Installed WarmWire Heating Elements

Figure 8

Now that your floor looks like a can of silly string exploded (figure 8 ) its time to add more layers to it and cover up all your hard work.  If you have not yet done all the hard work then your floor doesn’t look like that. Check out How to install WarmWire Part 1. I’ll wait.

Okay, you may want to check out a speed reading class. Just sayin’. :D My preferred method is Schluter Ditra underlayment installed atop the WarmWire for your tile installation.

The best method of leveling out your floor for your Ditra would be an SLC or Self-Leveling Cement. This product is mixed with water and poured over your WarmWire. When mixed properly (follow the instructions to the letter – really) and poured it will – wait for it – level itself. When cured you will be left with a level, flat floor.

You can actually install your tile directly to this layer if you chose to do so. I do not chose to do so. I prefer to have an additional uncoupling membrane above these layers then my tile. That’s just how I roll.

For purposes of speed (SLC requires 24 hours to cure) I will level the floor above the wires with mortar. If you chose to do this, and you may since it is considerably less expensive, you need to take absolute care with the method I utilize. You risk damaging the wire while leveling the floor so be careful.

To level the floor above the WarmWire with mortar I use a 3/16″ square notch trowel. Mine is metal – yours should not be! You can purchase a plastic trowel make exclusively for use over the wire. These are much safer to use as they would require actually trying to damage the wire with it. It’s difficult to damage it accidentally if you use the plastic version.

The most difficult thing to do over in-floor heating elements is installing tile properly. That means flat, flat, flat. By using the ditra and utilizing my method you will begin your tile installation with a flat substrate over the heating element.

I mix my mortar (thinset) fairly thick for this. It assists in holding the shape and getting absolute coverage with the mortar – no voids in the mortar bed. I will first use the flat side of my trowel and fill all the areas between the wires moving my trowel in the same direction the wires are running.

Leveling over WarmWire for Ditra Installation

Filled and Combed

In the left side of this photo I have the flat troweled the mortar and in the right side it is ‘combed’. Notice everything is running the same direction as the heating wires.

Once that is all filled in I will flip the trowel over to the grooved side and ‘comb’ the thinset in the same direction by placing the trowel so the wires are between the grooves. That is so that the teeth of the trowel are actually touching the floor beneath the wire and the wires are between the notches. This will give you a grooved bed on which to install your Ditra.

Once that is finished place your Ditra over the top and grab your straight edge, level, 2 x 4, or whatever you have that is straight and handy. You want to press the Ditra into the thinset to it fully embeds into the fleece on the back of the Ditra. Place your straight edge on top of the Ditra and run it back and forth in the direction the wires are running or at a slight angle (figure 9).

Leveling Ditra over WarmWire

Figure 9

If you run your straight edge in the other direction you will end up with a roller coaster for a floor. Your straight edge will go from the top of the wires into the spaces between the wires and back up. It will not be flat if you do it in this manner. By keeping it either in the same direction, or a 45 degree angle, as the wires it will always remain on top of the wires for the length of your straight edge. Your floor will come out flat and even.

You need to make sure you put enough pressure on the straight edge to embed the Ditra fleece into the thinset. If you stand back you can see the difference in the color or shade through the top of the Ditra. It will turn a darker shade when embedded correctly and you will be able to see any spots you may have missed.

Leveling Ditra over WarmWire

Flat!

Installed and Uninstalled Ditra over WarmWire

Embedded and not

The left side of this photo shows the Ditra embedded correctly and the right side the Ditra is simply laid onto the mortar bed without embedding it yet.

Simply keep doing this as you walk (crawl) your way out of the room. Be careful not to step or kneel on any parts you’ve finished. There is a considerable amount of mortar beneath your Ditra so it is easy to put ‘dents’ in it with your foot or knee. As long as you use a fairly decently sized straight edge you should end up with a perfectly flat, stable floor ready for the tile of your dreams.

After 24 hours you can walk on the Ditra to wire your heating element and install your tile. You need to wait this long for it to cure. Stepping or crawling on it prematurely will create dents or otherwise compromise your membrane and substrate. Be patient.

Ensuring Ditra is flat over WarmWire

Contractor Glamour Shot!

Wiring the control box and heating element is fairly straightforward. Read through the directions included with your control box to ensure it is wired the same as I am describing – it may not be. I don’t know, I can’t see it from here.

There are three things you need to attach to the control box: the power from the house, the heating element, and the temperature control probe. The power from the house gets wired to the ‘LINE’ side of the control box and the heating element is wired to the ‘LOAD’ side.

The power from the house consists of three wires. They should be white, black, and ground which is usually green or a bare copper wire. The ground is not wired to the box, only to the heating element. The black is wired to the black and white to white of the control box. Easy enough even if you’re colorblind. The black wire is the hot wire! It’s not like your car radio in high school. The white is neutral. This is the way it should be but I didn’t wire your house so don’t blame me if it isn’t.

WarmWire Control Box Wiring

Figure 10

The probe has two wires – red and black. They are wired into the appropriate clips in the back of the control box.

