are too small for this system. The tiles are 7/16 “ thick and it’s a small bathroom. 30 square feet and doesn’t get a lot of traffic. If I did a thicker motor set over the membrane that holds the wire do you think I can get away with using these tiles? Have my heart set on heated floors. And can’t and don’t want to return the tiles. Thanks for the info.
The issue is that the tile size is under the minimum size for Ditra-Heat mat. You can still heat the floor if you want but not use the Ditra-Heat system (or any other uncoupling membrane heat system).
Nuheat makes heat mats [affiliate link. Privacy policy] that are already sized and might be easier to install if you have a room where their standard size mats work. You can also have them make you a custom-sized mat.
Alternatively, you can run the heat wires over the floor and self-level over them. This is the option I would go with.
I should add that you need a very flat floor for 5/8 inch marble tile to look good. So even with a Nuheat mat, I think you are going to need to self-level over whichever heat system that you opt to use.
Thanks so much for the information!! And speedy too!
Appreciated your insight. Would I use just the same wire as the ditra system use ?
You can but I’d probably go with a different one if you aren’t using Ditra-Heat membrane. Unless you already have the wire and can’t return it. I like Suntouch Warmwire and Nuheat has a good one too. They are probably cheaper than Ditra-Heat wire.
Hi again,
Now the wife wants me to install a 2’ x 2’ small tile pattern stone/marble accent in the middle of our bathroom floor Ditra heat mat installation. I am using 12” x 24” porcelain tiles so math wise I could fit them in. Do you see any issues with this or the stone/marble over Ditra heat? Small tile stone/tiles are same height/thickness of large porcelain tiles. Thx
Thnks for all the advice you’ve given so far TileGuy!
So, I ripped out my old tiled floor with 1/2 cement board under it, just screwed down. I replaced it with 1/4 durock cement board. I am installing a ditra heat kit. I have a laticrete hydro ban sheet membrane for my shower, so i bought LATICRETE Multimax Lite and 253 gold. Do you have any advice on if I can use these products with the ditra heat. Can I use any of it glue down the ditra mat or pre fill the ditra mat? How about to stick down my shaped 8×10 porcelain shaped tiles for the floor. If so how long should I really be letting these layers dry?
I guess another one is what to use between ditra heat mat in my shower(deck mud sloped pan) and the laticrete sheet membrane for waterproofing? I even bought some of the Laticrete Thermal Packs to mix with the mortar under the tiles, but now rethinking those as well. I know most of your experience is not with Laticrete, so your advice is appreciated. Thanks for your time!
The 2×2 size should work fine although it’s right at Schluter’s minimum tile size. One thing that you’ll run into is height differentials even though they are similar in thickness.
You’ll probably need to use an installation technique similar to what I discuss in this post but modify it for the size of your installation.
https://www.diytileguy.com/tile-accent-strip/
Since your tile isn’t considered large format tile I would just use the 253 for everything. Sticking Ditra-Heat down, prefilling, installing the tile, and installing the sheet membrane. Keep in mind that Schluter won’t give a warranty with these mortars but 253 is a great mortar for your entire project.
If you want to use Multimax lite then I would use it to install the tile. I found it to be a bit weird to work with the one time that I’ve used it. But it’s a good product.
Schluter will want you to use an unmodified mortar for everything or their own house brand modified mortars.
Had someone put ditra heat down in our bathroom since we had a huge renovation project and i had my hands full. our problem? heat never worked. thermostat tells us the temp of the tile. but setting it to a warmer temp changes nothing. any advice to trouble shoot?
If you want to pull the thermostat out, you can check the wires with a megohmmeter using Schluter’s protocol. They’ll have certain numbers, that are particular to the wire that you bought, that you can check to see if yours are in the proper range. That will tell you if the wires are operating as they should.
The process is similar to this post except Schluter has an additional test they want to be conducted with a megohmmeter.
Hopefully, the wire checks out. Then you want to check the thermostat. I don’t have a technique for this other than replacing it but Schluter can probably assist with this and I’m assuming yours would be under warranty still.
A third possibility is that your floor is as hot as it gets. It depends on how thoroughly the wires were run, where they were run, where the heat sensor was placed, etc. I’ve heard this complaint about Schluter’s Ditra-Heat because of their strict spacing rules for the wire.
Additionally, if your heat is over a concrete slab, or if the insulation under the floor is inadequate, then that could play into it also.
