How to detect leak under a slab with underground pex

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by madonnab, Oct 13, 2009.

  1. madonnab

    madonnab New Member

    Messages:
    4
    Location:
    texas
    Hi,
    I am new here and was hoping to get some advice. I am building a home and right now it is in the stage of waiting for sheet rock so all the plumbing is exposed. We have encountered a leak somewhere and it has to be under the slab since the top out is not leaking. We have checked the supply line to the house and no leaks. Our plumber will be coming later this week but he already stated that it must be where the water enters the house. He doesn't seem to know too much about checking for leaks if it is under the slab.

    Basically, my question is how do you check for leaks in the slab. My husband said if we could isolate it he would just cap it off and run the line overhead. The question is what equipment do you use? I wish we had the plumbing run overhead but the plumber kept insisting that we should run it in the ground because that is the normal practice and it would not be noisy.

    By the way the house is in Texas.

    Thanks,
    madonnab
  2. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    27,032
    Location:
    Cave Creek, Arizona
    leak

    You need a professional leak detector company, NOT a plumber who advertises "leak detection". He will have the means to test each line, although, I also have a problem believing the PEX is damaged, unless the concrete company drove a stake through one of them.
  3. Lakee911

    Lakee911 I&C Engineer (mostly WWTP)

    Messages:
    1,328
    Location:
    Columbus, OH
    DIY ... pressurize it with hot water and borrow a thermal camera ... look for the hot spot.
  4. jeffeverde

    jeffeverde New Member

    Messages:
    79
    Location:
    L.A.
    Through a 4" concrete slab and a foot or so of soil? Isnt that an awful lot of thermal mass to get a reading through?
  5. Cass

    Cass Plumber

    Messages:
    5,980
    Location:
    Ohio
    If you run enough HW into the area you can feel the heat with your hands...although it is much more difficult through carpet...
  6. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    27,032
    Location:
    Cave Creek, Arizona
    leak

    The harder part may be getting that much hot water and connecting it to the pipe. Leak companies use co2, helium, and other means to locate leaks in pipes, even when they are NOT connected.
  7. Doherty Plumbing

    Doherty Plumbing Journeyman & Gas Fitter

    Messages:
    810
    Location:
    Penticton, BC
    If it's just pex and a fairly simple job then just do what you suggested yourself and run a new line. If you have a bunch of lines that it could be then I'd hire a professional company as well.
  8. madonnab

    madonnab New Member

    Messages:
    4
    Location:
    texas
    Thanks for advice

    Talked with some leak detector companies and they said to just cap it off and put a pressure gauge to see if it loses any air pressure. The plumber is testing to see if it the cold or hot water lines.

    I was wondering if the meter is possibly reading wrong. The leak detector dial spins forwards and backwards in spurts probably due to pressure changes in the main line. Could this be causing the meter to read water usage, 3/4 gallon an hour?

    Thanks for any help,
    Madonnab
  9. Thatguy

    Thatguy Homeowner

    Messages:
    1,459
    Location:
    MD
    We put a valve on one pipe at a time and shut it off. Once we found our 3 minutes per gallon leak we capped it off and ran the pipe elsewhere.

    Running the pipe in the soil may eventually cause pinhole leaks.

    You also might listen with your ear pressed against the candidate pipe. If the leak causes turbulence this might be reasonably loud. I heard our leak in an upstairs bathroom faucet from across the room. Metal pipes transmit sound pretty well.
    Last edited: Oct 19, 2009
  10. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    27,032
    Location:
    Cave Creek, Arizona
    meter

    If the meter is indicating usage, then you have a leak. Oscillations would just cancel themselves out which means one time the reading could be higher, but the next time it would be less, or vice versa.
  11. madonnab

    madonnab New Member

    Messages:
    4
    Location:
    texas
    Need some help

    okay, my plumber has put air pressure gauge and he can not find a loss of air pressure. We are stumped. He did both cold and hot supply lines and still no loss in air pressure. We have changed the meter to make sure it wasn't a faulty meter. We are still losing about 8 gallons in a 24 hour period now. The plumber said if there is no loss in air there is no leak but how can you account for the meter ?
    Any suggestions? Is it possible to have a leak even if air pressure doesn't show any loss?

    Thanks for any help,
    Madonnab
  12. Thatguy

    Thatguy Homeowner

    Messages:
    1,459
    Location:
    MD
    This doesn't make sense to me, which means I am assuming something that isn't true. Figuring out what that faulty assumption is, is real work.

    "When one has eliminated the impossible, whatever remains, however unlikely, must be the solution."
  13. madonnab

    madonnab New Member

    Messages:
    4
    Location:
    texas
    Sorry if it sounds confusing.
    What I meant to say was that the air pressure showed no loss in pressure. So we thought a possible faulty meter. After changing out the water meter and turning the water on the meter still shows water usage about 8 gallons in a 24 hour period.

    Now my plumber is currently testing again with air pressure but he states that if there is no loss in air pressure there is no leak. So how do you account for the water usage from the meter? The water is running out somewhere?

    Anythoughts?
    Madonnab
  14. Thatguy

    Thatguy Homeowner

    Messages:
    1,459
    Location:
    MD
    I guess you could install valves at different locations downstream of the meter and turn each one off until you have isolated the leak?

    This is a very strange problem.

    If you can find an area where the electrical conductivity of the ground is higher than in other areas, this may be where the water is going, but doing this test is pretty complicated.
  15. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    27,032
    Location:
    Cave Creek, Arizona
    leak

    If you are "losing" 8 gallons per day, you DO HAVE a leak, but must not be testing the section where the leak is. Air will leak from holes that water won't, but the opposite is not true. We do not have enough information to diagnose your problem remotely, but can assure you that if there is a leak, it will NEVER get any better, unless you fix it.
  16. Thatguy

    Thatguy Homeowner

    Messages:
    1,459
    Location:
    MD
    Is there a substance like StopLeak, approved for resi. plumbing, that can plug this leak without contaminating the water?
    Last edited: Oct 29, 2009
  17. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    27,032
    Location:
    Cave Creek, Arizona
    stop leak

    No, no, no!!!!!!
  18. bashbish

    bashbish New Member

    Messages:
    7
    Location:
    Fl
    Mysterious Oozing Water

    I cant figure out how to set up a new post and this one comes as close as I could get, so I apologize if I am breaking any forum Etiquite.

    There is water slowly oozing out of the grout seam where the front outside wall of my house meets my front outside entryway slab.
    That slab is actually 3 inches below the slab that the interior of my house sits on. This maybe why none of that water is getting inside.

    My first inclination was plumbing leak. So I called an "expert" in leak detection. He broke the wall where the main feed comes into the house to see if the leak was there (that location is 2’ away from where the water is coming from.) No sign of leak.

    He said it is under the slab somewhere. A leaky pipe he said. He explained how with his equipment he will find out which pipe and bypass it, running a new pipe through the attic. Big $$

    This made sense until he left. I did my own research of how to read our water meter . I have been monitoring the water meter. Once at bedtime and once in the morning. Each reading 10-12 hours apart. Every reading for the past week has shown that the meter has not moved even 1/10 gal in that 10 to 12 hour time span.

    It rained only 1 day in the past 10 and that was 4 days ago. Yet the water is oozing again, since at least this morning.

    Has anyone a clue where the water is coming from ?
  19. krow

    krow Plumber

    Messages:
    906
    Location:
    Ontario, Canada
    My first guess would be a high water table and you may have a crack in the foundation or block wall filling with water and slowly seeping into the home
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