The heating element has white, black, and silver. White to white, black to black, silver to ground. Please note that in this photo (figure 10) I have two different heating elements running to the control box so there is twice as much electrical spaghetti hanging out of the wall. You should not have that many wires.

After it is all wired up just stuff all the wires straight back into the box and

WarmWire Control Box Pins

Figure 11

attach the control box to the wall. The face of the control box is plugged into the back plate with the pin cluster in the back of it (figure 11). Place it in there carefully. They bend easily if not lined up correctly – just trust me on that one without testing it for yourself.

Now you can turn the breaker back on. Oh, you turned that off, didn’t you? Sorry, if you are currently sporting a Yahoo Serious hairdo, it may be my fault. You want to turn the breaker off before you start wiring.

Now the bad news – after you install your tile you must wait 3 – 6 days before turning on your underfloor heating. You need to give your mortar plenty of time to fully (relatively) cure before zapping it with unnatural heat. Doing it sooner may compromise the strength of the mortar and, in turn, your tile installation. You don’t want to do that now, do you?

WarmWire Control Box Installed

Warm Tootsies!

You’ll just have to wear socks for a couple of more days.

There you go – warm tootsies for those cold mornings. If this has helped you out please send me a photo of your completed tile installation. I would love to see what people do with my good advice and bad humor. I keep tellin’ my wife that it is a great combination but, you know, she doesn’t believe me. Oh well, extreme jackassery is getting to be my tag line so why quit what works?

Send me your photos at FloorElf@FloorElf.com and lets see what you can do.

{ 221 comments… add one }

Leave a Comment

  • Nick

    I plan on adding a similar “cable” type of heating in my bathroom floor. It is in a basement and the floor right now is the concrete foundation. My questions are:
    1) should I be worried about heat loss to the concrete slap? if so what would I put between the cable and the floor?
    2) Do I need to use the ditra membrane or can I simply tile without it?
    3) If I don’t use ditra, once I’ve put the layer of thinset down just high enough to cover the wires, I was going to trowel it w/ the smooth side while also keeping it level … you only “comb” yours if you’re using ditra, correct?

    Reply
    • Roger

      Hey Nick,

      1. There are thermal breaks available. You will have heat loss to the concrete, the amount is dependent on localized factors – temp, humidity, etc.

      2. You can tile without it, but ditra or another membrane is always a better idea.

      3. Yes, I only comb it for the ditra.

      Reply
      • Nick

        In regards to adding a thermal break in there … do you have any products that you’ve used or know of that would be best? I’m assuming without it, it would just take longer to heat the floor and be as efficient on the bills.
        thanks

        Reply
        • Roger

          I prefer hydroban by laticrete, but redgard works as well. Yes, it would take longer to heat and uses 20% – 35% more energy to do so.

          Reply
          • Nick

            Hey Roger,
            After contacting both companies, they told me that neither product has any R value at all, and only serve as a waterproofing. Sounds like these aren’t going to help prevent heat loss through the slab what so ever. thoughts?

            Reply
            • Roger

              Whether or not they have R value is not relevant in that situation. They do not guard against cold intrusion but they do effectively retard heat loss from the wire to the slab. It is not a typical insulator but does work as a thermal break.

              Reply
  • jay

    Roger –

    Sounds good man, Thanks!

    Reply
  • Jay

    A couple follow-up questions on your Warm Wire installation method….

    1) Because DITRA can’t be walked on, knelt on..etc, right after it’s put down, you obviously have to work in sections only as deep as you can reach from the un-DITRA’d section. In your experience, what size pieces of DITRA do you typically work with? I’m thinking maybe 3-4 feet deep? And wide as possible, right?

    2) The recommendation to run the straight edge perpendicular to the wires to prevent wills and valleys is good. But what do you do when you get to the straps? The straps are parallel to the straight edge and a little higher than the wires (due to the clips). How do you prevent high spots at the straps? The area I’m doing is big enough to require a couple straps in the center of the room, so I do have to deal with them.

    3) How much work time do you have to mess with getting the thinset/DIRA flat?

    Thanks

    Reply
    • Roger

      Hey Jay,

      1. Ditra is in 3’3 1/2″ rolls, I work in sections that wide and normally as long as the room is.

      2. I tilt my trowel a bit more to go over the straps. It doesn’t need to be perfectly flat – that’s what the straight-edge is for.

      3. Depends on what thinset you’re using. Normally you have plenty of time – 30 minutes is easily enough and most thinset fit into that time frame.

      Reply
      • jay

        Roger-

        Thanks for the comments. Regarding question 2, i wasn’t referring to the step where you trowel on the thinset, i was talking about when you’re running the straightedge prependicular to the wires and you encounter a strap (which will be parallel to the straightedge). Just wondering what your technique is when you cross these points?

        Thanks again

        Reply
        • Roger

          The ridges of your thinset before you place the ditra down should be higher than both the wires and straps. You aren’t pressing down hard enough to get the ditra directly against the wires, just enough to embed the ditra and get it flat. It should be sitting about 1/16″ – 1/8″ above the wires when you’re finished flattening it out.

