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Old 08-09-2018, 11:58 AM   #1
honski_16
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Concrete slab shower drain guidance

Hi all, I recently broke ground on a DIY shower renovation. This is my first undertaking of this scope but after finding countless tutorials online I felt prepared to move forward.

I live in Texas with a concrete slab home and plan to build out a 3' x 4' shower pan using mortar. I removed a fiberglass pre-fab pan which revealed the existing drain setup and am seeking guidance on how to adjust the existing exposed piping without having to excavate further, if possible. As it sets, there are two I believe 22.5 degree elbows which ultimately result in the open fitting being flush with the concrete slab.

I purchased a Kohler K-9136-BN drain which will flange to a 2" or 3" PVC fitting. If I slip on the bottom portion of this drain to the existing PVC and piece together the rest of the drain including screw the drain all the way in, I have 3 inches or more that will need to be filled in by the preslope to get the shower liner to the right elevation on the lower drain piece. This area of my concrete slab is not recessed and will therefore require a larger curb that I would prefer to have not to mention an elevated shower pan and probably require adjusting the height of the shower head. This does not seem practical, correct me if I am wrong, and believe I need to modify the piping arrangement.

I am attaching photos for reference. How do you suggest moving forward while minimizing concrete bust out, cutting PVC, etc?

Your help is much appreciated!
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Old 08-09-2018, 12:13 PM   #2
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Welcome, Andrew.

I dunno what the white material might be that surrounds your drain riser, but you're gonna need to find out as you remove it to get down low enough to change what you've got above the P-trap.

Hopefully you'll find the trap low enough so you can cut off just the riser and re-do it to suit your drain needs. Or, perhaps you'll find you need to move the trap such that its inlet is better centered under the shower footprint and you can bring the riser straight up at whatever height you need.

My opinion; worth price charged.
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Old 08-09-2018, 03:15 PM   #3
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Thanks for the response!

I will remove the white material - relative to concrete seems "soft" - perhaps to serve as some type of protection/flexibility to the PVC to avoid cracking. I will report back with findings. Fingers crossed I find a beautiful situation beneath, my worst fear is cracking pipe below!
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Old 09-25-2018, 05:15 PM   #4
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FYI, the white material seems to have been material that separated in the concrete mixture whenever it was originally poured. I carefully chiseled out about ~6" of concrete until I reached a good spot to put in a coupling and spacer for the drain. Luckily I had no issues along the way.
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Old 09-25-2018, 05:46 PM   #5
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Brick shower curb height/width

Hello all. I've sifted through the material in the liberry as well as other sources online and feel that I am about ready to move forward with setting a brick curb followed by preslope, shower liner, cement board, mortar bed etc.

I'm seeking guidance before I do something stupid; see the image attached. My biggest area of hesitation to push forward at this point is how short the bricks are, my understanding is to have at least 2" from drain to top of bricks, is that correct? As they sit there is only 1.5" from the drain to the top of the bricks. If I flip them sideways that gives me 2.75" but results in a narrow curb and I have not seen this done online, however, once I account for tiles on either side with mortar I think this will be a non-issue as I estimate the width to be ~4.5" (brick is 2.25", ~3/4" mortar x2, and 3/8" tiles x2). Thoughts and suggestions?

Some finishing touches I have yet to complete include the shower valve replacement and adding some 2x4s to the studs so that a glass enclosure has something to mount to where the curb is. Am I missing anything and should I be doing anything different? Thanks for the help!
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Old 09-25-2018, 05:52 PM   #6
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Just put brick mortar on the top to make it 2". Plus, you'll have some underneath to bond them to the floor.
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Old 09-25-2018, 06:59 PM   #7
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Your preslope will be about 1-1/2" or so at the edges, then the liner, then the setting bed of about the same thickness. The height of the curb to the top of the drain is for the finished surfaces. IOW, with the slope, the top of the grate to the drain will be at least 2" above the subfloor, and probably more with the height just inside of the curb probably closer to 2-1/2 to 3".

You can make that thinner if you go with a surface applied membrane and a suitable drain since there would only be one layer of mud - the membrane goes on the preslope...i.e., no setting bed on top of the liner. If your goal is to keep the curb height as low as possible, a conventional pan shower is not the way to go.
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Old 09-25-2018, 07:04 PM   #8
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Welcome, Andrew.

Is that the top of the bottom portion of your clamping drain we see sitting flush with the floor we see in your photo?

The code requirement, as I recall it, requires, incorrectly in my opinion, that the top of the finished curb be at least two inches above the drain.

