What type of thinset for Kerdi + Nuheat [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


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07-31-2019, 01:48 AM
I have Schluter Kerdi membrane in a shower and want to install Nuheat floor warming mat over it.

Schluter calls for unmodified thinset over it and Nuheat calls for modified thinset under it.

What to do?

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07-31-2019, 01:55 AM
Welcome back, Roy. :)

Basically, you'll have to violate one of the manufacturer's rules, and deal with the lack of sleep it causes. ;)

If it were me, I'd use a modified mortar and not look back. Allow for a little extra drying time if it makes you feel better.

One other option would be to find Schluter's modified mortar, which would preserve both warranties. If you can find it. It's called Schluter All-Set. If you have a Schluter dealer nearby, you should be able to get it. Get ready, though, it runs about $40 a bag.

07-31-2019, 07:35 AM
how large an area is it? you can always mail order schluter approved all set, but its like 60 bucks a bag with shipping


pretty sure its around 40 a bag if no shipping

07-31-2019, 02:16 PM
I misspoke in my original question but I think you guys got the gist. I should have said Schluter calls for unmodified thinset over it and Nuheat calls for modified thinset under it (not over it). I edited my post to correct this.

The overall shower is 24.75 sqft and the Nuheat mat is 15 sqft, so one bag of All-Set is more than enough.

But I wonder if it even makes sense to have floor heating in the shower? Won't the temperature of the water override whatever this mat is doing? Even if parts of the shower don't get much water, won't the dry floor areas just warm up from the higher overall temperature inside the shower enclosure?

The rest of the bathroom will have Nuheat and I have an extra mat that can't be used in the originally planned location so I was going to relocate it to inside the shower. It's been a while but IIRC I didn't originally plan for Nuheat in the shower because I didn't think it would have any effect in there.

Should I skip Nuheat in the shower?

07-31-2019, 03:05 PM
Not sure of your location, but I would NOT mess around with a heated floor in a shower.......gets warm enough with hot shower water on it.

08-01-2019, 06:18 AM
A 25 SF shower is pretty good size, so it's unlikely the whole floor will see enough warm water to keep it warm. Also, the heated shower floor will dry faster than an unheated floor - assuming it's on and up to temp whenever the shower is being used, which may help stave off mold/mildew growth - especially in the corners and wall/floor junction.

But the above assumes you're heating the whole floor - which you aren't. And since you aren't you'll also be faced with the challenge of making the floor section that has no heat mat the same height as the section that does.

Hate to toss a perfectly good heat mat, I'm sure, but I'd bag the idea of putting it in the shower.

08-02-2019, 10:02 AM
I went to Houzz to ask for advice about utility of putting floor heating in the shower. Was hoping to hear from people with heated floors in their bathrooms. The responses went three ways:
1) You are crazy to put anything electric in the shower! Nobody does that! Even some certified "pros" didn't know that it is done and perfectly OK to do.
2) People who said the shower will be warm enough from the water so you don't need to warm the shower floor.
3) People who heated the bathroom floor but not the shower. They all said that they notice the difference, even with the hot water on, and wish the shower floor was heated too.

#3 was very persuasive and it is all I needed to convince me to do it. Especially since I already have the mat so not much more effort to install the additional mat.

I ordered a bag of Schluter All Set from Amazon for the shower. Thank you for drawing my attention to that! Solved the problem of modified/unmodified.

08-02-2019, 10:11 AM
I wouldn't really care what anyone on Houzz.com has to say unless it is for aesthetic purposes.

I am in wisconsin and have in-slab radiant heat. Corner shower below grade and due to the shower drain "box" when roughing it all out, there was not as much heating pipe set in the slab in the shower area. In winter the shower floor is cold and I wish it wasn't. The slab has 2in of foam under it and the shower tray is foam.

I don't see anything wrong with electric lines under the tiles. You are looking at running anywhere from 2 to 5 amps in the cables for your 25sqft area. Hardly a "you are crazy to consider it" scenario. I would be as cautious of it as a light fixture in the shower.

08-02-2019, 10:19 AM
Well, I didn't go there asking for advice on thinset, that's for sure!

Just wanted some real world advice on benefits to putting it in the shower. The experience of people who had it everywhere but the shower was very helpful in the decision.

08-02-2019, 10:33 AM
Aren't you going to have the same issue, Roy? Your shower size is 25SF. Your mat size is 15SF. Some of the shower floor will be heated, some of it will not. Just thinking out loud, but it ain't my shower. ;)

Just curious, how are you going to deal with the height difference between the area of the shower floor that has the mat and the area that does not?

08-02-2019, 10:44 AM
It's a rectangular shower with a linear drain on the long side against the wall. Can't put the mat over that. And nobody stands right under the shower head because the water comes out at an angle. Don't need a heated floor there. Doubt anybody is going to stand against any of the walls either.

15sqft is bigger than most showers so the mat will go where the average person will be standing 90%+ of the time. If you want to stand with your back against the wall/glass, you might sense a temperature difference on the floor.

I am not a tile installer so I don't know how the difference in height will be addressed but the installer says he can keep things level and it won't be an issue. I assume more thinset to make up for the difference in height where there is no mat. Wouldn't that be the obvious way to do it?

08-02-2019, 11:42 AM
When i sit on my shower bench and enjoy the 6 shower heads spraying me, I like to recline against the back shower wall. The cold tile always snaps me back to reality.

I also with I has tile warming on the walls:idea: