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Thread: Wrapping pvc for concrete pour

  1. #1

    Default Wrapping pvc for concrete pour

    I get conflicting opinions from people about this, so hopefully you guys can set me straight. I searched previous threads and couldn't get an authoritative "do this" answer, so...

    I'm installing sewer pipes for a new shower, toilet, and sink. all of these need concrete poured over them. Due to pitch requirements, I can't put them under the slab. They have to be directly in it. It seems to me that they should be wrapped to allow for expansion and avoid chemical reaction between the pvc and concrete. However, some people say just pour the stuff over them and forget about it. Which is correct?

    The toilet uses 4" sch 40 and of course has a joint and the point where it goes vertically into the flange. The Shower is the same deal only with 3", and the sink is the same, but with 2"...

    Thanks!

  2. #2
    Moderator & Master Plumber hj's Avatar
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    Default pipes

    Inspectors do not like horizontal pipes in the concrete. The concrete will crack wherever they run because the concrete will be thin in those areas, and wrapping the pipe will just make the concrete thinner.

  3. #3

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    It's definitely not what i wanted to work with either, but if I ran the pipe underneath the slab, it would go uphill to get to the street. Even still, the toilet flange sits a good 4-5" above the existing slab, so I'm going to have to pour about that much over the whole thing. It won't be a thin layer. So in this scenario, would you wrap it?

  4. #4
    Remodel Contractor GabeS's Avatar
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    Default

    why don't you just lower the flange then.
    Gabe

    Don't follow my advice, I only know a thing or two about a thing or two.

  5. #5

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    Everything as it is now is unfortunately sitting as low in the slab as humanly possible. There isn't a single inch that I can eliminate without making the whole line run uphill.

  6. #6
    Radon Contractor and Water Treatment 99k's Avatar
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    I'm not sure if it is a code violation, however, putting pipes in cement is NOT GOOD. You may not like this answer, but a pump up system is the way to go.

  7. #7
    Remodel Contractor GabeS's Avatar
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    Default

    I'm sure they have something to wrap the pipe with or a different kind of pipe that you can use. I don't know what it is, but sometimes if you search long and hard, you find what you're looking for.

    As far as pumping, I would only do that as a last resort. If you can have a gravity system as opposed to mechanical, that's the way to go. I mean they do bury copper pipes in concrete with wrap.
    Gabe

    Don't follow my advice, I only know a thing or two about a thing or two.

  8. #8

    Default

    Quote Originally Posted by creepyoldguy View Post
    I get conflicting opinions from people about this, so hopefully you guys can set me straight. I searched previous threads and couldn't get an authoritative "do this" answer, so...

    I'm installing sewer pipes for a new shower, toilet, and sink. all of these need concrete poured over them. Due to pitch requirements, I can't put them under the slab. They have to be directly in it. It seems to me that they should be wrapped to allow for expansion and avoid chemical reaction between the pvc and concrete. However, some people say just pour the stuff over them and forget about it. Which is correct?

    The toilet uses 4" sch 40 and of course has a joint and the point where it goes vertically into the flange. The Shower is the same deal only with 3", and the sink is the same, but with 2"...

    Thanks!

    Is this located in a basement? Are you getting a plumbing inspection done?

    Last night I saw a nice episode of Ask This Old House where someone had a main line backflow problem due to heavy rain. The basement filled up with 40" of sewage due to the failure of the backflow device in the main line!

  9. #9
    Geologist sjsmithjr's Avatar
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    Default

    Sounds like your in a bit of a jamb. While you should always pull permits and meet code, my experience tells me that while there is no need to wrap SCH 40 or 80 PVC embedded in concrete, you want to avoid embedded solvent weld joints. I would be more concerned with the heat generated as the concrete cures deforming the piping. If this is the way you have to go, make sure to cradle and strap it well and at closely spaced intervals. I'm thinking every five feet off the top of my head.
    Last edited by sjsmithjr; 01-23-2009 at 03:18 PM.
    -Sam Smith
    Licensed Professional Geologist - AL, TN, KY

  10. #10
    Moderator & Master Plumber hj's Avatar
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    Default drainage

    When the elevations are such as to cause a problem like this, I would go with a sewage lift station, rather than fight minimal grades. Why wasn't the house raised to the proper elevation, unless this is an existing house. IF you have to raise the floor 4" to 5", there is already a problem.

  11. #11

    Default

    I have no idea how they ever got permission to build this house in the first place. the lines were put in with grossly insufficient fall to get to the street. I have already installed a pump to remedy this. So far the pump has been great, but it is downstream from the main exit line for the house.

    The pipes I am asking about are from a bathroom (with just a toilet) that somebody had hastily thrown together years ago in a converted carport. The toilet was jacked up on a 12" wooden platform in order to get enough fall to make the 80' run to tie into the main line. My goal was to lower the toilet to an acceptable level so that tall people won't bang their head on the ceiling, plus add a shower and sink and make a real bathroom out of it.

    I have gone through the whole line and adjusted the angles to reduce the length, upgraded from 3 to 4" lines, and adjusted the fall to a uniform minimum, and I now have the toilet flange sitting at about 4" above the slab with the pipe running horizontally through concrete. I know it's not ideal, but it's what I have to deal with. What I want is to pour 4" of concrete on top of the existing floor, thus raising it enough to accommodate the toilet, but not so much that the low ceilings are an issue.

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