Isolation membrane needed or not? [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


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01-28-2010, 11:34 AM
-Need to install 450 SF of Travertine over an on-grade slab (5+ years old)
-300 SF to be covered with Nuheat mat.

Anyone know if the Nuheat mat itself acts as an isolation membrane? Can't seem to find anything on their website. If it did, would installing ditra just on the unheated area give me a worthy/isolated substrate for installation.

Another option is to put down the mat. SL the whole floor, then ditra, then tile. This option will get spendy and I don't want to scare the homeowners unless this is the only viable option.

Or, on the economical side, just stick the mat to slab and start tiling. I've done this before with no ill-results, but not with stone and not an area this large.

This is a fairly large job for me...nice tile, large area, and heated. A miscalculation on my part could be costly. If anyone has suggestions, I'm all ears.


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01-28-2010, 12:21 PM
Just talked to a NuHeat rep, mat not an isolator (no big surprise there). They recommend putting down a heat insulator mat over the slab first such as "easymat". Can anyone speak to the effectiveness of that as far as heat-loss and efficiency is concerned?

So I suppose my options are either to use an uncoupling system over the mat or not. I just want to be able to tell the owners what the likelihood of a future problem will be without ditra.

01-28-2010, 12:27 PM
No guarentees of failure if you didn't put a membrane over the neat mats, but a membrane would be a good insurance policy.

As far as thermal isolation, any foam board will be better than none. Any membrane will be better than none. But none of them will prevent thermal losses into your slab. There's just not enough room for effective insulation.

01-28-2010, 12:33 PM
What Injineer Bob said.

I would personally not install tile over a radiant heating system without first installing some sort of uncoupling membrane, Aaron.

Ditra would be my first choice in that application, but there are others out there, too, such as ones made by Noble Company (

My opinion; worth price charged.

01-28-2010, 12:47 PM
Thanks bbcamp. What about rolling the floor with a crack-isolation membrane like redguard, thin-set the mat, feather out the edge around the mat and then tile....all with modified TS.

Seems like that would be better than nothing and would keep the cost down.

I plan on giving the owners the option of what to do. If it were my house I'd probably feel comfortable w/o ditra given that the slab is older and doesn't have any noticeable cracks, but hunches can be damning.

01-28-2010, 12:51 PM
I'll post a positive experience using the USG Tile Membrane kit as an isolation membrane/waterproofing. You can buy it online for cheap. I used it on top of an SLC pour over bare wire radiant heat. Was very easy to install with their included glue/crack supression stuff. Waterproofing included. I think it is very similar to noble's product. Great experience so far though.

01-28-2010, 03:09 PM
Aaron, your crack suppression membrane works best just below the tile. Apply it on top of your SLC.

01-28-2010, 04:09 PM
bbcamp Aaron, your crack suppression membrane works best just below the tile. Apply it on top of your SLC.

I was actually thinking not using SLC with this application. See the homeowners wanted to use the rollout mats instead of the cable system because it's designed to be tiled directly over without the use of SLC. The NuHeat rep said to just feather the edges around the mat with thinset to ease the small transition upward.

I figure if the mats are 1/8" thick then feathering that down over a couple of feet shouldn't be noticeable, especially if I sling a little extra mud on those tile falling outside of the mat.

Quite frankly, I'd like to give the owners two options.

1. install mat, SLC, modified TS, ditra, unmodified, travertine


2. install mat, ultra-modified TS, travertine(no membranes/no SLC, just rely on mortar for handling movement)

Would anyone here say absolutely not to the second option? IMO it would last a long time without incident, but I'm not a full time setter and haven't been to every rodeo. Probably laid around 10,000 SF in my life.

BTW - Price difference would be in the neighborhood of +2K for option 1.

01-28-2010, 07:24 PM
Hi Aaron. I would use a membrane, myself. I use to not but then I had some cracks transfer thru the tile on a bath floor. Replacing those tiles was tough and also scary knowing those wires were under there. Since then I won't do a heat mat without a membrane. :)

Old World Tile and Marble
01-28-2010, 09:50 PM
i thought the recomendation over concrete is due to the fact that the heat will go down into the concrete causing the mat to have to work harder to stay at the desired temp, now youll have to put down 2 mats?

01-28-2010, 09:55 PM
Jason, any insulation below the heating system would be for the benefit of the heating system.

The uncoupling or isolation membrane we're recommending is for the protection of the tile installation. Hasn't anything at all to do with the efficiency of the heating system.

Two completely different considerations.

How many of'em you wanna do is entirely up to you as the installer.

My opinion; worth price charged.