Asking for opinions on straightening shower drain pipe

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bronzefury

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Hi,

I'm planning on building a shower pan using a mud bed, Kerdi drain, and Kerdi membrane. There is a box shaped hole around the shower drain that I plan to fill with gravel followed by filling with Quickrete 5000. I was dry fitting an ABS Kerdi Drain on the shower drain riser and noticed that the riser is not perfectly vertical. It is about 4 degrees off from vertical.

It appears that if I want to install my shower pan properly, the shower drain riser has to be close to a perfect 90 degrees. The position of the drain hole is very close to where it needs to be as it is equally distant from the 3 walls and where my proposed shower curb will be. The top of the riser is about 1 1/8" below the top of the concrete slab. I've marked the various distances between components in the attached image.

There were three options I was thinking about to fix this situation.

1) Cut the ptrap off at position Cut_A and replace with a new ptrap and riser and try to make it level.

2) Cut the ptrap off at position Cut_B and replace with a new ptrap and riser and try to make it level.

3) Cut riser at position Cut_C and try using 22.5" couplings to make it level.

My questions are:

1) What do experts on this forum think is the best methods to make the shower drain riser level?

2) How do you measure the levelness of the shower riser? I'm using straight levels held up against the pipe but is there a more accurate way?

3) First time I'm doing this. Are there other things I need to consider to get this done right?

4) Would there be a way to not touch the pipes and use the mud on the mud pan to hide this imperfection?

ShowerDrain_001.jpg
20201126_101446.jpg


Thanks!
 

wwhitney

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If you can use moderate hand pressure at the top of the riser to move it to plumb, then you could just pack the box with gravel to hold it in that position. This assumes that the 1-1/8" projection above top of slab is sufficient for your mud bed and Kerdidrain.

Otherwise, go with cut A (or slightly to the left if there's glue build up around the coupling hub).

Cheers, Wayne

P.S. Another way to check for plumb is to take a coupling and dry fit it on top, then use a level on top of the coupling. If you knew the pipe was cut square (e.g. you cut it on a chop saw yourself), you could skip the coupling.
 

bronzefury

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Thanks Wayne. There is a bit of glue around the coupling hub at Cut A. I was worried that if I angle the pipe a bit to move it to plumb and fill with gravel, it would unnecessarily strain the pipe - and over time, a potential crack or leak could happen. I think using a coupling is a good idea to determine that the pipe is plumb.
 

wwhitney

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I think with moderate hand pressure (20 lbs?) you're not going to damage the pipe, so it's a question of whether that's enough to get it plumb, or it's stiffer than that. I'm unclear on what the long term behavior of the plastic would be--it might creep, relieving the stresses as it adopted the new geometry. Or it might not.

Cheers, Wayne
 

bronzefury

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I think there is another issue here that I didn't think about until now. The drain pipe's draining channel is 1/2" per foot. I guess the house has shifted over time?

So, even if I cut the pipe at cut_a or cut_b, add ABS pipe to extend or shorten the drain line, then connect a new P Trap, the rotational axis of adjustment is only around the drain pipe's axis. The result being that the shower drain will still be crooked and can never be perfectly vertical due to only one axis of adjustment.

I'll need something more flexible that allows the ability to adjust the riser in more directions. I'll see what I can find....
 

wwhitney

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Did you try pushing easily on the riser to see how close you can get to plumb?

If you redo everything, you will have two degrees of freedom (assuming the riser can move 1/4" or 1/2" in plan), the two rotations at both ends of the elbow piece of the p-trap. Plus when you glue up a joint you might be able to get a fraction of a degree bend at the joint (not sure). I think between those you can get closer than 4 degrees.

Otherwise, you could use a shielded rubber coupling to connect new and old work, and maybe get a degree out of it, although you'd have to bury the p-trap and riser in gravel to hold it in place before tightening up the coupling. And of course, with a pair of 22.5 degree bends, you can get any adjustment you need up to 45 degrees, but it would be nice to avoid having to do that.

Cheers, Wayne

P.S. It looks like you might have enough space to put in a 22.5 degree elbow right at cut A and then approach your riser location from a different angle. That would give you another degree of freedom.
 

