Have I made a mistake [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


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08-07-2019, 08:38 PM
I've scoured youtube for the answer, but I cannot seem to find it. I have a basement shower that I am building. I have poured the preslope on the cement floor, and installed the Oatey PVC membrane and 3 piece drain. So far so good right?

My question is around the walls. I have installed Kerdi board from the ceiling to half way down the walls. I did not go all the way with the walls because I wanted to install the liner first. I would like to use Kerdi board on the walls, but not the floor. Can I use Kerdi board next on the walls bring it down to the membrane? After the Kerdi goes in, I would pour the final slope for the shower floor and tile over top.

I like the Kerdi product for my walls because of the pre-fab niche, and lightweight materials and smaller board sizes that are available. I really don't see any videos of people installing Kerdi boarded wall with an Oatey membrane. Are the two incompatible for some reason?

If this is possible, how do you seal the joints between the kerdi wall and the final mud slope? Thinset like on Kerdi walls?

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08-07-2019, 08:59 PM
In this case, you wouldn't seal the Kerdiboard to the liner. You do want to seal the seams between the boards and the anchor (screw) holes on the walls, though.

One of the major benefits of a surface membrane shower is that it is entirely waterproof, and almost nothing to absorb and hold moisture. When you have a mudbed, by design, it will become damp and essentially stay that way. Each shower will add a little moisture to the setting bed beneath the tile and weep to the drain, constantly flushing the system.

In a surface applied waterproofing, the thinset is denser than the mudbed, and it is a thin layer beneath the tile. Essentially, what may get through the grout isn't drawn down into the mudbed, and generally, dries out in between showers.

You could pull the liner, then change the drain to a Kerdi conversion drain (or tear it out and replace with a standard Kerdi drain), but what you have will work as you planned. Run the Kerdiboard down to within about 1/4" from the top of the liner on the floor, then pack your mud to make your setting bed as if those panels were cbu.

Tool Guy - Kg
08-07-2019, 11:24 PM
Kerdi/KerdiBoard is meant as an all or nothing system. Yeah, you could do a hybrid of surface waterproofing and a traditional pan liner as Jim says. But you’d be forgoing one of the main benefits of surface waterproofing.

So, did you make a mistake? Well...you’re learning. And you’re doing it before blindly plowing forward. So, good on you. Now it’s time to decide what benefits you want to obtain so that you can either make a hybrid and know what benefit you’re foregoing or swap out the lower stuff to complete the whole Kerdi system.


08-08-2019, 07:02 AM
In general you are fine..I am not speaking for Schluter or Oatey , however the basic method you are describing is and has been in the Tile Council of America Handbook since the 80s.
As the original Manufacturer of both type of membranes we would warrant it and have for over 25 years. Mortar bed showers floors as you are talking was the only way before the 80s and they hold up just fine. Noble Co. introduced our Chloraloy in 1964.Millions of showers are still in service and are both functioning and look just fine!
We also have more Niche options then anyone!

08-08-2019, 01:48 PM
Thank you for the replies. I am curious about securing the bottom few inches of overlap of kerdi and liner. Obviously i dont want to perforate the liner, so can I safely assume that 6 inches should be the last kerdi fastener from the bottom, and that the final mortar bed slope will apply enough pressure to keep the kerdi pushed against the membrane and wall?

08-08-2019, 02:26 PM
Joe, you can't have any mechanical fasteners through your waterproof liner lower than two inches above the top of your curb.

Yes, the final mud bed would capture the bottom of your wallboard.

08-09-2019, 02:30 PM
Thanks CX. Follow up. In this hybrid configuration what ddo I install in lieue of corner dams on my curb? I see Kerdi makes a product, but so does Oatey. Given that the dam curb is where my kerdi walls meet my membrane curb, what product should i use for a dam? And what adhesive as well....

08-09-2019, 03:16 PM
If I correctly understand your construction, the only thing different from a conventional shower with traditional receptor and impervious wallboard is that you're using KerdiBoard as your wallboard. An overly expensive choice of wall waterproofing in that application in my opinion, but workable.

Given that, you still must make a traditional curb, with either wood framing or CMUs as the core, your liner covering that core, compatible dam corners at the ends of the curb, and lath and mud over that. Same construction you'd use if you had used a moisture barrier behind CBU or mud walls or a direct bonded waterproofing membrane over CBU walls.

My opinion; worth price charged.

08-09-2019, 04:38 PM
Got it. Already covered the wood curb with pan liner. OATEY says to use x-15 for dam corners. I expect it may not adhere to kerdi, so that seam will likely need kerdi tape and thinset.

08-09-2019, 04:42 PM
Joe, the way you're building your shower you would not need to bond your dam corners to anything other than themselves and the pan liner. You would have done that before installing the wallboard of whatever type you elected to use.

08-09-2019, 05:27 PM
You've clarified it. Install the dam corners before the wall material like this guy does (only with a diff product)?

Thats the layering youre describing I think? Dam corners to complete the pan base in a way....then apply walls?

