Master Spa Bathroom Part II – Floor

In part one of this master bath project, I gave an overview of the project. Now I’m going to dig a bit deeper.

The entire idea and inspiration for the master bathroom was to make it a real retreat, so a lot of prework went into the room before we did any of the finishes.

The two things that make this floor special are the linear shower drain and the heated tile. I  am a big fan of Schluter Systems for their shower waterproofing membranes, pre-sloped shower floors, tile edging and floor heating cables. I’ve been using their products since we remodeled our house in Knoxville and I’ve had great success. The products are not cheap, but they save me a lot of time and that makes the bit of additional cost worth it for me. This floor uses the Kerdi Shower system, Kerdi-Line drain and Ditra-Heat mat which acts as a substrate for the heating cable and tile. I’ll cover the basics of my installation here, but if you want more information, Schulter has a YouTube channel where you can learn about all of the product lines and watch step-by-step instructions. 

The first thing was to prep the battlefield. That meant getting the shower waterproofed. Even though the Kerdi membrane can be applied over drywall, for some reason I always install HardieBacker first. I guess I just have seen too many rotten showers installed with tile over drywall. Call me old fashioned. 


The shower bench made a nice work surface for tools and materials.

I had to do a shower pan flood test to satisfy the building inspector. But since this is a curbless walk-in shower, I had to make a temporary dam for the membrane to get the required 2-inches of water over the drain. 


The temporary dam keeps the water in to get through the flood test, then will be bonded to the heating mat to create a waterproof floor assembly.

When you do a flood test, the water has to hold a level line for 24 hours. I read a trick somewhere about using a stack of quarters to mark the water level, which is a more precise reference compared to a fat pencil or marker line on the wall. 


Here you can see the water is level with the top of the stack of coins.

Once that was done, I could get working on the floor layout. Typically, I start in the center of a room and then decide if I am going to start with a full tile or a half tile, depending on which looks better. But in this case, I chose to honor the shower walls, since it is the focal point in the room, then based my layout from there. It ended up working out well, meaning there are no ugly slivers of tile at any of the walls or doorways. 



I had this transition at the shower entrance to deal with, but due to careful planning, it looked great once everything was finished.

Once the layout was complete, I got started on the heated floor. I didn’t really document the process of installing the heated floor in the posts about the main bathroom. So I’m going to go into the weeds a bit more here. There are multiple systems out there that all use electrical resistance for the heat source. I’ve personally used the mat systems from WarmlyYours and they work well, but in this house I went with something new. Schleuter Ditra-Heat. Instead of a mat, this system uses a single cable that gets laid out in a totally custom pattern. With this system, the installer can direct heat to the areas where it’s most desired, for instance, in front of the vanity or at the shower entrance. The system can even be run into the shower floor itself, however, extra waterproofing steps are required. In a cold climate, I would probably consider it, but here in SoCal, it was not warranted. 


The wiring starts with a 4×4 metal box on the wall where you want the thermostat. A dedicated circuit from the panel enters here and the wires to the floor exit.

I made a minor mistake when I roughed in the wiring, in that I didn’t run two lengths of flexible conduit from the box to the floor. One is needed for the current carrying wires and a second one for the two temperature sensor wires. They can’t run together or the sensor wires might give false readings. Luckily, I was able to fish the sensor wire through the wall cavity without having to cut any new holes in the drywall. If the wall hadn’t been insulated with soundproofing insulation, I could have just pulled a new length of conduit, but Roxul is way too stiff to pull something that large through. 


On the left, the wire that actually makes the heat. On the right, the two temp sensors. Only one is connected to the thermostat, the other is a backup. The baseboard — or tile in my case — will hide these connections and holes.


The connection between the voltage wire and the resistance wire is bulky, so I have found that removing a bit of the mat allows room for the tile to lay flat.


Now begins laying the cable into the studded mat. I lay out the thermostat wires first and then run the heating cable around them.


You just press the wire into the gaps between the studs in the mat with a 3 stud spacing between wires.


The two thermostat wires are as close to the middle of the room as I could get them, and evenly spaced between two heating cables.

I avoid running the cables under cabinets to there is no issue with overheating, and because it’s wasted anywhere you won’t step on the floor. Floor warming systems are for comfort, not to heat the room. Also, I avoid running wires close to the toilet because even though it’s not likely, the heat could cause the wax seal to deform and possibly fail. Once the cable was in I got to laying the tile. 


The transition between the floor and shower features a single tile cut in half and “folded” over the entrance for a clean look with perfect pattern match.


The shower floor, except for the tiled drain cover, which gets installed after the wall tile.

I was able to set up my wet saw in the bathroom, so that saved a lot of trips back and forth, which also created less mess in the house. Though there was water everywhere from the spray. Fortunately, I could just squeegee it down the drain. 


The tiled drain cover. All you see is a tiny slot in between the tiles for the water to run.

If you’re wondering about cleaning, the system includes a stainless steel hook to lift the drain cover and clean out the tray. 

OK, I think I’ve rambled enough. Next time, I get into the shower tile job. 

2 responses to “Master Spa Bathroom Part II – Floor

  1. Pingback: Creating The Master “Spa” Bathroom Part 1 – Overview |·

  2. Pingback: Master Spa Bathroom Part 4 – The Shower |·

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