Jeff H Young

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what is a drain pipe draining channel?. keep it simple! push it over to where the verticle is plumb. or cut the trap off and reset a new one.
 

bronzefury

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Hi Jeff,

By "drain pipe draining channel" I meant to say that the drain pipe's grade is 1/2" per foot (or said another way, is at a 2.8 degree slope). Please see my hand drawn pipe below on the left side of the drawing.

Hi Wayne,

So, even if I have two axis of rotation, the drain pipe axis in orange/pink and the p-trap axis of rotation in light blue, the top of the riser will still be angled since it will still have a 2.8 degree slope, which is determined by the drain pipe (i.e., the piece that has a 2.8 degree slop in the drawing below).

I tried experimenting with two 22.5" degree couplings but that would end up shifting the drain off center.

I've seen some shielded couplings but so far have yielded aboveground couplings. I'd have to think that there must be undergound flexible couplings somewhere that can handle being buried under gravel. I wasn't planning on encasing the piping in Quickrete - just gravel all around but topped with about 2-4" concrete laid on top of the gravel.

showerdrain_002.jpg
 

wwhitney

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A shielded rubber coupling can be used underground, the shield is stainless. For 2" plastic to 2" plastic, use Fernco 3000-22 or Mission CP-200.

Have you looked at the single 22.5 degree option?

If the u-bend is a true 180 degrees, then I agree with you, I was mistaken to say that you can get the riser (closer to) plumb by adjusting both the blue and orange angles in your nice drawing. Because if the riser is plumb, the u-bend entry is plumb, but you can't get the p-trap elbow exit plumb.

I'm unclear if the elbow part of a p-trap is a true 90 degrees, or if it's 91.5 degrees or so. Because you'd think it should have the 2% slope built into it (assuming the u-bend is a true 180 degrees).

Also, if your fixed pipe is at 3 degrees off level, then certainly you can get closer than 4 degrees off plumb on the shower riser if you redo things.

Cheers, Wayne
 

Jeff H Young

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yes i understand too much grade will cause that to be out of plumb so put a coupling down low on the vertical hold it plumb for a few minutes while glue sets or use a mechanical coupling (shielded coupling with bands) hold plumb while tightening presto !
 

wwhitney

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The question your suggestion raises is how many degrees of bend can you get out of a 2" solvent weld coupling, or a 2" shielded rubber coupling? 4 degrees seems like a lot of bend to get at a single coupling.

Cheers, Wayne
 

Reach4

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1. How long is the trap arm on the shower before it reaches what vents it? We can use that number to check something.
2. Note there are Youtube videos on bending ABS with some heat. I think you would bend the pipe outside, and then cut and glue the bent pipe in.
 

bronzefury

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wwhitney

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This bears a bit more research, I believe Home Depot has the descriptions off. My understanding has always been that the unshielded couplings are for underground only, and I generally avoid them. And that the shielded couplings are for underground or above ground. If I get a chance to verify that, I'll follow up here.

But I do agree that if you're trying to get 4 degree bend, that's more likely to be possible with the unshielded coupling.

Cheers, Wayne
 

wwhitney

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Thanks for pointing out the discrepancy, this has led to some interesting information. There are three relevant ASTM standards (which I don't have access to):

ASTM C1173 Standard Specification for Flexible Transition Couplings for Underground Piping Systems
ASTM C1460 Standard Specification for Shielded Transition Couplings for Use with Dissimilar DWV Pipe and Fittings Above Ground
ASTM C1461 Standard Specification for Mechanical Couplings Using Thermoplastic Elastomeric (TPE) Gaskets for Joining Drain, Waste, and Vent (DWV), Sewer, Sanitary, and Storm Plumbing Systems for Above and Below Ground Use

Both the IPC (705.16) and UPC (705.9) refer to all 3 above standards in their section on mechanical joints between dissimilar DWV materials. Mission Rubber and Fernco seem to make C1173 and C1460 couplings, but not C1461 couplings. And C1173 couplings are available in both shielded and unshielded versions [Fernco's 2" PL to 2" PL offerings: unshielded ASTM C1173 is 1056-22; shielded ASTM C1460 is 3000-22; and shielded ASTM C1173 is 1056-22RC].

