Few things bring a project to a screeching halt like that of "new process" intimidation. But that's just the thing about DIY, you're constantly learning and trying out new processes, so this unfortunately comes with the territory.

The paranoia over royally screwing up a DIY project can be almost paralyzing. This is especially true when you obsess over the results of your efforts the way we tend to obsess.

In our last post we gave you a rundown of our WarmlyYours radiant heat mat install, but we stopped short of the final step of pouring the self leveling cement, or SLC.

This layer of liquid stone encases the mesh and heating wire like Jabba the Hutt encased Han Solo in carbonite. 

But there's no Princess Leia disguised as a bounty hunter there to save us if it all goes wrong. (Though I do sort of see a Wookie in Lulu, and Ewok in Mel.)

To say I was hesitant to move onto this very permanent step in the process with no real experience using the material or methods is a significant understatement.

The simple fact is, regardless of previous experience, I hate any step of a project that represents a major element where I have little room for correction if we begin to run off of the rails. Whether I'm sealing up a wall, closing up the floor, or filling in a ceiling, there's a vague to severe panic that sets in when I've reached a point of no return moment in a project and have that "uh-oh, hope I did it right because there's no turning back now" feeling.

This is an odd sensation, as I know this step in a project means major strides towards finishing said project, but it doesn't matter in the moment. I so fear making a mistake we can't recover from that I begin procrastinating on actually doing the work. And that, my blog friends, is why we have a bathroom project that is still going on years after it was begun.

Okay, enough rambling about my fears, paranoias, and crippling obsessive nature when it comes to working with many things, including SLC. On with the show!

The Preparation

After completing the radiant mat install two nights before, Wendy and I decided to set aside a few hours to prepare the floor and pour the SLC. We had already purchased the three bags of 55 pound SLC mix several months before and were sick and tired of tripping all over them every time we walked into the basement.

If we're being honest here, the hope that we would rid our basement of the hulking 165 pound obstacle may have been the only reason I was able to pull myself from my cave of paranoia to actually work on the project.

But before we could launch ourselves into the unknown of SLC mixing and pouring, we had to prime the floor with some of the SLC bonding agent.

This milky white sticky primer substance had to be diluted with one part water to one part primer, then rolled and brushed onto the entire surface.

Just like paint primer, this cement primer gives the SLC something to really grab bond to. But there's one major caveat when using this primer. You can't just paint it on one day, then pour your SLC the next. Nope, you have to prime, let it dry, then pour your SLC within 2 hours.

When I finished up the primer it kicked off the mental countdown. There was no turning back. We had to pull the trigger. We had to mix up our SLC, begin the pour, and hope we didn't make any horrible mistakes.

As I read various guides on the best way to pour SLC, the one item I kept seeing over and over again was the advice to "make sure you do this with at least one helper." Heeding this advice, Wendy and I took to the basement as a two person team to mix up the first batch of SLC.

Wendy was on drill duty and I was on powder patrol. We prepared the 6.5 liters of water in a clean bucket and I began pouring the heavy gray powder into the waiting bucket while Wendy gently mixed.

Once the whole bag was in the bucket, and all of the water and powder had become one, the resulting slurry reminded me of the consistency of pancake batter.

Now that the easy part was done, we had to haul the now 70 pounds plus mixture of cement, water, and fear up two flights of stairs and into our waiting bathroom.

Wendy and I do our fair share of arguing when it comes to the house. But there's something to be said for the couple that can put aside any bickering when one of you is carrying something very heavy while the other runs ahead and makes sure the path is clear of obstacles.

Our home can be a veritable minefield of dog toys and carrot slices often littering the primary traffic patterns. What can I say? Lulu likes her toys like she likes her dinner, half eaten and left all over the house.

Once I reached the bathroom and we were ready for the first pour, I felt like a grossly underdeveloped version of Strongman Magnus Ver Magnuson, arms quivering from hauling my bucket of mud up the stairs, trip one of three complete.

As I somehow mustered the inner strength to wrestle the bucket into the air and begin pouring without dumping the whole thing all over the room, I took mental stock of our score. Team OTH 1, SLC 0.

The Pour

The SLC, with it's gooey pancake batter-like consistency, did exactly what its name suggests. It slowly spread itself out across the floor in the channel between the HardiBacker, leaving a level blob from one end of the pour to the other.

I filled in the areas in the corners with small and more deliberate pours of the SLC to top off the gaps...

...then scurried back down to the basement to begin mixing the next bag.

Each successive bag went a little quicker with the mixing, and a little slower with the carrying up the stairs. By the time we had reached the third bag my back was aching and I was feeling about as old as our house.

