The Hardi board was great because all of the areas were pre-marked for driving the screws in. After the boards were cemented and screwed down, I secured the seams in between the boards with more thinset cement (this was a non-modified type) and joint seam tape for sub flooring. This made the floor rock solid. It will take a California earthquake to crack this floor. After my sub floor was secure, I laid out the mat according to the custom installation plan provided by WarmlyYours engineering staff. I ran into one problem with the plan, but that was because I forgot to mention that there was a floor vent in the "water closet" of the bathroom.No worries because the nice thing about the WarmlyYours floor heating system design is that I was able to cut and turn the mat to fit around the vent while still using up the entire length. I definitely appreciated the flexibility of being able to cut-&-turn the WarmlyYours heating mat to fit the actual jobsite layout (note to myself to take better measurements next time!). To secure the heating mat to the sub floor, I decided to use a hot glue gun since my staples were just bending and not piercing the Hardi Backer board. I used a lot of glue every few inches to make sure the mat would hold in place. The glue dried quickly so by the time I finished gluing the surface was ready for my first coat of thinset cement. I tested the ohms on my floor heating mat before I laid it down on the floor, and again after my cuts and turns, and then one last time after I applied my layer of thinset. Ohms were almost spot on to what the white label said they should be on the mat. Using the flat side of my trowel I mixed up a really watered down modified thinset. I could have used self leveling cement; however, I had bought too much thinset mix already.
The thinset laid down pretty flat, but some of my hot glue dots were too high. So if you ever glue down a mat don't get too crazy with the glue. It doesn't take much to hold down the WarmlyYours floor heating mat as it already lays out pretty flat to start. Some areas of the bathroom were not covered by floor heat (under the sink vanity) so I had to level out those areas to be even with the rest of the room. I could have used a large float to make it level, however on a construction site there are plenty of 2 x 4's, so I just used one of those. My goal was to cover the floor heating mat just enough so that I wouldn't have to be as careful with the trowel when I laid the thinset down for the tiles. So my initial layer of thinset was about the thickness of the mat and I could still see the shape of the mesh after the thinset dried.
The electrical line was installed by a licensed electrician (my uncle). I wired the thermostat up myself after the bathroom floor was in. I've wired basic light switches and outlets before so wiring the thermostat was really no different. I reduced the amount of cold lead wire coming out of the box so that it wouldn't be all coiled up in there. By the way, this does NOT affect the heating ability of the mat. It is summer and the house is still under construction so my brother has yet to fully experience the warmth of the floor. We did turn it on for about 30 min to make sure that you could feel the bathroom tiles warm up. Generally it will take 30-45 min before you feel a noticeable difference by touching your hand to the floor. We felt an unheated tile in the closet to compare and wow what a difference it makes – my brother is now actually looking forward to the winter season to really make the most of his new heated bathroom floor!