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Unread 06-26-2022, 06:03 PM   #1
slugger
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Waterproofing tub deck in wet area

Hi all,
I am renovating our master bathroom and seem to be doing something that is a bit different. I am doing a tub within the shower area, but instead of a freestanding tub, or an under-mount tub, I am doing a drop-in tub. In my searches I have not seen any drop-in tubs used in a wet shower area. The wife has found the tub she loves and it comes in drop-in or alcove versions only, so under-mount is out (and cost of under-mount might be prohibitive).

To give a rough idea, the entire "wet" area is a little over 6' square. The tub takes up half that area (6x3) and the shower the rest of that area. The tub deck will have about 2" around the lip of the tub before it hits each wall on three sides, and 2" before it waterfalls to the floor on the shower side.

I plan on using Kerdi waterproofing membrane and or board in the shower (KerdiBoard on all walls, Kerdi pre-fab slope on floor, Kerdi membrane on top of deck). I built a shower for my parents a few years back using Kerdi membrane, so I am familiar with it, but have not used their board yet.

Here are my questions:

1) If I plan correctly, where the tub sits firmly on the subfloor, do I need to use mortar under it as I see in many install vids?

2) The tub deck will have 3/4" ply on top - would Advantech be better?

3) As I see it, from there I have two choices -- apply Kerdi barrier direct to the plywood or use 1/2" KerdiBoard on top of the ply. Which is the better option or is there another I am missing?

4) Should the tub be installed before the tile on the top of the deck? Wondering which would be best for waterproofing and if the tile can support the tub weight?

5) If tub is installed before tile, what is best treatment where tile meets tub?


thanks,
Roger
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Unread 06-26-2022, 07:27 PM   #2
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The reason you haven't seen a drop in tub in a shower area is because it's not recommended. It will eventually leak. You'll be trusting a bead of silicone to keep the deck waterproof which is never a good idea.

I have had at least three people over the years want me to do what you're wanting and I've walked away every time. A tub deck just isn't designed for what you're wanting. Can you do it and make it last? Maybe, maybe not.
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Unread 06-26-2022, 10:01 PM   #3
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Welcome to the forum, Roger.

Since you'll have a horizontal surface around the outer edge of the tub, and a shower splashing water over that area, there's really no good way to keep water running off it.

If you look at a properly built shower, you'll see that every horizontal surface is sloped toward the drain. You don't want any standing water in a wet area. All it would take is one tiny break in your sealant at the tub-deck junction and you'd have water getting in places it shouldn't be.
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Unread 06-27-2022, 07:58 PM   #4
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Kman & Davy,
Well, those obviously weren't the comments I had hoped to read. That said, can you suggest alternatives?

One option, I think, is that Kohler offers the same tub in an alcove configuration. This has a tile flange on three sides and a lip on the front edge that would wrap over and down the front of a tiled apron wall. That would take care of three sides. The tricky spot would be where the aprons taper off at the two front corners. Buuuuttt, if everything is wrapped in kerdi under this it might work.

Screenshot of tub diagram for reference.

Thoughts?

many thanks (even if you didn't tell me what I wanted to hear ).
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Unread 06-27-2022, 08:53 PM   #5
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If you treated that tub as a tub/shower, it may work, with just one other (possible) issue.

You could run the Kerdi up behind the front edge of the tub. No problem there. The potential issue is how it would all tie together at the tub corners. Working Kerdi around the corners and tying together the wall pieces to the tub-front pieces may be a challenge.
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Unread 06-27-2022, 09:31 PM   #6
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Yes, these corners are gonna be a problem. The more I walk through the sequence of how to run the Kerdi, the worse it gets. The kerdi has to be in front of the flanges, but behind the lip -- no way to tie the two together without issues that I can see. Will have to start drawing it out to better visualize the problems.

ugh.

No great solutions that I am seeing and this configuration in the bathroom is the only viable layout I have found.

seriously open to any and all suggestions.
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Unread 06-28-2022, 03:45 PM   #7
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Hi Roger,

I think the alcove tub would be the way to go, but it looks like you've got six feet in length. Is that the length of the alcove tub they have?
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Unread 06-28-2022, 06:16 PM   #8
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John,
Yes, the alcove tub is right at 6' long. Luckily I have fudge room in length by a an inch either way so easy to adapt for that.

Definitely going to be spending some time noodling out the waterproofing details on those two corners. I might be back to run my solutions by all of you for feedback.

