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Old 11-09-2018, 10:47 AM   #1
kevber
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Shower mud pan question

New user here. Have been a DIYer for years but getting into new areas with this project. My google searches keep pointing me to this forum so thought I might as well go to the source

I am converting a master bath garden tub area into a fairly large (5' x 6') shower. 12"x24" tile over Durock on walls, hex mosaic tile over mud pan on floor. Have laid the pre-slope and getting ready to install membrane and top mud pan (not sure what the right term for that is). My curb is 3 stacked 2x4's. Due to size and a slightly high drain, the pan is getting pretty close to curb height (pre-slope is 2-3/4" below the top 2x4). I have read in other posts that 1-1/2" is the minimum thickness of the top layer of mud. It seems that would leave a rather short curb from inside the shower. I don't really like the look of a higher curb from outside the shower and trying to find a compromise.

So my question is: Is there any issue with a thinner top layer?

Or any other suggestions?

Appreciate the feedback. I can provide other details as necessary, just did not want to bore if a very simple answer (i.e., absolutely yes or no on the thickness question).
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Old 11-09-2018, 11:07 AM   #2
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Welcome, Kevin.

That 1 1/2 inches for the top mud bed is the recommended minimum per the ceramic tile installation standards as you've noted. I would not recommend you decrease that at all.

The industry standards also call for a minimum of 2 inches from the top of your curb to your shower floor, but that is based upon the use of a shower curtain rather than a door at the shower opening. Don't know what you plan there.

If you want to reduce the overall height if your shower floor, I'd recommend you change your plan from a traditional shower receptor to one using a sheet-type direct bonded waterproofing membrane. That would reduce your height to about what you have now with your pre-slope.

My opinion; worth price charged.
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Old 11-09-2018, 02:02 PM   #3
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Thanks! Not what I hoped to hear but what I suspected.

I do plan to have shower doors. And one piece cultured marble on top of the curb.

By a direct bonded waterproofing membrane, are you referring to redgard and similar products? I am a little apprehensive to go that route just because I have never done it before and it does not seem to be standard practice yet. I realize I need to use it on the walls but it seems a lot more critical on the floor pan.

Sounds like I need to increase my curb height by 1" and have a short tile on the inside. I can add another 1-1/2" with another 2x4. Is there a best way to add 1"? I should back up and acknowledge my original plan was to Durock sides and top but my initial research indicates I should not do that. Is there a standard way to get to the tile base? If so, would that be a way to add 1"...I thought I saw one method of basically building up the curb out of mortar.
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Old 11-09-2018, 02:16 PM   #4
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Quote:
Originally Posted by CX
If you want to reduce the overall height if your shower floor, I'd recommend you change your plan from a traditional shower receptor to one using a sheet-type direct bonded waterproofing membrane. (emphasis added)
I would not recommend RedGard or similar liquid-applied products for a shower receptor at all, even though many are indicated for such use by their manufacturers.

My current favorite sheet-type membrane is USG's Durock Shower System membrane and it is easy enough to use that you can expect satisfactory results on your first attempt. Schluter's Ditra is another brand of a similar material and there are others.

If you continue with your traditional method, you must not use a CBU anywhere on your curb. If you'll visit our Liberry and find the Shower Construction thread you'll find good information on how to build your curb with fat mud, including photos.
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Old 11-09-2018, 02:30 PM   #5
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Another vote for switching to a foam pan and kerdi. Or the usg system ect. Very easy to do if you follow the directions and you'll be certain of a leak free installation.
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Old 11-09-2018, 05:29 PM   #6
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That would be only one vote for the foam pan, Joe. I would much rather he stay with a mud shower floor made to fit his shower footprint and drain location perfectly. Better floor at a far, far lower cost, eh?

Or simply make the curb taller for his traditional receptor if he wants it higher above the shower floor. There is no code compliance requirement for that height, though.

My opinion; worth price charged.
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Old 11-09-2018, 05:35 PM   #7
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Thanks to both CX and Joe for your input.

The more I study and analyze, the less I am concerned about a higher curb. I think I just worked myself up for no reason. So I think I will just proceed with a top mud bed of 1-1/2".

I reviewed the "How to Build a Shower Curb" page. I assume there is no issue in making the mortar on top over 1" thick? I don't know if there is a "too thick"
limit.
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Old 11-09-2018, 06:19 PM   #8
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might I suggest you look into Schluter Kerdi ? Must confess I know too little about the USG system, but I think either will solve your problems.
Another vote for mud bed rather than foam pan.
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Old 11-09-2018, 08:19 PM   #9
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No issue at all, Kevin.
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Old 11-09-2018, 10:06 PM   #10
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So I am trying to get my sequence of events down now that I have the mud bed thickness resolved. I am a bit confused about cement board on wall vs top mud bed and finding conflicting advise.