I had to get creative with the pours once most of the room had been filled, straddling the three foot wide channel of gray goo as I poured the final bits into the last remaining voids.

The Result

Overall, the whole process went pretty smoothly, except for one major issue. It seems that three bags of SLC was just a little shy of "enough" for our project. Once all was said and done we were probably about 95% full across the whole room with a few low spots.

Since SLC is a quick setting product, once it's poured, it's poured, and it's not easy to just add more on later. So we opted to call it complete and move onto using thinset to complete the install. Wendy and I both paused for a minute to look at our completed work and feel great about what we had just done.

My crushing fear of catastrophic failure was largely unfounded, and we were able to work together as a team to crush this aspect of our massive todo list.

Well, that is until we both looked down and saw this.

One very important aspect of pouring SLC has to do with properly damming the perimeter to ensure the pancake batter stays in the intended pan. I had been diligent in doing my prep and caulked gaps in the plywood, built up corners, and ensured there was no area where the SLC might try to make a break for it.

As it turns out, I must have missed one area, and it was slowly leaking out of the corner of the room through a gap in the plywood subfloor. WHOMP WHOMP!

This wasn't the end of the world, but it was disappointing to know I had overlooked a somewhat critical aspect of the project.

After an overnight dry period we awoke to a solid slab of dark gray carbonite concrete encasing our heating wire. We hadn't made any major mistakes that couldn't be corrected and we have a good base of experience to build on for the next time we use SLC.

You can see the transition between two of the pours in the middle of the room. That shows me we weren't working quite fast enough. Also, it's hard to see, but there are two dark spots near the bottom right of the photo. Those are my sweat droplets. That shows me that we were working plenty fast given the stair climb.

There were a few areas where I troweled the SLC into shape in an attempt to have a more consistent surface, but in retrospect, I should have just left it alone. The trowelling actually created minor humps and bumps in the surface.

In the end, working with SLC was not difficult at all. In fact, it was sort of nice to just pour and go. Wendy even said, "Boy, that went a lot faster than I thought it was going to." But that's probably simply because it took less than 40 times my initial time estimate.

Comments 11


6/13/2014 at 1:42 PM

Yeah, SLC can throw curve balls at you.

The "self-leveling" nomenclature is also deceptive. It's self-leveling so long as the subfloor is relatively even. I used it last month to seal an exterior concrete deck that had developed settling cracks which were creating leaks in the garage underneath. After chiseling out the cracks to make a channel I bought hydraulic cement to fill those cracks flush with the deck before using the SLC.

But it didn't take long to determine that I hadn't bought nearly enough of the hydraulic caulk. So I filled the cracks a half-inch shy of the face of the deck and figured that the SLC top coat could take care of the last half inch. Wrong.

As soon as the SLC started to set up I saw to my horror that it simply sank into those channels leaving little concrete dry river beds all over the deck. Apparently self-leveling also means "terrain following". Ugh.

I had to chisel again and then fill the channels with standard concrete. It didn't matter much since I was going to paint the deck but, man, what a PITA.


Ugh! What a pain. I did see that a bit with our pour, but since we didn't have enough to really get to the level point we weren't in quite the same boat with you. I guess, in a way, I'm lucky I didn't buy enough to do what I thought I was going to do.

Sheri K
6/13/2014 at 1:48 PM

Great job! Thanks for sharing. Can't wait to hear how it "feels" once it's up and running in the finished space.


You and me both! Alt smile

Franki Parde
6/13/2014 at 3:44 PM

Just started "following you"....we are DIY folks and felt every one of your concerns!! Carry on!! franki


Thanks, Franki! Hope to see you around these parts more. I think you'll enjoy some of our projects.

6/13/2014 at 5:08 PM

TWO big projects in one week AND in the master bath at that--good work!! Keep going and keep posting the progress, I am rooting for you. And Mel is def at least quarter Ewok.


I know! I think I need to take a month off now. I'm spent Alt smile

Mel is probably quarter Ewok on his mother's side. Good call.

7/16/2016 at 10:09 AM

I know this is an old post, but here's a question in case you see it: was your bathroom floor generally level to begin with?

We're DIYing a heating mat under tile, and since we have an old house, our bathroom floor is out of level by about 3/4". We'd love to use self-leveling cement, but it's not going to correct that much variance. Did you have to level out your floor first?

Love your blog?

7/16/2016 at 4:55 PM

Woops! I meant "love your blog!" (no question there, for sure) Alt smile

3/21/2017 at 1:03 AM

How has the heated floor turned out? Do you love it?

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