So although it has been a fairly common industry practice to use C1460 couplings underground within the footprint of a building (because the connection appears more robust than an unshielded C1173 coupling), it seems that if one wants a shielded underground coupling, it needs to be a shielded C1173 type, not a C1460 coupling. It's worth noting that in the above example from Fernco's line, the C1173 couplings are both 3.5" long, while the C1460 coupling is only 2.13" long.

Now with all of the above, for your application, it could be argued whether the coupling is underground or not. It's certainly below grade, but it's going to be surrounded by gravel, not dirt.

Cheers, Wayne
 

bronzefury

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This next post shows what the problem looks like using a torpedo level as a comparison and the solution.

The photo below show a coupler with a torpedo level on top to show how I measure how much off the vertical riser is. The coupling is below the level because the riser isn't cut perfectly but the top of the coupling is cut perfectly.

20201128_094747.jpg


The snapshot below shows how far off out of level the riser drain pipe is..

20201128_094800_markedup.jpg


After some experiments, the solution I came up with looks like the photo below. The ABS pipe is 2 1/2" long and about 7/8" is sticking out (measured from the shortest exposed point). The part that is sticking out is what will mate with the kerdi drain. The stainless steel clamps is as tight as possible and it will be inserted as far as possible into the riser pipe to minimize exposure of water to the rubber inside the coupling.

20201128_094045.jpg


This next image shows how level my floor is with a level on top of a 2" coupling - about 0.4 degrees from the horizontal plane.

20201128_094710.jpg


The next image shows my solution - angled ABS pipe in a P1056-22 coupling. The top is approximately 6.2 degrees from the horizontal plane. I found this position to be the best after several experiments dry fitting it to the kerdi drain.

20201128_094656.jpg


This is how I measured the solution's levelness.

20201128_094557.jpg


Result of applying the solution using the torpedo level

20201128_094934_markedup.jpg


The P1056-22 with ABS pipe will be located closer to the kerdi drain above and away from the standing water in the P trap.
 
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wwhitney

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Nice solution.
The P1056-22 with ABS pipe will be located closer to the kerdi drain above and away from the standing water in the P trap.
I suggest putting the bottom of the P1056-22 just above the top of the horizontal drain pipe. That keeps it 2" above the trap weir, but hopefully down in the gravel, rather than in the concrete. You'll want to wrap the shower riser in foam isolation material before placing the concrete.

Cheers, Wayne
 

bronzefury

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Wayne,

I bought both the P3000-22 and P1056-22 just to experiment with. Yes, the P1056-22 is longer (3 7/16") than the P3000-22 (2 1/8"). Also, the walls of the P1056-22 appears to be thicker (3/16") than the P3000-22 (just over 1/16", probably closer to 3/32").

I'm thinking that the drain isn't under pressure so should be safe for a while. Most of the P1056-22 will be surrounded by a 4" coupling of which probably an inch of the bottom will be buried in gravel and the top portion exposed to nothing because the 4" coupling will be holding back the cement.
 
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bronzefury

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Reach4,

I tried an experiment bending ABS with a heat gun. Couldn't get it hot enough and its really awkward to bend a 2' pipe. Probably don't have all the right tools or strength.
 

Reach4

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This bears a bit more research, I believe Home Depot has the descriptions off. My understanding has always been that the unshielded couplings are for underground only, and I generally avoid them. And that the shielded couplings are for underground or above ground. If I get a chance to verify that, I'll follow up here.
Cheers, Wayne

https://www.fernco.com/plumbing/shielded-couplings/proflex-couplings has that wording... I wonder if that is new. This may be an effort to move people to their more expensive "Strong back" couplings, which are ok for above or below ground. https://www.fernco.com/plumbing/shielded-couplings/strong-back-rc-couplings

However I went to the Mission site, and found that the cross-referenced products had the above-ground limitation in their descriptions too.
 
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