          Reply
  • Jay

    OK, thanks Roger. just wanted to make sure I wasn’t missing something. Sure glad I don’t need the SLC!

    -Jay

    Reply
  • Jay

    Hi Roger-

    Great site. I’ve been stressing over my DIY kitchen floor with radiant heat, then came across this article. Great stuff! I’m using the Warmwire system and thought i’d need SLC over the wires. SLC freaks me out – it’s definitely not a one-man job, at least not for the 250 sq ft i have to do (to unknown depth!). Your technique is neat, and I think i’ll do it that way. One question though: I understand how you spread the first layer of thinset in the direction of the wires, letting the wires go into the notches of the trowel (cool!), but doesn’t that mean that the notches have to exactly match the 2-1/2 (or 2″) spacing of the wires? I’m sure i can MAKE the wires fit between hold-down strips, but sooner or later you come to the strips and if the notches don’t match the spacing at those points, what do you do? Just hop over as best you can?

    Thanks,

    -Jay

    Reply
    • Roger

      Hi Jay,

      Yes, just work around them the best you can. The wires will move a bit back and forth as you spread the thinset, just take your time with it. It is a pain, but it is easier than slc for rookies. :D

      Reply
  • Chris

    Hi Roger!

    Awesome site! I really appreciate all the help you give to us DIY’ers. I have a couple (maybe 4) questions for you…

    I will be putting WarmWire down on a new and existing kitchen concrete slab substrate (both areas total 1 floor space, addition to existing structure). I’ll be using your method above (wire embedded in unmod. thin-set/Ditra/unmod thin-set and tile). The existing slab had tile on it, which is now removed. The new slab has a smooth finish on it (newly poured concrete, no brush finish, rubber float finish). Before I install the first layer, do I need to take a grinder to roughen up the surface of the new concrete in order to get the thin-set to bond better? Do you think this is necessary?

    From your experience, have you ever seen a slab fail from the use of electric radiant heat? If so, should I use some type of thermal/moisture/anti-crack barrier like Aquadefense mentioned above between the slab and wire?

    Do you have any secrets on how to properly clean and prepare a concrete slab before tile install? The sheet rockers dropped some joint compound and I dripped some paint on the floor. I am using warm water and a little dish soap to clean the entire floor and then paint remover on the paint drips.

    Last question, I promise…

    I will also be crossing over two expansion joints. I guess I will need soft joints around that area, plus the size of the room is about 24’x17′. I did read your FAQs on soft joints! I will be placing tile in a pinwheel pattern (20×20″ with 6×6″ inserts). How far beyond each side of the expansion joints should I place the soft joints?

    Sorry for the long winded post, but I’m meticulous and paranoid (not a good combo, lol) and I want my floor to be perfect. I’m just trying to think of any other future problems that I could potentially have. Much thanks!

    Reply
    • Roger

      Hey Chris,

      If you splash water on the slab and it soaks in fairly quickly you don’t need to rough it up, the thinset will bond just fine.

      You can install a thermal break if you want, it makes the heating more efficient. I have never seen one fail if properly installed.

      Just scrape it really well and make sure it’ll absorb water. Get all the surface contaminants cleaned off of it.

      Ideally you want your soft joints directly over the expansion joints. With Ditra you can go up to six inches (I think :D ) on either side of it.

      Reply
      • Mike

        Roger,

        Love the site. Chris mentioned in this post embedding the wire in unmodified thinset with Ditra on top then using unmodified thinset to bond the tile to the Ditra.

        But I thought you said to use modified thinset to embed the wire and Ditra?

        Thanks again for the help,
        Mike

        Reply
        • Roger

          Hey Mike,

          Unmodified over concrete and modified over wood.

          Reply
  • Mike

    Roger,

    In the bathroom on the first floor of my house, there are boards that run diagonally on top of the floor joists, then about 1.5-1.75 inches of cement sub-floor on top of that which tile is installed to. If I am able to remove the tile from the cement sub-floor, then I plan to install the radiant floor directly to this surface, followed by ditra, then install tile on top of that. Does that sound reasonable?

    I’m still confused about how to level the floor with thinset instead of self-leveling cement, but I will cross that bridge when I get to it ..

    Thanks,
    Mike

    Reply
    • Roger

      Hey Mike,

      Yup, if you can get the tile off that mud deck that’ll work fine.

      You can level it with slc if you want, thinset is simply how I do it. I install the wire then, with the grooved side of the trowel cover the entire floor (and wires) with thinset so you have it all combed in there – a bunch of little lines. Then the next day you should have a floor with ridges of thinset. Go over the entire floor with the flat side of your trowel to fill between the ridges.

      You can also simply fill in the spaces around your wires with the flat side of your trowel using the wires as the depth gauge. Then install your ditra the next day. There are several ways of going about it but the end result should be a layer of thinset the same height as your wires.

      Reply
      • Mike

        Roger,

        Thanks again for all your help.

