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Unread 10-27-2020, 05:44 PM   #1
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Mid Project Questions.. Tile Shower

Hey all, this is going to be my 2nd bathroom. The first was 10 years ago and now I am discovering so many new products.

I am doing a full Kerdi pan, kerdi on the walls over greenboard and a kerdi curb. My question is - Can or *should* I use Mapei Aqua Defense on the pan / curb and midway up the walls on top of the Kerdi for extra waterproofing? I have been watching videos of the Tile Coach on Youtube using Ardex 8+9 over Kerdi and having good luck with waterproofing. This is over concrete on main floor, going to be my long term residence so I definitely want to do it right. Maybe its overdoing it? I did a search and didn't find this specific question asked, thank you for all of your assistance.

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Unread 10-27-2020, 06:00 PM   #2
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Welcome back, Pat.

I see that the last time you asked about a shower was only six years ago.....but who's countin?

Did you do that one yourself or did you have someone else do it?

Very bad idea to do what you're asking about. If you don't trust your Kerdi shower to be properly waterproofed, don't use Kerdi. If you think AquaDefense is a better product to waterproof a shower, use that.

I would personally not use a liquid-applied direct bonded waterproof membrane to do a shower receptor. Shower walls, OK; shower receptor, not for me."

I would also not recommend you use "greenboard" or any other colored drywall except plain white. That's what Schluter recommends as a backing for Kerdi and that's part of the Kerdi "System" that has the ICC ER allowing gypsum drywall as a backing material in wet areas.

Will the Kerdi bond properly to plain drywall? Yes. Will it bond properly to other types of MR board? Maybe.

My opinion; worth price charged.

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Unread 10-27-2020, 06:18 PM   #3
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I will admit - I rounded up to 10 years. Haha!

I did my last shower myself and did the same thing essentially, but the pre-embedded kerdi pan wasn't available and I didnt know about the kerdi curb. Both of which I am using this go-round. I do trust kerdi in regards to their water management, the reason I am questioning the additional liquid membrane is just because of some of the water tests I've seen online. Maybe I'm over paranoid?

Has anyone had experience using liquid membranes over Kerdi? I saw a thread with people talking about a "mold sandwich" in between two impermiable membranes. Maybe thats why its a no go?

Thank you again for the help,
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Unread 10-27-2020, 06:41 PM   #4
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Maybe someone here has done that, I can't say. I agree with Cx, the Kerdi is waterproof. There's no need for anything else.

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Unread 10-27-2020, 09:03 PM   #5
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Only time Kerdi isn’t waterproof is when it’s installed against manufacturer’s instructions. To me, it’s that simple.

I also agree to not use greenboard. That stuff has a coating that makes it tougher to bond to. Stick to the manufacturer’s instructions and use plain white drywall.

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