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Unread 10-16-2020, 11:19 PM   #1
dreade
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First-time shower pan questions

Hi,

I'm looking for some advice on a first-time shower pan rebuild. I noticed some issued with my shower floor so I decided to rip out my shower pan & first row of wall tile and I'm starting to rebuild.

I've installed a 3-piece drain, and plan to float the pre-sloped dry pack tomorrow, install the liner, second mortar bed, then tile later next week. I've got a couple questions:

1. Behind the 1st row of wall tile was green board. I cut this out to accommodate installation of the pan liner. Its my understanding green board isn't commonly used in showers now. That said, can I replaced this section with Kerdie board screwed to the studs?

2. How do I waterproof the transition from greenboard to Kerdie board on the walls? Would a couple coats of Redguard do the job or is there a better method?

3. Do I used modified or unmodified thinset on the wall & floor tile?

Photo attached for reference.

Dennis
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Unread 10-17-2020, 06:08 AM   #2
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Question

Welcome to the forum, Dennis.

Green board has been prohibited by many codes for 15 years. Typically, there are a few fundamental issues with doing a pan replacement like you’re doing that are difficult to accomplish: The first is getting the lower waterproofing behind the upper water proofing so it sheds water. But it doesn’t appear that you’ve got any wall waterproofing to begin with. It appears that your tile and grout are acting as the waterproofing. It’s quite rare that your shower hasn’t already deteriorated into wet, swollen, soggy greenboard. With that circle pitch around the drain, it makes me wonder if that’s a proper pitch to the entire floor...and perhaps this was a rarely used shower that allowed it to beat the odds on longevity.

The second is adequately tying the lower and upper substrates together. You happen to have a couple inches of exposed upper substrate that would allow for pieces of ply to be reinforcing behind the seams of the two substrates. This is something of a small miracle.

And the third is to avoid the bulky build up of new layers that will prevent the new tile from being installed flush with the existing.

What’s awkward about your proposed repair is that your clamping drain has behind-the-substrate waterproofing, your KerdiBoard has surface waterproifing, and your existing walls have no waterproofing.

And any other proposed repair has a fundamental lack of a waterproofing method to tie the new to old...seeing as how you have no existing wall waterproofing. Most pros will sigh and tell you to start over, although most customers don’t want to hear that. Can you repair this and continue your lucky streak that the greenboard will survive? Obviously you think so. What do I think? I think your luck will need to continue for this to last. One thing we do on this forum is educate what methods have been “approved” that have proven long service life histories. So, if there’s a method that’s unproven, we like to come right out and say that so you can more accurately assess the odds to judge whether you want to spend money on such.

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Unread 10-17-2020, 07:26 AM   #3
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A couple more things to consider, Dennis.

Given the current drain placement I'd guess that the previous shower floor was something other than a mud bed/liner/mud bed configuration.

Since your drain is position closer to one end, and since the bottom mud bed must be - I believe, a minimum of 3/4" thick at the drain, in order to achieve the necessary minimum slope of 1/4" per foot it appears to me you bottom bed will need to be close to 2" thick at far rear corners. Then add the thickness of the 2nd mud bed. I can't tell from here, but is your curb going to be high enough?

Beyond that, you'll need some blocking between all those wall studs to contain the mud beds. You'll also want to notch out the bottom of the studs to accommodate the thickness of the liner - especially in the corners because of the folds, so that when you do install whatever wall board you decide on it will lay flat on the wall.
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Unread 10-17-2020, 08:25 AM   #4
dreade
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Guys, thanks for the information.

The previous shower had a pan liner on top of the subfloor, and tile directly onto the liner with thinset. No preslope mortar bed, no secondary mortar bed.

I'm trying to wrap my head around the preslope mortar thickness. The drain flange is a 1/4 inch above the subfloor, and the furthest wall from the drain is about 4 ft. For a proper slope, will I need 1.25 inch thickness at the wall down to 1/4 thickness at the flange?

Also, there was a thick coat of gray stuff applied to the greenboard that I chiselled off along with the old thinset. Any idea what this is? Heres a picture before I cut out the greenboard.
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Unread 10-17-2020, 08:38 AM   #5
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Welcome, Dennis.

A geographic location in your User Profile might help us understand the construction method used in that shower. Or it might not. But it will help in answering some types of questions.

How long had that shower been in use before you "...noticed some issued with my shower floor?"

Given what you currently know about the construction, I'm gonna be one of those people Goldstein said would sigh and tell you you really need to tear out the whole thing and start over. But that's only if you want a long lasting shower. If you're content to just patch up what you've got 'till a time more convenient for the complete re-do, I can understand that, but only so long as you realize that's the best you can do with your approach.

My opinion; worth price charged.
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Unread 10-17-2020, 08:50 AM   #6
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You mentioned having issues with the shower floor. What kind of issues? Tiles can't be bonded directly to a shower pan liner like they can to a surface applied membrane (Kerdi for example).

I agree with the others. Without any waterproofing behind the wall tiles, you'll be better off to take it all down and start over. I was also thinking that this shower hasn't been installed very long or wasn't used much.

