Monday, March 21, 2011

In-floor heating cable install

This past weekend I worked on installing the electric heating cable in the bathroom floor. I started off by putting down CBU (Cementous Backer Unit) in all areas of the floor that will not be heated. There is no reason to put heating cable underneath the tub, toilet or right up next to the walls. The CBU is attached to the floor with thinset and roofing nails.

The next step was to prime the floor so the SLC (Self Leveling Cement) will adhere to it well (more on this later). After priming (it dries clear), it was time to install the metal strapping that holds the heating cables in place, also the thermostat pick up (white wire) and the actual heating cable. It is the the copper colored cable, but it is insulated black where it goes into the wall.

After all the strapping was down, it was a matter of weaving the heating cable back and forth across the room and hooking it into the tabs on the strapping. I will mention that before installing the cable you need to check the electrical resistance of it, to make sure it has not been damaged. The cable is comprised of a resistive electrical wire, with a copper shielded casing. It can be damaged, punctured or cut if you aren't careful, and any damage would cause it to short out and not work. Now is the time to return a damaged cable!

Because I was installing the heating cable and SLC directly over plywood, I had to install a reinforcing membrane over everything. It is basically a plastic mesh that I had to staple down literally every 2", I used about 2000 staples to get all the bumps out of the mesh. Luckily I was using an air stapler. I also had to be extremely careful to not hit the cable with a staple, that would have been very bad! Once all the mesh was installed, I needed to prime the mesh, cables and strapping. I used a garden weed sprayer and basically just sprayed everything down.

After everything was dry again, it was now time for the final step. I was really nervous about this step because of some of the horror stories I've read. I had never worked with SLC before, and there was a hundred dollars worth of material on the line if it didn't turn out right. Thats not including the heating cables and mesh which probably couldn't be saved if they were coverd in chunks of hardened cement. The SLC is pretty touchy, you have to mix a pretty exact amount of water with each bag, mix it for a designated amount of time, and be careful not to get air bubbles in the mix. The other catch is it lists it as a 10 minute working time. After checking the resistance on the cable one last time, before the point of no return, it was time to get started. I had 10 minutes to get all three bags mixed, poured and spread out onto the floor. My dad ran the mixing paddle while I poured and spread the SLC. We got it all down really fast and the only problem we had was a couple lumps where it didn't get mixed up good. Fortunately I was able to pick those little chunks out with ease. As far as the spreading process, I just had to push the SLC around the room and into the corners, after that it just had to live up to its name, and self level. After this all dries, the final step will be to tile the floor.
This pic was taken before we mixed up the last batch.

On a side note. Earlier during the day when I was stapling down the plastic mesh, I heard a super loud crashing noise from downstairs. The first thing I could think of was the kids had knocked the TV off the wall or something. I ran downstairs to a cloud of dust and giant chunks of plaster all over the floor. Luckily nobody was hurt. The dogs had actually been sleeping in the room when it happened.

Turns out the air compressor, running upstairs for a couple hours, had vibrated the plaster off the ceiling below it. When we got it all cleaned up, it filled a large trash barrel and weighed at least 100 pounds. Looks like I have to add another project to the list on a schedule sooner than I anticipated!



You are a total rockstar from Mars!! Looks like you know what you are doing. Nice job and sorry I couldn't help.

mom said...

what a mess it was!~

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