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Unread 01-23-2019, 08:24 PM   #1
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Linear drain with classic 3 piece drain and pan liner

Doing some research and wondering if anyone has installed linear drains in a mud bed (pre-slope, pan liner, mud bed) and utilizing a 3 piece mechanical clamp down drain like this one: https://www.amazon.com/Inch-Shower-D.../dp/B079P273QN


Used a product like this DERA-Line in a mud bed: https://showergrateshop.com/linear-d...id=1&plan_id=1

Install video for DERA-Line: https://www.youtube.com/watch?v=apByCOVw8jo

Seems like what I'm finding is that most linear drain installs utilize a membrane over mud bed method vs the what I would call the traditional (pre-slope, pan liner, mud bed) system.

Just wanted to know if people have had success or failures using a linear drain with a pre-slope, pan liner, mud bed.


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Unread 01-23-2019, 08:52 PM   #2
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If done properly this should work just like a round/square center drain done with a traditional pan liner. I don't know enough about the specific products that you linked to. But yes, this should work in principle.
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Unread 07-03-2019, 06:02 PM   #3
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Shower mortar/thinset sanity check

Working on a shower and wanted to verify if the mortar/thinset products I was planning to use is acceptable.

Shower construction:
Concrete floor, mud deck pre-slope / Chloraloy 240 / mud deck/ linear drain / large format porcelain tile
Walls: wood frame / vapor barrier wrap/ Durock / Kerdi / Porcelain tile.

Intended mortars:
CBU Joints – Polymer Modified - Mapei - Large-Format Floor Tile Mortar - (have it on hand to use elsewhere outside of shower) http://www.mapei.com/public/US/produ...-mortar-en.pdf

My concern here is that Durock states “Fill joints with latex-fortified mortar or Type 1 organic adhesive and immediately embed alkali-resistant,fiberglass mesh joint tape” Page 4: https://www.usg.com/content/dam/USG_...en-CB237EG.pdf

So polymer vs latex not sure how big of a difference it make with the CBU joints??

Kerdi to CBU and Tile to Kerdi – Mapei Kerabond

Shower floor tile to mud deck – I need a recommendation on modified vs unmodified. I’ve read several post that seem a little ambiguous about it. Saw a few “you should be ok using XYZ” and "I was told by so-and-so not to use XYZ". Seems like there was not a strong consensus or a firm standard that I saw??


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Unread 07-03-2019, 06:44 PM   #4
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Latex is a polymer. In this case I think you can assume the words are used interchangeably. The LFT is not ideal as I imagine it's thixotropic. I don't know Mapei line well, but if Home Depot is nearby you could get Custom Versabond which would be fine.

One concern, however. If you have a moisture barrier behind Durock and Kerdi fabric (also a moisture barrier) on top there's a potential to harbor moisture between the two...not good. Often referred to as a moisture sandwich, if vapor gets between, it has no where to dry too and in most climates the moisture drive would be towards the outside.

Silicone (not silicon) Sealant Ranger
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Unread 07-03-2019, 07:55 PM   #5
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Lose the vapor barrier unless you're planning on completely botching the installation of your Kerdi.
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Unread 07-03-2019, 08:20 PM   #6
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Ken, if you're using a traditional mud/liner/mud shower receptor and have a moisture barrier behind your CBU wallboard, there is no need for the Kerdi and, as has been pointed out, you do not want both wall waterproofing methods.

If you elect to defeat or remove the moisture barrier and install the Kerdi membrane, you do not need to, nor do you want to, fill and tape the wallboard joints prior to installing the Kerdi.

My opinion; worth price charged.

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Unread 07-03-2019, 08:49 PM   #7
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Good to know about not needing vapor barrier behind CBU. I assumed it was just over kill, certainly don't want to cause an issue or a potential moisture trap.

So lose the vapor barrier behind CBU since will be using Kerdi.

Ok to skip mud/taping CBU joints under Kerdi.

Outstanding question: modified vs unmodified on shower floor tile.
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Unread 07-04-2019, 05:07 AM   #8
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If tile is being set over a mud bed, I'd use modified. If it's being set over Kerdi, unmodified per their instructions. Other setting substrates check manufacturer recommendations.
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