        I have been himming and hawing about what order to install these layers in before I get started. The installation manual for my product (Suntouch TapeMat) shows a picture in the manual (in case you are interested, the 3rd picture on page 14 of this manual: http://www.suntouch.com/literature/download/ST_SunTouch_Manual-EN.pdf). They recommend installing the “crack isolation membrane” (Ditra, I assume) over the slab (mud deck) and then installing the tile directly over the TapeMat with thinset.

        Any thought on why they would recommend to do it that way instead of the way you describe (which I understand would be installing the radiant heat mat over the mud deck followed by ditra, followed by tile on top of the ditra).

        Thanks,
        Mike

        Reply
        • Roger

          Because when the specs were written for that product all (or most, anyway) of the crack isolation membranes were either elastomeric liquids (redgard, hydroban), full sheet products (Tavy thin-skin) or sheet tapes used over cracks for isolation.

          That particular requirement is more for an insulating barrier designed to regulate the temperature differences in the slab. Concrete can suck heat right out of a floor in certain instances. If you insulate it (beneath the wire) it is much more efficient.

          Ditra and other uncoupling membranes were not in popular use until about 2002 – they were around at least 15 years before that, just not regularly used, nor used as crack isolation. All schluter products require in-floor heat be installed beneath the mats rather than above them.

          Reply
          • Mike

            Roger,

            I am confused after reading too much on this topic. To clarify, you recommend doing this in these steps:
            1. Trowel thinset over the radiant heat and then use flat side of trowel to embed the ditra into the thinset
            2. After allowing this to dry 24 hours, tile over the ditra

            Thanks,
            Mike

            Reply
            • Mike

              Again, thanks again for your help. I’ve learned so much from your site. One last question .. I was just planning to use modified thinset for everything. But in reading some of these posts, I’m confused about when to use modified and when to use unmodified.

              Could you clarify which layer(s) I should use modified and which layer(s) I should use unmodified?

              Thanks again,
              Mike

              Reply
              • Roger

                If you are installing backerboard you need to have thinset beneath it. It makes no difference whether you use modified or unmodified for that. Install the heat wires and use modified thinset between the wires and ditra. Schluter wants you to use unmodified thinset between the ditra and tile.

                Reply
            • Roger

              Yes, those are both correct. You can use the flat side of the trowel or a straight edge to embed the ditra into the thinset.

              Reply
  • Brian

    Hi Roger,

    Dig the site–thanks for the help. I have an 1898 house with sloping floors. Pretty flat in the bathroom, but with a 1/4″ pitch. I’m guessing SLC for embedding a floor heating system would just run down the slope, no? Next best thing would be Ditra-set?

    Reply
    • Roger

      Hi Brian,

      Yes, the slc would run down the slope until it leveled the entire floor. Ditra set is a mortar that’s used to install ditra. I believe you just meant ditra, yes? Then yes, ditra would be your next best bet.

      Reply
      • Brian

        Thanks Roger. Actually, I did mean Ditra-set, in lieu of SLC, to embed the heating system. Not sure if I want to embed the wires, let the thinset cure, then put down another layer of thinset for the Ditra, -or- do it all in one pass like you do. The Kerdi I put in the shower went up well, so I’m feeling kind of bold.

        Reply
        • Roger

          Oh, in that case then yes, it’ll work fine. You can do it either way, let it cure first then install the ditra or do it all at once.

          Reply
  • Grant

    Hi Roger,

    This may be a stupid question, but I’ll ask it anyway. If you were to embed the heating wire with SLC and let that cure, do you then use another layer of thin set on top that to install the Ditra? Can the thin set go right on top of the SLC or is there another step at this point?
    Thanks for all your help,
    Grant

    Reply
    • Roger

      Hey Grant,

      Nope, no other steps. The ditra can be installed directly to it with thinset.

      Reply
  • Other Lee

    Would you be able to do Ditra in one step like you did above if leaving part of the floor unheated or will it require two-steps like in this comment? Since I will be doing 12×24 floor tiles (new 1-1/4″ subfloor), I am thinking SLC and then Ditra may be the best bet.

    Thanks,
    Lee

    Reply
    • Roger

      Hey (The other) Lee,

      You can do it in one step, but it’s difficult and takes practice. If you have the option to use an slc that is definitely a better option.

      Reply
  • mpitts

    Hi Roger,

    Great site and thanks for putting the time into it.

    I am doing 2 bathrooms in a 60 year old house. Compleatly gutted both rooms right to the joists & studs. Joists are solid rough cut 2×10’s with no more then a 10′ span. I redid all plumbing and screwed down back to back layers of 5/8″ ply for a subfloor = 1 1/4″ in total. Screwed the first layer into the joist’s and the second layer into the first layer every 4 inches (square). I now plan to instal infloor heating so I just want to confirm that I can do so on top of the ply, they pour SLC, then do I need Ditra? How does it bond to the SLC? If I don’t need it…I won’t bother.

    I am also building a walk in shower with (3) 2×4’s stacked as rails with 1 /2″ porter cement around the rials over mesh and as a bed (tapered). Then put down mambrane and pour 2nd layer of cemnet and taper to drain. Then tile over (no heat in shower). Does this sound good to you?

