What is a Slab Leak? Here’s How to Spot One

If you’ve ever been a plumber on a new installation project, you know what a slab leak is. You also know how much of a nightmare they can be to repair, especially if the concrete slab has had time to solidify and cure.

However, for those of you who are new to the plumbing game or who are homeowners wondering why on earth there’s water coming out of your floor, you’ve come to the right place to find out about slab leaks.

What is a Slab?

Before we discuss slab leaks, you must first understand what a slab is. A slab is a concrete foundation that is poured as the first step in the construction process. Your house is then built on top of the slab, as it’s a sturdy foundation and much better than building directly on the ground. People pour concrete slabs when they don’t want a basement or if they live in an area where one isn’t an option.

What are Slab Leaks?

A slab leak is when one of the plumbing pipes underground within the slab has a leak. This is most common with water lines that carry hot and cold water, but it can also happen when there’s a bad leak in a drain pipe.

To better understand how slab leaks happen, let’s look at the process for installing plumbing pipes in a concrete slab foundation.

  1. Before any concrete gets poured, plumbers will install any water lines, drains, sewer pipes, and vent pipes that need to go underground.
  2. On a typically house, these pipes would go in the basement. However, because slab houses don’t have basements, the pipes need to go inside the slab itself.
  3. After installing their plumbing system, plumbers are supposed to conduct air and water tests to ensure there aren’t any leaks.
  4. Concrete workers get the go-ahead to pour the concrete slab if everything checks out.
  5. The concrete then hardens around the pipes.
  6. Once the concrete hardens, the construction process can proceed, and the plumbers will finish their plumbing services accordingly.

Common Causes of Slab Leaks

Because of the multi-step process involved with installing plumbing pipes in a concrete slab home, there are several common causes of slab leaks.

Improper Installation

The most common reason for a slab leak is because your plumber didn’t properly install your plumbing system. This is especially true if you didn’t hire a professional plumber, or it was one of their first slab jobs. Failing to tighten a single crimp or properly tighten or solder a single pipe connection can result in a slab leak.

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Damage Due to Concrete

It’s also possible that one of your pipes became damaged during the concrete pouring process. Certain plumbing materials like PEX and PVC are essentially hardened plastic, and are prone to piercing or cracking under enough pressure.

Tree Roots

Although it’s nobody’s fault, another potential cause of your slab leak is that a tree root pierced one of your plumbing pipes. This is common when you build near trees or in the woods because tree roots will grow through nearly anything. They can even make their way into your concrete slab and pierce your water or drain lines.

Natural Wear and Tear

Depending on the type of pipes you installed, natural wear and tear is another possibility. While PEX and PVC will likely last forever when installed in concrete, other materials may not fare as well. Galvanized pipe and copper pipes, for instance, can rust and corrode inside of concrete, resulting in pinhole leaks that slowly grow into massive problems.

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Busted Fittings

Busted fittings can happen because of improper installation or because of faulty design. Regardless of why they happen, however, busted or faulty fittings are fairly common causes of slab leaks. Depending on the reason, the fitting can give out right away or last for years before having issues. Either way, you have an expensive and inconvenient repair ahead of you.

Why Damaged Pipes in Concrete Slabs are a Big Deal

With a typically plumbing leak in a basement, it’s fairly easy to see where the problem is and fix it. However, when the leaking pipe is buried under a foot or two of concrete, you can’t see where exactly the leak is. Even if you know where the leak is, the repair process is quite difficult, because it involves cutting into or jackhammering concrete.

Therefore, repairing slab leaks is more expensive and difficult than a typical water leak. You will also need to invest in floor repairs since the leak is coming from under your main floor, and the only way to get to it is to rip the floor up.

Finally, depending on how long you’ve had the leak, there’s a chance you’ll need to repair a portion of your concrete slab. Concrete is a very porous material, which means it soaks up water like a sponge. If it’s too saturated, you’ll need to remove the damaged portion and pour new concrete.

How to Spot a Slab Leak

In addition to being inconvenient and expensive to fix, slab leaks are also tough to spot. Because they happen underground and inside concrete, you typically won’t notice any slab leak signs until the leak has been present for some time. Here are some warning signs to watch out for:

  • The most obvious sign that you have a slab leak is if you see water puddles building up on your foundation or floors. Unless you can find a source on the surface, the water is likely coming from under your slab.
  • Prior to water bubbling to the surface, you might see water stains. This happens when there is a slow leak that isn’t giving off water fast enough for it to make it to the surface.
  • Another sign of potential problems is that your water bills have gotten higher for no apparent reason. When this happens, check your above-ground plumbing pipes and appliances, but if the problem isn’t there, a slab leak could be the problem.
  • If you notice mold or mildew on your floors, it’s likely coming from a slab leak.
  • Low water pressure or cracks in your concrete are also potential signs of a slab leak.

Final Thoughts

If you notice any of these warning signs and suspect you have a slab leak, it’s important to diagnose and repair the problem as quickly as possible. While slab leaks are inconvenient, they’re fairly common plumbing problems, and professional plumbers have developed ways to diagnose and repair them in a timely manner.

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