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Unread 05-11-2010, 10:17 AM   #1
markd5469
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Recessed Slab on Grade Shower

I'm about to start a master-bath remodel. The house is typical Southern Florida Slab-on-grade construction and the shower is recessed below the slab level. I haven't torn out the old mud-slope yet, but it appears that I have about a 6" slab raw-concrete recess.

I do not intend to use a liner, as it is not code required in this installation. However, I do intend to run 15# felt behind the backer-board up to shower-head level, and let it lap down into the recess slightly. In a worst-case scenario, water that gets past the tile and sloped mud can drain directly into the sandy fill under the slab recess.

The shower slope will be the 5:1 mix recommended, water added to appropriate consistency, with 1/4" / ft slope. Shower floor will be 4x4 textured for added slip resistance.

There is an existing curb. It is about 4" above the bathroom floor, and about 7" above the shower floor tile. If I reconstruct it to a size that will be at least 6" above the shower drain, that should meet code and be less of a stumbling hazard when I get old(er).

I'll be using 18x18 tile on the walls, so water penetration through grout joint chances will be minimized (on a /SF basis), and the roofing felt should preclude any water passing beyond the backer-board from entering the walls.

I'm going to use batt insulation for sound in all walls between bath and living space, and will split the paper if I can't find unfaced.

I'm using pre-formed niches and a better-bench. I intend to use granite or marble (budget has to some in here somewhere) on the curb top, window sill, niche sills and bench top to eliminate grout-joint issues on those semi-horizontal surfaces (even though they will all be pitched).

Am I missing anything, or does this sound like a viable approach?

I'm a commercial GC who hasn't gotten his hands this dirty since I redid the kitchen 5 years ago. Work is slow, so I've got the time now. Starting Friday.

Thanks in advance for pointing out any pitfalls I overlooked.
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Unread 05-11-2010, 11:28 AM   #2
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If I understand you correctly, you have no slab under the shower, and you intend to make a mud bed on top of the "sandy fill?" And this mud bed is the only thing under the tile? If so, please consider adding 3x3 or 4x4 welded wire in the mud, since there is currently nothing structural in your floor plans.

Also, you are not concerned about termites, ants or tree roots in south Florida? You are concerned with water penetration in your shower, but seemingly un-concerned about what happens to it when it leaks under your slab. I recognize that's the way it's been done down there, but now there's better ways to do it.
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Unread 05-11-2010, 12:02 PM   #3
markd5469
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There is already a slab under the shower. The under-slab is at least 4" thick by local code. Side walls are also minimum 4" thick. I've got a "concrete tub" in my concrete floor for my shower. That's why I'm not required to do a liner. I may put one in anyway, but I'm not required to.

Otherwise does my plan look right?
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Unread 05-11-2010, 12:38 PM   #4
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Welcome, Mark.

We see a lot of re-dos on Florida we-don't-need-no-steenkin-pan showers on here and I'd not recommend you do that, code or no code.

I've built lots of curbless showers in SOG residential by dropping the shower 5 1/2" during the foundation pour. These areas are of thickness and reinforcement exactly the same as (a little thicker, usually) the rest of the slab. We installed a clamping drain and liner the same as with any on-grade shower construction.

You might wanna poke around a bit in the bottom of your shower area. Most (all?) reports we get from Florida indicate either no structural concrete under there at all or a bit of concrete not attached at all to the surrounding SOG.

Be easy to determine what you've actually got while you're replacing that floor drain with a proper shower clamping drain. Gonna be doing a lot of work in there and might as well make it right, eh?

My opinion; worth price charged.
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Unread 05-11-2010, 12:46 PM   #5
jadnashua
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If I had that situation, I'd consider a curbless shower and I'd use a surface waterproofing system. then, you could even roll a wheelchair in there, if needed. Keep in mind that there will be moisture that gets below the tile, and eventually, all of that mix will end up saturated. It will hold that moisture and keep the grout lines moist. That, along with the heat and humidity of FL, means mildew control becomes much harder. Much better to at least use a liner which would limit how much water it could hold, and even better to prevent it from happening altogether with a surface membrane. There are industry standards for a reason, and all of them require a sloped waterproof liner, whether it is embedded in the pan, or on the surface (and the tile doesn't count!).
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Unread 05-11-2010, 01:54 PM   #6
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I'm leaning to some sort of membrane. If I find I have a structurally sound slab recess (if I don't I've got a much bigger job, and may just fill it up and to a flush-floor shower instead) I'm now thinking that my shower membrane should be sloped, but I hate the idea of doing a mud-pan-mud-tile installation, just because of the extra time it will take.