Call Ditra, I asked the same question. Short answer, yes you can install other materials over Ditra Heat Duo, they sent me a bulletin explaining what to do. In my case, I’m installing vinyl plank (floating) over the Ditra. The bulletin says use a “cementious self-levelling underlayment” for which I used Levelquik RS. I poured in just this weekend, unfortunately some areas came out not fully covering the Ditra “dimples” so I’m considering whether I need to pour another layer on top (priming first). Also, I’m getting that cracking sound in some places, hoping that another layer might alleviate that or that the vinyl plank lessens it. Knowing what I know now I may have just gone for tile. This is in a basement BTW
Thank you for the input. I’m surprised that Schluter wasn’t more specific with a type of self-leveling.
To add more, it’s your call on whether adding more is the way to go or simply going over spots with a feather finish floor patching product (like Silk, from Custom Building Products). Hopefully, the cracking sound is just because you are walking on the cement.
yes I agree about not installing tile the same say as you put the membrane.
but the issue I had about prefilling the membranne is that often the mortar in the center of the small circle often come off if you walk on it before they sort of pop up. so i’m doing as they do buy I sadly have to be 10 time more careful of the wire
Just to follow up on this for others who might be thinking of the same approach. I decided to add a second layer of the Levelquik RS (priming the first layer) and it turned out very well. Very solid and no issues with the cracking sound, although I do have some hairline cracks in the Levelquik RS layer, although nothing serious. For those doing this with only 1 later on the Ditra Heat Duo, make sure you build the layer up so that it completely covers the dimples to avoid having to do a second layer! You should not see the dimples at all, if you do, add more Levelquik and shift it around until it’s covered!
Hi, what are your thoughts on SLC over a ditra membrane with heat wires? Schulter says no but my installer still wants to use SLC and then a layer of unmodified thinset. He said it protects the wires. Thoughts?
Thank you for following up on this!
Like you mentioned, Schluter doesn’t approve of it but other manufacturer’s do. But you have to be careful which product that you select as not all self-leveling underlayment products will work in that application.
For example, Ardex approves their Liquid Backer Board product over their Flexbone uncoupling membrane. So, it would stand to reason, that Liquid Backer Board would work with Ditra-Heat.
Self-leveling over heat wires probably isn’t a good idea if there is a lot of unevenness as you don’t want the wire to heat unevenly. But it the leveling is simply to cover the wires then it’s fine.
When you are doing the skim coat to fill in the top of the membrane. Are you using the consistency that you use to adhere the membrane to the floor or the consistency you you would use for the tiles
With normal Ditra, I will take whatever is leftover from installing the membrane and use it to fill the top. But if I’m making new thinset up then I will make it more like I would for tile.
I have installed new ceramics aver existing one that were heated with cables…and never saw a difference in heat..And that was 12 years ago …still going strong
I had a company come in and install a schluter pan and ditra heat. It was supposed to be a curb less shower. Well they did the heat first and then the pan. After which there was a 1/2 gap from heated floor to pan. They want to just add self leveling concrete to bring it all up to level. But schluter says you can’t add that and do tiles over it. What do I do now? I also noticed that they did 3 stud spacing on the heat wires then switched to 2 stud spacing for the last 6 rows. Again schluter says 3-2-3 or 3-3-3 never 2-2-2. They have already added thinset to cover the heating wires as well. What are my options here, very confused and unhappy. Should I have them remove it all? Is that even possible?
Thanks in advance
It sounds like there’s been a lack of planning on this project. I don’t know why there is such a gap between the pan and the floor. Maybe they didn’t order the correct pan, maybe they didn’t recess it properly, I’m not sure, but 1/2 inch seems excessive to me. If they want to use a self-leveler to bring it up then this can be done but, as you’ve mentioned, it will void the warranty.
The spacing is a problem and the project shouldn’t move forward with the spacing done in this manner. Part of the floor will be warmer than the other part. Like I said, they need to plan better and maybe read the instructions.
Thank you for the reply, is it possible for them to pull up the ditra mat and then lay down 1/2in plywood or cement board on top of the thinset that was put under the mat? Then put down a new ditra mat and heat wires?
I don’t imagine it’ll be fun but, yes, that can be done.
Well they ended up adding another layer of ditra heat mat and all nes heat wires. This approved by schluter. The 1/2 gap is gone and I can tile it this weekend!! Thanks for the help!
