Kerdi on a curved joint [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


View Full Version : Kerdi on a curved joint

04-12-2014, 07:39 PM
I am in the process of remodeling my master bath with a new shower. I have included a tiled barrel ceiling in the design. I'm getting ready to waterproof with Kerdi and realized that I need Kerdi Band along the curved joint between the ceiling and wall.

This leads to the question: How can I apply the Kerdi across the joint without the Kerdi pleating/puckering on the wall side of the barrel? I think of wrapping a gift with one curved side and not being able to get the opposite side perfectly flat without pleating the fold. Of course, pleats aren't a big problem in gift wrapping because I don't expect to put tile over it!

This is one of the few topics I haven't been able to work through with a simple google search. Has anyone here dealt with this previously?


Sponsored Links

04-12-2014, 10:23 PM
Call Schluter's tech support line on Monday and see what they may come up with.

If I was going to do it, I think I'd probably do the barrel vault with their Kerdiboard, and maybe just use some Kerdifix to attach a piece on the edge up to the ceiling. But, assuming it's already need to tear things out. Is this a steam shower? If it is, that complicates things.

Got a picture of the ceiling and where it sits relative to the whole shower?

04-12-2014, 11:29 PM
Welcome, Greg. :)

Unless this is to be a steam shower, I'd be inclined to eliminate the Kerdi from the ceiling all together. That's not generally considered part of the wet area of a standard residential shower.

But if you insist, you can simply make cuts in the ceiling material like piano keys and let those tabs overlap, then cover that section with your wall Kerdi. A fella can get a pretty close approximation of the advertised corner folds for that product.

My opinion; worth price charged.

04-13-2014, 07:01 AM
Thanks all for the info. I think a few more details are in order based on the replies. First, while not technically a steamer, I am building to steam specs so I can add steam later without tearing the whole thing out. I'm also so spooked by the bad places in which water has turned up, I am going out of my way (some might say obsessed, but a wife would never say that, right?) to make certain it never leaves its proper domain (at least from the bathroom perspective) again. That's why the Kerdi (not to mention the tile) on the ceiling.

Next, the attached photo shows the current state. I have framing, insulation, water supply for rainshower, and lighting in the ceiling. I also have several sheets of Permabase Flex board - I'm currently cutting out for penetrations. I looked at flex Kerdi Board, but thought it more expensive without benefit vs. Kerdi on my Permabase. I assume that I could still create the Kerdifix movement joint that Jim described based on this.

That said, would the Kerdi solution CX described be more reliable? CX, I'm also trying to envision how your "Kerdi wedgie" of a movement joint would fit with the solution you propose. I think you're just saying to cut the Kerdi where it would crease and then overlap (I assume creating a thinset sandwich) on the wall. Do I have this right?


04-13-2014, 07:23 AM
That's a much bigger radius than I was envisioning, Greg, but I still don't think you're gonna have much luck doing a wedgie there for a movement accommodation joint with the regular Kerdi or KerdiBand. Schluter does make a KerdiFlex product that may or may not work there. I've never used the product and don't really know just how flexible it might be.

The only other option I could suggest is that you move your movement accommodation joint to a straight line across the bottom of your vault on those end walls. There you could make a wedgie with good results.

You do understand that Kerdi does not meet the current requirement for a continuous use steam shower, right? I'd personally be quite happy to use Kerdi in any residential steam shower, but I don't know who's requirements you're trying to meet.

My opinion; worth price charged.

04-13-2014, 03:23 PM
The industry recently moved the perm rating for commercial showers from <1 to <0.5. Kerdi meets the residential spec, which is still <1. KerdiDS meets the spec for a continuous use shower.

Industry wants a 2"/foot slope on the steam room ceiling. If you want to avoid caulk in those radiused seams, Schluter will notch the leg portion of a profile for you at a cost so that it will bend smoothly. You can do it yourself, but would be unlikely to make your cutouts as consistent, and it may or may not bend as smoothly.

