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-   -   Vince's Kerdi shower - Edilcuoghi Rocks (https://www.johnbridge.com/vbulletin/showthread.php?t=59738)

vfgilber 02-22-2008 07:00 PM

Vince's Kerdi shower - Edilcuoghi Rocks
2 Attachment(s)

Still working on my layout before I can get started.

I'm replacing a tub with a kerdi shower and discovered that there's a floor joist running down the middle of the shower lengthwise - right where the drain would normally go.

Any ideas where in the image would be best to put the drain?

The red line is the joist to scale and the red circle is the drain cut-out to scale.

What doesn't help any is that the builders put this joist on an angle!!! It's 16" from the long wall at the one end and 13" at the other.

Thanks again for all of your help,


Brian in San Diego 02-22-2008 07:44 PM


Is this the first thread on this project? I know you've started a bunch of threads and wonder how many are related to this project. We'd like to get one thread for one project. Otherwise all the background information gets buried elsewhere and it makes it more difficult for us to help.

Put the drain where you have it drawn. Sometimes you have to work with what you have. Center it on the length and get it as close to the joist as you can. I couldn't center mine either...real world rules.


vfgilber 02-22-2008 07:59 PM

Hi Brian,

Yes, this is related to the same project. I hate to just add new questions to an old thread with lots of replies because then it tends to get lost as just another post in the thread.

From now on, though, I'll keep everything together.

I'll take your advice and centre along the length. It's really going to peeve me, though. It's going to be way closer to one side than the other. If I had any access underneath, I'd chop that whole damn joist out and add another one in off to the side.

Brian in San Diego 02-22-2008 08:15 PM


We appreciate your understanding and ask that you ask all your questions on this thread. What happens on most projects is that someone who starts helping you sticks with you throughout so you don't have to worry about questions getting "buried". Also if someone wants to see what's involved in your project they don't get the "whole" picture only snippets here and there. I don't know if you are aware but you can "subscribe'' to a thread and you are notified every time a post is made to that thread. So if a "lurker" subscribed to one of your earlier threads they would not necessarily know you've started new threads. If you want to rename this thread you can ask the name be changed by requesting it on a post to this thread.


smarsh 02-22-2008 09:48 PM

What about keeping it centered lengthwise, but moving it closer to the curb/knee wall side as close as you can get it and then pitch the floor in sort of a V from the far corners to the drain? I know how you feel about symmetry, but at least there would be some "visual logic" for doing it that way. :)

vfgilber 03-15-2008 09:11 AM

OK to put Ditra under Kerdi Tray?

I'm going to need 30sqft of Ditra for my bathroom floor, which leaves 24sqft (approx) left from the 54sqft roll I bought.

My question is: Can I put a layer of Ditra under the Kerdi tray?

The Kerdi tray is 1.5" at the perimeter, but goes down to less than .5" at the drain. I'm wondering if a layer of Ditra would helpisolate the shower floor from any subfloor movement.

As it stands, I have 2x8 joists on 16" centers (average - some are farther - some are closer) and 11ft span with 3/4" OSB and another layer of 3/4" exterior Fir plywood. Under the shower area, I put in a jackpost and beam in a baseement closet to cut the span to 5ft.



Brian in San Diego 03-15-2008 05:28 PM


You don't want ditra under the tray IMO.


vfgilber 03-15-2008 05:52 PM

How about on top? In the Schluter instructions for Kerdi, it has a blurb about what to do if you are using Ditra as the shower floor. Seeing as it is waterproof, would it help the floor tiles?

Brian in San Diego 03-15-2008 05:58 PM

Inside the walls of the shower, no ditra...kerdi only. Outside the walls of the shower on the floor, Ditra is fine. Kerdi-band is used at the seams of Ditra to make the surface waterproof but it there is no way to contain the water where the Ditra is laid then it's worthless and senseless trying to waterproof it.


vfgilber 03-15-2008 06:04 PM

Hi Brian,

Just so we're on the same wavelength, here is the quote from Schluter:

"If Schluter®-DITRA is used as the waterproofing layer, the DITRA must be held back to the outer edge of the bonding flange. Adhere a 20" x 20" (50 cm x 50 cm) cut section of Schluter®-KERDI to the top of the DITRA membrane and bonding flange using unmodified thin-set mortar. The Schluter®-KERDI must overlap the DITRA membrane a minimum of 2" (50 mm). With the flat side of the trowel, firmly press Schluter®-KERDI into the thin-set mortar to ensure 100% coverage and a watertight seal."

This is the only reason I asked. Oh well, I guess there'll be extra Ditra to give away too :)

Brian in San Diego 03-15-2008 08:26 PM


I think I found where you found that quote. I found a similar quote in brochure 6.1 Schluter Ditra. The quote is for bonding of kerdi to Ditra for a floor drain...not a shower drain. This would be typical in a commercial application or ina laundry room etc. I have read the installation instructions for the kerdi tray over and over and have not found any reference to Ditra.

I would hold on to the Ditra. It isn't hard to store and you may find another use for it. I have a big roll and I sold some to a member looking for 16 sqft.


vfgilber 03-16-2008 08:15 AM

Cool - sounds good. Actually, since you mentioned it. Our washer/dryer is on the main floor with no drain or pan. I think it was an afterthought. Maybe I'll think about doing that area next.

Case closed.

vfgilber 03-20-2008 11:13 AM

Will Kerdi hold water?

If I tile a walk-in shower using Kerdi per the instructions, will it hold water?

That is, in the current tub-shower, we like to put the plug in and let the shower fill the tub. Keeps the toes warm and is fun to splash around in.

Can a kerdi shower be flooded and remain water-proof, or will the seams fail?



jason1083 03-20-2008 01:19 PM

done properly a kerdi shower is waterproof.

vfgilber 03-23-2008 12:57 PM

Waterproof to the point of holding 6" of water in for 20 to 30 minutes? Is that 2" overlap really going to hold hydrostatic (??) pressure?

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