Our contractor already secured .25 in Hardee Board to our .75 plank subfloor. Can we install Ditra Heat over the Hardee Board?… We know it would increase the floor height.
Thanks
Hardibacker is supposed to be counted as having no structural value so installing Ditra-Heat over it wouldn’t be an approved method according to Schluter. It should be 1/2 inch exterior plywood in place of Hardibacker and Ditra-Heat over that.
So even with the Hardibacker over .5 inch plywood, which is over.75 inch planks I’m still stuck?…The Hardibacker is down solid… it would be a lot of work to remove it.
If I did choose to lay it over the Hardibacker, what would be the worse that would happen… aside from voiding the warranty?
Thanks for the response
No. If you have 1/2 inch plywood down then that should be OK to install either Hardibacker or Ditra-Heat over. If it fails, the worst thing that can happen is your tiles loosen up and the heat stops working.
Great questions and answers here but I didn’t see anyone struggling with my particular issue. I am putting Ditra Heat down over a 19 mm (3/4″) thick plywood subfloor. I added a 2.7 mm thick plywood underlayment on top of the 3/4″ subfloor with a zillion screws spaced 4″ from each other.This is to make it nice and level with the hardwood flooring at the doorway. Now I am ready to move onto the next step and install my Ditra Heat membrane and just read how the underlayment must have a minimum thickness of 10 mm (3/8″). How can it possibly matter with all those screws? I did notice that the 2.7mm plywood sheets had a sticker on them with some tile application accreditation/standard.
Please tell me to go ahead and that everything will be fine!
The issue isn’t the thickness of the plywood but, rather, the composition. So, you need the good exterior plywood that has a face grain rating of no lower than ‘C’. This is quite common to get in the 12mm (1/2 inch) and 19mm (3/4 inch) thicknesses. It can also be found as thin as 9mm (3/8 inch). However, to my knowledge, it is not made in 6mm (1/4 inch) and thinner sheets.
But, if yours has some approval stamp for tile on it then you may have a special product that is specifically for tile. I would investigate the product that you have and the brand name, if possible. Otherwise, it’s probably best to remove that thin layer and install something different.
FYI, they make a 5mm (1/8 inch) Kerdi board if you need more height for the floor.
I have a question I bet even you “DIYTileGuy” could not answer with absolute certainty. And my question is extremely relevant seeing that LVP and LVT is becoming so popular. I would like to install Ditra-Heat and heat cable through out my house. Can I install glue down LVP, non rigid core WPC (most LVP is) over Ditra-Heat. The matt would be applied over plywood with unmodified thinset. Next day prefill and float unmodified thinset over the Ditra matt with flat side of trowel making a surface similar to a concrete floor and let dry for a day or 2 or 3. Then glue down the LVP? In my case I am using Karndean glue down Vinyl Planks. No where can I get confirmation of this even though Ditra-Heat has a section in the handbook that addresses alternative floor coverings. Will I be the first to try this because the 1250 of LVP and the Ditra-Heat sysem has already been purchased and sitting in my shed awaiting installation. I can not return and need this to happen. I wait in anticipation for your reply Sir.
You got me. I’ve never installed LVT and don’t know what the rules are for it. There are some manufacturer’s that will approve self-leveler over uncoupling heat mats but Schluter isn’t one of them. But a company like Ardex may approve their Liquid Backer Board over Ditra Heat and if LVT sticks to self-leverler then maybe that’s a solution.
Sorry, I wish I could be of more help.
You actually did provide help, more than any other tile setter I as asked to help clarify. You replied back! I knew you would, thanks. And also you provided me with thoughts to consider. I believe I have more research if I am to do this…and I AM going to do this! Thank you once again. Always been a fan of yours.
Thinking of using Ditra heat for a current project. Here is my challenge. Schluter specifies no tile to be installed over Ditra heat that is smaller than 2×2″. I have 1.5×1.5″ ( at best ) net mounted marble mosaics to install. I contacted the tech support line, and asked if it would be an acceptable work around, if I were to Scratch coat the Ditra heat with a high quality thinset (which I see you recomend ) and then after the thinset has cured, apply Kerdi over the entire floor. I was told that this would be acceptable, but would void any warranty. Curious as to your thoughts, and wether you have used this method.
I’m surprised they would deem it acceptable without offering a warranty. But, you’re probably fine. In fact, you’re probably fine even without the Kerdi although the Kerdi will help the cause.
It depends on what the use is and what type of traffic it’s going to see. For instance, a residential bathroom doesn’t get the same wear & tear as a shopping mall.
