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Unread 01-06-2022, 10:15 PM   #1
Astro
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Mid Century Bath rebuild

Hi all, Long time lurker here and this is my first post.

I recently bought a Mid Century home on a slab in Palm Desert, CA. It is a fixer for sure. The bath was a tear out. After removing the leaky spa tub, I discovered a sunken shower. It is basically a open hole in concrete slab with a mud bed and had originally what appeared to be a stucco shower stall. At least it had evidence of tar paper, chicken wire lath and remnants of stucco chunks in the wall cavities. Same construction as the exterior walls.

So here is the deal. I have removed the tile and exposed the slab opening and mud bed floor. The drain area had a pile of cement plopped on top of the drain assembly and I removed it and the rusty cast iron trap. The mud floor appears to be about 4-5 inches thick in what appears to be two layers. The slope is only about 1/2 “ in the 4-1/2 feet of the show length. There is also a rusted water feed pipe buried in the top layer. I have re-routed the main water line to be in the walls and the rusted pipe is no longer in service.

I have all kinds of construction and remodeling experience, but have never done a site built mud bed shower. If anything, I will do any demo, basic replumbing and any re-framing and prep and then let an experienced tile /shower guy do the install.

My initial questions are: Should I cut out the rusty pipe and remove the mud bed and start over with compacted dirt? Is the bed worth saving or will I end up digging a deeper hole, so to speak? Thank you.
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Unread 01-06-2022, 11:04 PM   #2
jadnashua
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REmove what's there. You'll probably want to move the drain to the middle of the shower, or, if you wish to go with a linear drain, one edge. A linear drain costs more, but your mud bed can become simpler as most of those are done using a single slope rather than sloping from each wall to the drain, so you can use screeds easier to build you mudbed.

You'll probably want to read the stuff in the 'libbery'. There are a bunch of methods to build a shower in the Tile Council of North America ( a good handbook). That's not a how to book, but the higher level this works, and the bits required to make it work, and is the industry bible on things tiled. You can buy the whole book, or smaller sections/procedures.

My preference is to not do a conventional, liner shower that is composed of three layers: preslope, liner, setting bed, then all methods get thinset and tile as the top layer, regardless of what's underneath.

There are sheet membranes that can be applied to a mud bed, and foam pans coated with waterproof membranes that can be faster, but more expensive. A preformed pan is somewhat less forgiving as the drain must be in very specific places, and the surface you apply it to must first be flat and level whereas doing a mudbed can adjust to your unique situation and is considerably cheaper if you don't count your labor cost.

With a sheet membrane, your entire shower enclosure becomes totally waterproof underneath the tile. A conventional shower is not waterproof on the walls, and the pan is waterproof underneath a porous mud bed and is expected to be damp almost continuously on a frequently used shower.

You'd want a stable, structural surface prior to installing whatever shower you wish, based on one of the TCNA handbook procedures you choose. They all work.

FWIW, CA tends to use hot-mopped shower pans partly because they are fast, and Mexican labor tends to be cheap. They work, but are not my favorite method to build a shower as they don't support a whole shower waterproof method, and if you're VOC senstitive, a hot-mopped shower is gross, at least during the construction.
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Unread 01-08-2022, 01:36 PM   #3
Astro
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Progress...

Thank you Jim for the response.

I took your advice (at least partially so far) and removed the top layer of mud (~2-1/2”). I broke free from the lower layer easily.

I am concerned that the bottom layer appears to have been poured with the original foundation. It seamlessly integrates with the outside wall foundation and is at least 3 inches thick. I am concerned that breaking it out will crack or break free the wall foundation along the back wall of the shower. The shower well is now ~8” deep on the drain side and 7” deep on the right side below the slab floor.

Does the base really need to be removed or can I get away with only removing what is needed for the new drain?

Also, the back wall foundation is 5/8” or so proud of the stud wall while the two ends of the shower well are 1-1/2” recessed on the left side and 1” recessed on the right side from the stud walls respectively. There is enough to pin the new sill plates down as is but my question is should I fill those spaces (with concrete or morter or?) prior top bolting down and installing the new walls or shall I bolt them down now and kick that fill to the shower install proper as there is still access from the side? If I fill them, do I fill flush with stud wall or make them proud to match the back wall configuration?

I appreciate the advice.
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Unread 01-10-2022, 10:09 PM   #4
Snets
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Astro, it appears you found a "Florida Shower" in CA...Impressive!

So looks like you are down to concrete that was under the dry pack pan? I don't see any reason to remove any more concrete than what you need for the drain. Speaking of drain, how will you be running your 2" drain? Where is it going? Trap?

I this were mine, I would put that drain in the center and fill any voids with new concrete then do a center draining, no-curb pan with a level entry at the slab height. If you do that, it will not matter where the water supply wall resides - level entry, center draining. That is an easy pan to build in my mind.

Do some research and pick a "system" to waterproof this shower. I am a Schluter fan, that is what I would use. There are many more waterproofing systems out there, you gotta pick what you feel comfortable using, just make sure you use the components that work together.