    One more thing…I will use cement board in the shower behind tile, but should blue board be fine for the areas that are not exposed to water? The tile we are using will continue after the shower wall to 2 out of 4 of the perimiter wall…8 feet high. We are using 12 x 24 natural stone (carrera marble) for the floors, shower and walls and will back butter all pieces. \

    Thanks so much for any help you can provide this DYI’er!! 8)

    Reply
    • Roger

      Hey Michael,

      You want to install primer over the plywood first, then the heating, then the slc. Placing the primer down eliminates the headache of trying to get a good bond to the entire plywood substrate without trying to do it around the wires. The ditra will bond directly to the slc. You don’t have to use it, but with the temperature variation in your floor it would be a good idea.

      The first sloped layer goes down along with the curb 2×4’s only, then the membrane runs up and over the curb and the wire lath holds it in place – then you install the 1/2″ of deck (wet) mud over it and the final slope for tile. The membrane needs to go beneath the wire and mud on the curb – not over it.

      Blueboard is fine for any non-wet areas. You also did not mention a topical or traditional waterproofing membrane on your walls, I’m assuming you’re waterproofing them correctly, yes? :D

      Reply
      • mpitts

        Thanks Roger, In the shower area, I have run 6mm poly behind the cmt board on any wall that in exposed to mosture. After looking at my notes, that was how I was planning to do the shower basin, so thanks for the confrimation. Cheers.

        Mike

        Reply
  • Jimmy

    Bless you for your hard work on all this.
    ?? on pouring slc over heat wire and under dirta.
    Is there a special type of SLC
    how do I control the thickness (I’ll be using the metal straps)
    Thank you very much

    Reply
    • Roger

      Hey Jimmy,

      All SLC’s are essentially the same (kinda), by that I mean there are not different types. SLC is SLC. Not sure what you mean by how to control the thickness? The product will self-level so thickness will vary over the distance of the floor.

      To get a general idea of how high you want it in a specific area you can install a screw into the substrate with the head at the height you want there, that in turn will keep a relatively consistent height throughout, but unless your floor is dead-level before you start the pour you won’t be able to do that over the whole floor – the thickness will vary. Thicker in lower spots on the substrate and thinner in the higher spots – KnowWhatIMean? But when finished it will all be flat and level.

      Reply
  • Michelle

    Hi Roger,
    I love your sense of humor! :rockon:
    I’m reading and reading and learning too I think… I already sent you a bunch of questions from a different article but forgot this question… I want to put heating in the floor too. I only want to put it where your feet will actually be so… not around the toilet or under the vanity. After putting it in on only half the floor I’m sure it will be uneven, how do I go from there? So that the floor is even for the tile?
    Michelle ;)

    Reply
    • Roger

      You can use self-leveling cement (SLC) or thinset. SLC is much easier, but more expensive. You can use thinset in two stages. Install your heating elements then with the notched side of the trowel install thinset over the areas that do not have heating. Let this cure overnight (Yes, just the ridges so you have stripes of thinset on your floor) then the next day go over the entire floor with the flat side of your trowel to give a level finish for tiling. The ridges will raise all the non-heat areas up to the level of the heating element so when you go over the whole thing with a flat trowel it’s all the same level.

      Reply
      • Michelle

        Thank you so much! You’re Awesome!
        You even make it sound fairly simple

        Reply
      • Eric

        Hi Roger,

        I have the same setup as Michelle and I get your day 1 application. But on day 2, after the thinset has dried, how do you get a level finish for tiling? Are you applying another coat of thinset in the grooves left over from the first application?

        Reply
        • Roger

          Hey Eric,

          Yup, on day 2 just go over the grooves with thinset and the flat side of your trowel to flatten out the grooves (fill) then install tile over all of it as normal. Filling the grooves with the flat side of the trowel with get you a level surface.

          Reply
  • Jesse

    Hello Roger,
    I’m in the middle of a bathroom remodel, I currently have 1/4″ hardiebacker over OSB, with unmodified thinset beneath. My plan is to put down floor heat over the top of this with SLC to embed the wire and level the floor. My intent was to tile directly over this, without the benefit of ditra. Am I doomed to failure by not using the ditra ? Should I use a modified or unmodified thinset under the tile ? I am using 16X16 tile. My other question is, the SLC I am using is from Mapei, and requires a Latex primer to be used prior to pouring the SLC. I have about 130-140 sq. ft to pour. The latex primer is quite expensive ($10 a quart), I notice there is also a “latex add mix” available and costs about half the price and appears to be the same stuff. My question is, can I substitute the “Latex add mix” for the Latex primer before putting down the SLC and expect to get good bonding ? Just to be clear I would brush on the “Latex add Mix” (just like the Latex primer) prior to pouring the SLC, not add it to the SLC. Am I way off base here or could this work ? Appreciate your input, thanks

    Reply
    • Roger

      Hey Jesse,

      The two latex products are not the same. You’ll need to use the slc specific stuff. It’s much easier to install the primer, then your heating elements, then the slc. You’ll be fine without the ditra, it’s just an added layer of protection for in-plane movement. You can install right to the slc with modified thinset.

