Heating, Decoupling, & Waterproofing Tile Floors

The main bathroom is moving along. We have the tub in, the last wall built, and the drywall up so it is time to work on the floors. The first thing we needed to do was install the electric in-floor heating mats. Yup that’s right we decided to add these two both bathrooms not just the master bathroom like we originally planned. From what we’ve heard they are the best thing for bathrooms since sliced bread. It seems like everyone says they are the best bathroom decision they have made and love the way they feel. When my co-workers heard I was remodeling our bathrooms this was the first thing that came up from multiple people…”I was at a friend’s house and he had these heating tile floors so I tried them out and they were fabulous!” …”We’re just finishing our basement bathroom and we’re using this new state of the art thing that heats the floors. Have you heard of it?”…”My dream bathroom, you know in my dream house, has heated floors.” In fact we had a hard time finding anyone who had heated floors and didn’t like them.

We knew we wanted some extra heat in the bathrooms because although we love our geothermal system the lower temperature heat isn’t the most comfortable when you’re getting out of the shower and the vent is right next to you. My parent’s bathrooms have those ugly red warming lamps which were effective but they always made me feel like a burger at a fast food restaurant so those were out. Electric baseboards could work but they are the prettiest thing. A towel warmer is another option but those things are pricey and don’t fit the more traditional look we’re going for. Electric in-floor heat seemed to be our best option. We went with the mat style vs. the wire you run yourself because it is thinner and easier to install. We opted for SunTouch’s TapeMat system and Nuheat’s Solo Thermostat.

The mat was a little long for our room so we cut the end and flipped it to cover a little of the nook the toilet is in. Don’t worry we were far from the clearance that is needed around the wax ring of the toilet. (This is the big reason we went with SunTouch’s floor mats because you can cut them to work. Though we’ve heard nothing but good things about Nuheat they don’t let you cut their mats and they cost more.) It would have fit fine that way but we realized the wires running to the thermostat were facing the wrong way. We considered flipping the mat but then we would have to cut another section away for the toilet area so that that would be on the right side. Instead we decided to keep as much mat on the main part of the floor and just cut the end with the wire so that it faced the right direction. That way the channel we had to cut for the electrical connection would be as short as possible. The temperature probe was run right next to it and a small square chiseled out of the floor for the end of the probe. We attached the mat to the floor with staples over the non-wire sections of the mat. We found it difficult to get it absolutely flat without a lot of staples. Looking back we should have tried unrolling instead of leaving it in the box.

I had read of people installing more than one probe in case one breaks (it’s buried under the tile so you’ll never be able to get down there to add a new one). Other people including the electric mat company said it wasn’t necessary. But the way I see it it’s a $35 insurance policy. We ran both temperature probes right next to each other and used the same chiseled out area. One will be connected to the thermostat on the wall and the other will just sit in the back of the box in case we ever need to use it. The single gang box on the left is where the thermostat is going.

A metal plate covers the notches we made in the sill and keeps us from running a drywall screw through the wires. The poof of white behind it is the spray foam we used to seal the old holes in the sill plate from the ceiling below.

Once that was all hooked up we could put up the last piece of drywall.


Then it was time to cover the wires with thinset. There are a couple ways you can do this. (1) tile or apply your Ditra right over the mat, (2) pour on self leveling concrete, or (3) skim coat the mat with thinset. (1) is what most of the pros do. They have plastic tile trowels or are skilled enough with metal trowels to nick the wire. But being first time tilers we chose to do everything in smaller easier to handle steps. After reading all of the prep work and disasters people have had with (2) we opted against that. Caulking every seam and crack in the floor and priming the wood didn’t sound like fun. So we thought we’d try option (3). So we mixed up some latex-modified thinset to spread on top.

Everything was going good until the drill we had started smoking. I guess thinset was just too much for it to handle. Luckily, Flannel Man had just bought a heavier duty drill but it was still sitting in the box because I didn’t think we needed it. Guess I was wrong.

At this point we double checked our resistance from the mat compared to what it was before and checked on our LoudMouth monitor to make sure nothing had been damaged.

We carefully spread the thinset out with a flat edged trowel making sure not to hit the wires.

When we got toward the end we ran out of thinset and had to break into our second bag of thinset which was white for the glass accent tile we’re using. We completely underestimated how much thinset we would need even though we had tried to calculate it out. The gray section was a full 50 lb bag.

It wasn’t looking perfectly smooth but it was our first time ever using thinset. We had mixed it a little runny hoping that would help it level out.

The next day this is what we had:

A crappy totally uneven surface! The thinset had shrunk as it dried or soaked into the plywood subfloor or something. You could clearly see the plastic mesh and wires of the mat in some places. Other places had trowel marks and low spots. It was a mess. At this point we wish we had tried the self leveling concrete. More prep work and a rushed process but we could have predicted what we were going to get. At this point we wish we had tried the self leveling concrete. More prep work and a rushed process but we could have predicted what we were going to get. We didn’t really have many options left and after discussing what to do with a family friend who was a pro tiler we decided to put a second skim coat over the top. This time getting it as smooth as we possibly could. We used up the rest of the white bag we had on hand for the second coat.


