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Unread 02-14-2022, 06:25 PM   #1
Ruca
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Florida shower install on slab

First of all - thank you to everyone here for existing! We've begun our shower install and finished our demo. We've already got a bunch of questions, but first off is tackling the drain & shower pan.

Our plan was to do a preslope, waterproof layer (liquid membrane), mortar bed, tile. But this is Florida, and we don't have rules here. So when we tore out the old tile, there was no waterproofing and the tile was on a single mud bed (and other debris) layer. More importantly, the existing drain flange is level with the recessed concrete slab. Our understanding is the preslope should go under the drain flange (with a minimum thickness of 3/4" and appropriately sloped), then waterproofing layer, then the 1.5" thick mortar bed and tile. The shower is 3' x 5', and the drain flange is currently 4.25" below the (yet untiled) bathroom floor.

Since our drain is currently level with the cement slab, what are the best options to address either a) minimum preslope/fitting under the drain and b) minimizing digging out and changing the drain? We'd like to do it the right way and not the Florida way, but FWIW there weren't any issues behind the old tile (which was CBU on drywall), aside from moisture around the drain.
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Unread 02-14-2022, 06:44 PM   #2
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Welcome, Lauren.

We're quite familiar with your Florida method of shower construction. And it's not correct that you do not have rules, it's more that you're in one of the few areas I know of where that particular rule is customarily followed. If your concrete floor is properly recessed more than two inches below the concrete grade outside the shower and was poured along with the rest of the concrete foundation slab, no waterproofing membrane is required.

Unstated with that rule, unfortunately, is any mention of how a drain is to be incorporated. The moisture barrier in the walls is still required by code, but is commonly disregarded in your fair State.

How to fix? There is no rule anywhere in the building or plumbing code (the shower receptor is part of the plumbing) about how a pre-slope must be constructed, only that the waterproof membrane must be sloped a minimum of 1/4-inch per horizontal foot. How that happens is up to the plumber, who generally does not even know it's required. A sad situation, but commonly true.

The requirement of 3/4" of mortar at the drain is a requirement for "deck mud" and particular to the tile industry. In your case, where you do not want to remove your drain, you could feasibly use any number of cementitious patching compounds to fashion the slope in the area close to the drain and continue it with the same of similar material out to the perimeter thickness. It simply must be solid enough to meet the requirements and properly sloped.

The top mortar bed, on the other hand, is a tile industry requirement and, as you suggest, must be a minimum of 1 1/2" thick and follow the slope of the waterproof membrane. It should consist of sand and cement in a 5:1 proportion (actually 4:1 in the ANSI standards, but 5:1 is more commonly used and more workable). It is not like concrete! It is meant to offer substantial compressive strength while being quite porous to allow water to flow to the liner and thence to the weep holes in the drain.

My opinion; worth price charged.
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Unread 02-15-2022, 08:35 AM   #3
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Thank you for the reply, CX. Even with everything we read and expected, it was still surprising to see no evidence of any type of waterproofing during the demo. And more surprising there is no damage.

It's my understanding that with the shower recessed 4+" from the rest of the slab, no waterproofing membrane is required. Does that mean it's *acceptable* to put the mortar tile bed, properly sloped, directly over the concrete? I'm assuming this means whatever moisture under the tile gets absorbed through the concrete and into the ground, as opposed to being directed through the drain? This certainly seems like a more straightforward approach and how it was made to begin with. From reading similar threads, I'm assuming this isn't advised.

IF it is advised, or at least acceptable, it's unclear how to tie in water barrier on the walls - would plastic sheeting behind the backer board be preferred in this case?

If we go the route of the more widely used preslope / liquid membrane / tile bed, you're suggesting to simply use any appropriate product (i.e. not 5:1 deck mud) to build the preslope, then continue as usual. Is that correct? We are looking into cement patching products now that adequate for the thickness we need.

Skills and budget aside, what would be the "most correct" or preferred way to build the shower floor (in regard specifically to the drain)?
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Last edited by Ruca; 02-15-2022 at 09:38 AM. Reason: clarification of last question
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Unread 02-15-2022, 10:13 AM   #4
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Hi Lauren,

The pre-slope is always required.

You can use deck mud/floor mud to create the pre-slope. The concrete must first be cleaned thoroughly.

I bond the mortar to the concrete with a slurry of thinset mortar as I go. You can feather the mud to almost nothing at the drain and somehow end up with about three-quarters of an inch at the walls.

We have an article for making the mud: https://www.johnbridge.com/how-to/deck-mud/
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Unread 02-15-2022, 10:33 AM   #5
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Hi John,

Using deck mud for the preslope was the original plan - then we found the drain flange level with and embedded in the concrete slab. It is my understanding that if deck mud is used, it should go under the flange with a minimum thickness of 3/4". What is your opinion on how to best do this given our current drain/slab situation?
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Unread 02-15-2022, 10:38 AM   #6
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Sorry John, I just re-read your post. If feathering to zero is acceptable, that seems like the way to go. I saw one other suggestion of doing this, but it certainly wasn't a common response. Sounds like we have a plan to move forward then.

Thank you so much.
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Unread 02-15-2022, 03:24 PM   #7
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I would think that one option would be to use the Schluter adapter and incorporate a Kerdi drain...pull one mudbed and cover it with Kerdi membrane...but I may be missing something here.

https://www.schluter.com/schluter-us...KERDI_DRAIN-AR
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Unread 02-15-2022, 03:45 PM   #8
Ruca
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That's about as straightforward as I could hope for, Lazarus.

