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Unread 11-16-2022, 07:26 AM   #1
ProjectDad
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Confirming depth of recess for slab on grade curbless shower

Yep, another curbless shower thread. I read the other ones, which have all been helpful, but I want to make sure I'm not making a mistake calculating the depth of the slab recess for my bathroom.

I'm building in Tampa Bay Florida.

6 ft by 6 ft bathroom, slab on grade, to be located in corner of garage workshop.

Bathroom will have tile floor, remainder of structure will be left as unfinished concrete.
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Goal is to have no lip between the tile of the bathroom and the concrete floor of the remainder of the building. And no lip at the shower.

Given the small size of the bathroom and shower, the current thought is to recess the entire bathroom, and slope the whole thing toward the drain. We would still have a shower curtain to try to contain the water, but if any escaped it would hopefully still drain.

I have not poured the concrete slab, and I'm trying to make sure that I am calculating the correct recess.

I'm having a very difficult time finding local craftsmen to help me with this project. I did find someone who's comfortable using the Mark E kits to help with pre-sloping in combination with a conventional shower liner. I'm basing my calculations on this assumption.

With 6 ft sides, the diagonal is approximately 8.5 feet. A slope of a quarter inch per foot, the result is 2-1/8" of declination.

Adding in 1" for mud and tile, and 0.25" for the initial thickness of the drain, and I calculate the total recess needed of 3-3/8".

The formwork is placed for recessing the entire bathroom 3.5 inches.
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Can anybody confirm whether or not I'm crazy? I definitely don't want to chip concrete out, so I really want to get this right the first time.

(and if you're in the Tampa Bay area, I am glad to exchange money for help :-)
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Unread 11-16-2022, 08:06 AM   #2
cx
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Welcome, Justin.

I would strongly suggest you simply drop that entire area the 3 1/2 inches you think you need and do the shaping for slope using deck mud/dry pack/floor mortar (whatever they call it in your area). I usta drop the shower area in all my new construction master baths a full 5 1/2 inches as a matter of course. That usually allowed adequate space for a step-down, doorless shower that my customers seemed to like.

You'll find that a whole lot easier than trying to shape your concrete floor while placing the concrete. Not only easier, but it will actually work, where attempting it with the concrete will likely not. And any competent concrete form-place-finish crew can easily deal with the dropped area.t

And tell us about cutting out half the CMUs all around. I've never seen that trick before.

My opinion; worth price charged.
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Unread 11-16-2022, 08:12 AM   #3
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On a recessed shower I would not use the liner method, but a surface waterproofing of your choice Justin. In-so-doing you also wouldn't have to pre-slope the concrete IF that was your plan. Since you only need one slope for the surface waterproofing method you will also save a little in height calculations.
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Unread 11-16-2022, 09:55 AM   #4
ProjectDad
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Great info, thank you both.

Regarding cutting the block, it is my understanding that this allows for pouring the slab and filling the stem wall with concrete at the same time.
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I do not have much concrete experience so I can't say anything very smart!

Regarding waterproofing, thank you for the input on a surface waterproofing system. There is a risk that I'll be doing this myself given my difficulty in finding a contractor to help me with this small project. I have explored the Schluter systems -- they seem okay but not quite as straightforward perhaps as I would hope.

I welcome any input on a beginner-friendly surface waterproofing systems.
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Unread 11-16-2022, 10:22 AM   #5
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Quote:
Originally Posted by Justin
I have explored the Schluter systems -- they seem okay but not quite as straightforward perhaps as I would hope.
All the sheet-type direct bonded waterproofing membranes (ANSI A118.10) will be very similar in their installation requirements, Justin. There are also liquid-applied membranes (same standard), but I personally do not recommend them for creating shower receptors. Others do, as do the product manufacturers.

Interesting concrete detail. We don't commonly see CMUs used as footers for SOG foundations in my part of the country.
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Unread 11-16-2022, 11:11 AM   #6
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I just helped my son with a similar situation but in an old house. Entire bathroom is recessed and is a similar size. Now I am here acting like an expert, CX was a big help. We did the mortar bed for the shower one day and the rest of the floor the next. I question the need to slope the entire room. How much water is going to get out and it will have to break surface tension to start flowing. My son applied a kerdi membrane to the shower floor by himself (first time) so it is not a super difficult task. Then kerdi band to waterproof the floor to wall seams.
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