How thick do yo pour SLC over radiant heat cables?

Help! I contacted the mfr of "LevelQuik" SLC to ask some questions. It turns out that they recommend that the SLC be poured 1/2" ABOVE the top of the heat cables to prevent the SLC from cracking due to the expansion & contraction. They also said that lath is not required in this application. This is too thick for my application. They actually recommended that I use PM Thinset instead of SLC.

I would like to know what thickness people here have used over radiant heat cables (vs. mats) and if there is a preferred SLC. I really want to just cover the cables (approx. 3/16" - 1/4").

I would also be interested to know if most folks install an isolation membrane between the cables and the tile.

Is Bud out there?

Thanks,
Joe

I have never used an isolation membrane. I always pour around 3/8" to cover both cable system and mat system. I mostly use CBP Level Quick and prefer it over the others. I think it is a great product.

I personally think 1/2" (over and above) what it takes to cover the cables is an asinine waist of money. You could expect them to tell you that tho 'cause they're selling the stuff. "Good job Custom Techie, now here's a biscuit, go lay down.

Use a flex thinset, the minimal cracking that may occur won't matter. Never had one show any cracking but do get occasional crazing.

Anyone that recommends you use thinset preferable to an SLC has never in his life installed a floor-heat system under tile and has no first-hand experience. That fool has no idea what he's talking about, the guy must be a Muppet reading from a book.

[Edited by Bud Cline on Thu, Jul 17, 2008 at 12:37 am CST]

Bud, I wont argue with ya, but your not warranting it either. (the TCNA calls for it to be ENCAPSULATED)

Eric I'm not sure I understand your comment.

In all honesty I no longer warrantee much. My competition doesn't stay around long enough to be found when their work goes to hell. If I have to compete with their low-balling then nothing includes a warranty anymore. Covering the heat-install with SLC IS encapsulating it.

I have never warranteed any heat installations. I test them coming out of the box and again after they are covered with SLC. That's were my responsibilty ends.

Not only that, I now add the cost of setting materials to all my jobs after quoting the labor-to-install-tile price.

There are no real warrantees on anything anymore and I have never been asked to make-good on a problem-installation in over thirty years anyway.

Bud - Thanks for the reply! From what I've read here, you have done a lot of these. Your answer is what I expected (although I was hoping to hear 1/4" would be fine.). I can live with 3/8".

I've got to believe that if the SLC does crack due to thermal changes, the cracks will be very limited in how much they can move except right at the edge. That is, unless the material just crumbles which I can't imagine. I will be laying porcelain over the top and the stuff seems pretty indestructable. As long as any cracks don't damage the cables, I'll be happy. I'm actually wondering if the SLC does crack, maybe the thicker layer might be worst in allowing more movement in the SLC across the crack. The thinner SLC layer might move less since it is supported better by the backer board under and the thinset & tile on top.

I'm just a rookie but I believe my PM thinset qualifies for a "flex thinset". Correct?

I was under the impression that if I followed your advice it would be covered by your standard warrantee.

Thank you for taking the time to help!
Joe

I agree with what you said, but was pointing out that IF there is a problem, the installation is not following the MFG. Directions and not to call them.
Our opinions are just that, opinions, AND MAY VOID THE WARRANTY OF THE MFG.

The manufacturer's written directions state that the SLC can be used from a feather edge up to 2-inches thick. There is nothing that would alert your average (or above average) DIYer or Pro that there would be any issue pouring the SLC to 1/4-inch thickness would be a problem. A reasonable person would have to assume that the tested properties would apply to the thickness range recommended by the mfr. That is why I am soliciting input on people's actual experience with thinner cross-sections.

-J