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-   -   Embedded Pipe in Mud Bed (https://www.johnbridge.com/vbulletin/showthread.php?t=128084)

ztrain727 09-22-2019 03:58 PM

Embedded Pipe in Mud Bed
First of all, thank you John and everyone here for this wonderful resource. It has been indispensable thus far.

Secondly, since I am new, not a pro, and filled with whimsical ideas, I’ll start right off by embarrassing myself with a somewhat preposterous question.

I have a pre-slope 1-3/4 mud bed bonded to the slab with thin set, along with the clamp drain and 40 mil pvc shower pan liner.

I love long hot showers and live on the high desert. Therefore I would absolutely love to recover the grey water for irrigation, but due to restrictive building codes was unable to do so with the under slab plumbing.

On to the absurdity... my concept was to run a 1” pvc pipe on top of the pan liner from the center drain, elbow to above the curb height once behind the CBU and then back down to a 5gpm pump, possibly on a mini float switch. The idea being no penetrations in the liner. This system would attach to a linear drain tray allowing one to plug the main 2” drain. If the system stopped workin it could theoretically be abandoned with no harm.

But, the main caveat of course (ignoring all the others) is whether the top mud bed will split open right along this pipe. The pipe is 1-1/4” OD and the mud bed would be 2” in this case. I would put a thin sleeve on the pipe for expansion, and possibly encase it in lath and Portland cement before starting the dry pack.

Yes it’s crazy. Could it work? Once this is settled hopefully I can move on to asking normal questions.


Davy 09-22-2019 06:09 PM

Maybe I'm missing something but I don't see how you're going to hide a pipe in your mud bed and get the water to run up hill up and over the curb. Also, there shouldn't be any CBU on the curb. :scratch:

ztrain727 09-22-2019 07:45 PM

Yes, it’s uphill! There would be a self priming pump at the other end on a float switch (installed in the linear drain pan) to evacuate the water. And just to be clear the pipe would go above the curb height before penetrating the liner to avoid leaks, but not into or near the curb itself.

Speaking of the curb though, I did cut CBU for it because I was trying to keep the height down and saw some videos of the curb being done this way. My understanding was that the top mud bed locks the inner piece in, then fasteners hold the outside edge of the top piece. Is this a bad idea? What is your preferred method?

It’s 3 pressure treated 2x4’s wrapped in 15# felt, lath and 1/4” Portland cement by the way.

Kman 09-22-2019 08:23 PM

Welcome to the forum, Zane. :)

I'd have to see a drawing to tell you if your idea would work. It's not something I've seen or heard of before.

What I can tell you is that you don't want pressure treated wood in the curb. Some installers will use one on the bottom, but not for anything above it.

PT wood will twist and warp as it dries, and tile can't handle that kind of movement.

ztrain727 09-29-2019 09:41 AM

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Thank you both very much for the information! I guess I now have bigger issues to deal with, so let's get that sorted first.

The bottom board on the curb was a nearly year old pressure treated 2x4, the others were purchased in May of this year. They are nailed off and glued down to the slab with polyurethane adhesive, then coated in lath and portland cement. This was installed in May, so it has been 4 months. As far as I can tell, they have not budged so far (no cracking of the cement), but I don't know the time frame for potential trouble. If you were me, would you demo it and put some sort of masonry in there instead? It would be no fun, but certainly easier now than later.

Message received on mudding the curb. I will ditch the CBU and follow one of the resources here.

As for the grey water, here is a crude diagram and some very approximate photos (with poly pipe instead of pvc). The main question is really whether a big old crack is likely to form right above the pipe with only 3/4" mud coverage. If that's a serious concern, I'll ditch the whole thing. If not, it's just a harmless experiment (hopefully).

Davy 09-29-2019 10:08 AM

I would trust the treated wood not to swell and twist since its been so long and if you plan to wrap the curb with lath and mud it out. I'm not talking about a skim coat of mud but a 1/2 inch mudbed on all 3 sides. You might check out the "shower construction info" thread in the "liberry".

No one knows if the mud and tile will crack over the pipe. That is going to be the weakest point and if it cracks anywhere, I'd say it would be there.

Looks like to me, your pipe (redline) will have to stay full of water for it to stay primed and allow the pump to pull it up and over the curb. I could be missing something but I don't see that happening. If it doesn't stay primed, the water will just run towards the drain.

ztrain727 09-29-2019 05:14 PM

Thank you Davy!

I read the "shower construction info" thread in the "liberry", and it was very enlightening! I have left over portland cement, lime and plaster sand from stucco. Is it a bad idea to mix my own mortar?

That aside, the article raised a couple more questions (I guess this is how it always goes!)

First, it appears the upper mud bed is not formed until after the wall tile and curb tiles are installed. Is this the preferred method?

