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Discussion Starter #1
We are creating a showroom in a rented space. The floors are very rough-ground concrete with high and low spots up to 3/16". Our intention is to lay down electric radiant heating mats (with an open weave mesh) and embed them in 1/2" of self-leveler. Our lease calls for any improvements we make (specifically flooring) to be removed when we move out. So our intended stack-up is to start with some form of isolation membrane or shear layer to enable the demolition in a few years, then lay in the heating mats and pour the SLC.
1) What membranes are best for creating a good shear/separation layer for later demolition?
2) Does anyone have recommendations for membranes that are compatible with SLC or vise-versa? All the membrane literature talks about being compatible with tile; all of the SLC literature talks about it being compatible with concrete or wood. Nobody is talking about SLC over a membrane.

I have a hunch that a thin (1mm) self-adhesive asphaltic sheet with a textured cloth surface would work, but I hate to pour 300 sq ft of SLC on a hunch. I also like 3mm EasyMat but have NO idea how SLC would react to it.
 

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I have no idea if it would work, but I'd think a layer of poly, then foam board or plywood with taped seams, then your heat mat and finally slc.

I know you want it to last, but I'd be thinking if ease if removal as well

-Rich
 

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Discussion Starter #5 (Edited)
RRK can you expand on that some? You say 30# Roofing felt has worked well in showrooms. Is that laid in dry, with setting compound and tile set directly on it? Would you glue it down with something not too aggressive that can be scraped up later?

I take your "no plastic it may release early" to mean you don't recommend a plastic membrane like Ardex Flexbone or Schluter Ditre because you have seen them "release early" (delaminate/decouple from the thinset) in the past?
 

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RRK can you expand on that some? You say 30# Roofing felt has worked well in showrooms. Is that laid in dry, with setting compound and tile set directly on it? Would you glue it down with something not too aggressive that can be scraped up later?

I take your "no plastic it may release early" to mean you don't recommend a plastic membrane like Ardex Flexbone or Schluter Ditre because you have seen them "release early" (delaminate/decouple from the thinset) in the past?
laid over crappy mastic that can be scraped up with an ice scraper
Ditra may work but felt is cheaper, when tile is pried off the felt just separates. Ditra may do the same I would imagine.

The tile places used 6mil plastic once and it pulled away from the concrete
 

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What about a layer of Redguard? A little expensive, but it could be scraped off the floor when you move out.
Rich suggested a layer of foam board. I would be concerned with 2 thing: added thickness, and if it flexes at all the SLC may fracture.
 

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Discussion Starter #8
Update: The guys at Ardex/Henry gave me some great information. Most SLCs shrink a bit and if they don't have good adhesion to the floor they can curl themselves up and delaminate. However Ardex has "Liquid Backer Board" and two other SLCs characterized as "Low Tensile Strength" that keep that tendency to a minimum. In fact, they regularly pour Liquid Backer Board over their Flexbone membrane for in-house mockups with good results. So it looks like we'll be using Flexbone, taping and gluing down the radiant heat mats, and then pouring Liquid Backer Board 1/2" deep in our showroom. One hitch is that Flexbone is very textured so when we tape it to the wall dams and tape the seams between sheets, we may need to go over and caulk those seams as well to avoid having gaps big enough for the SLC to flow through. But that's a very manageable problem and I expect great results.
 

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I've heard that SLC is not approved over Ditra but can be used below it.

that's a lot of expense for a leased building and I would be concerned they wouldn't want to move forward after finding out the cost.

that said, if you're looking to remove it in the future felt is cheap and easy. if you used Ditra you would have to grind off the thinset that was used to adhere the Ditra to the concrete.
 
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