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Unread 11-21-2020, 11:05 PM   #1
Ceramictilenube
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Kerdi niche to water proof hardi backer transition?

Hi any help would be awesomely appreciated! I Installed the new water proof hardi backer but used a ready made kerdi niche. I was planning on using speed set thinset on the seams so I could redgaurd same day. I'm having difficulty figuring out how to transition kerdi to hardi, fiber tape or kerdi fabric? What thinset?
Thanks any info!
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Unread 11-22-2020, 08:44 AM   #2
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Welcome, Rich,

I'd want to use Kerdi band membrane to seal the niche to the Hardie, and adhere the membrane to the niche and Hardie using a lose mix of thinset mortar to minimize the buildup. Versabond, from HD, will do the trick, and it's likely you can use the same mortar for many other aspects of your project.

Hardie is very thirsty; be sure to dampen, and keep it so, before trying to stick anything to it with mortar.
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Unread 11-22-2020, 09:43 AM   #3
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So this is that new hydroboard hardi bbacker so I thought maybe the versions wouldn't dry out in-between the kerdi fabric. Also did you mean install kerdi fabric to niche with unmodified thinset?

I was thinking of red gaurding the hardi board first then using unmodified thinset for both, would that work? Does unmodified adhere to red gaurd better than hardi board?
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Unread 11-22-2020, 10:06 AM   #4
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If I understand how you intend to install the niche, Rich, once the niche is set into place there will be a gap between it and the Hardie around the perimeter of the niche, and you want that gap thoroughly water proofed.

Since you intend to use RG, you could possibly use the RD reinforcing fabric to cover that gap, then apply your RG over the fabric and onto the Kerdi niche. What I don't know if how well RD adheres to Kerdi, If Schluter said it will, of if CBP says it will.

I do, however, know that thinset mortar will adhere to both the Hardie and Kerdi. You might check to see what type of mortar Hardie specifies for bonding to their panels, and Schluter will state that they want unmodified, but a great many folks here have reported that a modified, like Versabond, will bond to Kerdi just fine. Will drying time be extended over a rapid set? Sure, I'd give it a day.
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Unread 11-22-2020, 10:44 AM   #5
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Welcome, Rich.

Since you've gotta use the RedGard (or similar) to seal all the joints and fasteners in that new Hardiebacker, I think you could do the seam between the niche and the wallboard the same as your wallboard joints. Or do it with the KerdiBand and Dan suggests.

Dan, do you know if the "waterproof" Hardiebacker presents the same absorbent surface as the original? I've never even seen the stuff in person, but if it comes presealed with some sort of waterproofing, seems to me it might not have that same problem as the original.

Don't think I'm seeing much of an advantage to that new product. Seems about 50 percent more expensive at Homer's with the only apparent advantage being you don't need to apply quite as much waterproofing membrane. Would it require another $7.70 worth of waterproofing for each 3x5 panel? I must be missing something, yes?

My opinion; worth price charged.
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Unread 11-22-2020, 10:51 AM   #6
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Good point about the new water proof Hardie, cx, but if it does have some sort of coating on it I'd want to know how well RD will adhere to it. Perhaps CBP has tested it.
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Unread 11-22-2020, 07:46 PM   #7
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So there's a couple threads I found here that seemed to say a rapid set works better under the kerdi fabric than regular thinset, so the plan tomorrow is to use the kerdi fabric over a speed set. Does this plan sound reasonable? Thanks for all the input!
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Unread 11-22-2020, 08:09 PM   #8
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Rich, if this is your first attempt at installing Kerdi I would recommend you not us a rapid-set mortar. And it does not work better under Kerdi or anywhere else, it just sets up faster. If you get a bit of experience installing Kerdi and decide you want to use a rapid-set mortar, that's fine, but I still don't see any potential advantage at all. Using a good quality "regular" thinset mortar gives you a bit of extra time before skinning over and you can still tile over the Kerdi immediately.

The Versabond Dan recommended is a good choice for installing your Kerdi and your tile. You won't get a Schluter warranty, but you don't need one; any failure you might have will be an installer error.

My opinion; worth price charged.
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Unread 11-22-2020, 09:25 PM   #9
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So the threads I found were implying regular thinset could take up to a month or so to dry under the kerdi fabric, whereas the rapid set would dry within a day or so. There were several experienced tile guys stating they've trial and errored this?

I wasn't going to use rapid set for under the tiles just under the kerdi fabric for kerdi niche,, but besides the quicker dry times are there any other reasons I shouldn't use it or be worried?
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Unread 11-22-2020, 10:56 PM   #10
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If it's just around the niche, you'd probably be okay with it. Anything that takes longer than a half hour and it would probably dry out before you could use it all.

When you say it could take up to a month to dry, that's probably referring to a full cure, which you don't need in order to set tile over it. You just want it dry enough that it won't move around. Versabond will dry that much after a day under normal conditions.
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