The ceramic tile industry recommendation is that the top of the curb also be 2" above the shower floor. The code is law, the industry recommendation is good practice. If you start with no more than 2" for your rough curb, you're likely to end up with no curb at all by the time you make a pre-slope (even if it feathers down to nothing at the drain) and the required minimum 1 1/2" thickness for your top mud bed.

If you're really trying to cut things close, I'd recommend you contact your local code compliance official to see what he'll accept.

My opinion; worth price charged.


[Edit] Andrew, please keep all your project questions on one thread so we can see what you're working on and what's been previoiusly asked and answered. Any moderator can give it a more generic tittle any time you'd like to suggest one.
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Old 09-25-2018, 08:20 PM   #9
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Yep, like the others said, to get the 2 inches from finish curb to finish floor, the curb will need to come up or the drain will need to go down.

Bolt the drain together and it'll show you what you're dealing with.
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Old 09-26-2018, 11:05 AM   #10
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I appreciate the responses. I was pretty close to making a mistake! The photo is indeed the bottom portion of the clamping drain set in concrete.

Based on the feedback, I definitely need to go higher, from my calculations I may need about five inches to be safe. With the brick curb this could be achieved by (1) leave the bricks as seen in the photo and add depth using mortar on top (I plan to use thinset to bond underneath which won't have much thickness) or (2) a combination of #1 with the bricks flipped on their sides.

I imagine there is maximum allowable depth of mortar one can reasonably expect a layer of mortar to hold up; therefore, #1 doesn't seem feasible with >2.5" mortar depth required on top of the brick to reach my desired 5".

Perhaps a better alternative would be to use a 4.5" by 6" Kerdi curb. I was hoping to avoid this as they aren't cheap but seems that it will get the job done properly.

Do you agree with my analysis?
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Old 09-26-2018, 01:39 PM   #11
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Andrew, you can get CMUs in many different sizes and shapes. You can cut them to size and you can stack them. Surely you can find/make something close to what you need for your curb.

Keep in mind also that you will be adding another 1/2" at least on the top and sides of your liner when you mud over it on your curb.

My opinion; worth price charged.
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Old 10-08-2018, 03:19 PM   #12
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Thanks for the guidance! I went in with the pictured bricks on their sides for the added height and it seems very strong. I've made some progress and am looking for thoughts...

With that behind me, I've attempted my first-ever deck mud sub-floor for the shower pan with 1/4" slope per foot. I used the topping/sand mixture they sell which I understand to be ~3:1 so I added a bit of sand to make it about 5:1. I was under the impression I had a good mixture but it didn't bond well after drying; I'm thinking I did not add enough water. I found that after drying in certain spots I could press down and it would break loose. To investigate further I took a wet vac to the surface at an angle and found a number of spots that very easily pulled right up. I put together a new deck mud mix (much better this time) and patched those areas.

I am concerned about the integrity of the patched subfloor and whether I should continue? Although it is probably weak, as long as the liner is sloped and fill in with a quality layer of mortar with the right slope I can talk myself into thinking that it won't be a problem. Interested in your input on whether I should try over from scratch.
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Old 10-08-2018, 05:22 PM   #13
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Andrew, you would not expect deck mud to "bond very well" to anything, including previous deck mud. You should have used a slurry of Portland cement or thinset mortar on the floor and placed your mud while that slurry was still wet. You really need to remove what you have, call it practice, and do another pre-slope. You'll need to be able to do the deck mud correctly when you do your final mud bed on top of the liner.

Too little water in the deck mud is usually not the problem. Failure to properly pack the mud before cutting to shape is far more likely. Curing the mud under a polyethylene sheet for a day or more also helps.

My opinion; worth price charged.
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Old 10-08-2018, 06:31 PM   #14
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You can rub it down with a rub stone and give it another vacuum test. If it stays down you could apply a skim coat of thinset over the top and let it dry. Or, you could replace it like Cx said in about the same amount of time, then you'd have a little more experience under your belt.
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Old 10-17-2018, 11:32 AM   #15
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Thanks guys. I re-did the pre-slope and finally got a hang of it with much better results. I believe I did a poor job packing the deck mud.

I've gotten started on the shower liner and have run into my next question. I have a curb corner that does not sit against a wall and therefore am finding it difficult to fold - I can't simply do a hospital tuck style as that results in way too much extra material. I looked around and the best advise I found was at this old JB post but it didn't provide a good conclusion. Best I figure is to cut a bit of the extra PVC liner and glue on a custom dam corner. Is there a best practice for this application?

Second question: I am thinking about putting in a niche in the vacant spot to the right of the PVC pipe. Is it OK to apply backerboard directly to the drywall? Would then apply a paint on waterproofing.
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