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Unread 01-13-2020, 08:35 AM   #1
TimNorth
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Kerdi-TS Shower Base - Slope Question

Hi all,

Long-time lurker, first-time poster - thank you for all the knowledge shared in these forums.

I am speaking with a tile contractor about getting a new shower installed.

The quote specs call for using Kerdi waterproofing on the walls and the KERDI-SHOWER-TS base, which is their 38" x 60" pre-waterproofed base. It has an offset drain, which would match the placement of the drain in the acrylic shower base he is tearing out.

My concern is that Schluter's specs on this base show only 1% slope across the length.

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1% is only 0.12" slope per foot, and every recommendation I've seen calls for 0.25-0.5" of slope per foot to ensure proper drainage.

Do you think the slope on this base is adequate? Has anyone used it successfully?

I'm confused why Kerdi would make it this way, and I don't want to take any chances and make an expensive mistake.

Thank you!
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Unread 01-13-2020, 09:16 AM   #2
D & D Reno
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Welcome!

I can’t say I’ve ever paid attention to the slope percent. 1/4” per foot is the plumbing code. I can say from doing numerous bathtub to shower conversions with 3x5 Kerdi offset drain pans, they drain perfectly. It’s geeky, but I’m always amazed out how evenly and nice they drain as opposed to some hand poured pans I’ve seen.
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Unread 01-13-2020, 09:54 AM   #3
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Wink

as mentioned Code is 1/4" per foot slope. This is even more critical when using smaller tiles and for sure natural stone. Also working on the base itself, extra care should be taken as not to indent the foam..

https://noblecompany.com/storage/doc...escription.pdf
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Unread 01-13-2020, 10:24 AM   #4
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Welcome aboard, Tim.

Another thing to check when using one of those foam shower pans, the floor that it will be installed on needs to be level. While it will probably be ok if the floor was a little low at the drain end, it'll be a problem if it's a little low at the far end, especially given the minimal slope that Schluter pan has.
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Unread 01-13-2020, 10:35 AM   #5
TimNorth
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Thank you all for the feedback.

Antonio - thanks for sharing your experience. Comforting to know you've used this base successfully.

Dan - definitely makes sense on pre-levelling the floor. I will make sure about that.

Eric - so this is the part that confuses me. If code is 1/4" slope per foot, this base looks like it only has about 1/8" slope (0.12") per foot at a 1% slope.

1/4" fall per foot would require about a 2% slope.

Doesn't that mean this base is not compliant with that code? Or am I missing something?

Thanks again!
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Unread 01-13-2020, 10:58 AM   #6
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you would be correct , not compliant with 1/4" p.f. slope.
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Unread 01-13-2020, 02:18 PM   #7
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Welcome, Tim.

You'll find old reference to that slope issue other places here on the site, a couple specifically from me wondering just how those manufacturers have secured approval for those foam trays with less than code compliant slope for use as tiled shower receptors.

I've still not found an answer.
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Unread 01-13-2020, 02:31 PM   #8
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its the membrane that has the listing, not the entire assembly. Kinda like installing a Listed Membrane on a flat substrate. The installation is not compliant but the membrane is. With all that said, Installing a base with out sufficient slope(1/4"p.f. from farthest point, the corners) would not meet Plumbing code.
as you always say--in my opinion!
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Unread 01-13-2020, 03:29 PM   #9
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Thanks guys. It's good knowing I'm not just missing something.

One alternative I considered is using the pre-fab base with the centered drain. It would require moving the drain slightly but it is an unfinished basement beneath the shower, so that will not be difficult to do.

With this version of the base, the slope is good all the way around.

However, the downside here is that the drain tends to be a bit more underfoot.

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Unread 01-13-2020, 03:42 PM   #10
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The base from Noble Company,( I attached in post #3,) End Drain 32" x60" is many times stronger/less compressible and has 1/4"pf slope, measured from the farthest corners.( Not sides making the 1% even less)
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Unread 01-13-2020, 07:08 PM   #11
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Thanks Eric, I'll take a look. I hadn't heard of these products before.
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Unread 01-13-2020, 07:12 PM   #12
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Tim, I would recommend you move your drain to the center of your shower footprint and create your own sloped floor using deck mud to precisely fit your shower footpring and drain location. Much less expensive and a much better floor.

My opinion; worth price charged.
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Unread 01-13-2020, 07:52 PM   #13
TimNorth
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Quote:
Tim, I would recommend you move your drain to the center of your shower footprint and create your own sloped floor using deck mud to precisely fit your shower footpring and drain location. Much less expensive and a much better floor.
Do you recommend the central drain positioning because it is easier to get a good slope that way, or are there other factors that make a centered drain preferable to having it offset to one end?

Is the mud floor better in your opinion as it is sturdier than a foam base?

Thanks a lot CX!
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Unread 01-13-2020, 08:49 PM   #14
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Center drain allows reasonable slopes all around while keeping the perimeter level, which makes for easier and more visually pleasing wall tile installation.

Not only sturdier, but eliminates the need for a near perfectly level subfloor.

My opinion; worth price charged.
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Unread 01-13-2020, 09:23 PM   #15
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Makes good sense. Thank you.
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