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-   -   kerdi foam shower tray over OSB (https://www.johnbridge.com/vbulletin/showthread.php?t=124679)

JMG 01-15-2018 09:01 PM

kerdi shower kit thinset coverage
Hello everyone

I have a 32x60 kerdi shower kit with foam shower tray and curb that I have had for a bit. I am finally ready to tackle our shower project.

The kit will be installed in an alcove in place of a bath tub. I intend on using 4x8 subway tiles for the walls and 2x2 tiles on the floor. One 12x12 niche, a couple of corner shelves and a soap dish. Nothing fancy.

I have a couple of questions.

First, I am trying to get an idea of how much thinset to purchase for embedding kerdi on the walls, embedding the tray and setting the wall and floor tile.

Second, unless I seek a specialty tile store I am limited on available thinset, unless I order online. Not a big deal either way, but the costs for something like Schluter All-set or Laticrete 317 looks to be quite a bit more than what is readily available down the street which is Versabond at the big orange store. Yes, I know Versabond voids the warranty, but cost vs value vs the right thing to do?

Any feedback?

Gozo 01-15-2018 09:50 PM

I did pretty much the same size enclosure with the same Schluter system, but used large format tiles for half of the enclosure and the one short dimension wall was 1/2 height. Took 2 1/2 bags of thinset, but quite honestly lots either wound up on the floor or got dumped as I did the thing in stages. I figured on 2 but had to pick up one more later, but my local tile shop has a wide variety of brands in stock.

Redlands Okie 01-15-2018 10:08 PM

Keep in mind all of the work your doing. Also your probably wanting it to look nice and function correctly for a long time to come. Your saving a lot of money by doing it yourself instead of hiring it done. So...... if you can somehow find the products you need and can pay for the schluter or laticrete and not worry about saving a few bucks on what might be a several thousand dollar job then why risk getting to do it over again ? Itís a lot easier to do it right the first time and cheaper also.
Please keep in mind I am not trying to make saving money sound bad. Just trying to put some perspective on the HUGE value of your time, effort, pride, and materials of getting your project right on the first try :)

JMG 01-15-2018 10:35 PM

Thanks! I think I was looking for someone to verify what I knew to be the answer...ha ha.

workhurts 01-15-2018 11:29 PM

There is never 'the answer' but 'an answer'. Quite a few people on this site have used versabond. Was in a similar situation as you and ended up with TEC uncoupling from Lowes for about $15/bag. Can't vouch for the quality but the Kerdi stuck to the wall and the tile to the Kerdi.

I'll let you know in a couple of years.

As for coverage, it was all over the place with quite a bit waste squeezing it out from behind the Kerdi and mixing too much of it.

Not sure if anyone really talks about this but if using mosaic, the Kerdi seams and corners kinda stick out. I'd use my extra thinset to feather out things.

JMG 01-15-2018 11:36 PM

Thanks for the reply, I appreciate it. Our local menards has Tec, but not sure they carry that. I will look into it.

JMG 01-29-2018 06:41 PM

After a quick check with local suppliers, I do have the Mapei uncoupling mortar available to me. Seems like a decent choice when no other is readily available.

We have finalized our selections: 4x8 ceramic subway on the walls, 2x2 porcelain on the shower floor. One 12x12 niche and two corner shelves

The Mapei uncoupling mortar can handle it all? i.e. kerdi on the walls ,shower tray and curb on the floor and all the tile on top?

If that's the case...im going for it!

JMG 02-06-2018 01:35 PM

kerdi foam shower tray over OSB
Good afternoon!

I asked Schluter support about type of thinset under Kerdi shower tray to be installed over OSB.

Support answered that they recommend modified. This seems to contradict what I have read but ok.

If that is the case, I am assuming Versabond is ok?

I will be using Ditraset to install the kerdi on the walls and to set the tiles.

houndzilla 02-06-2018 01:55 PM

they like to see modified when you are attaching to any sort of wood product and unmodified pretty much everywhere else

JMG 02-06-2018 02:14 PM

Thanks for the reply George.

Tool Guy - Kg 02-06-2018 08:03 PM


Schluter will approve the use of modified OR unmodified for the installation of their foam tray on OSB. While they would prefer modified (if everything else was equal), they are perfectly happy with unmodified because their studies show that it works just fine and Schluter doesn't want you having to buy a separate bag of modified for the sole task of installing thier foam tray.


John Bridge 02-07-2018 09:56 AM

However, :)

I've found that unmodified thinset will not stick to plywood or OSB, and I have always disagreed with Schluter on that point. The VersaBond will work well. :)

JMG 02-07-2018 10:05 AM

Thanks John.
I was actually surprised that Schluter told me to use modified over the OSB!

I swear the printed directions and all schluter videos mention unmodified but I was happy to have their blessings.

Versabond it is!

JMG 02-11-2018 12:31 PM

7/8" OSB in shower alcove issue
Good afternoon

I removed an old builder grade tub shower in preparation to install a 32x60 kerdi shower kit in an existing alcove.

Water lines are plumbed in and I am getting ready to rework the drain.

My question is:

I need to replace a section of OSB subfloor. In my case, it is 7/8" thick OSB as my second floor I-joists are 24" on center. None of the big box stores in the area carry 7/8" OSB (though I have access to a good lumberyard on Monday).

Would I be ok replacing the small section with 3/4" OSB? If so, advice on how to make up the 1/8" difference? Im a bit at a stand still until I get this resolved.

Kman 02-11-2018 02:04 PM

Jason, let's keep all questions related to this project on this thread so that questions and answers aren't duplicated, and the history is in one place. :)

Other than using a combination of 1/2" ply and 3/8" ply ( which I definitely would not do), I can't think of anything off the top of my head that would add up to 7/8".

I'd wait til you can get to a lumber yard and find the right thing. You'll probably save time in the end.

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