It's always something.

thx.
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Unread 06-29-2022, 07:44 AM   #9
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Given the thick flanges of that alcove tub, Roger, you might consider furring out the studs so that your tile backer will drape over the flange. That's what I ended up doing, but the layout of the bathroom allowed for that. I then used a foam backer board which was very easy to cut and notch around those front corners, I used 4X8 sheets to minimize joints. I then carefully placed and cut the water proof band around those corners and sealed them to the tub corners with an adhesive sealant. After the tile is installed it, too, will get silicone around those corners.

You'll have to plan the framing for the tiled apron so installed tile face ends up being flush/close to flush with the front of the tub lip.

I'm pretty confident. But mine, being just a standard tub/shower combo, isn't going to see nearly the amount of water as yours.
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Unread 06-30-2022, 10:03 PM   #10
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Dan, when I ready your reply, I was on my phone and it did not show me the pictures. So coming back to it now on my desktop, your comments make much more sense.

What is interesting is that I pulled down the CAD files from Kohler for the tub and there are conflicting details about the flange edge. On most the drawings the flange is 0.69" wide (see screenshots), but on some the drawing makes it seem like the flange is just an upturned edge of the fiberglass that's ~1/8" thick. I hate it when there are these types of conflicting info (especially when they have gone to the thought and effort of providing such detailed files).

Have any of you guys seen a flange that is almost 3/4 of an inch thick before?

Assuming it is this thick, is the idea (in a normal bathroom situation, not mine) to bring the 1/2" backer board down on top of the flange and the thinset and tile makes the tile hang lower than the flange some? I'm used to the thin flanges so this one threw me (and it looks thicker than Dan's flanges too).

I thought I had the corners figured out in my head, but with these thicker edges, I may have to rethink them some.
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Unread 06-30-2022, 10:26 PM   #11
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Dan, do you have a photo of the structure under the tub? Would be very helpful to see.

thx
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Unread 07-01-2022, 07:04 AM   #12
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Roger,

A 3/4" tub flange is going to be problematic. Assuming the use of typical 1/2" wall board ending just above the flange, you'll still have about a 1/4" difference between the face of the flange and the face of the wall board, and you'll not likely be able make up that difference with thinset mortar. FWIW, the flange on my Kohler was almost 1/2". I used rips of 1/2" plywood to fur out the three walls around the tub.

I set the tub in mortar. Took several in's and out's with the tub before I got it right and level. Let it sit over night before screwing the flange to the studs, then started to build the frame for the front.
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Unread 07-01-2022, 07:13 AM   #13
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Just realized you might have been asking for the underside of the tub. This is what it looked like. The actual tub is pressed into that darker bottom section. From what I recall the installation instructions suggested it could be set flat on the floor, with nothing but some adhesive between those ribs and the subfloor.

I wasn't down for that, I wanted it to feel solid, and make less noise. Hense setting it in mortar.

There's a chance the bottom of the tub you are considering will look like mine. Also a chance it won't, so don't bank on it.
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Unread 07-01-2022, 09:52 PM   #14
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Dan, awesome pics, thx.

> Why ProtectoWrap on the exterior of the tub?

I have done more digging and feel the flanges for my tub will be thinner than the previous post might suggest (based on some photos of the product that I have seen). Assuming that is correct, I have developed construction sequence of waterproofing the most difficult corner of the tub.

Please click on this link to see the animated sequence.
https://up-ideas.com/_files/misc/ShowerDetail-v1.gif

The idea is for the initial membrane to backstop the final kerdiboard. I realized I needed a pathway for the water to get out from between these two layers, so I created the beveled board at the bottom. the final layer of kediboard will have a thin open gap so that any water can exit the back area area and drain down into the floor area as any other water would.

I am confident in this approach eliminating any water getting to structure (albeit a pain in the butt to construct).

If the flange is thicker than my ability to rabbet out the back of the final kediboard (thicker than 1/4"-ish), I will have to do something like you did to accommodate.

Any and all comments welcome.

Thanks again for everyone's help.

Roger
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Unread 07-02-2022, 07:48 AM   #15
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Seems like a lot, Roger, and quick look at Schluter's "Shower Systems Installation Handbook" indicates Kerdi cannot be installed directly to plywood wall panels, which I think I saw in your build up animation. I cling to the idea that furring out the studs is the way to go, but I don't know what obstacles you have that might make that option a challenge.

I applied the Protecto Wrap in an attempt to deaden the sound of the water hitting the sides of the tub while showering. Same idea that some manufacturers of stainless steel sinks employ by sticking matts to the underside, or even a thick coating of some gooey stuff. the PW might also help hold in some heat when taking a bath. But, with no "before" test to compare to, I'm just gonna go with "it works!!"
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