      Reply
  • AP

    Hi –

    First off, I am so happy to have found this site. My SO is a big DIYer (me, not so much, but it’s hard to avoid it completely when we live together!), and it’s hard to find a concise, easy to understand explanation online for a LOT of projects. This has made our bathroom floor project a lot less daunting. BUT… (of course there’s a but, right?)

    Since we’ve already got the floor ripped up, we were thinking to put in a heated floor, right? The previous installation was 3/4″ floorboards, 11mm plywood, tile. The tiles and grout were cracking like crazy, so we’re thinking Ditra is a must this time around. However… is it possible to do this project the right way and not have the difference in height be extreme? (Previous install was level with the hallway.)

    We were going to go with a NuHeat mat for heat, but I think Suntouch would be doable too (especially after reading your guide) – BUT, we’re concerned about the height…

    Thoughts? Are we just going to have to not do heat? Should we just carefully lay the old tiles back down and pretend like we never ripped them up? Burn the house down?

    Reply
    • Roger

      Hey AP,

      Burning the house down may be the easiest option. :D

      Rarely can the height differences be overcome. There are very specific layers and heights of things that need to be under your tile for it to be a proper installation, no way around it. You can go over the 3/4″ with the heat, pour SLC to level it, install ditra and tile, but that’s about as low as you’re gonna get and still have a solid installation.

      Or you can tile the hallway as well. :D

      Reply
  • Pernille

    Hi Roger! Well We’re done! (I posted questions under the Ditra subject earlier this month). I am so happy with the outcome. One thing…how screwed am I by having the floor heat on for one day? The floorheating went into thinset about 10 days ago, Ditra a day later, the tile was installed this past Saturday. We were so excited to turn on the heat to see if it worked that we left it on all day before realizing I should have waited! (you say 3-6 days, Suntouch claimes 30 days!) (I am going to send you some pics of the results of my Delft Blue Bathroom project) Thanks again for your help!

    Reply
    • Roger

      Hey Pernille,

      It should be okay. The reason for waiting is to allow the thinset to cure well before exerting heat which may prematurely dissipate the moisture in the mix (which concrete-based products need to cure). 10 days should be all right, just leave it off for a while.

      Reply
  • Paulo

    This was a great post, but I have a question. I plan on tiling over a basement  slab (50+yrs old hard than snot) with floor heating as well. Would you be concerned with going on directly with the heating wires and tile?
    Thanks

    Reply
    • Roger

      Hey Paulo,

      Nope, no problems with that at all if that’s the way you wanna do it.

      Reply
  • NewRoticSlob

    I’m curious what your method is, since you’re an elf, to ward off the gremlins, sprites, trolls and other nasty faerie creatures that can mess up your efforts to complete a job in an efficient manner?
    This info has been a great find! Whew! We’re just starting a bathroom remodel. We have a really long bathroom. It’s 13×6. It’s a tunnel. We’re taking 8′ and turning it into the bathroom. The rest will be the laundry room with front-loading washer and dryer. I’m running one strip of SunTouch down the walk area in the bathroom area. We’re hoping to intermix 12″ and 6″ ceramic tiles to create a pattern. Do you think this setup is viable if I am running one strip of heating element? I am wondering if the intermixing of sizes could cause any cracking or instability in the overall system? Would it be best if I put Durarock or Hardibacker underneath to ensure stability or stick with one size tile?
    Also, with the front-loader, when it is on spin cycle, it can really shake. Where it is located now (center of a single-story house, over the center beam), I have placed cross-members in-between the pre-fab floor joists. It has helped. However, I am moving them to the other side of the beam. About 6′, as a crow flies. (I hate when crows are buzzing around the house, too!) Do think that is sufficient to protect the tiles from the vibrations? Or is there more I should do? If so, what?
    Thanks for any feedback! I enjoy your writing style. If I wanted to have the dry facts of flooring and it’s inherent issues, I’d buy a book. :) (For example: What is that a picture of!?! Who wrote these stupid instructions? An illiterate moron from Timbuktu!?! I don’t have that tool! Is that my grandpa in the picture!?! or my all-time favorite, AAHHHHH!!!!!!!!!)

    Reply
    • Roger

      Hey NewRotic (If that is your real name :suspect:)

      Your setup sounds fine. I would place the heating element and install ditra over it, then tile. The size of the tile makes no difference whatsoever regarding how stable your floor it. The thing you need to be concerned with is getting 100% coverage and plenty of thinset beneath your tile. As long as your structure will support that machine while it’s dancing around, the tile will also. If you want to absolutely ensure you won’t have any issues with it, wait 28 days before using the machine on the tile. This allows the thinset to get a full cure, after that it won’t go anywhere, even if you try to make it.

      I always give my posts that test. If someone would look at it and ask “who wrote this crap” I’ll usually edit it a bit. :D If I go AAAHHHHH!!!!!! I’ll usually just delete it.

