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.

Don't 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.

“A home owner calls you out because they have a wet spot in their ceiling directly below the upstairs tub/shower.  It’s getting worse over time.  To make the scenario easier, we will eliminate the possibility of the leak coming from the toilet or lavatory sink.  We will focus on the tub/shower combo.  How do you go about diagnosing the source of the leak?”

Plumbing Leak In Ceiling

Almost every single interviewee responded that they would cut a section of sheetrock out of the ceiling and look through the hole with a flashlight.  Sounds reasonable, right?  It’s the wrong answer!  Here is why:

First of all, what if the leak is being caused by a fault in the faucet itself or the tub spout?  Maybe the leak is due to the trim plate not sealing properly or some bad grout or caulking in or around the tile.  In all of those instances the plumber would have created a hole in your ceiling that does not need to be there.  It would be a shame to remove a large section of sheetrock when all that is necessary is better waterproofing of your shower!  Some may argue that the sheetrock is bad and needs to be replaced anyway.  The easy answer to that is that we are plumbers – not water damage repair techs.  It is not for us to determine what needs to be done to fix water damage.  It is us to fix the plumbing that is causing it.  When that is done, we can refer our customer to a suitable water damage company.  We do our job and let them do theirs.

So how do we diagnose this type of leak?  Let me preface the answer by saying that during any type of plumbing diagnostic, you want to eliminate a single cause at a time.  This means that everything you do eliminates only one possible cause.  Here is how you do it:

Typical Water Meter

First you make sure that no toilets are running, no sinks leaking and no water is being used anywhere in the house.  You check your water meter.  Most meters will have a small dial that detects even a small amount of water usage.  You can test this by turning on one of your hose bibs so a trickle of water is coming out of it.  Then look at your meter.  The small dial (usually round or triangle) should be turning visibly.  When you turn of the hose bib, the dial should stop.  If it continues to move, you have a “supply side” leak somewhere.  You can further narrow it down by turning off the main shut-off valve to your house.  If the dial keeps moving, your leak is outside, before the house.  If it stops, the leak is in your house somewhere (maybe the tub/shower).  You can narrow it down even further by turning of the cold supply to your water heater.  If the dial stops, the leak is on the hot side somewhere.  If it keeps going, it is on the cold side.

Let’s assume that the meter is not spinning, so we know it is not a leak on the supply side of your plumbing system.  The next thing to do is start from the bottom up.  Get a ladder and put it under the wet spot in your ceiling.  This will make it easier to hear if water is dripping onto the sheetrock.  You may even want to poke a small hole in the sheetrock with a small screwdriver and let any standing water drain into a bucket.  That way when the leak starts it is easier to see.

Plug the tub drain, fill up a 5 gallon bucket (from a different source or water) and pour it into the tub, being careful not to splash.  Do that a few times until your tub is holding a fair amount of water.  Does that recreate the leak?  Don’t forget that you need to give it some time for the leak to show up.  If that does create a leak, the problem is with the “strainer” itself.  It may be loose, or the putty (or whatever sealant was used) wore out.  Often this can be fixed by loosening the drain, packing putty between the strainer and the tub and retightening.

If that does not create the leak, pull the plug on the tub and let the water drain.  Does that do it?  Again, give it time for the leak to show up, this is not a 5 minute process.  If the leak shows up them, it is the drainage plumbing.  In this case, removal of sheetrock will likely be necessary to be able to fix the problem.  If it does not recreate the leak, you have eliminated the drainage and can proceed to the next step.

Next, turn on the water to your tub.  Since you have already eliminated the drains, if the leak shows op now, you know that the problem is either in the faucet itself or the pipe going from the faucet to the tub spout.  The easiest thing to do now, is to take off the shower handle(s) and trim and see if you can see anything happening in the wall.

Next, turn the shower on.  Be careful to make sure that the water is going directly to the tub and not splashing the walls.  If the leak shows up now, it is either the pipe between the faucet and the shower head, or the shower arm itself.  The latter is the most likely.

If you still have no results, it is time to start splashing around some water.  Try running water over the overflow cover, the shower handles, different areas of your tile, etc.  Splash water on your shower doors too – anywhere where water might go when showering needs to be exposed to water.  The trick here is to do everything one at a time, so that when you get a positive result, you know what caused it.

If you have followed these procedures to the letter, your plumbing leak will be found by the time you get to the end.  Just be patient and keep your eyes and ears open.

Now for the spoiler – Can you guess what the majority of upstairs plumbing leaks is caused by?  By far, the most common cause is a problem with the tile.  Usually something that can be fixed by simply applying tub and tile caulk to the defective area.  It’s kind of silly to remove sheetrock from your ceiling to diagnose that your tub needs to be re-caulked, don’t you think?

Stay tuned for more plumbing info and tips to come soon!  As always, I am available to answer any questions you may have via comment, the contact page or our plumbing forum.

Thanks for reading.