Shower base leveling - Kerdi shower base

[Dchesky]

Hi all, I’m in the middle of my master bath Reno using schluter. Installing the subfloor. Floor is not level so I need to level the area where the shower pan is going. I can’t decide what the best option to level is. I’m putting down two layers of 3/4” ply. Was thinking to use SLC (use the 2x4 curb as dam), let cure, then cut hole for the drain and install kerdi shower base. Other alternative is to find someone to cut me some shims to the correct size and place them every 6” between the two layers of ply. Any opinions on the preferred method?

TIA


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[PC7060]

Hi Dave,

SLC will certainly work as would a standard mud bed. Shimming is really not feasible.

How far out of level are we talking about?

Also, what’s the rationale for the second layer of plywood? Just curious, certainly doesn’t hurt.

[Dchesky]

Thanks for the reply,
Slope is 5/8” over 42”
Using two layers cause that’s what what I took out and I like the strength two layers of 3/4” provides. The other two bathrooms I’ve done in this house the same and they’ve held up great. First time using schluter though.


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[smifwal]

Why not sister another joist(s) on and get your floor level before you put down your plywood.

[Dchesky]

Originally Posted by smifwal

Why not sister another joist(s) on and get your floor level before you put down your plywood. That would be a whole lot easier the SLC route

No room to sister the joists. Lots of electrical in the way.


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[Dchesky]

Another question... for the kerdi tray, is there an issue with using mosaic tiles with the tray? Am I reading the kerdi manual correctly that schluter recommends using a mud pan with mosaic floor tile because of the mesh and glue?


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[cx]

Welcome, Dave.

Not sure what Schluter info you're looking at, but Schluter has no interest in the mesh or glue used to mount mosaic tile sheets at all. And as far as I know they have no published restriction on the size of tile used on their foam shower trays. Perhaps that's something new?

But I would certainly recommend you make your own sloped shower floor from deck mud, which would not only save you a chunk of dinero, but would also eliminate the need for any SLC and would give you a better shower floor.

My opinion; worth price charged.

[Dchesky]

Ok, so if I do go ahead and make my own floor from deck mud, can I still use the kerdi drain and kerdi board on the walls? No issue with combining the two methods? Use kerdi band at the junction between the mud bed and kerdi board?


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[cx]

You must have Kerdi over your entire mud bed and drain, too, Dave, but yes, you can build the same Kerdi shower using the mud bed in lieu of the foam tray.

My opinion; worth price charged.

[Dchesky]

CX, check out page 39 of the Schluter shower systems handbook


https://sccpublic.s3-external-1.amaz...20Handbook.pdf




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[cx]

Well, good for them!

That section doesn't even appear in my old (6 years?) Schluter binder and I'm very happy to see them address that. Even when I do look at that Handbook online I would not even venture to look for that kind of information there.

And I agree with it, which I'm sure is very important to you.

And regardless how you construct your shower, do pay heed to the caution about some of the mounting of mosaics. Some of them simply should not ever be installed in a wet area, especially a shower floor.

We (TYW) have in long past tested the use of 1"x1" glass mosaic tiles installed over Kerdi over the Kerdi foam by driving a forklift on it and I would have no problem at all making such an installation (absent the forklift) for a customer. If, that is, I would ever use a foam tray in a customer's shower, which I would not.

My opinion; worth price charged.

[Dchesky]

Curious though why the same issue they’re calling out, which appears to be related to the glue used on the backing material, wouldn’t apply to a mud bed as well. How does the underlayment affect that. Having a hard time wrapping my head around that...

CX, I’m new here but have been lurking some... you seem to be very much pro mud bed and anti foam pan... experience?
Thanks again for the help!


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[cx]

The problem with the poor examples of backing material on mosaic sheets has nothing at all to do with Schluter's products, Dave, which is why I'm very surprised to see it mentioned at all in their literature. But I'm happy to see it there as an educational tool for shower builders.

I'm very much pro-mud because that's how I first learned to build showers, I suppose, and I see absolutely no advantage whatsoever for the use of the pre-fab foam trays. The foam trays have several disadvantages, including cost, subfloor requirements, lack of proper slope to drain, ease of deforming under the knees of the installer, inability to fit drain locations, etc.

Deck mud is dirt cheap, can be learned by the DIYer in one or two tries, fits the shower footprint and drain location perfectly every time, does not require the substrate to be level, can always be made to have proper, code required, slope, is solid enough to walk or kneel on without damage, cares not at all about the tile size used on it, etc, etc. Just makes a lot more sense to some of us.

My opinion; worth price charged.

[Dchesky]

Thanks much for the reply and info. Spoke with a rep from schluter to get clarification of the info on page 39 and their concern is with small format pebble type tile. The tile I’m using is a 1” x 3” herringbone by Florida tile which they said is perfectly acceptable. Spoke with Florida tile as well and they confirmed that this tile is rated to be used in wet locations and their brochures actually show this tile in a shower.
Totally get and appreciate the opinion on the mud and if it was earlier on and I knew that my joists were so out of level I might have been ok with doing the mud bed but I already purchased the kerdi base and already cut it to fit so unfortunately there’s no turning back now. Gonna go with it.... will use SLC to level then the kerdi pan.
Thanks again


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[jadnashua]

If the size of the shower meets the stock sizes of the pans and if the floor is already flat, you can get the whole area installed and waterproofed easily in one day or probably a lot less, water test, then tile it the next day and move on. The prep is the key. It's been awhile now, but Syracuse university was having all of their dormitories bathrooms redone with Kerdi showers, and they were knocking them out quite quickly because things were standard sizes. The old ones with a different method had become maintenance nightmares.

While you can probably be doing other work in the bathroom, or maybe elsewhere if you're a pro, a conventional mud bed needs to sit at least overnight before you can put the Kerdi on. Then, you still have to wait 24-hours before you can do a flood test (good practice, and required by code most places), then you can tile it. So, your timeline ends up longer...maybe not in actual labor time, but scheduling time. For a homeowner, while time may be a factor, usually, it's that they can't work on it as often, so the extra days in the schedule may not be an issue.

While the materials are cheaper with a mud bed, It's certainly quicker to just spread the thinset and slap down the tray. That assumes you've done or were awarded with the flat surface. If it's way out, the mud bed may save time, and to a pro, time is money. Material costs are important, but time is the bigger issue most of the time.

Protecting the pan is important as point loads will deform it. Once you've got the Kerdi on (if it's not already covered) and tile on it, it's fine. They use foam like that in approaches to bridges when building highways because it's stable and can handle the load...it will work in your shower without issues when installed properly.