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Unread 02-04-2020, 03:33 PM   #1
Ahmad
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2" Oatey Drain height on Pre-slope

Hi everyone,

I'm trying to build a 4x3 shower pan and have a 2" Oatey drain, my first question is how high should the drain flange be from the plywood sub-floor? or to ask differently, should it be flush with the plywood? or higher? if flush then, with even half inch thick mud, the pre-slope will be higher than drain, is that fine? or some mud (how thick?) should go under the drain flange?

2nd question:
I will have pre-slope, then shower pan liner and the final layer of mud, do I still need to apply any kind of waterproofing on the top layer of mud before installing tiles?

3rd question:
I will use cement board for the walls, and on the external wall, it already has some king of tar paper installed, on top of which I will install the cement board. After installing the cement board, do I still need to use any kind liquid or peel & stick water proofing?

4th question (yeah I know, too many questions
I will build the curb from 3x 2x4s, but the curb will not be directly on top of joists, is that fine? or does it have to be on top of the joist. (the sub-floor is made in 1x4 lumber and on top of that I will install a 1/2" plywood.

5th question (okay no more questions)

Thanks for your help in advance!
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Unread 02-04-2020, 05:48 PM   #2
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Welcome Ahmad,

I'm trying to build a 4x3 shower pan and have a 2" Oatey drain, my first question is how high should the drain flange be from the plywood sub-floor? or to ask differently, should it be flush with the plywood? or higher? if flush then, with even half inch thick mud, the pre-slope will be higher than drain, is that fine? or some mud (how thick?) should go under the drain flange?

I believe the minimum pre-slope mud bed thickness at the drain is 3/4". You'd first need to install a cleavage membrane on top of your subfloor and then you need to install some expanded metal lathe. (the mud guys will be along shortly to add additional details if I've missed any).

2nd question:
I will have pre-slope, then shower pan liner and the final layer of mud, do I still need to apply any kind of waterproofing on the top layer of mud before installing tiles?

No, you do not. However, you can, if you chose, install only the single sloped mud bed and then cover that with a water proof membrane.

3rd question:
I will use cement board for the walls, and on the external wall, it already has some king of tar paper installed, on top of which I will install the cement board. After installing the cement board, do I still need to use any kind liquid or peel & stick water proofing?

I would remove the tar paper, install the cement board, then use a liquid water proofing of your choice. Leaving the TP behind the CB AND water proofing the front of the CB can potentially trap moisture in the cement board.

4th question (yeah I know, too many questions
I will build the curb from 3x 2x4s, but the curb will not be directly on top of joists, is that fine? or does it have to be on top of the joist. (the sub-floor is made in 1x4 lumber and on top of that I will install a 1/2" plywood.

If you're covering the sawn 1X4's with 1/2" exterior glue plywood, and then installing the 2X4's that'll be fine. You will want to make certain those 1X4's are in good shape and screwed down. Everywhere.

5th question (okay no more questions)

We'll be right here.

I have my own question. Have you evaluated the joist structure to ensure it'll support a tile installation? Joist size, on center spacing, joist open span? And those 1X4's, are they perpendicular to the joists or on a diagonal?
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Unread 02-04-2020, 06:30 PM   #3
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Welcome, Ahmad.

3. I'm gonna disagree with Dan on #3. If the roofing felt has been properly installed over the joists, i.e. shingled and draped down a couple inches over the waterproof pan liner, that's quite adequate for your wall water containment. In which case you would not want any waterproof liner on the inside of your shower walls.

My opinion; worth price charged.
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Unread 02-04-2020, 09:19 PM   #4
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1. I install the drain so the 4 round nubs on the bottom rest on top of the plywood. That way the drain has support and leaves about 3/4 inch for mud. You want the preslope to be flush with the top of the bottom flange.
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Unread 02-05-2020, 07:07 AM   #5
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Re: #3:

While tar paper applied to the face of the studs, properly overlapped, is adequate and acceptable and is proven to prevent water from getting into the studs and insulation (if present) it doesn't prevent moisture from getting into the cement board itself. Surface applied water proofing will.

Hence ,"I would...".
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Unread 02-05-2020, 08:03 AM   #6
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makes it easy.

http://noblecompany.com/storage/docs...escription.pdf

drains,membranes,bases,niches,curbs,benches,etc
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Unread 02-05-2020, 05:44 PM   #7
Ahmad
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Thanks for the help everyone!

About tar paper on the wall, it's directly on the concrete, i.e. behind the studs, so I believe I need water proofing on the cement board to avoid the moisture transfering to studs from the cement board? I believe the tar paper there is to stop the flow of moisture from the external wall to studs.

