Which Comes First..ditra Or Floor Heat? - Flooring - DIY Chatroom Home Improvement Forum

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Old 03-04-2010, 08:03 PM   #1
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which comes first..ditra or floor heat?

I plan on installing A NU-HEAT electric floor heat mat in my bathroom. The subfloor is OSB. I plan on using DITRA as well.

Should I install the ditra to the osb, then the floor heat on top of the ditra, or vise versa?


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Old 03-05-2010, 05:55 AM   #2
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Is this Advantech or regular OSB? Regular OSB should not be tiled directly to. I believe Schluter says you can set Ditra on 3/4" Advantech without issue, though I don't personally believe in this. Recommended subfloor thickness for tile is two layers of 5/8" Plywood for rigidity.

After this you prime the subfloor, install the heat system, pour your self leveling compound (or you can use thinset but this is more difficult), then you apply the Ditra and tile. Look on Schluter's site for the Ditra handbook. It has details for a heated floor install.


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Old 03-28-2010, 07:37 PM   #3
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Go to schluter.com and read their specs. They have a pdf (Ditra Handbook) which will tell you the order.
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Old 03-29-2010, 05:56 AM   #4
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heat first. Ditra is installed with thinset not self leveling compound. Advantec is a superior material for floors and is well suited for tile applications. If you prime (not needed) you need to use an oil primer, latex will not stick to the wax surface of the Advantec.
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Old 03-29-2010, 07:37 AM   #5
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Hi Big Guy,

I noticed several mistakes in the answers you've received. So, follow the directions from NU-Heat for that part of the install using either thin set mortar or SLC. Ditra is installed over the mat with an appropriate thin set, modified or unmodified depending on step one.

TILE GUY - retired- TROY, MI - Method & Product suitability consulting.

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Old 03-29-2010, 08:33 PM   #6
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I just did this in my bathroom so I understand where you're coming from. The Ditra goes on top of the heater strips. There's two ways to do this:

1 - With Self Levelling Compound (the way I did it). I could explain to you how to do it but here is a step by step tutorial http://www.johnbridge.com/vbulletin/...ad.php?t=36020 Once the SLC is dry, lay the Ditra then the tile. Make sure to use UNMODIFIED thinset only. If you use SLC, spend a LOT of time prepping the floor and filling in all the cracks/holes with silicone, otherwise your SLC will not turn out well.

2 - Without Self Levelling Compound. Attach the heater strips to the plywood then CAREFULLY trowel MODIFIED thinset on top of them and lay the Ditra then use UNMODIFIED thinset to set your tiles.

Basically anywhere the thinset is going to be between two layers of material that don't breathe you need to use Unmodified thinset (and don't get the cheap stuff, you should be paying about $15 for a 50 lb bag). Ditra doesn't breathe and neither does SLC, plywood breathes enough to use Modified.

Hope this helps...
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Old 03-29-2010, 09:52 PM   #7
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I finished installing electric heat in my kitchen about six months ago, same process you are going to use. Most of the issues have been addressed, just a couple of things I noticed when doing the job in my kitchen. First, be very careful not to nick the wire if you use a metal trowel to put down the thinset over the wire. We used wire on mesh, it seemed easier than using wire without mesh, but regardless the wire is delicate.

We set the wire in place using hot melt glue, that worked OK, but in a few places we used electric staples through the mesh, that worked OK also. It is important to get a good reading on the resistance, our manual recommended use of a digital ohm meter, so I bought one.

The Ditra worked very well. I noticed that they changed their recommendations on using modified versus unmodified thinset in the last year, apparently something to do with issues involving large format porcelain tiles. I read the Ditra manual, it was very thorough and informative, and I followed their instructions. So far, no problems.

We used some self levelling compound to get part of the floor level before installing the wire and Ditra. I did not install silicone or any other product before the SLC, however it worked fine, and we had some significant dips and missing layers of flooring that had to be filled. Our subfloor was very solid, a layer of 3/4 inch diagonal boards overlain by 5/8 inch plywood, however as I noted there were some areas where the plywood had delaminated and needed to be filled.
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Old 03-30-2010, 08:29 AM   #8
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Originally Posted by Daniel Holzman View Post
We used some self levelling compound to get part of the floor level before installing the wire and Ditra. I did not install silicone or any other product before the SLC, however it worked fine, and we had some significant dips and missing layers of flooring that had to be filled.
You didn't need to use silicone because you were just doing patch jobs which typically entails working completely on one piece of plywood. But if you're covering the whole floor and the heater strips like is shown in that tutorial, the SLC will find the cracks between your plywood. The stuff is very liquid when you pour it. It flows similar to oil or pancake batter and it will find the smallest cracks and holes and go through them.

One thing to note, using SLC on plywood you are usually required to pour the SLC a minimum of 1/2". That being said, I don't know if you should really do patch jobs on plywood with SLC. Plywood flexes, concrete does not, therefore you need a thick enough layer that it won't break when the plywood flexes. If you're pouring it on concrete, that's a different story. But read the back of the bag to get the mfr's minimum thickness on plywood and go with it.


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