It wasn’t perfect but it was much better than the first coat. So we went ahead and cut the Ditra for the room. Schluter’s Ditra system is a decoupling membrane for tile that allows for some movement in the structure below without cracking the tile or grout above. No matter what we do there will always be some movement from the structure below because it’s wood. Wood expands, contracts, and flexes. Back in the roman era tile was set on a thick layer of mortar, a fine layer of compacted sand, and another thick layer of mortar. This allowed for the two layers to move independent of one another. Ditra does the same thing but with a lot less thickness added to your floor.

The majority of the floor we were able to cover with two long pieces of Ditra and the toilet nook had it’s own piece. Because we’re tiling under the vanities and into the linen closet there were some trickier cuts.

To adhere the Ditra to the floor we mixed up unmodified thinset because we were sandwiching it between a thinset layer and the Ditra neither of which are breathable. Unmodified thinset doesn’t need air to cure like modified thinset does. And bonus unmodified cost a fraction of the price modified does! I’ll go through the types of thinset needed for each layer in a follow up post.

We spread the thinset down with a 5/16″ x 5/16″ V-notched trowel.

Then we laid down the Ditra and smoothed it out with a 2×4. Pulling up corners as we went to double check that all of the pockets were being filled. We started from the front because getting the Ditra over the piping in the floor was the hardest to line up.


Once all of the Ditra was down we used some Kerdi strips to waterproof the floor. Ditra itself is waterproof so by paying a few bucks more we had a waterproof floor. Being on the second floor over a drywalled ceiling and wood structure this was appealing incase water spills over the lip of the tub, a toilet overflows, or a pipe leaks. My parents had this happen in their powder room and it was raining in the basement below. The worst area was under the trim where there was an air gap between the tile and the wall. At the same point we do have a floor register so it’s not like the room would hold 3″ of water. It is just an extra protection to keep small spills from leaking to the drywalled ceiling below.

We used thinset to adhere the Kerdi strips to the Ditra seams and around the perimeter of the room. I had read you needed different widths of Kerdi strips for each area but after calling Schluter they said the standard 5″ strips available at Home Depot were fine.

The next day the unmodified thinset had started to dry but wasn’t completely dry yet.


The next day the unmodified thinset had started to dry but wasn’t completely dry yet.

Next up tiling the floor!


11 Responses to “Heating, Decoupling, & Waterproofing Tile Floors”

  1. 1 mike @HA February 6, 2012 at 1:41 pm

    Cool! We’re planning on adding the same stuff to our basement and main floor bathroom (next two projects after the basement is finished). It’s good to see what all is involved!

  2. 2 Kim@NewlyWoodwards February 7, 2012 at 9:38 am

    Very cool! I’m insanely jealous of your in-floor heating. I would love this in our bathroom and didn’t even think to ask for it when we were renovating. Oh well, I’ll live vicariously through you.

  3. 3 Roeshel February 7, 2012 at 12:00 pm

    I love watching the progress and all of the tips. We’ll be doing this in the future and it’s so helpful watching your journey!

  4. 4 Carrie @ Hazardous Design February 7, 2012 at 4:48 pm

    I don’t think people realize how much prep work goes into tiling a floor. Any home improvement show makes it look so easy!

  5. 5 Debbie Leonard February 8, 2012 at 12:41 am

    We renovated our master bath and put a heated floor in also…we love it. You will be so happy you did it!

  6. 6 chris miller February 8, 2012 at 10:04 pm

    looks good, very thorough job. noble company is an alternative to herr schluter. from the pros i’ve spoken with noble company has better customer service, they allow you to use modified thinset, and is a more compatible product. it’s also made in the usa, which is nice.
    we went with kerdi on our last project, though, and felt it worked well for us. i think we’ll give noble a try next time around.
    looks like you have plenty more kerdi band in your future with those niches. have fun!

    • 7 Robin February 8, 2012 at 10:22 pm

      Good to know thanks Chris! Yeah it’s very confusing. Schulter and all of the thinset companies say to use modified thinset with the Ditra but also say they won’t warranty anything because that is Ditra’s job. Ditra says use un-modified and since they carry the warranty if the tiles crack we went with that suggestion. I’ve read a lot of people who have used modified with Ditra and no problems though. So who knows!

  7. 8 Carolyn@Sweet Chaos February 10, 2012 at 1:13 pm

    Gosh… I’m tired just from reading about all this work! You guys are troopers! And, you’ll love the heated floor. Couldn’t find your e-mail, but wanted to answer you question about our bedding. It is an ivory matelasse duvet cover that I got eons ago. I’m sure you could find something similar in any bedding place though. Have a great weekend!

  8. 9 Robin February 10, 2012 at 1:59 pm

    Thanks for stopping by Carolyn! Yes a matelasse duvet cover is exactly what I’m looking for. So far the ones I like the best are quilts not duvet covers but I’ll keep looking. Thanks.

  9. 10 Bathroom Waterproofing Adelaide May 24, 2012 at 5:18 am

    Amazing, wonderful way to renovate bathroom.

  1. 1 And….We Have Tile! « 3 acres & 3000 square feet Trackback on February 21, 2012 at 7:06 am

Leave a Reply

Please log in using one of these methods to post your comment:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

This is the story of two twenty something newlyweds who are learning to adjust to life in their first house, a 1973 fixer-upper.
DIY Savings

%d bloggers like this: