Kerdi Board to Drywall Transition [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


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07-23-2019, 01:40 AM
On the Kerdi website, for no access plumbing they show the middle piece of Styrofoam being popped out and set under the drain flange prior to setting the shower tray.

But for an accessible drain, they set the tray and then install the flange. This method looks easier.

Why doesn't the second method work for no access plumbing?

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07-23-2019, 07:42 AM
because you don't have access to the pipe underneath?

07-23-2019, 08:57 AM
By watching the videos, both methods appear to just be setting the collar down on the ground. The only difference is one method has glue on the end of the pipe as you set it.

07-23-2019, 10:08 AM
Richie, you can set your drain in any manner that makes you comfortable. You do not need access to the drain from below.

I recommend you make your sloped floor of deck mud so you can make it fit your shower footprint and drain location perfectly (as well as saving much dinero and having a better floor). In all my showers on SOG concrete I leave the floor bare until the ceiling and walls are installed, waterproofed, and tiled except for the bottom row. I then set the drain with the flange at least 3/4" above the concrete and pack the deck mud under the drain while forming the sloped floor.

Using the foam tray you could do much the same except come time to set your drain you would either remove the center piece and set it separately or you could cut the riser to height, install your tray, and then set your drain in position.

So long as you get the drain set correctly in your floor, be it foam or mud, it'll be fine no matter how you went about it.

My opinion; worth price charged.

07-23-2019, 10:24 AM
Hi CX, I have a wood subfloor but still don't have sufficient access from underneath the subfloor to consider it an "accessible" drain.

I already have the Kerdi foam shower tray kit, so I'm gonna go with that method.

I'm just trying to understand what the difference is between setting the drain independent of the tray, like this:

Or setting it through the tray, like this:

07-23-2019, 10:34 AM
I think the only difference might be that the newer shower trays (second video) with the Kerdi membrane already attached may not have the removable center piece. I honestly don't know, having never even seen one of the newer trays.

But I think the bottom line is that you can do it either way with the old tray and maybe even with the new tray.

Important thing is to get the drain level and firmly set onto the foam tray.

My opinion; worth price charged.

07-23-2019, 10:40 AM

Yeah, the new tray does have the same removable center piece.

07-23-2019, 11:09 AM
After thinking about it some more, I think I see the reason.

With no access plumbing, you need to be able to carefully set the drain flange in, to make sure you line it up with the existing plumbing, and get it pushed in and fully set. In order to do that, you need to be kneeling immediately above the drain hole.

If you try to do that with the tray in place, that means standing/kneeling on the untiled Kerdi tray, which I assume is a no no. So instead, you remove the center piece of the tray and install the drain before the pan, so you can be standing/kneeling on the subfloor instead.

07-23-2019, 11:58 AM
Could be. Damaging those trays by just kneeling on them is only one of the reasons I recommend against their use.

07-23-2019, 08:23 PM
I've never installed one either, but if I did, I'd save installing the tray for last.

Waterproof the walls, then set the tile on the walls beginning with the second row, using a ledger board.

Then set the tray and waterproof it, then the floor tile and first row on the walls. This will minimize the time spent on the tray, and reduce the chance of damaging it.

07-23-2019, 08:35 PM
I don’t think it’s so much related to kneeling on the tray. Although I’d want to minimize that.

When there’s no plumbing access, if the drain is fully seated and glued on first then it can be gently pried up if needed to slide the tray’s center section underneath.

If you set the whole tray first, the riser height has to be exact. If the drain flange bottoms out on the tray before it’s fully seated, there’s no recourse.

07-24-2019, 09:24 AM
One thing that can zing you is if the drain pipe is not fully supported. THen, when you try to push the drain onto it, the pipe flexes and you can't seat the drain properly. IN a worst case scenario, you could negate the proper slope on the trap arm, causing it to build up crud. Well, not fully seating the drain could cause a leak. My experience with their drains is that they do not have as much taper to them as a standard hub, so they slip on easier. In a standard fitting, you can't bottom out the pipe in the hub until you've added the cement. The cement essentially has solvents and dissolved melts the plastic in the pipe and drain so it can be fully inserted. On the Kerdi drain, it's less tapered and you can tend to dry fit it...not true with most hubs on fittings. THat means to get a good seal, it should be bottomed out and a liberal coating of cement applied to both surfaces.

07-30-2019, 12:25 PM
As I am installing my Kerdi board shower, I am thinking about how difficult this might be if I ever want to remodel the shower. I would imagine it's going to be difficult to remove all the screws once they are covered over with dry thinset.

So many of these building products are designed to last forever, but in practice many people want to change the look of their homes every 10 or 20 years.

Just curious if anybody has experience ripping these things out?

07-30-2019, 12:53 PM
I would much rather be tearing out a Kerdi shower than some of the other methods. That foam makes things a little big easier IMO.

If the tile is installed properly hardi board can be quite difficult. Also the old wire lath showers can really take some time.

When I am installing a shower the absolute last thing I am concerned about is the level of difficulty of the demo. I am trying to have the thing function as long as possible.

07-30-2019, 12:59 PM
Oh, I agree. I definitely want this thing to be able to last 50 years. But in the back of my mind, I always think "what if we want different tile in 5 years?"

Tearing out my existing fiberglass shower enclosure was pretty easy.

The best would be if there was a way to remove all the tile from the Kerdi, while keeping the Kerdi installed, intact and waterproof.

clifton clowers
07-30-2019, 01:26 PM
Popping thinset out of screw heads is not usually that difficult. Or you can grab the screws with a vice grip.

07-30-2019, 01:55 PM
well, you could always take your shower with you when you move if it was easier to remove!

07-30-2019, 07:56 PM
I wouldn't worry about it. What John said, I want the next guy to cuss a lot when tearing out my showers. :)

08-15-2019, 11:29 PM
Hi all,

I have installed a Kerdi Board shower, and getting ready to start setting tile. But, I have searched around (here and elsewhere online) about how to handle the transition from Kerdi Board to drywall. I am planning for my (12x24) tile to overlap onto the drywall by 3 or 4 inches. The drywall transition will be on the outside edge of my curb and on the dry side of my shower door.

Some people suggest maybe using Kerdi Band for the transition. I have also seen recommendations of alkali-free concrete mesh or even paper drywall tape. Does it matter which method I use?

Why would I need to use anything at all? Won't the tile/thinset essentially work as a cover for the joint?


08-15-2019, 11:49 PM
Fiber Tape and thinset that joint or kediband and use thinset. The substrate needs to be binded together and move as one or you have a stress point on your tile when the two planes move independently. Insure the tape/kerdi band doesnt cross over beyond where u plan to tile.

08-16-2019, 12:17 AM

So essentially, tile and thinset doesn't bind the two substrates together like tape or Kerdi Band would?

Why would that be? If I am using thinset to attach either way, how does the tape create a better bond than the tile?

(Sorry to dig a little deeper on this. I like to understand the science/logic behind these things.)

08-16-2019, 06:47 AM
Can't tell by your photo where the joint falls, Richie. If it's well outside the wet area, you can finish it like a drywall joint or with mesh tape and thinset mortar as previously recommended. If it's not well outside the wet area, you should move it.

If you finish the joint with KerdiBand or similar and that extends beyond your tile, you can finish over that with drywall mud and your wall finish.

My opinion; worth price charged.

08-16-2019, 10:49 AM
The edge of my Kerdi Board lines up with the outside edge of my curb.

So I would say it is not "well outside" the wet area.

08-16-2019, 11:07 AM
Since your tile will extend past that joint by 3-4 inches I'd use Kerdi band and thinly mixed mortar to do that seam, especially since the seam aligns with the front of your curb. Indeed, you really want to ensure you water proof that seam to curb junction.

If you've not done so, do run some more screws in along the edge of that drywall.

You could perhaps argue that the tile bonded to both the DW and the foam board will hold that seam together, and the DW and foam board shouldn't really move independently if they're both screwed to the same stud, but given the small amount of work necessary to dress that seam at this stage why take the risk?

08-16-2019, 11:12 AM
Thanks Dan!

08-16-2019, 01:01 PM
There is engineering behind why the seams in the tile substrate need to be taped together rather than just depending on the tile itself to bridge the substrates together. The main one is resistance to vibration. I can take two sheets of substrate and tape them together and then take a rubber mallet and start lightly pounding over and over again simulating movements in the walls from things like doors slamming to people walking. Because the tape is very strong yet also flexible it will maintain that connection indefinitely. Stress cracks in the thinset mortar may begin to form in a line right at the seam but because the tape is flexible (be it fiberglasstape or kerdi) the stress cracks will be unable to propagate across and break the bond between the tape and the substrate. Thus despite the stress crack at the flex point the two planes of material will remain interlocked not allowing the two planes to deflect from one another substantially. Now consider the same thing with tile only. Tile as you know is very rigid and thus will translate all movement across it. Over time stress cracks in the mortar bonding the tile to the wall will unzip the mortar across the tile because of two different planes of movement. As those cracks grow the two planes of substrate will move more and more until eventually the entire tile will come loose. Anyone who has done a tile demo knows the devastating effect a heavy blow of vibration from an impact has on the bonding of the tile to the substrate. Yet long after all your heavy hammering knocks all your tiles loose the fiber tape bonding the substrates together will remain in tact.

Bottom line. TAPE YOUR JOINTS. It's industry standard for a reason.

08-16-2019, 01:04 PM
Awesome. Thanks for the background theory John.

I always feel like understanding why something is done helps me in future similar projects to avoid pitfalls and know what to look for.

08-23-2019, 11:19 AM
Jim (or anybody else), how would you do this if you have multiple tiles that will be using a single piece of metal edging?

For instance, in my shower I want to use a piece of edging for my shower curb (60" long), but my tiles are only 24".

Here is an example of what my situation would look like:

08-23-2019, 12:24 PM
I usually set the metal first then tile later. Like on top of that curb. If the metal is set and both level and even width then its easy to cut tiles to fit. Also then the two rails are guides. You can take a straight board and press down until the tile is flush. Do one tile then spread thinset for the next. This allows thinset to squeeze out and you spread for the next tile. If tile is not high enough you can pull out and trim is solid and wont come up. Then maybe even use kerdi trowel to back butter to get more height. Grooves going same way.. my tiles were .38 and .360 in and my glass Mosaic was.34"and I used a 12.5 millimeter size metal
I think the literature is inaccurate because schluter says 100 is for 3/8" tile amd 125 fir 1/2" but that's no room for thinset. . I used to half inch by half inch square Notch trowel I did not want my metal below the tile edge. I did have to build up for my glass waterfall using a calibrated scree stick to get it where it would match. It's actually quite a complicated thing to use this Mel metal especially around a niche. I put my metal flange on the wall but this requires knowing how thick the inside mesh wall tile will be so you know where to cut the metal so the corners will fit or if you're going to chamfer. Plus this metal on the wall creates a plane that the wall tile needs to somewhat adhere to at least meet to around the niche. Overall it's very complicated thought process to use and I decided I would charge $800 for metal and niche if I was charging someone. Many times I put thinset and then set the metal into the thinset and wipe off the excess that oozes up out of the trapezoids. But there were times around my door where I use hot glue to set the metal first because so many planes and Corners had to meet and all be accounted for. I also made a butt joint in my metal 2 rows up from the bottom of the shower where I had my ledger board. I didn't see any other way to do this and I was able to get the butt joints to line up quite well when I did the bottom two rows. This wouldn't apply to rondec but I used the dilex eke in my wall corners and jolly down the wall outlining my waterfall glass.

08-23-2019, 12:28 PM
Thanks Teddy. My problem is the metal edging I have is 3/8" and my tile is 3/8" thick. If I set the edging flush to the curb, and then set the tile on top of the edging with a 1/2"x1/2" trowel, I will end up with about 1/8" of thinset between tile and curb - which means my tile will sit about 1/8" taller than the edging.

(I learned this the hard way because the edging I used on the wall is now 1/8" below my tile. UGgh.)

08-23-2019, 06:00 PM
Does the edging come in 1/2” thickness?

08-23-2019, 06:05 PM
Good point. 1/2" is available, but nobody around me appears to stock it. But at this point I'm 3 weeks into my shower build, so what's a few more days delay if I have to just order the 1/2".