Pre-slope is in. Next is PVC liner. Then install backer board or top mud bed? I am concerned about damaging liner when working on it when installing backer board, but I am reading the top mud bed locks in the backer board. Have seen alternate suggestions of installing top mud bed first, then installing backer board with a 1/4" gap to be filled with silicone caulk.
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Old 11-09-2018, 10:43 PM   #11
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There are two different classes of cbu:
- 'real' cbu
- fiber-cement boards

They each have different installation instructions, so that's why you see conflicting instructions because, literally, they do require different procedures.

A fiber-cement board CANNOT be embedded in the mudbed, so you need a gap. This makes it harder to secure the bottom since you cannot install fasteners down low as you'd pierce the liner below limits. A popular version of a fiber-cement board is HardieBacker.

A 'real' cement board CAN be embedded in the mudbed, so it's the better choice if you're going to build a conventional shower (which I prefer not to). Doing this does lock it into place.

The installation instructions of the board you choose will dictate the method you must use.
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Old 11-10-2018, 07:46 AM   #12
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Smile

Thanks Jadnashua,

I am using USG Durock Cement Board, which I believe is true cement board. The manufacturer installation instructions state to put 1/4" spacers to hold the bottom edge off the shower pan. That seems to contradict what you suggested but they also seem to be directing towards using their membrane for waterproofing. Maybe I will go "new school" on the next shower but I guess at this point I would prefer to continue along with the conventional method.

So my sequence would be liner, then cement board (being careful not to damage the liner), then top mud pan, then curb.

Waterproofing the cement board is another step I guess I should confirm. I realize I am opening myself up to more questioning

I was intending to imbed fiber tape into thinset for all joints and corners including the floor. Then waterproofing with redgard or equivalent.

I have been searching the website for an overall guide but have not been able to locate. If anyone can point me in the right direction, I would appreciate it and maybe I could stop questioning every step LOL
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Old 11-10-2018, 08:29 AM   #13
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Kevin, you want to hold your CBU above the liner where it is laying on the pre-slope. Half an inch or so is good. You'll then place your final mud bed against the bottom of the CBU to secure it in place. Putting a few dollops of thinset mortar or similar behind the bottom of the CBU is also a good idea if you've got any gap from having properly notched your wall studs to accommodate the liner folds. That will brace the CBU from behind and allow it to remain in vertical plane when you place your mud bed.

You do not want any caulking on the bottom edge of the CBU. That's the only route the moisture in your wallboard will have to escape into the mud bed.

Using RedGard or similar to waterproof the CBU walls is fine if you have not installed a moisture barrier over the stud wall behind the CBU. You don't wanna do both.

My opinion; worth price charged.
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Old 11-11-2018, 07:58 PM   #14
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Liner in, cement board up, top mud pan in. Next step is building curb.

When waterproofing walls with RedGard or similar, are the joints to be covered with mesh tape and thinset first, and then the fiber tape and RedGard? Or can one of the tapes be omitted? And do the floor corners require any different treatment?

On a second topic, I am trying to decide what to do on the outside corner (see attached pic). I don't have a finished design for the rest of the room yet but likely there will be a linen cabinet on the left wall (so doors) with about 6" of wall space left. So wondering whether to wrap tile around the outside corner or transition to drywall (and what that transition should look like). I am also considering continuing the shower tile around the outside corner all the way to the inside corner and just installing towel hooks on the tile. I realize that is kind of a design question but it gets into methods. If an outside corner of tile, I am leaning towards a Schluter profile but open to other suggestions.
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Old 11-11-2018, 08:47 PM   #15
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When using the liquid-applied direct bonded waterproofing membranes over CBU walls, the installation of the CBU, including finishing the joints, is completed first per the manufacturer's instructions, then the waterproofing membrane is applied per that manufacturer's instructions. The use of a membrane with the waterproofing, if required, will be specified.

You can combine the finishing of the CBU joints with the installation of the waterproofing membrane only if using one of the sheet-type membranes installed with thinset mortar.

Your outside corner can be tiled using the trim piece you suggested, a bullnose tile if available, or by beveling the edges of of your tiles at 45 degrees to make the corner.

My opinion; worth price charged.
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