Sometimes a customer calls us because a flooring company told them they need an under slab sewer leak test. The flooring company saw or detected moisture before or after installing a hardwood floor.
While all of the calls are triggered by different situations, all generally have one thing in common: they have nothing whatsoever to do with an under slab sewer leak.
How Your Under Slab Sewer System Works
An under slab sewer pipe is buried under a 4- to 5-inch thick concrete slab as well as being 6 inches to 3 feet under the dirt that is under the slab.
And as we’ve explained in a previous post, your sewer lines are installed at a slight decline in order to use the power of gravity.
Meaning water and waste flow downhill taking it from where it starts—sinks, toilets, washer, tubs, showers, etc.—out to the city sewer line/waste treatment plant or a septic tank depending on your particular situation.
So unless you the water is on somewhere in your house, there is nothing in the sewer line. And since there’s nothing in the line, it cannot at that time be leaking.
It also means that if water is leaking out of your sewer line, once your turn off the water, any that leaks out of the pipe could—and most likely would—leak back into the sewer line.
At that point, it acts like a rain water drain system flushing any water away from the leaking area back down the pipe to the city lines.
This eventually leads to other problems, but probably not the problem the flooring company found.
A Rare Situation
In extremely rare situations, a sewer line could have a leak with a stoppage around the leak. This situation causes much more water to leak or be forced out of the leaking pipe. The stoppage then prevents that water from coming back into the pipe so it can drain out of the system. With nowhere to go, enough water builds up under the slab and forces it’s way up and through the slab.
However, if you have a sewer stoppage, you’ll most likely notice it long before the water has time to build up enough for this scenario to occur.
Most of the time when a customer calls us at a flooring company’s recommendation, it’s because the flooring company found moisture covering almost the entire floor of a room or rooms. And even if you are in the rare situation mentioned above, it is impossible for an under slab sewer leak to cause this.
Causes of Moisture On The Floor
Now let’s consider some possible causes.
Above slab sewer pipe leak
If the problem is localized to one specific area and that area is right around some kind of sewer pipe, it is possible there’s a leak in a sewer pipe above the slab.
This is another rare situation and you probably wouldn’t see moisture or even evidence of it. Instead, you would see water pooling in the area of the leak.
An easy way to check for this is to run a lot of water in your house, especially around any fixture near the area—tub, shower, sink, washing machine, etc.
Fill up all of your sinks and tubs and then let the water drain while keeping the water running. If the wet area is around the toilet, flush it over and over. The goal is to flood the sewer system as much as possible.
As water is draining and running, watch the localized area for water. If after doing this, you don’t see any water or moisture; it’s highly unlikely you have a sewer leak above the slab.
Fresh water plumbing leak
Unlike your sewer system which only has water in it when you are running water in the house, your fresh water system always has water in its pipes.
A fresh water leak is like leaving a faucet on 24/7. And because of this, you will see water and lots of it, not just moisture or evidence of it.
It’s easy to check for a fresh water leak yourself. Go to the city water meter and open the cover. If you don’t have a meter key to open the cover, you can often get one for less than $10.00 at your local hardware store.
Turn off all the water in your house and watch the water meter. There should be a small circle or triangle in the center of the meter. When you have a fresh water leak, that detector will be moving or spinning.
If that meter is not spinning or moving at all, rest assured that there is no fresh water leak.
Monitor the meter for 5 minutes or more to make sure it doesn’t move. If there is no triangle or circle, watch the big hand of the meter for 20 minutes or so for movement.
You can turn on some water in the house before you go out to the meter and observe the meter hand to see how it moves when water is running. This gives you a clearer idea of what you’re watching for.
The temperature under the slab is often different than the temperature above the slab. And this temperature difference can create condensation or moisture. This is a lot like when the temperature in your car is different than outside and the windows fog up.
To combat this problem most wood floors are installed with a vapor or moisture barrier laid between the wood and the slab. This keeps any moisture created from touching the wood. Unfortunately, some companies neglect to install this barrier which could very well be the problem.
We have also seen instances where an area rug or a chair mat for desk chairs create condensation. Any place where the humidity is high, or there is a lack of air flow could easily create this problem.
Wood floor acclimation
Before hardwood floors are installed, they should be brought into, spread out, and left for at least a few days—or the manufacturer’s recommended time—in the rooms they are to be installed.
This is so the wood will adjust to environmental conditions such as altitude, temperature, humidity, etc.
If wood floors are not allowed to acclimate to these weather variations, it’s possible it will warp after installation. Although this is not the most common reason for wood floor problems, it’s certainly a possibility that shouldn’t be overlooked.
Outside sprinkler system
Sometimes water from outside gets inside the home and causes the formation of moisture or other hardwood floor problems. A couple ways this happens are from sprinkler systems and/or rain.
To check for this, turn on your sprinkler system and see if any of the heads are spraying directly at the house. Also go inside while the sprinklers are on and check for any water getting in the house.
Even if the water is not spraying on or in the house, it’s could be pooling in an outside area and then flowing into the house. So make sure you check for pooling spots as well as any sprinkler heads spraying on the house.
Now let’s talk about rain water. First you want to make sure there aren’t any leaks from the roof, fireplace, chimney, walls, etc. If you don’t find any leaks, it could also be rain water pooling like with the sprinkler system.
When it rains, especially during a heavy downpour, look around outside to make sure that water isn’t pooling anywhere next to the house. And if it is, make sure the water is flowing away from the house. Also check all outside walls, chimney areas, etc. to make sure that water is not entering the house and pooling on the floor.
One other important thing to keep in mind—especially with brick homes—there should be 2 inches of concrete showing at the point where the slab and the bricks meet. This is called a brick ledge.
The soil in this area should be sloping away from the house and not towards it. If that 2 inches of concrete is not showing, or if the soil is sloping towards the house, or is flat and not sloping at all, contact a good rain water drainage expert to evaluate and determine what to do about it.
The True Cause of Your Flooring Problems
The truth is most of the calls we get about flooring problems are not plumbing related at all. With this in mind, we hope this information has given you some ideas about what to check and will ultimately lead you to the real issue causing your problem.
You don’t want to waste time contacting the wrong people. You’ll get your problems fixed sooner rather than later when you know who to call.
If you think you have a plumbing problem causing your flooring issue, or you have any questions, comments and/or concerns please don’t hesitate to contact us at 972-494-1750 or firstname.lastname@example.org.
We’re always happy to help!