What about a mud base for slope, with a roll-on-membrane running up onto the backer-board? Then water that gets through the tile and grout should hit the membrane and run to the drain.

Or, should I bite the bullet and get the pre-sloped bottom (Noble or other) and roll-on a membrane up to shower-head level?
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Unread 05-11-2010, 03:30 PM   #7
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Quote:
Originally Posted by markd5469
In a worst-case scenario, water that gets past the tile and sloped mud can drain directly into the sandy fill under the slab recess.
termites love that water feed near your wood.
also roots love the water feed too along with mold and rot.

Quote:
Originally Posted by markd5469
I'm leaning to some sort of membrane.
smart idea.

Quote:
Originally Posted by markd5469
What about a mud base for slope, with a roll-on-membrane running up onto the backer-board? Then water that gets through the tile and grout should hit the membrane and run to the drain.
but it wont, it will absorb into your cementboard and then rot the studs.
the membrane should go all the way up the wall.
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Unread 05-19-2010, 09:47 AM   #8
markd5469
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Question Demo done, now what?

I've completed the demo and found the following conditions:
Concrete slab recessed +/-6" for full area of shower.
Hole in center of recessed slab (approx. 12" square) open to soil below house slab
Standard hub-drain (no weep holes)
Ceramic tile loose-laid over the hole around drain PVC
Sloped mortar base over top of recessed slab and tiled-over-hole
Side walls of recess mortar-ed out to meet face of greenboard above
No liner, no waterproofing of any kind, wet green-board behind wall tiles as expected

The curb was constructed the best of all, brick with tile and marble top cap mortar mounted to the brick. Brick set slightly overhanging the recess.

Now for the put-back, I'm planning on the following:
  • Replace shower drain with proper weep drain
    Concrete in the hole in the center of the slab recess with reinforcement (I'm a GC, I can do that)
    Sloped mud base
    New brick curb, aligned with slab recess on inside face
    40 mil PVC liner with glued corners at curb, run up onto and secured to wood backing on all three walls, lapped over the curb (any suggestions for securing it on the outside?)
    Mud base for tile slope, mesh and mud over brick for curb
    Visqueen on inside face of stud walls, lapped over top of liner edge
    Cement Backer-board in all tile areas
    Mud out base walls to be flush with CBB face
    Tile it

Is that about right?

I'm not going to be in the house long enough to go with a waterproofing membrane under the tile on top of the CBB. I'll be using 18" wall tile with narrow grout joints, and sealing the grout.

Other that a membrane on the walls, any other points I missed?

Thanks in advance for the help
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Unread 05-19-2010, 10:08 AM   #9
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The liner is held over the curb by the metal lath. You form it slightly over bent so it holds the liner by spring tension.


You don't need a membrane on the backerboard with the plastic sheeting you plan to install over the studs.
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Unread 05-19-2010, 11:55 AM   #10
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Quote:
I'm not going to be in the house long enough to go with a waterproofing membrane under the tile on top of the CBB.
speaking for the next owner, thank you very much for handing me a stinky shower.

seriously, mark, how difficult is it to do a couple extra steps to do it right?

Have you considered a Kerdi shower? My AZ shower was very much like yours (including soggy drywall) and the results came out great. I even used the recessed floor to allow a much lower (1") curb. I also know I can confidently tell the next owner that the shower is the last of his worries on this house.
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Unread 05-19-2010, 12:54 PM   #11
markd5469
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I understand there are those who only think the way to build a shower is with a WP membrane on the inside of the board. I've looked at it and understand the plus-value.