08-09-2019, 05:35 PM
Yeah, and then you can tell people you learnt it all from Michael Byrne! :D

That's likely a better installation than you'll have with only Oatey PVC liner and dam corners because of the Noble Company pookey used in that video and the installation of the extra flap of liner material over the dam corners and onto the stud. Your X-15 will bond only PVC to PVC, but if you do a very neat job you can get by with that.

My opinion; worth price charged.

08-10-2019, 05:52 AM
Thank you so much...can't find those precut corner pieces at lowes or home depot here in Canada. Ill head to a specialty plumbing when they open again on Monday.

You're a live saver.

08-10-2019, 06:24 AM
If you'll put that geographic location into your User Profile it'll be helpful in answering other types of questions, too. If you don't, the information will be lost before we leave this page.

You might look online to see if you can't order those dam corners directly from the Noble Company, the company that produced the video you linked. Might be able to order their pan liner, too, and maybe even that pookey they used in the video.

My opinion; worth price charged.

08-10-2019, 09:09 AM
All those layers of material will cause the Kerdi board to bulge out on the lower section of the jamb. In that situation I would notch the wood for the dam corners and for the folds in the shower corners. That will allow the Kerdi board to hang straight down.

If you haven't, check out the Shower construction info thread in the liberry.

08-15-2019, 05:11 AM
Hi All,

Sorry for the mis-title. I'm referring to a Curb made of Kerdi Board...and not specifically the Kerdi Curb kit.

A bit of background can be found in https://www.johnbridge.com/vbulletin/showthread.php?t=127906

I've got a shower with Kerdi walls and a PVC Pan Liner Base. Thanks to all for telling me that this IS possible.

My pan liner is currently over the curb as recommended in all of the install videos.
My mortar and mesh skills are horrible to say the least, so I was thinking of buying one of those Goof Proof Curb kits where you cut the pre-fab plastic to size and run it. Unfortunately, I will require 3 kits for my curb span, and they are incredibly expensive to get in Canada and even more difficult to locate.

I am curious if I can use my leftover Kerdi Board and cover all 3 sides of the curb? It seems much more accessible, and certainly way cheaper after you include exchange rates ($0), and import duties ($0) compared to the goof proof kit.

My expectation is that I would install the kerdi over top of my 2x4 liner covered curb now, and secure using the screws that I used on the kerdi walls. I would then pour my sloped mortar bed down in the shower pan. My assumption is that this makes it a a 'shorter' kerdi wall really. All edges would then be finished using kerdi band, kerdi corners and thinset to seal any penetrations thru the board to the liner.

I looked at a Kerdi Curb kit, but it seems that it has cross members inside of it for support, so I would have to cut those out and still don't know if it would fit over my 2x4 curb and membrane in place today.

Your advice is greatly appreciated.

08-15-2019, 07:43 AM
Housekeeping first, Joe.

Please keep all your project questions on one thread so folks can see what you're working on and what's been previously asked and answered. A moderator can give it a more generic title any time you'd like to suggest one, or you can just stay with what you've got.

It's helpful if you'll add a geographic location to your User Profile so it remains permanently in view to aid in answering some types of questions. Otherwise the information will be lost before we leave this page. I'll fix your signature so folks don't think you're shouting. :)

You cannot make a curb over your traditional pan liner using anything that requires mechanical fasteners. That includes your Kerdi Board. By far the easiest and best method is to bend expanded metal lath over your liner over your curb structure and finish it using fat mud. The mud is dirt cheap and DIY labor is free, so a little practice doesn't cost much in either time or money. I do not recommend the plastic pieces from Kirb-Perfect, but you can use something like that if you want. Far better and less expensive is the lath and mud.

The only foam curb pieces made specifically for what you want to do come from the Noble Company. Also not inexpensive, but made for your application so long as your curb is a single straight piece and you've done a good job of forming your membrane over it. You might check that out.

My opinion; worth price charged.

08-15-2019, 02:32 PM
Thanks CX for the housekeeping note. Ill work on those items.
Is wire and concrete really that easy to work with? It seems like im going to buy a huge sheet/roll dor this tiny little application.
In my way to the big box store to look.

08-15-2019, 05:45 PM
The lath is about 27x96 and is about 10 bucks a sheet at Home Depot. You might look at the "shower construction info" thread in the liberry. It has info and pics on mudding curbs.

08-15-2019, 10:58 PM
You cannot make a curb over your traditional pan liner using anything that requires mechanical fasteners.

That's almost 100% correct. :)

You will have to secure the lath with nails to only the outside of the curb. Nowhere else.

It's a good idea to over-bend the lath a little so it hugs the inside of the curb.

08-16-2019, 06:56 AM
I'll claim 100 percent, Kevin. I maintain the metal lath, properly bent, does not require mechanical fasteners in that application. Acceptable to add a few staples on the outside if you wanna, of course. :)

08-16-2019, 10:22 AM
I'll claim 100 percent, Kevin. I maintain the metal lath, properly bent, does not require mechanical fasteners in that application. Acceptable to add a few staples on the outside if you wanna, of course. :)

Yeah, but you're a renegade. :D

08-16-2019, 11:03 AM
I'll claim 100 percent on that, too! :D