      Reply
      • NewRoticSlob

        It’s my codename. My wife just calls me Slob or some name to that effect. However, if I told you my real name, someone would have to die, most likely me. And we don’t want that, it’s the Christmas season. :guedo:
        Also, curious about vinyl flooring. It’s the existing flooring. We have bamboo flooring that meets the threshold of the room. The bamboo flooring is 5/8″ thick. (Bear with me as I know the probable answer, but would like to hear it from an “expert”.) Should I rip it up to eliminate/lessen the height difference between the 2 flooring materials? 
        Again, thanks! It’s a good thing that it’s not imperative to move the washer and dryer, quickly. ;)I can share my experience with you if you want. I can take pictures and post them as I go. You can point out all the “oops’s” I make and share them on your flawed page. :bonk: I’m figuring it’ll take about a month to do it all. I’m going Lone Ranger. So, yippee-kai-yay!
        Let me know if you’re interested. If not, no biggie.

        Reply
        • Roger

          Yes, you should remove that flooring. Now that someone else has told you what you already knew you can force yourself to do it and blame it on me. :D

          I would love photos of your project as you go along. I’m setting up a page and methods for reader’s photos and projects but I’m doing it in my spare time so it isn’t moving quickly. You can email them to me at Roger@FloorElf.com and I’ll stick ’em in my file.

          Reply
          • NewRoticSlob

            YAY!! Deconstruction! I’ve already started some deconstruction. Trim and cabinets are out.
            I should tell you that the project began as, “Let’s replace the vanity and mirror.” I pulled the vanity and wasn’t paying attention to the valve placement and how that would affect the new cabinet. It’s funny how drawers and valves won’t exist in the same area. Perhaps if I watch enough Star Trek episodes, I could find a solution. Instead of that, “Let’s remodel!”
            I’ll send you the pics I take as soon as I take them. :) (Now, how the hell does the camera work and where the hell is it!?) 

            Reply
  • Lee

    Hi Roger,
    Thanks for your tips. You provide one of the best tiling resources out there! After reading this article, I have a new question for you. I have installed 20″ porcelain tiles in my bathroom over Ditra using unmodified thinset, per Schluter’s instructions. Under the Ditra (installed with modified thinset under) I installed Thermasoft in-floor heating in a SLC bed. Since you noted above that you should wait 3-6 days to use the infloor heating, now I am wondering about the drying time for the thinset and how long I should wait until I grout the installation. Do I need to wait longer than the usual 24-48 hours to ensure the thinset bed has fully cured? Thanks in advance for your advice again!

    Reply
    • Roger

      Hey Lee,

      Nope, no reason to wait. Unmodified thinset does not require air to cure, it’s all done though hydration. It will actually cure underwater – and it will be stronger. (Really) You can grout it 24 hours after you set your tile.

      Reply
  • Lee

    Hi Roger,
    I’ve really enjoyed referring to your site for information for some of my tiling projects, and I like your writing style.
    I have an enquiry/request for confirmation regarding a similar bathroom floor project like this one you have described:
    One difference is that I purchased the Thermasoft in floor heating product many months ago when I was early into my 100 yr. old house reno. So, I plan on going forward with this brand. I am planning to install it on my new double layer of 3/4″ plywood subfloor (which is actually installed over the old 3/4″ plank flooring). So, the base I will be working with is solid and new and relatively flat. I was wondering if there is any significant heat loss in the in floor heating system when installed over plywood vs. a layer of hardibacker, if it is imbedded in SLC or a bed of thinset? I would think being in either of these mortar based materials would maintain the effectiveness of the infloor heating system. My plan is to either use thinset or SLC (probably the easiest choice) and spread same out to keep the entire bathroom floor as flat as possible before installing Ditra on top of the heating cables (imbedded in the SLC or thinset). My final floorcovering is 20″ porcelain tile. So with Schluter’s recommendations, I would be installing the Ditra over the substrate/ heating unit with modified thinset and the finished tile surface on top of the Ditra with unmodified Mapei Kerabond. Sound ok to you?

    Reply
    • Roger

      Hey Lee,

      Your plan sounds just fine. The SLC will be the easier choice installation-wise. The heating elements will lose no more heat when placed over wood as opposed to backerboard. They will be the same.

      Reply
  • Deb

    Okay, so I’ve only just discovered your wonderful instructions AFTER I have installed a heating cable underneath a layer of Ditra. I was not patient, and walked and kneeled on the Ditra right after I layed it, so I could measure and cut tiles. :oops: (In my defence, the Ditra instructions said that you didn’t have to wait for the stuff to dry before tiling – I guess I should take manufacturer’s instructions with a grain of salt!). Now I am left with dents and uneven sections on the floor and am worried that when I lay the tiles they will not be level, and the tiles will crack. :cry:

    Is it possible to even out the dents with a thick layer of mortar in between the Ditra and the tile? It is a small bathroom floor (30 square feet), and I only have the cable in 10 square feet of it (in front of tub and sink), so it is a small area that is uneven with the rest of the floor. I’m really hoping that will work! Unfortunately, it is the area that everybody will be walking on, so it is important that it is level.