I also understand that those products weren't around for many years, and showers, when built right, were not a problem. Thanks for the advise. I've ready many threads on here and see the two groups clearly defined.

If this were on a 2nd floor, or anywhere with space below, I'd be using a membrane. However its on the slab, and the old system worked for nearly 30 years. My new shower will long outlive me, even without the membrane on the inside of the backerboard.

If you have other comments about anything I've overlooked, I'd love to hear them. If you only want to slap be for not using a membrane, thanks, but no thanks.

This is a great site and I will continue to monitor it and refer clients who want to tackle a shower too.
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Unread 07-18-2010, 12:07 PM   #12
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Markd5469,
Listen to what Sanbagger told you, pleeeeease:

" speaking for the next owner, thank you very much for handing me a stinky shower.

seriously, mark, how difficult is it to do a couple extra steps to do it right? "

I am, till this day, with allergies and others DUE TO the lack of presloped mortar UNDER the liner!!!!

I had been living since '92 in this condo (yes, 2nd floor) with cement slab 4" and ....cough...cough...somethings were missing. I guess they built the shower with the same stinky plan you have in mind!!!

In 2009 I did my own demo and ..I JUST COULD NOT STAND (I am not shouting, just enphasizing!) the odor coming from all this, as I tried to lift the floor tiles. It was all moldy, blacky,etc. I had to pay a handyman to continue with the shower demo due to my coughing as soon as I enter in the bedroom.

Please, for the sake of yourself's and your family's lungs, do the presloped also, UNDER the liner. Contractors refuse to do even though building departments advise you to do it.

I am planning to spray all over the presloped and around with waterproof "whatever", if possible, because it has been a nightmare the feeling since 1992.

If you want to have a bad job done, let the contractor or handyman to do it. The purpose of doing it yourself is TO DO THE RIGHT THING. Something you will be proud of telling to others and the reasons why.

God Bless
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Unread 07-18-2010, 12:56 PM   #13
Brian in San Diego
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Welcome to the forum, kilhefner. The last post to this thread was two months ago and the OP hasn't visited since the 10th of June. So your pleading is probably falling on deaf ears.

We appreciate any input you may have but posting to a thread that hasn't had any activity for a couple of months may be a waste of time.

Brian
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Unread 07-19-2010, 07:32 AM   #14
markd5469
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The job is complete. I demo'd the old shower, found the "drain it into the ground" approach I described earlier. I tore everything out, compacted the sub-base fill and re-poured concrete around the drain. While the old wall between the shower and vanity area was demo'd my wife and I decided it would look better open, so I only had two walls to tile for the shower, but my enclosure would cost more.

I installed a proper drain, installed the new mud slope and pan properly cornered and backed with glued corners at the curb. I hung visqueen on the walls from ceiling to pan, lapped down into the pan. I hung my CBU's and taped the joints using appropriate mesh-tape and thinset. I built my curb out of bricks set in mortar, with the proper slope to the inside. I then mudded the floor and laid 4x4s on the floor and used marble sills for the top of the curb. I laid up 18x18's on the walls, with 2 niches (used the pre-formed ones). I decided the shower would look too "busy" with the bench, so left that out.

I then laid 12x12 porcelain tile that looks like slate (but doesn't have to be sealed) on the floor.

The job ended up great. I know many of you are appalled that I didn't put a membrane on the CBU's. I may live to regret it, but with the 18x18 tiles, there is only about 10% of the grout joint space the old walls had, and I sealed all the grout (3 coats) before the shower was used.

Remember the idea was to remodel an old bathroom, not just the shower. The new room is bright, open and much nicer than the old one ever was. It took longer than I would have ever imagined, but was worth it.

Thanks to all of you on this thread who's information helped be make decisions and value judgments along the way. I'm very happy with the completed project, and have a great deal of new respect for those in your profession.
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Unread 07-19-2010, 08:41 AM   #15
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Quote:
I know many of you are appalled that I didn't put a membrane on the CBU's.
Quote:
I hung visqueen on the walls from ceiling to pan, lapped down into the pan.
Your shower seems adequately waterproofed to me. I don't think anyone will be appalled.
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