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Old 01-16-2018, 07:45 PM   #1
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Location: Minneapolis, MN
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Erin's Bathroom-Cork, heat mat epoxy and green marble doable?

Short and sweet version: how to manage cork underlayment, heat mat, epoxy and green marble floor tile.

Hello all!

I found this site a while ago and have been lurking and learning quite a bit. I'm now getting to the point where I can't find answers in previous posts. I'm guessing I'll be coming up with questions along the way. I'll put the questions in BOLD so that they are easy to find after all the background info.

I have a little house in Minneapolis that was built in 1914 and majorly renovated in about 1950. I am in the process of redoing the whole basement, including the bathroom. The bathroom that was there was a raised floor wet room with a toilet and a shower but no sink, the knobs for the shower were above the back of the toilet, with a groovy plastic panel between the toilet and the shower. Everything was taken out down to studs and block wall foundation, the slab was torn up in that area and the plumbing (supply and drainage) was redone by a plumber, so starting from scratch.

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The shower pan is a mud pan done by a professional. The walls are cement board. Kerdi membrane over walls and pan.

I did self leveling on the rest of the floor and put 6mm cork sheet over that (used adhesive troweled on the floor to stick it down good.). I did that as a thermal break so that my Suntouch heat mats aren't warming my entire foundation/neighborhood. I've finished securing the heat mats down and will wire them tomorrow, but in reading the instructions I came across my problem.

1. heat mats, green marble, thinset and epoxy?
The tile that I was planning on using on the floor of the non-shower part of the bathroom is a 12" x 12" pale green marble. It was called "green opal" in the tile store. Made in China, no other info on the box. Looking online, I'd say it most resembles "ming green". I recently learned that green marbles absorb water and that you need to use epoxy instead of thinset so they don't cup/warp.

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The heat mat manual says: "Do not use solvent based adhesives or pre-mix mortars because they are not as heat resistant and do not conduct heat well."

I was originally going to do the tile (and almost all the basement finishing) myself, but there just doesn't seem to be enough time and the process seems to be getting more challenging, so I have a contractor who is going to do this. He hadn't known about the issues with green marble and thinset but checked with his trusted tile person, who confirmed the issues.
He was also a little leery of doing the epoxy right over the heat mat and was leaning toward doing a thin layer of self leveler or thinset or some type of cement-based stuff to cover the wires, then the epoxy to stick down the tile.

Will this (a thin layer) be a problem over the cork?

Is the epoxy for the marble incompatible with a heat mat?

How long does the self leveler/thinset/whatever need to cure before laying the tile with epoxy (if I still can)?

Over all tile plan is standard size glass subway tile in the same green in the shower with an accent stripe of a mosaic of the green marble, clear green glass and frosted green glass 1" tiles, and a 3" Hex "greecian white" from the orange store for the shower floor, and a 20x50 cm or so white ceramic tile on the walls for a wainscot.

Thanks in advance for the advice!


Last edited by Cria; 01-17-2018 at 05:23 PM. Reason: put specifics in title and start of post
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Old 01-17-2018, 05:27 PM   #2
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Anyone have any ideas? It's too cold for the crickets I think I'm hearing!
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Old 01-18-2018, 11:22 AM   #3
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Hi Erin,

That particular marble could be more "serpentine" than other serpentine stones, especially coming from Asia. I don't know whether it'll stay down with the method you mention. The curl factor could very well cause it to de-bond. My advice would be to move on to some kind of porcelain tile.
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Old 03-03-2018, 05:42 PM   #4
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Found a solution

Thanks for the suggestion, unfortunately/fortunately I'm very stubborn. I e-mailed Ardex, and they have a thinset that is specifically designed for moisture sensitive stone, so I ended up having my contractor use that. Those tiles have been down a little over two weeks now and are looking good! Sorry I can't figure out how to get the picture rotated correctly.
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