flexible pipe under subfloor

Discussion in 'Plumbing Forum, Professional & DIY Advice, Tips & ' started by pronouncedeyen, Oct 2, 2009.

  1. pronouncedeyen

    pronouncedeyen New Member

    Messages:
    46
    Location:
    Baltimore, MD
    I have a 1/2" flexible copper pipe (type L) coming out of a chunk of concrete and the top of that pipe is about 1/16" above where a plywood subfloor will be laid and meet the concrete.

    Is it OK if the floor rests on the pipe? Or will it cause problems to have half of the pipe embedded in concrete and the other half weighted down by concrete/backerboard/tile because of the difference in expansion between wood and concrete?
  2. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,689
    Location:
    Cave Creek, Arizona
    copper

    The copper should NOT be "weighted down" by ANYTHING. There should be a space between it and the wood, AND the concrete. The different expansion rates may cause problems but it will not be with the copper tubing.
  3. pronouncedeyen

    pronouncedeyen New Member

    Messages:
    46
    Location:
    Baltimore, MD
    hj: the pipes (supply & drain) were buried in 4" of concrete when the previous owners did the bathroom in the 1950s. I guess I'll try to bend the pipe down so it doesn't hit the subfloor.
  4. jimbo

    jimbo Plumber

    Messages:
    8,997
    Location:
    San Diego
    Copper should never be in direct contact with concrete'
  5. pronouncedeyen

    pronouncedeyen New Member

    Messages:
    46
    Location:
    Baltimore, MD
    jimbo: really? Gheez. The people who did this bathroom back in the 1950s buried copper pipes, both supply and drain, in 4" of concrete! Not only that they buried a ton of knob and tube wiring in it as well.
  6. shacko

    shacko Master Plumber-Gas Fitter

    Messages:
    561
    Location:
    Rosedale, Md
    If that is not a joke about the knob and tube you have a major safety problem if that is still active!! :eek:
  7. Gary Swart

    Gary Swart In the Trades

    Messages:
    7,351
    Location:
    Yakima WA
    There are frequent posts regarding leaks in slabs where copper water lines have been buried in concrete. The problem is concrete attacks the copper. It is stupid to encase copper in concrete, but it has been common practice in slab built homes for years.
  8. pronouncedeyen

    pronouncedeyen New Member

    Messages:
    46
    Location:
    Baltimore, MD
    shacko: Are you saying the existence of knob and tube is a safety hazard or that it was buried in concrete?
  9. frenchie

    frenchie Jack of all trades

    K&T is supposed to be open air, so it can keep cool... bury it, it can heat up & start a fire. Often a concern when retrofitting insulation in old houses.

    Concrete doesn't corrode copper, but it might as well - the difference in expansion rates abrades the pipe. Eventually it will leak.
  10. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,689
    Location:
    Cave Creek, Arizona
    concrete

    I cannot imagine ANY sane person direct burying ANY wiring under a concrete slab. Concrete does not "abrade" tubing passing through it because it is held rigidly and cannot move. Expansion/contraction WILL abrade tubing which has a rock pressed against it under the concrete, however. Trying to bend a short section of copper tubing will almost ALWAYS kink it.
    Last edited: Oct 6, 2009
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