Here's a shower that belongs to a friend of mine. It had greenboard behind cement board with no moisture barrier. It was 17 years old but the homeowner talked about it needing to be replaced 10 years earlier.
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Unread 10-18-2020, 08:24 PM   #7
dreade
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Starting over

New plan. I ripped out the rest of the shower and will start it over.

I originally planned a dry pack pre-slope, but after watching some Youtube videos and reading this website last night, I'm wondering if a Schluter system will be an easier install for a first-time shower attempt. I could simply swap out drains. Any recommendations on the method I should pursue to make this as painless as possible?

My only concern with the Schluter pan is the off-center drain pan will need to be trimmed to fit my shower on the sides, and I'll need to add mortar to the end to extend the pan to the wall, resulting in different heights of the pan on two sides. How do I compensate for this when I place my first row of wall tile?

As a side note, ripped out the basement pan as well last night and discovered no pan liner. Somehow no water damage to the studs - shower was rarely used.
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Unread 10-18-2020, 08:34 PM   #8
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Dennis, you use either the traditional method of creating your shower receptor or one of the direct bonded waterproofing membrane methods (Schluter's Kerdi is one) and either will work fine if done correctly. I think it a mistake to think the Kerdi shower would be an "easier install" for a first timer. Both methods require some attention to detail, but of the two the traditional method is probably the least technically demanding. There is no rocket surgery involved in either!

Regardless your choice, I would recommend you create your own sloped floor using deck mud to fit exactly your shower footprint and drain location. You can do that with a single mud bed for the direct bonded waterproofing membrane type construction, or two such mud beds for the traditional receptor construction.

The traditional method will be less expensive if that's a consideration. And using a mud bed with the waterproof membrane method is substantially less expensive with the mud bed floor than with the foam tray. And the mud bed is by far the better floor.

With either method I would recommend you move the drain to the center of the shower footprint.

Did you note post #5?

My opinion; worth price charged.
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Unread 10-19-2020, 07:47 PM   #9
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CX, The house is 14 years old and I suspect this shower would of had regular use before I purchased it several months ago. I've never used the shower. I'm quite surprised there's no water damage. I'm located in Alberta. Not sure if that tells you anything about how it may of been constructed.

Before I begin the pan, is it necessary I reinforce the subfloor with a second piece of plywood? If so, since the drain is already installed, will two pieces of plywood positioned perpendicular the floor joists, each with semi-circles cut to accommodate the drain provide similar structural support as a single piece of plywood? Or should I cut out the drain and start over?

Also, if I use kerdi board for the walls, will I require a vapour barrier behind the board, like I suspect one may need if installing cement board?
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Unread 10-19-2020, 07:51 PM   #10
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Kerdiboard is waterproof on its own, so no, nothing needed behind it. Kerdiboard is designed as part of a system, which would include their drain, and waterproofing on the pan as well as sealing all of the seams and joints with KerdiBand.
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Unread 10-19-2020, 08:33 PM   #11
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What is your current subfloor structure?

Are you planning to move the drain?

I'm thinking that shower was waterproofed with some sort of cementitious waterproofing membrane. I don't know what Ardex 8+9 looks like after installation, but I think it must be something like that. No way that shower could be in that condition after 14 years without it was waterproofed in some manner.

'Fraid your being in Alberta doesn't give me any insight into the shower construction method, though. Perhaps someone else know something about the common methods in that area. Will help in answering some other types of questions, though.

My opinion; worth price charged.
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Unread 10-19-2020, 10:25 PM   #12
dreade
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The subfloor is 3/4 inch plywood on 2X10 joists spaced 16 inches apart.

I would prefer to leave the drain where it is. The drain is 4 ft to the far wall, and the flange is about 3/8 inch above the subfloor. I figure this means the pre-slope will roughly be 1.5 inch at the wall, and the second dry pack will add another 1.5 inches or so. My curb is currently two 2x4s stacked, but I figure I can add a third 2x4 to accommodate the 3 inch thick pan.

That said, perhaps you have a good reason for why I might want to move the drain that I've not considered.
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Unread 10-20-2020, 08:44 AM   #13
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You really want the perimeter of your shower to be level to make the wall tiling look best and the centered drain allows you to have a more consistent slope to your drain.

With your current drain location, the areas closer to the drain will have a much steeper slope than the areas farthest from the drain. Less than ideal.

You must measure for your slope to the farthest corner from the drain, not to the far wall, and 1/4" per foot is the minimum required slope.

My opinion; worth price charged.
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Unread 10-20-2020, 08:54 PM   #14
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Just my two cents (a homeowner - not a pro) from someone who has done a traditional shower with a pre-slope/liner/mud bed and cbu/poly behind the wall and also a shluter system shower using the tray and Kerdi board where the drain was off center...you’ll be much happier centering the drain and building a mud bed no matter which shower construction method you choose to use. Personally, if I do another shower I will probably use Kerdi board again for the walls and build a mortar bed for the floor. Just my opinion. Like I said, just my two cents, which is probably worth a penny.


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Unread 10-20-2020, 09:23 PM   #15
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Great advice, Greg.
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