Schluter might allow Kerdifix at that wall/ceiling seam, but I think I'd fold the band in half, then cut slits from the edge to near to that fold line, then install the band with the continuous side on the ceiling, and then carefully overlap the band's flaps (created by the cuts) on the wall. THen, maybe a bead of Kerdifix at the seam. If you then used one of the notched expansion joints, it has a little relief on the back side and most have a pocket to hold the edge of the tile and hide the cut (which would make the wall tile cutting much less exacting, as well). If you choose the profile color and a similar grout, they can disappear. I'd ask Schluter which one might work best in this situation.

04-13-2014, 04:09 PM
Hi All,

I was aware of the new requirements which require Kerdi DS in continuous use steamers, but I didn't think that would apply to a residential application. Is my assumption correct? The radius on the ceiling drops 6" from the center and the shower is 4.5'. Therefore I have better than 3" per foot - designed with the sloped ceiling requirement in mind.

Jim, by profile, are you referring to the Dilex product? That is what I was planning to use but I haven't used it previously and therefore didn't know how to bend it. Sounds like the tip here is to have Schluter do it for me. True?

So based on the info so far, it sound like the order of operation is to install my backer leaving the customary 3/4" gap at all perimeters, then install Kerdi on flats, give it a wedgie with Kerdi Band w/ backer rod on the 2 flat joints, fill the curved joint with thinset and Kerdi Band with nip/tuck along the wall side, then install Dilex which has been bent appropriately where I have the radius joints.

Does this sound correct? Do I have too much overkill? I tend to be a belt and suspenders type of guy - if it's worth doing, it's worth overdoing. Since this is all DIY, I don't have to worry about putting food on the table this way. A good thing - stuff is always done well but never on schedule!

04-13-2014, 04:22 PM
IMHO, 3/4" is too much of a gap in the corners! I haven't reviewed the TCNA guidelines on this, but would be surprised if it was that large on a steam shower - typically, it's more like 1/4" or so. If I get a chance, I'll look.

Dilex comes in a bunch of different configurations. But, yes, that is what I was thinking. Depending on the one you choose, it may bend without cutting or notching. Having them do it in say one of their SS versions would lead to a much smoother curve possibility. It is still shipped to you flat and straight...the cutting of notches is an option at extra cost. I think I'd probably only have them do it on a metal piece because the cost of getting it wrong is much higher.

04-13-2014, 05:21 PM
Thanks Jim. On the gaps, you're right - was thinking 1/4 but wrote 3/4.

04-17-2014, 07:26 AM

I just spoke with the Schluter tech rep. For the joints where wall meets ceiling, they said their profiles cannot be used. Recommendation is tho bring Dilex up the four wall corners and transition to caulk for the wall/ceiling joints. Additionally, along the curved wall ceiling joint, they said that Kerdi Bank is pliable enough to form itself to the curve without puckering. We'll see about that one.

Cx, they she didn't know about your Kerdi wedgie, but did say not to pack the gaps with thinset. I still like the wedgie idea - for the wall, not for me!

I'm ordering supplies today and there is a bit of lead time. Please let me know if there are other pearls of wisdom. I'll let you know how it turns out.

04-17-2014, 07:33 AM
I've tried to train them, Greg, but they're a stubborn lot. :)

04-17-2014, 11:11 AM
Greg, you can look at my build to see examples of cutting darts to go around corners -

I think you are way over-thinking this though. This looks like a huge shower, and your joint is in the ceiling - there is very little to drive water through there anyway.

IMO, simply kerdi the wall and ceiling normally, kerdiband the joint with cuts to accommodate - if you want extra protection run a bead of kerdifix down the corner to cover the pinholes that might exist where the darts and two edges of kerdi join (like any corner "vortex").

You talked about a movement joint, but I think you are just referring to the normal corner change of plane where it is suggested to use caulk - right ? If so, just caulk it like the rest of your corners (or grout it like many reprobates here do.)

