Under slab leak detection

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Old 01-20-15, 07:22 PM
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Under slab leak detection

I think I have a leak under my slab. There is no appearance of water or dampness. I can hear water flowing when all the faucets are off. I have turned my water off but I do not want to live this way very long. I am not sure how to proceed. First thing will be to see if I can measure how big the leak is by timing water flow with a stop watch and reading the water meter. Then I will try to determine if it is in the hot water pipes or the cold water pipes. Then what?

If I hire a "leak detector" contractor, and if he does whatever he does and says the leak is "here" (a specific spot under the slab), will he guarantee that that is where the leak is (within a foot or so) -OR- will it just be his best guess as to where the leak is?

If I hired a plumber to excavate the slab and repair the broken pipe -- based on the leak detector's determination, I would be very disappointed if a hole were cut in the slab and there was no leak there! What would I do then? Hire a different leak detector, or ask the same one to check again? I appreciate that life offers few guarantees. I just want to know in advance.

I saw the idea of using thermal imaging for a hot water leak in another post. Sounds like a good idea. I will check into this.

Thanks for your help.
 
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Old 01-20-15, 08:57 PM
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I'm a contractor in CA, not a plumber. I work on kitchens. A house older than 15 years built on a slab is due for a slab leak. It's all too common.
Some tips:

- It's almost always the hot water.
- Call your insurance company as soon as possible. Insurance can be complicated, some people say it was covered and some not.
- A plumber can find and pinpoint the leak. The slab can be opened and leak repaired. However, no plumber will recommend this approach as the leaks can reoccur. Normally slab leaks are repaired by rerouting all pipes through walls/ceiling. Sometimes the pipes are ran on outside of house for a short distance if that's what it takes.
- For a re-pipe, you are looking at $5K to $8K. It's extensive drywall repair, texturing and repainting.
 
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Old 01-21-15, 05:46 AM
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You only need to determine if there is a leak or not. There is no need to calculate the rate of leakage as it changes nothing. You've got to fix it no matter.

You may find some leak finders that "guarantee" their work but read the fine print. You may only get your cost of the leak finding back but not reimbursement for extra digging or repairs. Keep in mind that you are looking for a pipe under your flooring (carpet, vinyl, hard wood...) and embedded in concrete. Unless you hire Superman noting is absolutely guaranteed.

I have a few rental houses with the plumbing buried in the slab. Copper was most commonly used around here and it and galvanized steel can corrode so it does have a limited lifespan. Once a leak appears I tend to get another the next in a couple years and they just increase in frequency as the pipe thins and becomes more fragile. Like Handyone mentioned I end up re-routing all the plumbing to get it out of the concrete as it becomes more troublesome over time.
 
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Old 01-21-15, 02:43 PM
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"A house older than 15 years built on a slab is due for a slab leak."

I guess they don't build them like they used to. My 1953 home had solid copper, not the thin coiled stuff like they sell at home depot. It lasted 45 years before it was replaced with CPVC around the outside of the house -- not much of a freezing problem here. That's about average around here although galvanized steel seems to last a little longer.

People around here get upset when I say this, but houses built after WWII were built to last ~50 years. Putting copper in a slab is exhibit "A" of that observation. Lime doesn't agree with copper.

Nowadays, seems like they are built to last the life of the first fixed rate mortgage.
 
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Old 01-21-15, 02:50 PM
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I used to paint a lot of new construction houses in fla and I never saw the plumbing embedded in the slab - it was always under the slab and vapor barrier [back in the 80's and 90's] Only the stubs that protruded thru the slab came in contact with concrete. The plumbing was always copper, I don't remember if they sheaved the copper where it poked thru.

I used to know a couple of plumbers back in the 80's that specialized in finding the leaks and then tunneling under the slab to make the repairs. They were usually paid by the homeowner's insurance.
 
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Old 01-22-15, 04:50 PM
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Skinner plumber gets my vote of confidence!

Re-routing the hot line above the slab would be a piece of work. There is not ceiling path, and no easy wall path.

A different plumber come out (not a general contractor). He listened. He looked. He decided to go for it under the stairs with a smaller jackhammer. He had to enter under the stairs through the HVAC air intake. But he got through the slab and replaced a section of 1/2" copper pipe with a pinhole in it. Then filled the hole and re-cemented the slab. All in about five hours.

Time will tell if another leak shows up. For now I think it was for the best because there was no way to wall-mount an on-demand gas HWH outside with all the clearance requirements.

What a relief. Thanks for all your input. I will be better prepared the next time something like this happens.
 
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Old 01-22-15, 06:12 PM
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Sounds good. Thanks for the update. Yes, A total repipe is a piece of work and expensive.

Whatever you paid that guy was worth it. He saved you a bundle.
 
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