    Reply
    • Roger

      Hey Deb,

      Did the instructions state that specifically when installing heating cables? It is correct that when using ditra over a flat substrate (no cables) that it can be tiled immediately. If they stated that with regards to heating elements as well it is incorrect as far as walking on it (and I’ll make a phone call to remedy that). It is true that it can be tiled over immediately – just not walked on. :D That’s difficult to do, though.

      Yes, you can flatten it out with a layer of mortar. Skim over it to get it flat, let that cure, then install your tile. It’ll be fine.

      Reply
      • Deb

        Thanks Roger – I have applied a thick layer of mortar, and then my tiles – they seem pretty solid, so hopefully no cracking. I sure used enough mortar (almost all of the 50lb bag on just 30 sqft), so I hope I never have to take off those tiles!

        The Ditra instructions weren’t wrong, but I got conflicting instructions from the person at Home Depot, so I made a mistake. What I should have done was install the heating cables, then apply a layer of self-levelling modified thinset to even out the floor and let it dry completely, and THEN use a thin layer of unmodified thinset to apply the Ditra (which is what the Ditra instructions say). But that was so many layers of mortar, so much time waiting for it to dry, so much patience required…sigh. OR, of course, I could have followed your fantastic instructions above and not walked/kneeled on the Ditra before the mortar dried – had I found your site before I did it! Lesson learned, for when we renovate the other bathroom next year. :)

        Now I’m going to thoroughly study your tips on making a shower niche and installing tiles in a tub surround, before I actually do the work – thank you so much for taking the time to help all us DIY’ers! If you are ever visiting Ottawa, Canada, I’ll pay you to do some work on our house :).

        Reply
        • Roger

          Hey Deb,

          Mistakes aren’t really negative things if you learn from them – right? :D If you have any questions don’t hesitate to ask.

          Reply
  • Greg

    Great site; great tips! One thing I was not clear on was why HardiBacker was used below Ditra. Assuming a good subfloor exists, why would it be necessary to use both? You’ve stated HardiBacker is not effective to strengthen floors, so what is the benefit of using it, if you’re intending to use Ditra? it appears to be needlessly making floor thicker.

    Reply
    • Roger

      There is no real advantage to using hardi beneath ditra. Provided you have the proper 1 1/4″ subfloor you do not need hardi in the equation at all. The only time I do that is when I have in-floor heating beneath the ditra, I prefer to have the heating element over cement backerboard.

      Reply
  • Bill - St. Louis, MO

    Nov 12, 2011
    Roger,
    Great site! I already have Ditra bonded to 3/4″ plywood subfloor with Versabond in a 5 x 10’ bathroom. Will it really make a huge difference if I put the Suntouch heating element OVER the Ditra since it is already there? And, no I didn’t plan on in floor heating until AFTER the Ditra. (Rrrr).
    I am planning to use Flexbond to bond the heating element to the Ditra and possibly a layer over the entire Ditra area to keep the floor even from having a slight bump were the heating mat will be. It’s a 30″ x 6′ mat. I will then let the Flexbond dry and then use unmodified thinset mortar to install the 12 x 12 porcelain tiles. I know it would be preferred under but I can’t see it making that big of a difference on a small area. Your .02 cents would be welcome. ~ Bill – St. Louis, Missouri USA

    Reply
    • Roger

      Hi Bill,

      You will lose some of the lateral dissipation properties of the ditra since the tile is not directly on the membrane, but over a small floor it’s not really enough to make too much of a difference. You should be just fine. And I would use the modified to install the porcelain.

      Reply
  • mountain eagle

    When heating a Kerdi shower what is your preferred order of build and method of getting through/over/under the curb transition?

    Reply
    • Roger

      Hey Mountain,

      I’ll usually run the wire between the first and second 2×4 I use for the curb. I’ll install the first 2×4 then use a chisel to cut notches for the wire up and over the top of the board so it lies flush with the top of the 2×4. When I pour my pans I’ll let it cure for a day then go in and carve grooves into the top of it in a spiral the depth of the wire. Then I’ll run the wire over that first 2×4, run it into the grooves and skim coat the wire with thinset to hold it in place. Once it cures you can install your second (and third if needed) 2×4, backer and install the kerdi as normal.

      Or the short answer – use a chisel. :D

      Reply
  • Porky

    Hi Roger:
    I was planning on putting a Suntouch electric mat on my basement slab. The slab is in good condition. I have some Mapei Aquadefense ( waterproofing & crack isolation membrane) left over, that I was going to apply to the floor. I was wondering if it was ok to do that or if the Mapei would get gooy or something with the heat setting on top of it. The Mapei company didn’t think there would be a problem, but I wanted to double check with you or somone else that may have done it. Thanks

    Reply
    • Roger

      Hey Porky,

      I’ve never done it but I don’t see a problem with it. Once cured it would take a very high heat to cause the Mapei to ‘melt’, so to speak. It should be just fine.

      Reply