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Unread 09-16-2020, 05:08 PM   #1
pjs826
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Kerdi shower with KBRs corner seat

I've been lurking for years and finding good pointers, unfortunately, I have not been able to find another post quite like my situation, so am looking for some advice.

I purchased a 48X48 Kerdi shower system with Pre formed shower tray.
I also have a KBRS10X10(X 20 high) triangular Shower seat, coated with Showerseal
(looks like their version of Redguard) on it. It feels like it’s a rubberized coating.

1- Shower has a ¾” OSB floor.
Do I use UNmodified thin-set under preformed shower tray?

2- Walls are standard ½” Gypsum wallboard. KBRS 10X10 triangular seat(like a smaller version of a Kerdi corner seat-except for the outer coating). Shower is only 32’ X 48”, so I did not want to lose too much real estate to the seat.

KBRS is calling for walls to be SHOWERSEAL coated first, then apply
Modified thin-set to adhere seat to wall and floor. Should then caulk seams
between seat and walls with Showerseal Polyurethane Sealant.
However, I’m using Kerdi membrane instead of Showerseal coating.

I would prefer to seal the KBRS corner seat with Kerdi.
Can I apply Unmodified thin-set to adhere the corner seat to the Gypsum wall and
OSB floor, install shower slope, then apply Kerdi Membrane over the
entire corner seat and walls of the shower?
Sealing the seat behind protective membrane, rather than inside of it.

KBRS calls for Modified thin-set to adhere to walls and floor,
then thin-set to apply tile(not specifying Modified or Unmodified thinset).
KBRS has not responded to my question about tile setting thin-set.

Kerdi calls for UNmodified thinset for their portion, which do I use?



I’m leaning towards Mapei Kerabond T. It’s what the tile store carries and read
it works with Kerdi system.

Thanks,
Phil
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Unread 09-16-2020, 08:30 PM   #2
cx
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Welcome, Phil.

Some clarification will be helpful here. You indicate that you have 48"X48" KBRS shower kit, but you have a 32"X48" shower. The only KBRS shower receptor products I'm familiar with are complete receptors that cannot be changed in size or shape at all. You cannot yet post links (anti-spam measure), but if you'll just spell out the link to the specific product you have, with an extra space in the www, a moderator will light it up for you. Then we can all be on the same page.

Trying to mix and match various manufacturers' waterproofing products is not always a simple procedure. Usually best to stay with a single manufacturer to prevent dilemmas such as you're describing here. But if you've already decided upon and purchased your products, we can usually help put them together. We cannot, however, provide any product warranties, nor will any of the product manufacturers in that case.

I'll wait for the link to what you're planning to use before trying to go any further. While waiting, I'll point out that thinset, or thin-set, is not a product. It's a method of ceramic tile installation. Thinset mortar, on the other hand, is a product used to bond tiles and other materials using the thinset method.

The dilemma between use of modified and unmodified thinset mortars seems to be limited to Schluter Systems for the most part. Initially they were concerned with latex modified mortars, but eliminated all modified thinset mortars from most uses of all their products. Today there are many (perhaps most?) modified thinset mortars that do not use latex as their modifier and work just fine with Schluter's products. Schluter even makes their own "modified" thinset mortar that they say is fine to use with their products. For a rather hefty price, of course. And all other manufacturers of similar membrane products require the use of modified thinset mortars.

Generally speaking, I'd say at this point Schluter has come up with a fine solution that is desperately searching for a problem.

Get us on the page with you and the KBRS products you intend to use and we'll go from there.

My opinion; worth price charged.
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Unread 09-16-2020, 10:22 PM   #3
pjs826
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KBRS corner seat

Thanks for responding.
I knew mixing products is not ideal, but CAN be done. I was hoping for a little guidance, based on experience, not expecting to hold anyone else responsible.

Kerdi says the shower floor can be cut to fit, that was why I bought the 48X48 kit. This is from the installation book.
Schluter-KERDI-DRAIN with Schluter-KERDI-SHOWER-T/-TS/-TT prefabricated
shower trays
The substrate must be clean, even, and load bearing. Any leveling must be done prior to shower tray installation. If necessary, cut the tray to size prior to
application; ideally, the tray is cut equally on all sides to ensure a consistent perimeter height. The base can also be extended beyond the tray using dry-pack
mortar.


Kerdi kit

The shower seat is 10X10X20 high, trying to save some space in shower.
Cornerseat from KBRS is here.

Again thank you.
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Last edited by cx; 09-16-2020 at 11:32 PM.
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Unread 09-16-2020, 11:45 PM   #4
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OK, the problem was that I thought you had a KBRS shower receptor when you actually have a complete Schluter Kerdi shower kit with a KBRS corner seat. Sorry for the misunderstanding.

I personally think it is a very poor idea to use a large foam shower tray like that and cut it down to the size you have, but technically it's legal according to the manufacturer. You could have saved a good deal of money and had a much better shower floor that was level around the entire perimeter, had the required 1/4" per foot slope to a drain, and perfectly fit the shower footprint and drain location. But if you're happy with what you've got, that's fine.

The reason Schluter tells you to use an unmodified mortar to bond your shower tray to the wood framed subfloor in violation of all mortar manufacturers' recommendations, is, they say, to make it more convenient for you so you need purchase only one type of thinset mortar for your project. Apparently they've done their own testing and are confident that will work well enough in that specific application.

As for your thinset mortar questions, with those differing manufacturers you're gonna violate someone's instructions regardless the type of mortar you elect to use. Were I doing what you plan, I'd go to my local Home Depot and purchase Custom's Versabond, a modified thinset mortar proven over and over to work just fine with all Schluter products. There are many other thinset mortars that will do the same.

If you elect to use a high quality un-modified mortar, I have no doubt it would work just fine with the products you've selected, too, but see my warranty information below.

My opinion; worth price charged.
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Last edited by cx; 09-16-2020 at 11:54 PM.
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Unread 09-17-2020, 08:41 PM   #5
pjs826
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Custom Versabond

So I can use Custom Versabond to adhere my shower tray to the OSB,
adhere my KBRS shower seat to the floor and wall, adhere my Kerdi to the gypsum and finish the Kerdi, then finally adhere my tile to the Kerdi?

If so, this sounds like the best option for my situation.
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Unread 09-17-2020, 09:37 PM   #6
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Once again I refer you to my warranty information, but that is exactly what I would do.

Presuming that I would use a Kerdi foam shower tray, which I would not.

My opinion; worth price charged.
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Unread 09-19-2020, 02:14 PM   #7
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Welcome to trying to mix in other manufacturer's products with the Kerdi system.

Schluter wants you to use unmodified mortar for their products. Most other manufacturer's, including KBRS, are OK with modified mortars.

You can install that whole system with unmodified mortar and it'll be fine. Or you can switch to modified but you'll lose your warranty.

I'm astonished the Schluter wants their shower trays installed with unmodified mortar over wood subfloor. But that's what the instructions say.
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