If you feel like your application is going to be residential and lighter impact then the Ditra-Heat is a good way to go.
Another way of doing it is to not use an uncoupling membrane and just run the heat wires over the substrate. Then self-level over that. This provides a solid surface that doesn’t have built-in soft spots like an uncoupling heat membrane which is more ideal for smaller tiles
You’d probably be best to switch heat manufacturers if you consider this option as I doubt Schluter would want their heat wire used outside their membrane. But Suntouch and Nuheat would work and are both good brands. Additionally, Ardex makes every component, from self-leveler to heat wire, and they could provide a complete system warranty.
Just a quick comment having read the discussion on filling in the DITRA grid prior to setting tile. While I understand the concern of damaging the heat cable, I believe the Schluter team doesn’t specifically state you need to pre-fill it in because that will defeat the purpose of an air gapped underlayment.
One of the (many) benefits of using this type of underpayment is the very small contact surface between the subfloor and tile on top, so when you pre-pack all of the joints between the DITRA mat, you’re going to greatly increase the conduction from the heat cable and surrounding tile to the floor below. This will slow the heating of the tile on top and reduce the efficiency of the system as a whole, since you’ll be dumping a larger amount of heat into the subfloor and surrounding mortar to reach an equivalent temperature on the tile without the added material. In addition, DITRA is also designed to allow movement below the tile – so when your subfloor floor moves (hence the required movement joints) the mat itself will move, and the tile sitting on top does not due to the higher stiffness. This stops your grout and tile from cracking over time.
I’ve installed a number of DITRA per the Schluter instructions without filling the mat in with no issues, and I’d recommend talking to Schluter prior to packing the mat chocked full of mortar.
I appreciate another point of view on this but I’m not sure I fully understand the argument. Uncoupling membranes are designed to have some areas filled with mortar. Those areas should be filled 100% whether that’s done in one step or two different steps. So the amount of mortar on the top side of the membrane would be the same in either scenario. So I don’t see how one method vs another would affect the heat conductivity
Nice site this – lots of very helpful info – I wish I’d seen it before I commenced my DIY install of a ditra-mat like product… You see I’ve mistakenly installed ditra matt upside down (so with the dovetail pockets mechanically bonded to the floor with adhesive, fabric side facing up), upon which I then stuck a heatmat, adhesive then 10mm 600×600 porcelain tiles. The floor and tiles are still decoupled, but should I expect significant problems from installing it upside down?
I really don’t know. I suppose, in theory, it should still work if it was installed properly but I imagine it would be difficult to fully fill the orange side of Ditra. The only thing I can tell you is to watch it and use your judgment.
Hello
I have a ditra heat application. One small section of one of the ditra heat squares seems to have popped up from the thinset. Almost as if there is a small air gap between the ditra and subfloor/thinset. Will this cause tile failure and can it be fixed before tiles are put down?
Yes, it should be fixed and you can cut it out and reinstall that small section
I think that’s all I can do really! hopefully the floor won’t move too much and worst case I’ll have to touch up the grouting every now and then… I’ll let you know! Thanks for the reply :-)
Is there any concern that the “movement” within the floor (especially with heating repeatedly applied) will cause the two layers of thinset (the waffle fill layer and the tiling layer) to separate and cause cracking or movement in the tile floor?
Another one if you don’t mind. Do you typically fill in the plywood expansions joints gaps when installing the Ditra, fill the gaps with caulk before installing Ditra, or tape them over?
The membranes are meant to allow movement. They can withstand more than one would think.
Check with the membrane manufacturer’s instructions. I have heard of some of them wanting the seams caulked with latex caulk but usually it’s OK to just thinset over them.
Just about to start a DIY Ditra Heat system bathroom install. Will be porcelain tile over the Ditra. My subfloor consists of a lower layer of 3/4″ exterior T & G plywood covered by a 3/4″ layer of T & G Advantec which is a high density type of OSB. Advantec is MUCH less permeable to moisture than regular OSB or plywood, in fact, water just beads up on it. As I’ve not seen any mention of it’s use throughout this Ditra Heat discussion, I have to ask if modified thin-set would be the appropriate type to use to bond the heat mat onto it?
Should you dampen the wafer layer of thinset before laying down thinset to tile?
No. If anything, that would cause water to collect in the waffles. The mortar doesn’t adhere to the Ditra layer and water won’t slow the drying process in this case.