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Unread 11-14-2019, 09:13 AM   #31
codude
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Trugard has their own waterproofing membrane similar to Schluter's. It's glued to the stainless linear drain with their proprietary adhesive (where the Schluter drains come with the membrane pre-adhered.) They say that you can apply thinset directly to the foam, adhere the waterproofing membrane, and tile directly on top of that. Tiles will be larger format, but I'm wondering if I should be concerned about cracking if I don't use a backerboard and just use Ditra.

Trugard, of course, recommends that I use their heated flooring system and not Schluter's, but I prefer the design of the Ditra Heat system.
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Unread 11-14-2019, 10:19 AM   #32
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Chris, that's how Durock and Schluter's foam pans (except Schluter's new pre-membraned' pans) are treated; set the pan in mortar, trowel on a layer of mortar, cover with waterproof membrane, and cover that directly with tile.

So I can't really see any reason you couldn't use DH matt instead of a membrane. Schluter claims that if you use Kerdi band where sheets meet it makes those seams waterproof (though I still don't know how with all that mortar under it) and I imagine if you used the band for your wall to floor joints that would work too.
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Unread 11-14-2019, 09:47 PM   #33
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Thanks. Any problem with Ditra Heat topped with thinset and the Trugard membrane over that? I want to make sure all of the Trugard stuff overlaps so that it's a complete system.
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Unread 11-15-2019, 06:37 AM   #34
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That I don't know.

Mortar doesn't actually stick to the top of Ditra Heat mat in the way it does to plywood or a membrane or CBU. Mortar on Ditra is mechanically locked in place by way of small, horizontal-ish ridges around the pillars, and the mortar bonds to the tile (pretty sure there's a minimum tile size for DH) which distributes the load across a larger area of the DH.

In your case, the membrane will be mechanically fastened to the Ditra instead of tile, then the tile on top of the membrane will distribute the load. You'd not have to worry about water getting trapped between the two water proof layers so long as the membrane is installed correctly. You would definitely have to pre-fill the DH with mortar and let it cure. At least twice I'd guess, because the first fill will shrink and you'll be left with lots of small depressions in and around the pillars. BTDT.

Only other thing I can think of is if the heat cable will have any effect on your membrane, short term or long.

I'd be inclined to call Schluter's tech line, but substitute their membrane (Kerdi) for yours. See what they say.
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Unread 01-10-2020, 11:22 AM   #35
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Best Sequence, Products & Cure Times for Ditra Heat and Waterproofing Membranes

Hi guys... Finally starting to wrap up my 3+ year master bath remodel. It's slightly unusual in that I have installed Ditra Heat over Plywood and will be installing a waterproofing membrane (TruGard) on top of that since I am using their linear drain, shower niche products, etc.

Any feedback on process, timeline, and especially whether to use modified or unmodified thinset over styrofoam is appreciated. Here is my plan:

Install Ditra Heat over Plywood/OSB with MAPEI Large Format modified thinset. (already done)
Install Ditra Heat over Styrofoam shower tray using ??? Thinset
Install heat cables and prefill waffles with MAPEI Uncoupling unmodified thinset
Allow thinset to cure 24 hours
Skim coat and install Trugard waterproofing membrane with MAPEI Uncoupling unmodified thinset
Allow thinset to cure 5-7 days
Install tiles over membrane with MAPEI Large Format modified thinset
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Unread 01-10-2020, 04:58 PM   #36
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Quote:
Originally Posted by Chris
Finally starting to wrap up my 3+ year master bath remodel.
Well, that certainly makes me feel better about taking 2 years to do mine.

1st, prefilling the Ditra heat is a good idea in my mind, and I did as well. However, what you will discover is that the mortar is going to shrink so you'll be left with shallow divots all over it. Those divots probably are not an issue if you're just coving it with relatively thick mortar and then tile but I don't know how it's going to go with a much thinner layer of mortar and membrane. When you go to smooth the membrane out I'd be concerned that the mortar will fill the divots but leave very little at the high points around the divots, and you might end up with a bumpy surface. Guess you could give it a try if ya wanna.

I ended up prefilling, and then applied another layer to smooth it out, and I wasn't covering any of it with membrane, only tile.

I'd be inclined to give it more drying time. The Ditra is of course water proof, and the membrane is too, so I'd want to be sure the mortar between the two is cured before covering it with the membrane.

I also used a foam shower pan, and I used Custom's Versabond for sticking everything to everything, except the glass accents, where I used...huh, what was it? Something stickier.

EDIT: I now realize I'd answered some of your questions previously!
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Unread 01-11-2020, 02:03 PM   #37
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Thanks Dan.

If I'm understanding correctly, you are suggesting a three-step process:

Pre-fill waffles and let cure
Skim coat and let cure
Install membrane with generous amount of thinset
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Unread 01-11-2020, 04:44 PM   #38
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Close.

Pre-fill, let cure 24-48 hours to ensure most/all shrinking is done.
Skim, ensuring a complete fill of all divots/dimples. Let that cure for 24 hours.
Install membrane following manufacturers recommended trowel size. You'll not need a generous amount since the skim coat will have filled everything.

You might be left with tiny ridges from the skim coat, just knock those down with any tool that won't hurt the heat cable.

Keep in mind though that I've used Ditra Heat exactly once. While I do know what mine looked like after the first fill dried yours may not look the same. I'm a novice and it seemed logical to me to have a smooth surface, but I also did not lay a membrane over mine. You'll need to assess if a skim coat is warranted after you see how the fill coat cures.

The area in front of the door shows mine prior to the skim coat. Don't know it the pic is detailed enough on here but the non-skimmed area had low spots/divots/dimples all around, and in the center of, the octangular columns.

Not sure that's a fight I'd want to have during a critical set like installing the membrane.
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Unread 01-11-2020, 04:45 PM   #39
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Found a better pic...
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Unread 01-11-2020, 05:35 PM   #40
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I've not used the Ditra Heat at all, but I'm sure I would not wanna "skim coat" what I see in Dan's post #39 with thinset mortar and let that dry before installing a sheet-type waterproofing membrane over it. You're almost certain to have some crumbling of the thin mortar over those orange areas where no mortar is not ever gonna bond and I can't imagine that helping with the installation of the membrane. Again, haven't ever tried it, but If I were to try it I would wanna install my membrane over just what I see in post #39 and hope that works well. The minor divots (which I cannot see) would likely fill quite nicely while trowling over the membrane to embed it.

Lotta mortar selection going on in your posts, Chris, but I would select some VersaBond from Homer's and use it for everything I see discussed here.

My opinion; worth price charged.
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Unread 01-12-2020, 08:14 AM   #41
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My one time experience was that crumbling/flaking was a non-issue, even after walking on it gently. Some here and there, easily brushed away. And the bits that did flake were less than paper thin.

You might be able to mitigate the shrinkage by mixing your pre-fill mortar a bit thicker, Chris, and/or by using a LFT type mortar. You'll work harder to get a complete fill though. In any case, you'll have to assess it once it cures.

My concern is the membrane manufacturer recommends a particular trowel size for applying mortar over a smooth surface to achieve a consistent thickness under the membrane. If the depressions are deeper than the thickness of the flattened mortar you'll have voids.
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