@Dan, if the cement board is waterproofed and where from will the moisture get into studs?

Regarding the condition of the subfloor, yeah I checked that's in good shape. Specifically that installed new 1x4s where the curb will be and as I said there will be 1/2 plywood on top.

@Davy , yes I was also thinking installing the drain on the screw snubs , but wasn't sure that it would have enough proper support.
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Unread 02-05-2020, 06:07 PM   #8
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Ahmad, if your current roofing felt is between your shower wall studs and an external concrete wall, the roofing felt has essentially no bearing on the treatment of your shower walls. If you had a geographic location in your User Profile it might help in better evaluating that situation.

You still have the option of using roofing felt or polyethylene sheeting over your studs as your water containment for your shower. Or you can use a direct bonded waterproofing membrane on the inside of your shower walls, but not both.

My opinion; worth price charged.
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Unread 02-06-2020, 07:28 AM   #9
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I'm struggling...

You've got concrete walls but a wood framed floor, Ahmad? And as you have concrete walls it probably means they are exterior walls. If they are exterior walls, and they are located in Toronto, it suggests there is some insulation involved.

Just trying to get a full picture...
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Unread 02-10-2020, 03:19 PM   #10
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Yes, the wall is an exterior wall that is why it's concrete & yes the sub floor is wood.

I'm not sure about insulation inside the wall, as I can't see that, but the only thing on the top of concrete & behind the studs are the tar paper.

I have one more question, when installing the cement board, is it okay if the top layer of mud touches the cement board? or should the cb be slightly higher than the mud? i'm worried that the concrete may absorb the moisture from the mud & transfer it to studs...
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Unread 02-10-2020, 03:25 PM   #11
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You do not plan to have insulation in that stud wall behind your CBU shower walls, Ahmad?

Quote:
Originally Posted by Ahmad
...when installing the cement board, is it okay if the top layer of mud touches the cement board?
Not understanding the question. What mud are we talking about?
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Unread 02-11-2020, 12:15 PM   #12
Ahmad
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@cx

If you are talking about insulation on the wall, I don't know as there could already be blow-in insulation in those walls, as it's an old house, but i can't see it and we recently bought the property so don't know for sure. I will have someone look into it in the future.

about the other question;

So i see online that the wall cement board is installed before the top layer of mortar is poured, this would mean that part of the cement board (about an inch or so) will be in direct contact with the mortar, is this fine? and wouldn't the cement board suck the any moisture from the mortar shower pan? or should I install the cement board after the top layer of mortar is dried and keep a small gap to fill with silicone?
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Unread 02-11-2020, 01:16 PM   #13
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Ah, now I understand. Yes, you can safely bury the bottom edge of your wallboard in the top mud bed of your receptor, Ahmad. That is a very effective method of supporting the wallboard down where you cannot use mechanical fasteners and the presence of the CBU will not adversely affect the deck mud.

But it must be a true CBU (ASTM C1325) and not a Fiber/Cement board or any sort of gypsum-based board.

My opinion; worth price charged.
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Unread 02-11-2020, 04:27 PM   #14
Ahmad
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Thanks CX, I really appreciate the help!

I'm about do install the curb and then should be ready to do the pre-slope. I have checked the mud calculator on this forum, it recommends a combination of sand topping mix and sand, while I looked at home depot, they have this sand mix, and the manufacturer doesn't instruct for it to be mixed with any extra sand. do i have to mix extra sand with this product?
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Unread 02-11-2020, 04:51 PM   #15
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Likely about the same material as Quikrete's Sand Topping Mix, Ahmad, but I can't prove that, 'specially with all that French on the bag, eh?

But with an advertised compression strength of 5000 psi, I gotta believe it's somewhere close to a 3:1 sand/cement ratio and for ease of placement as a shower floor pre-slope and proper functioning as a shower top mortar bed, I'd still want to mix it with some sand to get closer to a 5:1 ratio.

You can certainly use it straight out of the bag for your pre-slope, but I think you'll find it a bit difficult to work with as a dry-pack material. There are no rules (well, almost no) for what you can use as a pre-slope so long as it provides a very flat properly sloped bed for your waterproof liner and is structurally sound. The final mud bed is more critical and must end up with the proper consistency to allow easy water passage while providing a solid substrate for your tile installation. The industry standard for the mix south of your border is a 4:1 sand/cement ratio, but many of us use the same 5:1 ratio as for all other tile dry-pack (deck mud) substrates.

I'm not sufficiently fluent in TTMAC to know the requirements up there in the frozen north, eh?

My opinion; worth price charged.
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