Basement bathroom subfloor?

[cidley69]

Putting bathroom in basement, going with natural slate tiles, with a WarmlyYours electric heating system.

What type of subfloor should I instal on the concrete slab?

[ExtraSlow]

I'm sure the smart guys will chime in, but do you even need a subfloor in that situation? I wouldn't think so.

[C_Dave45]

Originally posted by cidley69
Putting bathroom in basement, going with natural slate tiles, with a WarmlyYours electric heating system.

What type of subfloor should I instal on the concrete slab?

Short answer: You can install directly onto your slab.

Detailed answer: It's best to have some sort of uncoupling layer between concrete and tile to prevent against future slab movement or cracks transferring into your finished floor.

Also what type of Warmly Yours heating system are you using? The mat, or individual wiring? If it's the wiring, then you have to figure out a way to attach the wire to the concrete. I've used hot glue to attach the plastic anchor strips and then poured Self Leveling Concrete over entire floor. Both expensive and a tricky job. (The mat isn't much better. That meshing tends to "pop up" throught the SLC as it cures, making annoying bumps and ridges when you're setting your tile. Major PITA.)

A much better solution is Schluter's "Ditra Heat" system. It's both your "uncoupling layer" sub-floor, as well as a holding system for the wire, without adding much thickness to your finished product. (3/16th's of an inch).

I'ts about 10 times easier than conventional wire heating systems at about the same overal cost. You save on SLC cost, and time using the Schluter Ditra Heat system.


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[mr2mike]

Good info Dave! That'll be my next thing to attempt one day infloor heat or a steam shower or both.

[jeffh]

Yep, thanks dave. I appreciate the advice as well. I intend to do just that for my future bar and basement bathroom.

[cidley69]

Thanks for the replies. Was going with the WarmlyYours mat. Had it installed in upstairs bathroom, and it was held in place with thin layer of thinset, this was allowed to dry, then the tile was installed next day.

It works great and we really like it, including the controller unit.

Would prefer to go with this same brand floor heat in basement too.

My concern with putting heat mat directly on slab, won't most the heat be lost into slab instead of going to tile where its needed?

On most of basement floor I used Delta FL, with 1" foam insulation on top, with 5/8" OSB on that, and tap-conned it all down. Floor is nice and warm, with no movement under foot.

I have leftover Delta FL, can this be used somehow?

What layers would be required? Delta, SLC, heat matt, tile?

[suntan]

If your slab was built properly there's supposed to be an thermal break below it.

I have the "usual" heated floor setup in my basement bathroom, it keeps it nice and warm.

[mr2mike]

Originally posted by suntan
If your slab was built properly there's supposed to be an thermal break below it.

Depends when it was built. I can tell you my place doesn't have one.
1950's construction.
New construction yes.

[frozenrice]

Dave, wouldn't the size of the tiles determine if you need some sort of anti fracture mat like Ditra too even on a concrete floor?

[C_Dave45]

No. Tile size is irrelevant, other than you can't use a 2x2 or smaller mosaic on Ditra.

[C_Dave45]

Originally posted by cidley69
Thanks for the replies. Was going with the WarmlyYours mat. Had it installed in upstairs bathroom, and it was held in place with thin layer of thinset, this was allowed to dry, then the tile was installed next day.

It works great and we really like it, including the controller unit.

Would prefer to go with this same brand floor heat in basement too.

My concern with putting heat mat directly on slab, won't most the heat be lost into slab instead of going to tile where its needed?

On most of basement floor I used Delta FL, with 1" foam insulation on top, with 5/8" OSB on that, and tap-conned it all down. Floor is nice and warm, with no movement under foot.

I have leftover Delta FL, can this be used somehow?

What layers would be required? Delta, SLC, heat matt, tile?
Delta FL is NOT an approved substrate for tile. (yes even if you cover with plywood)

http://www.johnbridge.com/vbulletin/showthread.php?t=92193

[cidley69]

Thanks Dave,

Just so I can understand, on a functional basis why would the delta fl not work?

[C_Dave45]

Originally posted by cidley69
Thanks Dave,

Just so I can understand, on a functional basis why would the delta fl not work?
Dunno. Probably too much movement is allowed. Those are decisions are made by R&D.
I'm sure it's done. Might even work. But it will void any warranty issues at every manufacturer. Use Ditra if you want an underlayment. All supported. Doesn't void warranties.

[cidley69]

Based on that link you posted, sounds like Wedi board is the way to go if I want to have subfloor under the heating mat.

does the wedi board have to be attached somehow to slab? Or just placed on it and allowed to float?