How to Fix a Slab Leak Plumbing Info

How to Fix a Slab Leak Plumbing Info

How to Fix a Slab Leak

By Steve, on August 10th, 2010

A slab leak can be one of the more frightening experiences a homeowner has to deal with when it comes to emergency plumbing problems.  Actually, that is a bit of a misstatement, because they aren’t usually an emergency at all, although they are often thought of as one.

Quite often a slab leak isn’t even discovered until a homeowner finds themselves with a huge water bill.  They will call a plumber out to try to figure out why, and the plumber will inform the homeowner that they have a water line leaking under the slab. That means that the leak has been there for around a month or so already – so much for an emergency.

First of all, I want to let you in on how I used to find leaks under slabs.  This might help you, since most pros do it the same way.  Obviously the first thing to consider is whether the house is really on a slab.  If you don’t know whether your house has a crawl space, just stomp on the floor once.  If you get a hollow sound, you have a crawl space, and the leak can be looked for there (once the access is found).  If it is solid and unyielding, you are likely on a slab.

The next thing is to try to figure out whether it is the hot or cold water.  Simply feeling for hot spots on the floor may be the easiest way to tell.  Even if I do not find any hot spots, I will usually turn off the hot water and see if the leak stops.  You can usually hear the leak when walking throughout a house.  In the rare instance where you cannot, watching the meter will tell you if the leak has stopped or not.

I do need to backtrack a bit.  It is very important that you or the plumber check every fixture very thoroughly to make sure that something else is not leaking. I cannot count the times when what others thought was a slab leak, I found was a leaking hose bib, irrigation valve or toilet.  Even good plumbers overlook this sometimes.  It happens.

If you are lucky enough to have a wet spot or a hot spot on the floor, then you have a bit of a head start.  That will usually show you the area of the plumbing leak, but not always.  Do not depend on that, however.  I have seen leaks that were up to 10 feet away from the only wet spot.  Water finds the easiest avenue to escape, so what might seem like a spot where the leak is could easily be the spot where there is a crack in your slab.

The next thing I will usually do is try to map out where the pipes go.  I can often do this based on my experience, but it never hurts to actually locate the pipes with an electronic pipe locator.  This is not essential, but it makes finding the leak a lot faster, because you only need to look where the pipes are.  If you don’t know where the plumbing runs under your slab, you will be “looking” for leaks everywhere, including where there are no pipes.

Next, find the general location.  If you don’t have a wet spot or a warm spot, you need to very carefully listen for where the sound is loudest.  Listen behind the toilets, under the sinks, etc.  The pipes are usually noisiest nearest the leak.  Once you have the general area located and know where the pipes are, you can begin the fun part.  I have an air compressor (a very quiet one) and an adapter that I made so that I can connect an air hose to an outside hose bib.  I keep the compressor in my truck with the doors closed to further minimize the sound.  Then I turn the water off at the main and pump air into the line at about 60-80 psi. I try to keep it near the working water pressure of the house, so I don’t force air into the city main.  I will go into the house and open up one of the faucets until that faucet starts to spit.

I then turn the faucet off and let the compressor catch up.  Some very helpful will happen.  The air, mixed will small amounts of water will make a very specific and recognizable sound as it exits the leak.  The pipes themselves will burble and such, but there will be a distinct “spitting” sound at the leak.  Now you just have to find that sound.

I use one of two things when listening for the sound.  The one that I use primarily is called a Geophone.  You can actually get these (if you are so inclined) from PollardWater .  There are also a variety of electronic listening devices on the market.  They are a lot more expensive.  The Geophone will cost about the same as someone doing leak detection for you, so unless you plan on having a lot of slab leaks, it is probably best to get a pro to find it.  Still, it never hurts to know the process, so you are informed.

Once the leak is found, fixing it is really not that hard.  It is a bit dangerous though, so I do recommend having this done by a pro.  Basically the process starts with removing the flooring; whether it is tile, linoleum, wood, carpet, etc. then using a small jackhammer to remove a section of concrete.  I try to keep the hole as small as I can – just big enough to work in.  Next, the leak needs to be positively located, and a section of the leaking pipe removed and a new piece tied in.  Do not allow someone to “patch” the pipe.  The section must be removed and replaced.

Dont do this (bad)

Now, let me stop for a second and tell you that this is meant to be done with copper pipe.  There are still homes out there that actually have galvanized water piping under their slab.  If that is you, I do not recommend trying to repair it.  The best course of action in this case is to do what is called a partial or full bypass.  That basically means that you need to cut off the flow to some or all of your slab piping and run new pipes overhead.  This is usually done within an attic.  I have run across homes that do not have attics, at which point I needed to run the pipes on the roof.  This is the way it has to be with Eichler homes.  In fact, my “falling off the roof” incident happened towards the end of an Eichler re-pipe.

Finally, when the repair is made, I recommend turning the water back on to test before closing up the hole.  Once it has been verified that there are no more leaks, I will get rid of the old soil that I took out to get to the pipe and fill with sand.  I do this because the old soil is wet and will cause the concrete patch to settle.  Sand will be compacted 100%, and will fill in some of the gaps as well that were created by the leak.

Next, you just poor concrete into the hole, level it off and let it cure.  I recommend leaving it uncovered for at least 7 days before replacing your floor covering.  It sound like a pretty big process to go through and it is.  Different companies in different areas charge different amounts for these, but I use to charge between $2500 and $3800 to find and fix the leak.  That included replacing the concrete to “patch” finish.

One final little bit of info for you, and this may be the most helpful part of this article:  Check with your insurance company and find out if they will cover you, and if so, what parts they cover.  In my area, many of the good homeowner’s insurance companies will pay for the leak location, the tearing out of the flooring and concrete to “access” the leak, and the replacement of the concrete and flooring.  Knowing this can really help.  The repair of the pipe is the easiest part, and can easily be shown on the invoice to have cost $150 or something, while the rest of it would be covered by your policy.  Out of all of the slab leaks I have repaired, I would say that about 80% were covered.  They will NOT usually cover a re-pipe however, but that is in my area, yours might be different.


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