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Unread 01-19-2021, 04:32 PM   #1
bliddell
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Kerdi shower with extended floor and window

Hello, did some searching, but couldn't quite find the answers I am looking for.

We are installing a new shower with a 38x76" Kerdi shower tray, with a linear drain at the narrow end. I need to extend the length of the shower floor about another 22" to the wall on the other end, so it will be about 98" total length. It's going over a wood subfloor. The shower heads (regular head plus a hand spray) will be at the same end as the drain, so the far side of the shower that is being extended would be the "drier" side.

Kerdi says you can extend the length of the tray using dry pack mortar. If using this method, any tips on exactly how to do that? What would be the steps to do this correctly? Is it the same as any dry pack shower bed? Also, what dry pack mortar product would be best? Never done this before myself, so I want to make sure I do it correctly.

Alternatively, are there other easier/better ways to extend the base? What about using another type of foam platform (Again, it would need to be about 38" wide to match the Kerdi tray, and 22" long to get to the wall). Any other methods that would work? I assume I would also have to apply a Kerdi membrane to either the dry pack surface or another surface, such as a foam base, and then seal it to the existing Kerdi tray.

Our idea is to maintain the constant slope to the linear drain, so that the floor tiles (likely mosaic) would be uniform along the length of the shower. But any other recommendations are welcomed!

Thanks!
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Unread 01-19-2021, 04:45 PM   #2
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The classic mud base is the best way to extend as the manufacture recommends. Not sure where you can get premix but I’m sure the ratio of sand to Portland (5:1?) is published in the liberry.
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Unread 01-19-2021, 04:57 PM   #3
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Yeah I think you're going to have to do a dry pack mortar bed extension. I can't imagine there's another foam product out there with the slope you need that would meet at the end of your shower pan which I believe would be 2 3/8" thick at that point. Dry pack it is. With it being a linear drain your slope is relatively straight forward. But I've never done a dry pack so that's about as much as I can help. Good luck!
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Unread 01-19-2021, 05:29 PM   #4
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Welcome back, Blidell.

Definitely use dry pack mortar. Over a wood subfloor you'll want to cover the area to be extended with plastic and expanded metal lathe.

For a relatively small amount like you have, I'd get a bag of sand topping mix and a bag of sand. Mix about half the sand with the whole bag of topping mix. It'll take very little water to get it damp enough to hold together, which is all you want. It should be like a sand castle, with no excess water, but able to hold together.

Pack it down good with a wood float a little higher than needed, then scrape it off to the proper height.

On a side note, make sure the subfloor is flat and level before setting the tray. If it's sloping against the tray, you'll have problems getting the shower to drain.
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Unread 01-19-2021, 05:40 PM   #5
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Dry pack is the least expensive way to do this, but you could use foam but you'd have to make yourself a jig to shape it to the desired slope. If you have a router, it would take far more time to set up the jig than to mill it, and less time to make a dry pack extension.

Yes, cover the dry pack with Kerdi sheet membrane with at least a 2" overlap, just like any seam when using Kerdi products.
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Unread 01-19-2021, 07:33 PM   #6
bliddell
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Thanks for the quick replies!

I think I will go with the dry pack for the extension, that sounds like the best option.

A couple quick follow-up questions:

Right now, the bed would be about 2 3/8" thick on one end, and 2 7/8" on the other. I have some more OSB I can throw down in that section to make it not quite as deep. What's a good thickness for the mud bed?

If I make my own dry pack mix using one bag of sand topping mix and 1/2 bag sand, what size bags of each are we talking? I see varying sizes of each sold in the big box stores. (Doing my own rough math, to get a 5:1 ratio I assume you would want to add 30 lb sand to 60 lb sand topping mix, or 40 lb sand to 80 lb sand topping mix).

Thanks again!
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Unread 01-19-2021, 08:36 PM   #7
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Just go with full depth with dry pack. Can’t say I understand the OSB plan but no need for it as far as I can tell.

Re the ratios, I don’t know the starting ratio of the sand mix so I’m afraid I can’t help you.
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Unread 01-19-2021, 08:46 PM   #8
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Quote:
Right now, the bed would be about 2 3/8" thick on one end, and 2 7/8" on the other. I have some more OSB I can throw down in that section to make it not quite as deep. What's a good thickness for the mud bed?
As long as you keep it about 1-1/4" thick or more, that's fine. I think with the sand and topping mix you'll have enough without the OSB. Your choice.


The sand topping mix bags are 60 pounds, and sand is 50 pounds. 30 pounds of sand is the right amount, but half a bag (25 lbs) isn't too little. As long as it's pretty close.
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Unread 01-19-2021, 08:49 PM   #9
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Quote:
Originally Posted by PC
Re the ratios, I don’t know the starting ratio of the sand mix so I’m afraid I can’t help you.
It's 3:1 sand to portland. So 30 pounds of sand makes it 5:1.
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Unread 01-19-2021, 08:57 PM   #10
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Thanks for the information, Kevin.
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Unread 01-20-2021, 08:05 AM   #11
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Here is one that I did. Since I was using Kerdi Board for the walls, I made screed strips out of some scraps to guide me in getting the correct slope.

I also extended the floor heat into that area. This job was done before Ditra heat came out.
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Unread 01-20-2021, 10:14 AM   #12
bliddell
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Thanks all, I am definitely on the right track now.

Rich- those pictures are very helpful, thank you. That's a good idea to use strips of Kerdi board as screeds. I'm also doing my walls in Kerdi board, so I should have some leftover scraps I can use for the same purpose.
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Unread 01-26-2021, 01:40 PM   #13
bliddell
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Shower Window with Kerdi Board

Hello all,

Need some advice on finishing a vinyl window (48x42") in a shower area. I'm using Kerdi board for the shower walls, and am planning on using strips of Kerdi board for the window jamb. The jamb is about 3" deep (including the 1/2" Kerdi board on the shower wall) and wood-framed. The shower area will be about 38x98", with the shower head at one end. The window is on the long side wall on the "drier" end of the shower, but I still want it waterproofed well.

Couple questions:

1) How should I attach the Kerdi board strips to the window jamb? Can I just use Kerdi-Fix as an adhesive, or should I use the Kerdi screws/washers, or both?

2) What is the best method to complete the waterproofing? I was planning on using Kerdi-band to cover the seams, and even considering using the Kerdi corners (using the outside-corner Kerdi Kereck product, but inverted to cover the inside window corners and overlap onto the adjacent wall, if that makes sense). Should I use Kerdi-fix where the boards or the band meet the window? In any event, I'm looking for details on how to do this exactly - how to attach everything, where to place the Kerdi-band, how to overlap and seal, etc.

Attached are a couple of pics of where I'm at so far. Thanks in advance for any tips!
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Unread 01-26-2021, 01:50 PM   #14
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Brian, it'll help if you'll keep your project questions on one thread so folks can see what you're working on and what's been previously asked and answered. A moderator can give it a more generic title any time you'd like to suggest one.

1. My preference would be both, but either would likely do.

2. I would use Kerdi Fix to bond the edge of the KerdiBoard to the window frame. And, of course, KerdiBand for the outside edges.

My opinion; worth price charged.
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Unread 01-26-2021, 02:21 PM   #15
bliddell
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Thanks CX, I wasn't sure whether to start a new thread, but that works fine, and thanks for the input.
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