04-18-2014, 07:13 AM
Hi Kevin,

Truth be told, this isn't the first time I've been accused of overthinking something. But I followed your link and wow, what a project - it was incredible. I have to believe that there may be some "takes one to know one" going on with the overthinking!

Seriously though, your Kerdi seat looks almost exactly like my challenge except you're on the outside of the curve and I'm on the inside. Your concept is along the lines of what I was thinking; it's helpful though to have seen your picture; I had an abstract idea of what it would look like and it makes me much more comfortable to see a concrete example.

Since I'm a belt and suspenders guy too, I'll take your Kerdifix suggestion - I was thinking along those lines as well.

Finally, you're correct in that the movement joints (in this case) are simply the normal change of plane. I will caulk the ceiling based on Schluter's recommendation. I'm using Dilex everywhere else and was trying to figure out how to use the Dilex for the curves too - evidently, it cannot be done. My other concern with those joints was with the space under the tile and caulk. I'm going to give it CX's wedgie where I can, but I don't believe it's possible along the curved ceiling joints.

06-14-2014, 05:52 AM
It's been awhile since I've posted a project update. There are a couple of reasons: First, I had to finish out the rest of the bathroom except for the shower to get the toilet working again. Having the additional toilet is more important to my family than the shower. Go figure. Second, I'm just flat out slow at this stuff.

At this point, the bathroom (minus shower) is complete except for part of the grout and some touch up. The shower is framed, boarded, joints thinset, and Kerdi almost done - still need to do most Kerdiband and corners. I'll post some pictures of current progress. I also have a couple of tile questions which I'll put in the next entry.

06-14-2014, 06:08 AM
It seems the image files don't want to post from my phone, so I'll have to wait on that until I upload to the computer and try again. Bottom line, the project is progressing well, if slowly.

06-14-2014, 07:35 AM
I thought I'd post a couple of tiling questions as I get ready to transition from Kerdi to tile setting.

I'm going to use some hollow body porcelain chair rail on the bottom of my niche. I'm going to have to cut a return and glue it - I've seen on the forum that this is commonly done using epoxy. My question - is there any special type of epoxy needed for this? There are plenty of choices - all fairly inexpensive - in the hardware dept at big box stores, but didn't know if there is something specific to tiling I need to use. I've seen the term "knife grade epoxy", but the assumption appears to be that everyone knows what that means. I don't know what it means, if I need to get it for this application, where to get it, or how to apply it. Incidentally, the sales guy at Lowes didn't know the term either.
My understanding is that it isn't necessary to fill hollow-body chair rail with thin-set - that the top and bottom edges will be sufficient to bond the tile. However, I was concerned about moisture and mold getting into and growing in the cavity if I don't fill it. Should I be concerned about this and fill it, or is it fine to leave it unfilled.
My niches are fairly tall (about 2 feet) and I'm going to make a shelf about 6" from the bottom - soap, razer etc. under, and shampoo bottles over. I'm trying to determine what type of material to use for the shelf. The tile throughout the shower is porcelain. My challenge is that I don't have any polishing/finishing equipment to clean-up tile surfaces, and the tile bottoms look like - well - tile bottoms. I had a big box rep suggest thin-setting 2 pieces back to back and then hand form a bullnose edge on the tile saw (it is through body porcelain) and that it really doesn't need to be polished. I've thought of natural stone, but I'll have unfinished edges. Someone recommended glass to me, but I'm concerned about durability of even tempered glass. My requirements for material is that it doesn't look out of place, that I can do it myself, and that it doesn't look like DIY-gone-wrong. Look forward to suggestions.
The field tile I'm using is a Cerdomus chiseled edge tile. Additionally, I will have some accent tile boarders, including around the niches and a 2" boarder in the middle. All of these have a straight cut edge. Question is, asthetically, should I cut the chiseled edge off the tile where it will be directly adjacent to a straigh cut tile. My thought is that the grout joint may look odd if one side has a chiseled edge and the other side straight.

