what mortar over radiant heat?

My question is about which thinset to use. In my kitchen I'm installing a 1/8 " mesh mat of electric radiant heat flooring called "Thermasoft" over new cement board and underneath 18" porcelain tiles. My plan was to staple or tape the radiant mat to the cement board, then do a skim coat of mortar, let dry, install tile. The instructions suggest that I could just staple the mat and do the entire mortar job in one step. That seems iffy to me. It also suggests latex fortified or flex thinset. Anyway, is the ready mix thinset at Home Depot worth considering? If not, what is the best mortar to use for this project and where should I get it in the chicago area? thanks a lot
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dave wrote:

Don't do the thinset in one step unless you're really confident of your abilities. The mesh makes it more problematic. Your two step plan sounds fine.
Don't use the ready mix. It's not that much work to mix the powder, and it's a lot cheaper.
Definitely use modified thinset (Home Depot's is fine), and use latex modified grout as well.
In lighter traffic areas, and with suitably large tiles (minimum 6") I like Wedi Board. It's a Dow Corning foam with a modified acrylic cement coating over fiberglass mesh on both sides. It's really easy to use and install, adds insulation under the heating mat so you get more heat coming up rather than heating the slab/floor, and some electric mat manufacturers specify its use.
R
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Thanks, that's great. If I've already put down 1/2" durarock, is it worth pulling it up for the Wedi Board?
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dave wrote:

I'm not sure on the area we're talking about, but I'd tend to doubt it. The Wedi Board is about twice the price of Durock, and what with labor and all, the payback time would probably be pretty long.
R
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Well, it's all kitchen, and the labor is all mine. It's also over an insulated wood plank over a basement. And it's all high traffic. I'm told it's a waste to put down radiant flooring in low traffic areas. I'll keep Wedi Board in the back of my mind for when i do the bathrooms. Thanks again
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dave wrote:

I'm not sure what the radiant heating has to do with the amount of traffic. A master bathroom is pretty low traffic and a great place for radiant.
The Wedi Board is a joy to use on second floor bathrooms. You can walk up the stairs carrying four sheets easily. Try that with cement board.
R
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