In my mind, your drain/trap plumbing is your biggest challenge at this stage.
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Unread 01-11-2022, 09:25 AM   #5
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Hi Ken,

Move the drain to the center if you are not going to use the sunken area as a tub. Otherwise, leave it where it is and install an overflow with a barrel stop.
I would fur the back wall so that the drywall comes even with the concrete below it. Then bring in your pro.

I recommend a Kerdi shower only if it's not going to used as a tub. Otherwise, a mud job.
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Unread 01-11-2022, 12:46 PM   #6
Astro
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Thank you Mr. Snets and John,

We dont plan to use it as a tub, only a shower.

The area of the sunken well is about 30” x 48”. We are thinking along the line of installing a half wall set back from the well 8-10” or so on the fixture side to hide a niche and form a partial shower wall and were considering a short curb from that wall to the other side far wall to contain any water splash and give a little more arm/body room in the shower, not necessarily for the feet. The slab on the shower side of the wall/curb would form a slab level “step” inside the curb then down to the sunken portion (hopefully that makes sense). We prefer to avoid having or needing a door or curtain. Not sure if that is feasible or advised.

I have a concrete saw and chipping hammer so moving the drain to the center seems easy enough. Then fill in and compact the sand. I probably will wait to top with concrete to the current level until I get to a position to move forward myself or que a shower install expert to ok my drain install.

In regards to the back wall, I read John’s advice to add 5/8” furring to allow sheet materials to mount flush with wall and down over the lower concrete wall proper. I assume it is suggested (by silence) that the two lower sidewall recesses can be addressed during shower install?

One more question comes to mind. I removed the cast iron P-trap. Behond it is also a 12” long, 2” cast iron extension leading to the wet vent, still buried that seems in good shape but has some solidified fill on the lower interior surface that doesn’t scape out easily. The pipe is ~80-90% free. Is that something I should be concerned about or leave it be. An earlier evaluation of my system by a plumbing company indicated that my pipes are in good shape and only advised a descaling, but they were not that concerned if I chose not to.

Is it prudent to burden myself and spend several days to dig that 12” extention pipe out now or let it be with the rest of my 65 year old under-slab system? This would be a substantial undertaking and include drilling out leaded joints under the slab and it would include only that one piece of pipe. The rest of the system is buried 4’ under my slab. Here is a pic of the pipe. Thank you.
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Unread 01-11-2022, 04:36 PM   #7
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Welcome, Ken.

Not at all sure I understand the plan for the plumbing end of your shower, but, be that as it may, I do think you're saying you're planning a doorless shower in that 30x48-inch space, albeit with a little more room added to one end of the 48-inch dimension. While it's certainly possible to do that, you'll need to plan for a good deal of water outside the shower opening. A partial glass wall, restricting the opening to only 22 inches or so on the end farthest from the shower head would certainly help a great deal.

You can build the existing shower floor up as much as you want, including to the level of the bathroom floor. Personally, I'd keep a step-down of three or four inches, and use a direct bonded waterproofing membrane for the receptor and the shower walls. Entirely up to you, though.

And I see no need to try to remove the existing floor except that it does not look to be monolithic with the remainder of the floor. You do seem to indicate that it is, so perhaps it's just my interpretation of the photo. At any rate, but the time you've cut out enough to center the new drain, you'll be patching a good bit of it.

I would absolutely want a new drain and trap and I'd cut back the existing cast iron drain line as much as feasible within reach of the confines of the planned opening in the concrete.

My opinion; worth price charged.
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Unread 01-11-2022, 08:29 PM   #8
Astro
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Thanks CX. You pretty much have it right. Instead of a glass wall half way across the 48” side next to vanity, we were planning a 6’ or so high wall half way across dropping to a curb for the rest of the way. That would incorporate 8-10” or so of the current slab inside the curb to widen the shower and the wall to provide water deflection and hide the niche.

We plan to keep the step down. It was originally about 4” and we plan to keep it at least that depth.

I will explore removing that last 12” of cast iron. I dread it but know that it is prudent. If I can remove the concrete floor in that corner, the wet vent pipe it attaches to is just inside the wall in that corner. The wet vent attached to it is also cast iron, but vertical and may not have as much scale.

As for the plumbing proper, I plan to have all new in the wall adjacent to the “half wall/niche wall.

I still hope to have no “door" hoping the half wall and the curb contain all the splash and water. We plan to have a polished concrete floor for the rest of the bathroom and house so further water proofing outside the curb other that concrete sealer to me is not practical. If the current vision does not contain the water, I’ll have to install a glass door over the curb so I’ll reinforce the wall as needed just in case.

Thank you so much for the advice and counsel so far. It is reassuring as I work through this.
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Unread 01-11-2022, 08:37 PM   #9
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I recall one shower I created out of a tub/shower that is about the size you're working with. Has a glass wall on top of a curb with an opening as I described. Tile floor over concrete SOG outside. When I did the conversion, the only accommodation we made for splash-out was the installation of a very low towel rack for the storage of the floor mat outside the shower when in use.

I know the shower to be used by pre-teen and teen small animals, affectionately called children by the owners, and I'm told the set-up is still acceptable. I expect a bit messy at times, but that's not my job, man.

My opinion; worth price charged.
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