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Old 12-08-2018, 04:01 PM   #1
superchunk
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Ditra Layer Over Ditra Heat Layer?

Hey Everybody,

New house, new questions...

I am paying a tile setter to do the bathroom this time and asked for a heated floor. They installed Ditra Heat membrane, heating wires and then skimmed mortar over the whole thing to the top of the vertical hex "pucks" or columns.

I was subsequently asked if wanted the bath floor to be flush with hallway floor. If left as is, the bath floor would be below the hallway. I said, "flush if you can do it."

I came home to see that the installed a second layer of standard Ditra (with squares) over the top of the Ditra heat layer. Is this ok? Doesn't feel right, but what do I know.

Thanks in advance!

- Mike

[I've attached pictures for kicks. (1) Close up trying to show Ditra Heat under Ditra. (2) Floor as it is now. (3) Ditra Heat and wiring.]
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Old 12-08-2018, 04:04 PM   #2
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Seems an easier and cheaper option would have been to bump up the subfloor with some 1/4 ply then install Ditra Heat over that.


Also, Schluter doesn't want the heating lines under the vanity. "The DITRA-HEAT heating cables cannot be installed under vanities, bathtub platforms, free standing bathtubs, kitchen cabinets and islands or any other fixtures or in closets. Excessive heat will build up in these confined spaces and may cause cable overheating."

I'm thinking that is a bad install.
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Old 12-08-2018, 04:14 PM   #3
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Schluter says do not install Ditra Heat cables under vanities and keep it 6 inches (I think it's 6 inches) away from toilet drains. The former is because it may build up excessive heat under the enclosed vanity cabinet base. The latter is because the heat will soften the wax ring seal.

If your vanity is a wall mounted floating vanity, or even one that sits on feet, and therefore the bottom is not enclosed, you should be fine.

No idea about the Ditra over the Ditra heat though. Seems like it could work.
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Old 12-08-2018, 05:37 PM   #4
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1/4” ply isn’t suitable as tile underlyament. It tends to warp and / or delaminate with the moisture in the thinset.

Looks like those wires are too close to the back wall in far end of pic. And the sensor in the front of the pic towards the door shouldn’t cross over the heating cables.

Re: ditra over ditra heat, I’d contact Schluter to ask.
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Old 12-08-2018, 06:01 PM   #5
superchunk
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Thanks for the feedback. I too was concerned about the wiring going under the vanity. It will be a pedestal sink however, so the risk area is low. Regardless, it would seem to null the Schulter warranty. I will ask about that.

I'm not sure how close it gets to the toilet flange; there was stuff in that corner masking it. Regardless, it seems the wiring goes under the front part of the toilet.

The sensor was just laying there, not installed yet. They routed it between the columns later (from what I remember, at least). I didn't take any other pictures since I was just doing progress pics and not thinking about 'warranty' pics.

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Old 12-08-2018, 08:07 PM   #6
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I'm guessing that you're going to lose alot of your efficiency by adding a layer on top of you heat...
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Old 12-08-2018, 09:34 PM   #7
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I don't think it would necessarily diminish the efficiency (which is 100% with resistive heat) but would slow down the warm-up as slightly more mass has to be heated. Also, the heat transfer would be slowed down due to the effect of the additional plastic between wear surface and where it's generated. That in turn could lead to slightly increased heat losses below the floor (where you don't want it, probably). Having said that, I don't think the thin plastic layer of the Ditra will present too much of a thermal break (but I don't know for sure). It's not ideal, though.
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Old 12-08-2018, 10:04 PM   #8
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This has come up before and best I remember Schluter said it was okay to put down a second layer of Ditra. I do believe we were talking about going over regular Ditra, not heat mat if that makes a difference. I agree with the others though, not ideal.

With a little planning ahead, the floor under the heat mat could have been ramped up 1/8-3/16 3-4 ft away from the doorway and wouldn't have been noticeable.
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Old 12-09-2018, 07:49 AM   #9
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I wouldn't blink an eye running it under a pedestal sink. And your warranty would be intact since there's no actual "vanity" or cabinet.

Do double check that no wires are crossing over or under the heat cables. Also verify the proximity to the toilet flange.
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Old 12-09-2018, 12:11 PM   #10
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Thanks again for the feedback everyone.

How can I double-check the location of the sensor wire(s) or distance from flange? It's all covered at this point. (Double-covered, actually).

What about heating cables under the toilet base, even if it's away from flange? Is that ok? Seems like another potential site for heat build-up.

If flange is 7", then heating cables need to be more than 3.5" from the outside of the flange, right? (Schluter: "... and 7" (180 mm) from the centerline of toilet drains.")
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Old 12-09-2018, 01:56 PM   #11
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Mike, at this point there isn't much you can do short of replacing the entire heating wire. I'd be mortally afraid of digging it out from the thinset and rerouting it away from the toilet if it were to be too close. Seems like a high chance of compromising it.

They also make toilet seals that aren't wax. I've never used them and don't know enough but you could look into them for sure.
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Old 12-09-2018, 02:01 PM   #12
speed51133
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https://www.fernco.com/plumbing/wax-free-toilet-seal

Ive used these with tons of success. Best on a new toilet or make sure you REALLY clean the horn of ANY residue.

another benefit is they are great for fatties what rock on toilets and always cause the wax seal to leak. These really positively anchor the toilet to the pipe.
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Old 12-09-2018, 05:06 PM   #13
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The first thing I would do is call Schluter and make sure it's okay to cover the heat wires with Ditra. I believe when we talked about this before, we were talking about a double layer of regular Ditra. And, even then we might have been talking about doing a small area or building out for a stripe or border.
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