Basement tile over hydronic advice

[Comish]

Hello all,

Super useful forum that I have learned a ton from over the years. Long time lurker looking for advice as the homeowner with the following situation.

We have a partially subterranean basement that we are converting to living space. 2 walls are above grade, 1 wall fully subterranean, and the 4th long wall is a big slope so goes from completely subterranean to just about above grade. We are insulating concrete walls with 2" rigid and in the 2 years we have owned the house it doesn't seem to get damp down there (yet???)

This is located at 8500' in the CA Sierra mountains. Cold/snowy in the winter, very dry year round. House is +/-40yrs old with an uninsulated slab.

Looking to put hydronic heat into this space with a tile finished floor. My current thought is the following, but looking to the experts for advice and suggestions on better/best way to do this considering labor is challenging, getting any materials is mail order as we are 200miles from any real store.

Thinking (from bottom to top) existing Slab, 1" foam insulation, Schluter Bekotec, 5/8" hydronic heat, ????, tile.

Main questions are what would you put on top of hydronic heat knowing that tile was ultimate floor finish? Designer is suggesting gypcrete, but I have read about the reservations of that with tile in the forums. Looking for items that require minimal labor as its super challenging to get anyone to show up and do anything there these days. Nothing has been done yet so very open to suggestions.

Thanks!

[jadnashua]

Have you read the installation instructions? https://www.schluter.com/schluter-us...OTEC/p/BEKOTEC

Gypcrete is an acceptable material and may be the easier one to install, but deck mud would work, too.

[Snets]

Originally Posted by Comish

Thinking (from bottom to top) existing Slab, 1" foam insulation, Schluter Bekotec, 5/8" hydronic heat, ????, tile.

Looking at the installation instructions, you will also need Ditra or Ditra XL between the "????" and the tile. Don't know how big an area this is but seems likely you'd need some help with whichever screed product you choose but you could more than likely do the rest yourself.

[cx]

Welcome, Doug.

I, too, was going to recommend you look up the installation instructions for Becotec.

And while it does call for filling with "mortar," it doesn't specify just what sort of mortar they want you to use. The installation method wherein they specify a thickness of only 5/16ths of an inch over the top of the studs would not seem a good application for deck mud or dry-pack type mortar. I'm honestly not at all sure what they've got in mind there. I would want at least 3/4-inch of dry-pack mortar above the studs were it my installation.

And, as Snets points out, they also require the use of their Ditra over the top of this mortar bed. This will not be an inexpensive installation, for sure, but it's one way of doing what you want to do.

My opinion; worth price charged.

[jadnashua]

The European instructions give a little more definition, but you'll have to research those Euro specs... https://www.schlueter-systems.com/en...elling%20layer.

Or, probably easier...call Schluter!

[Snets]

CX is correct, the online instructions specify a "Mortar Screed" - Vague at best.

If you check out THIS Schluter video it is clearly dry pack mortar, even says that in the description.

That guy in this video is my hero if that floor is flat, I'd need a good helper for sure, but I'm not a pro. Seems like the SLC would be less work but I don't have that experience to really know.

[Comish]

Thanks all for the responses. Yes, I had read the instructions, but the "morter screed" was too vague for me...

Problem is getting Gypcrete or similar to this location. They have to come from hours away and only come once in a blue moon so cost can go from like $6psf to $10psf.

Rethinking the the bekotec since it is such an expensive install with the cost of gypcrete or the like...

thinking slab, foam, roth radiant heat panel, pex in the roth panel, ???, ditra, tile.

Question in this scenario, do I need backer board over the Roth panel or can I just thinset ditra to the panel?

If I have to go backboard then not sure how to install since there is no wood to fasten it to? Trying to avoid wood in the install for the possibility of moisture in the basement? not to mention there is a hot tub out the door with wet kids coming in through the snow so moisture will be transported into the space. Hence my interest in tile...

[cx]

Is this the Roth panel you're looking at, Doug?

Doubt any tile installation product manufacturer is gonna be thrilled to warranty an installation over that sort of foam panel, but I don't really know that.

Bonding anything to that aluminum surface is not something most thinset mortar manufacturers are likely to be real happy with, either. I suspect most would want the use of their epoxy mortar, which Schluter isn't gonna like for bonding their Ditra. Likely to get a bit complicated.

My best guess is you'd do better with something like NobleSeal TS, installed with their proprietary NobleBond EXT pookey. I don't know that they'd warrant that, but it might be worth a call to find out. Good products, those.

I'd still vote for an unbonded mortar bed over the hydronics, but I'm not at all sure just how that would work with the foam over the concrete.

Lot to consider there.

My opinion; worth price charged.

[jadnashua]

I've read that lots of Schluter installs in Europe over foam.

Give Schluter's tech support a call and see what they may suggest. 1-888-472-4588 Depending on where he's based, you might get the tech rep to make a visit.

[PC7060]

You’ll need 2” of foam (R10) under the hydronics or you’ll end up wasting a lot of energy heating the underlying slab and dirt.

Id removing the slab and 3-4” of soil and install a drain tile system with 3” stone and then 2-3” closed cell foam, with hydronics heat lines in 4” slab. Not sure if the benefit of the Schluter system. I’d use a pex (with O2 barrier) embedded in the slab paired with a modulating condensing boiler. Make sure you use an experience designer, important to manage loop lengths, spacing and flow rate for optimal performance. I’d recommend you stop by heatinghelp.com, very savvy groups there with decades of hydronic floor heating system design experience.

What type of fuel are you using? Oil or propane are going to be pretty expensive and only become more so. Natural gas will be cheaper but it’s also going up (and up)