Frankly, we've largely avoided the Kerdi system on account of free labor and cheap mud winning out over cost and convenience of the Kerdi products. I suppose we need to revisit that as an option, as it certainly fixes the drain issue (if we can't agree on the other suggested fixes).

We're planning to put in (mostly dark) marble mosaic for the floor, and we were hoping to avoid installing a curb since the shower is recessed. Not sure if that's possible with the Kerdi membranes or not, but we'll check it out.

Thanks for that suggestion, even if it means we have to rethink the whole plan!
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Unread 02-15-2022, 05:31 PM   #9
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If you have reasonable labour and free mud, The Kerdi really isn't that expensive. Sure, the Kerdi flange and drain might be over $100 and the Kerdi membrane for the floor & walls .....about the same, but if it lasts forever, a cheap price to pay.
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Unread 02-19-2022, 03:24 PM   #10
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We're finally trying to straighten/shim out the funhouse walls in our shower stall. The construction has the shower built out from the framing with 2x4s, and they are less than straight. The original construction had 1/2" drywall then went to the top of the slab, then 1/2" CBU that went below that and into the shower pan. If I remember correctly, the CBU was buried (and tiled!) below the mortar bed. The walls were not flat and you could see how the tiles followed the misalignment of the walls and shower recess.

Since we are not drywalling behind the CBU, and the walls/framing do not perfectly line up with the edges at the top of the shower recess, what is the preferred way to have the CBU terminate at the bottom and meet the preslope? It doesn't seem possible (without wall reconstruction) to have the CBU meet evenly with the "wall" of the shower recess, but if we build it out, what do we fill the void with that is under the overhanging CBU? Hopefully the description makes sense. We haven't created the preslope yet, but plan to use a FloFX drain with a deck mud preslope and liquid membrane water proof layer and tile on top of that.
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Unread 02-19-2022, 06:45 PM   #11
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Lauren, I would recommend you augment or/and fur-out your existing framing such that you have adequate framing for your wallboard (max 16 inches on center) and make such framing flush with the vertical edges of your recess such that your CBU wallboard extends down into the recess while also being plumb and flat. Whatever that requires is what you should do.

My opinion; worth price charged.
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Unread 02-20-2022, 09:59 AM   #12
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That seems reasonable enough to accomplish, CX.

Bordering on panic and defeat. The new trouble is now how the extended tile wall meets the existing wall. Previously, the builder had installed the CBU on top of the fully drywalled bathroom, and used mud cap tile around the edge of tiled spaces to cover the protruding CBU. Short of rebuilding all the walls in the bathroom, are there creative ways to address this thickness difference that don't involve using mud cap tile? The CBU will be roughly 0.5" proud of adjacent drywall. We planned on using Schluter edge profiles - is there some sort of Schluter profile or similar that could cover that up? I'm not even sure how to look for solutions to this problem.
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Unread 02-20-2022, 11:42 AM   #13
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Quote:
Originally Posted by Lauren
The CBU will be roughly 0.5" proud of adjacent drywall.
Seems that would lend itself to the use of a mud cap if your chosen tile has a mud cap available, non?

Lot of other ways to trim such edges, depending, again, on the type and style of tile chosen for the walls. There are quarter-round trims, pencil trims. stone bullnose strips, etc, etc. May or may not fit your design style, but there is always something that can be done. Including, of course, furring out all the walls or just adding a second layer of drywall to the remaining walls. That gets into other issues, of course, but it's a consideration.

In some cases even a wood trim to compliment the trim in the rest of the room might be an option.

My opinion; worth price charged.
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Unread 02-21-2022, 02:37 PM   #14
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We're heading out to find other tile options. Unfortunately, we had already planned the tile design and other options, so we were hoping not to resort to starting over. But considering we didn't know what we were getting into, we shouldn't be surprised we might need to revise the design... (Understood the option of "fixing" all the drywalled walls by furring them out and replacing, but with doors and other things, we're still exploring other options.)

One option that was suggested was just to raise the shower pan to the level of the slab. Using a liquid membrane or kerdi-type waterproofing would allow us to set the preslope max at the slab, instead of below it, which would allow us to keep the CBU even with drywall and above the misaligned recess. Does this seem reasonable? IF it's reasonable, would a curbless option be allowed (with all the appropriate waterproofing), or is our shower pan too small? Otherwise, a tall enough curb to allow for the 2" drain height would be alright? I'm seeing mixed information on curbless showers and the 2" drain height difference being a requirement. Are curbless showers just generally much bigger? I don't understand with the 1/4" per foot you'd need a drain 8' from the shower entry?? Anyhow, bringing up the shower floor seemed like an option that would prevent us from redesigning the tile borders/tile design or re-drywalling the room.

I understand that much of my questioning is about construction/plumbing, but there's so much about tiling we've learned here that we *think* we have that part covered. Thanks again in advance for any advice.
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Unread 02-21-2022, 02:56 PM   #15
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Lauren, there are just too many ways to make that little jog in the wall a "feature" to worry much about making it go away. But that's up to you.

There's also no place in the building code or industry standards says you can't chip out that depression to match the plane of your framed walls, although that would seem a lot of work to solve a pretty simple problem.

The consideration of having the drain two inches lower than the curb applies only if you have a curb. No curb, no requirement. Makes sense? No, I don't think so, either, but that's how the code is written and interpreted.

I don't know how big your shower is, so it's difficult to say what the considerations would be in making it curbless and flush with the outside floor. With no enclosure at all, it would be pretty wet outside the shower, but I don't think we know the plan for that. Curbless and also depressed makes that somewhat easier, but I'd still want to know all the dimensions and fixture locations.

My opinion; worth price charged.
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