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Old 05-14-2019, 07:43 AM   #1
NathanInSTL
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Drywall/Kerdi in Mud Pan

DIY'er here that has spent hours and hours reading this forum for two projects now. Very grateful for everyone's input.

I am about to do my second layer of mud shower pan using drywall with kerdi bonded to it. I was planning to set the drywall 1/4" off the first level, thinset Kerdi to it, kerdi tape all the seems and then do my 2" mud base.

Just wanted to confirm I was correct in thinking to embed the membrane with the drywall.
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Old 05-14-2019, 07:53 AM   #2
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Nathan, I think you should expand your reading to include the Shower System Handbook available for download on the Schluter Kerdi website. As with your tub/shower project, I think there is some basic information missing from your research.

The Kerdi membrane is listed as a Direct Bonded Waterproofing Membrane, ANSI A118.10, meaning you can bond your tiles directly to the membrane. There is no second mud bed involved in a Kerdi shower receptor. You bond the membrane directly to your sloped mud bed and drain, then you bond you tiles directly to the Kerdi membrane.
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Old 05-14-2019, 08:15 AM   #3
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Thanks for the reply, cx.

Thought I would try and clarify a little more before diving into the handbook. The attached is more or less the construction I am following. For the layer of cement board in the picture, I was planning to use drywall with Kerdi attached (instead of cement board) that will then enclose the 3 sides of the shower.
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Old 05-14-2019, 08:22 AM   #4
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Nathan, what you have there won't work. The raw edge of the sheetrock will be exposed to moisture and will degrade quickly.

You're trying to mix two different methods, which is like trying to use Ford and Chevy parts to make up a single vehicle. They just don't work together.

You can still use the drain, liner, and the mud bed, but you'll have to use cement board for the walls. I'm afraid if you want to use Kerdi, you'll have to scrap the floor you have done so far.

Bottom line, choose a single system and go with it. That gives you the best chance of success.
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Old 05-14-2019, 08:39 AM   #5
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Thanks, KMan. Now I might be slightly turned around.

I'm not tied to the Kerdi membrane by any means but thought it was an easy enough way to waterproof the walls. All that is down right now is the preslope so I have plenty of flexibility.

Thinking out loud here...could I embed Hardi (I can use cement board but I am not as comfortable working/cutting it), build the second layer of the pan, then waterproof the walls down to the pan using Kerdi membrane & tape or Redgard?
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Old 05-14-2019, 09:22 AM   #6
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Did a little more research on the Forum and will plan to use Durock/Wonderboard to embed. Sounds like Hardi probably wouldnt be an issue but no reason for me to test it given my amateur skillset as it is. Thanks all.
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Old 05-14-2019, 02:03 PM   #7
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Kerdi is an easy enough way to waterproof the entire shower receptor, not just the walls. It really seems like you're trying to reinvent the wheel here by using several methods together (that don't work together) to build a shower. Pick a method and use that method only. Follow the steps properly. Don't try to piece together something that may, or way more likely, may not work.
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Old 05-14-2019, 02:40 PM   #8
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it starts with the drain..What do you have? like the one shown? if so lets talk about a Nobleflex Drain Flashing.
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Old 05-14-2019, 02:41 PM   #9
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Nathan, I don't think you understand what is being said.

The picture you posted WILL NOT work with Kerdi. That picture is for a specific method of shower construction, which CAN'T use Kerdi.

Either build your shower the way it is outlined in the Kerdi handbook, or go with a different method/product.

STOP reading random posts, pictures, videos on how to build a shower. You can't just use one method (no matter how good it is) with any material you want (no matter how good it is).

Each material you pick will have its OWN method for construction and installation. This includes thinset, tile size, tile shape, tile material, drain type, drain manufacturer, waterproofing material, backerboard, shower pan, etc.
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Old 05-14-2019, 11:56 PM   #10
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That falling sound you’re hearing is my confidence free falling. I “thought” I was prepared for this.

I am using a Kohler 3 piece drain that is essentially the same as the pic. Right now, all that is done is the pre-slope and liner. Water test is on going right now.

My next step in my, apparently very wrong, thought process is to hang cement board 1/4” off the liner and install the top layer of the mud pan. That, I feel somewhat confident about. After that, though, I am back to the beginning.

I was originally wanting to use Kerdi membrane over everything for ease of application. I will have a small window, shower niche and bench in the shower and was looking for what I thought was an effective “shortcut”.

Now, I am back to taping/thinset all joints and covering with Redgard. I don’t mind using the product but thought I could bypass all the taping and mess with kerdi membrane. Thankfully this was a total gut so all walls are still open and only have the previously mentioned preslope completed.
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Old 05-15-2019, 05:49 AM   #11
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Post some pics of progress so far so folks can tell if you’re on the right path. Specifically how the liner is wrapped over the curb (especially where curb meets walls), as well as wider angle pic of entire shower.
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Old 05-15-2019, 09:19 AM   #12
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remember never put a nail/screw/staple into the PVC liner ANYWHERE below the height of curb (also a few inches above the curb). This includes the top of the curb as well.

since you already have the preslope in, when you set the drain, did you set it a few inches off the floor, or did you set it flush with the floor?? The drain flange should be like 2 inches above the floor (someone will chime in with the exact minimum) allowing you to taper the preslope mortar bed while keeping it the minimum thickness throughout. You can't feather the mortar bed to nothing, which is what you need to do if you set the drain flush with the floor. The mud just doesnt pack well when it gets so thin.
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Old 05-15-2019, 09:36 AM   #13
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Speed - yes, nails were at the very top of the liner well above the curb. Overnight I did not have any leakage....BUT I am going to pull and out rip out the preslope and start over. I have about a 1/4 under the drain which isnt thick enough as you know.

I got my wires crossed somewhere along the line with mud thickness. I read where the 2nd layer should be 1.5" at the drain and I guess assumed (incorrectly) that would be the main support. I'd rather lose $30 in materials and a couple of headaches than the whole shower at some unknown point down the road.

Once the current preslope is removed, I'll adjust drain height to give me 0.75" - 1.0" under the flange with the "nubs" of the plastic drain sitting on the subfloor.
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Old 05-15-2019, 09:40 AM   #14
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I used the last of felt scrap for the first preslope and would like to avoid buying a huge roll I don't need. Tyvek is a polyethylene that I have available. Would this work as an alternative to felt over plywood subfloor?
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Old 05-15-2019, 10:07 AM   #15
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Nathan, the problem isn't the Kerdi membrane- it's the drywall. You can still use Kerdi, if you want, but over cement board- not drywall.

Specifically, the problem with drywall is embedding it into the mortar bed using the method shown in the drawing above.

-------

You might consider what Eric (e3) said in the above post.

Since you are going to redo the preslope anyway, why not just use a Noble drain flashing (Schluter makes one too if you want to keep everything in the same family)?

This allows you to use your existing drain and you'll have to order a little more Kerdi to go over the mud pan. Then you can go back to using drywall over the shower walls if you want. (I can't believe I just typed that )
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