Second, I bought my tiles second hand. The floor tiles are 12x12 travertine mosaics and the wall tiles are 18x18 rainforest marble. I do not have any bullnose/quarter round tiles for either. I found one other forum post here saying butt joints on the curb come down to personal preference. Is this ever done by you pros? What about cutting the edge at 45* on the saw?

I'm going to put the grey water scheme on the back burner for the moment. The idea with keeping that pipe primed was to tweak the pump to be just a bit behind the shower head GPM so water pools are bit around the drain. It's all very finicky and I'm having second thoughts.

Davy 09-29-2019 07:10 PM

You want wall mud (fat mud) for the curb. The shower floor needs deck mud. I mix my own fat mud all the time. 4 sand to 1 Portland and about 3/4 lime usually makes a good mix.

The floor can be done before the walls or after. I do the walls first.

You'll want to cut the floor tiles down to 3x3 or 4x4's. Large tiles don't work well on shower floors.

I wouldn't butt joints anywhere. You want 1/32 to 1/16 for grout. You can miter the tiles or leave them square and polish the edges. Or, you can bullnose and polish the edges. Polishing the square edge is easiest in my opinion.

ztrain727 09-29-2019 09:00 PM

Awesome! Thank you so much for the detailed information Davy!

I'll mix my own fat mud in that case. Already mixed 5:1 deck mud for the pre-slope and it turned out great.

The floor tiles are 2x2 mosaics on mesh backing. The sheets are 12". Sorry for the confusion. No need to cut the mosaic sheets down right?

As for the butt joint, I guess my lingo is off, but you still managed to answer my question, so thank you! Do you use a grinder and rock polishing wheel set for the square edges?

HooKooDoo Ku 09-30-2019 09:32 AM

I'm another DIYer that likes to think outside of the box...

Zane, let me see if I first understand your problem:
You have a house on a slab and you are building a shower.
You want to be able to collect shower "grey water" but you were not allowed to install a grey water diversion pipe during construction into the slab.

So what about this... rather than building the shower at slab level and running your grey water diversion pipe up and OVER the curb... what if you raised the drain and the entire shower... say about 2"... and installed your grey water diversion pipe UNDER the whole shower (well, I would slope it slightly so that any water that ever gets into it drains).

Where the diversion pipe comes out of the wall, you could place a threaded join flush with the wall. That way, if you ever wanted to abandon the project, you just need to close your diversion pipe with a cap.

ztrain727 09-30-2019 06:25 PM

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Thanks for the idea HooKoo! I actually think that would be an elegant solution. Problem is, I already installed a rather thick 1-3/4" pre-slope mud bed, so this would entail demoing or redoing the preslope after laying the pipe. Basically, I kind of missed my window, and I'm willing to live with that.

In the meantime, I'm going back over my CBU with a 4' and 2' level to check for flatness. I have some areas with 1/4-3/8 indents over a 4' span. Should I take the CBU sheets down in these areas and shim out the studs, or float those areas with thin/medium set, red guard, and call it good?

It's hard to get a photo, and this is exaggerated a bit by the tapered edge, but for reference:

Davy 09-30-2019 06:43 PM

3/8 is quite a lot. It's worth taking down and getting the walls flat and as plumb as you can. If you didn't, it would be a good time to notch the studs for the pan liner folds. It's covered in the Shower construction thread, post 13. That keeps the pan liner folds from bulging out the CBU.

ztrain727 09-30-2019 07:56 PM

How did you know Davy! Sure enough, notching the studs is also on the list, so most of it has to come down anyway. The CBU was hung a bit hastily so some important details were overlooked.

What would be considered a reasonable amount of variation over say 2' and 4 respectively? The tiles are 18x18.

While it's down, what your take on adding horizontal seam blocking? I read it's not essential with Durock, but can't hurt.

I want to get this CBU dialed so I can mud and mesh the seams and get the red guard up.

cx 09-30-2019 08:31 PM

Zane, the ceramic tile industry standard for flatness for tiles that size is no deviation from intended plane of more than 1/8th" in ten feet nor 1/16th" in two feet. That's a very, very flat surface and you'll be glad to have it come time to set those tiles.

I'll also recommend you consider using a sheet-type waterproofing membrane so you can eliminate the potential "speed bumps" we see so many folks produce when filling and taping the seams in their CBU.

My opinion; worth price charged.

ztrain727 09-30-2019 08:40 PM

Excellent! Thank you for that information cx! A bit daunting, but better now than later.

When you say waterproofing membrane, do you mean Schluter and the like? I thought it was designed to be set on drywall? In any case, that would eliminate the speed bumps because you skim the whole wall and set the membrane? Do you still mesh the seams if you go that route?

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