I look forward to the advice. Thanks...Greg

06-18-2014, 10:02 AM
1. I've never glued such corners, but I'm sure you can. I'd use Laticrete 310 because I have some.

2. I don't fill those cavities, just bond the edges to the substrate. I wouldn't worry about mold growing there even if I were a person who worried about mold. You'll get other opinions on that.

3. You can look inna Liberry under Shower Shelf for one method of making stone shelves. I would use tempered glass, but that's an aesthetic choice.

4. Aesthetics are best left to the person making the decisions.

My opinion; worth price charged.

06-18-2014, 10:20 AM
I finally have the pictures of the project progress on the computer. Lets see if this works now. This is everything from demolition way back in January, through framing and finishing of the bathroom - excluding shower.


06-18-2014, 10:29 AM
...and these are pictures of progress inside the shower - current to about a week ago. I currently have Kerdi 90%+ completed - just need to seal some corners (including the curved one) and around fixtures. I also have some repairs where I either (a) poked holed in the Kerdi, or (b) had some areas that flat our didn't adhere. I also found that the Kerdi Kerrik outside corners didn't work all that well on my bench corners in that I couldn't get the areas that were folded in for packaging to smooth out. It could also be that the bench doesn't form a perfect 90 degree angle - it is pitched about 2 - 3 degrees to allow for drainage. Still, I didn't have that issue with my home made niche corners.


chuck stevenson
06-18-2014, 12:35 PM
Thanks for the pics Greg.
I hope this is a 'before' pic. The boring and notching exceed guidlines.


There is a good pdf on 'Notching and Boring' in the Liberry found in the dark blue banner above. Joists can be headed off to avoid some boring and notching

Is the plywood installed parallel to the joists or perpendicular?


06-18-2014, 02:41 PM
Hi Chuck,

Well that's a bit scary. The pic is definitely of the "after" variety. I actually hired a plumber to do that part because (a) I knew it would be exceedingly difficult to fix a DIY error after the fact, and (b) because I was concerned about making a mistake that could adversely impact the structural integrity of the house.

In speaking with him, he said that he had to come up higher on the joist than he typically would to clear a HVAC duct. However, he wasn't concerned because the joists were 2x12 lumber on 16" centers - overbuilt by today's construction standards.

I did the rest of the floor which is 3/4" T&G plywood and runs perpendicular to the joists and the bathroom floor is porcelain tile over Ditra. The shower floor will be a Kerdi foam floor.

So, how bad is this situation?


John Bridge
06-18-2014, 05:30 PM
Hi Greg, :)

I don't see that the plumber could have done it any other way. I think if you screw the plywood down tight with lots of screws you'll be okay. The plywood will actually go into a compressive mode and strengthen the floor. On a larger floor I would worry.

chuck stevenson
06-18-2014, 05:32 PM
So, how bad is this situation?

I could not say without knowing the span of the joists Greg. Is it possible to build a support wall below the Fernco in the area below? Maybe a beam. If not a steel flitch might help on the joists.

Hopefully your plumber made the right call in his work. :shrug:

06-18-2014, 05:54 PM
Thanks all. I followed the specs on the subfloor - ring shank nails every 6" on perimeter, 12" in the field along with subfloor adhesive. Also, while I can't tell the exact joist span (best guess is 10' - 12') because the floor below is finished and closed, the notched section is either directly over or very close to the 1st floor exterior framing because of a 2' second floor bump out.

It doesn't sound like I'm in danger of my toilet ending up in the foyer (based on the comments), and the finished bathroom floor is complete as illustrated a few pic below that. Any alteration at this point would be a complete R&R.

06-19-2014, 11:34 AM
Greg, I'm not a pro, but I wouldn't worry too much. The worst could be a little grout cracking. I agree that your plumber was lame is not the best professional. :shades:
A pro wouldn't break those guidelines, especially if it was getting inspected. Project looks great though. :tup1: