What Causes a Slab Leak?

A slab leak is a break or pinhole in a water line that runs in or under the concrete floor of a house. Water lines under a slab are out of sight and out of reach, so the leak can run for a long time before anyone knows. Understanding what causes them helps you judge your own risk and ask a plumber better questions. If you think you may already have one, start with slab leak warning signs.

Does Your House Even Have This Risk?

Slab leaks only apply to houses where supply lines run through or under a concrete slab. Many Gwinnett houses are built on slabs, and many others have a basement or crawl space where the plumbing is easier to see. If you have a slab, your risk depends on the pipe material, the age of the pipe, the soil and your water pressure.

The Main Causes

Corrosion from the inside and outside

Metal pipe slowly wears from two directions. Water inside can eat at the pipe wall, and moisture, minerals and chemicals in the soil outside can attack it. Copper tends to fail as pinholes, often in more than one place. Galvanized steel, in the oldest houses, rusts and narrows. Pinholes in copper are the most common slab leak failure that plumbers describe, but how fast they develop depends on the pipe and the water.

Georgia red clay moving

Red clay swells when it is wet and shrinks and hardens in dry spells. That seasonal movement pushes and pulls on the slab and on pipes that run through it. Over years, the constant stress can wear at joints and bends. It is a big reason slab plumbing in this part of Georgia deserves a closer look than in places with steadier soil.

Pipe rubbing against concrete or gravel

When a house is built, the lines run through the slab or just below it. Every time the pipe heats and cools, or the ground shifts, it can rub on a rough edge. Over time that rubbing can wear a thin spot into a leak. This is usually described as abrasion and is a well-known cause of slab leaks.

Hot water lines work harder

Hot lines expand and contract more than cold ones, and heat can speed corrosion. For that reason many slab leaks turn up on the hot side first, which is why a warm spot on the floor is such a good clue.

High water pressure

Household pressure that sits very high puts constant strain on every joint. Plumbers often use about 80 psi as the upper limit. You can check yours with a screw-on pressure gauge attached to an outdoor spigot. If it is high, ask a plumber about a pressure reducing valve.

Installation problems

Kinked or dented pipe, joints that were not made well, a line left unsupported or pipe that was stressed while the slab was poured can all create weak spots that last for years before they fail.

Water chemistry

The makeup of your water can affect how fast pipes corrode. Gwinnett County Department of Water Resources publishes a water quality report each year if you want to see what is in your supply. Ask a plumber whether anything in your water is a concern for your pipe type, since the effect depends on the pipe.

Nearby digging and settling

Nearby digging, heavy equipment and new construction can disturb the ground around a slab. Houses also settle, especially in their early years. Call 811 before any digging in the yard so buried lines are marked, and mention any recent work to the plumber.

Why This Matters in Gwinnett

Many Gwinnett homes were built from the 1980s through the 2000s, and a number have copper supply lines under slabs. After decades of heating cycles and clay movement, some of that copper is old enough that leaks can appear. That is not a prediction for your house, just a reason to pay attention to the signs: a warm floor, a hissing sound, a high bill or a moving meter.

What You Can Do to Lower the Risk

• Check your water pressure and ask about a reducing valve if it is high.
• Know your pipe. Ask a plumber what material is under your slab, and whether your house has been repiped.
• Read your water bill each month and notice jumps.
• Know your meter. Learn where the low-flow indicator is and check it with everything off, once in a while.
• Fix drips early. A small drip often means pressure or wear elsewhere.
• Do not ignore warm spots. Hot lines can leak for a long time.

Repair Options in Brief

A plumber may recommend rerouting the line through the walls or attic, opening the slab to repair the spot, lining the pipe, or repiping if there are multiple leaks. See slab leak repair and pipe repiping. We do not set prices. Ask the plumber for the price before work starts, and ask what is included, since flooring and drywall repair are often a separate matter.

Insurance

Many policies cover resulting damage but not the failed pipe, and gradual leaks are often handled differently from sudden ones. Ask your insurer before the floor is opened, and ask the plumber for a written report that explains what failed.

Calling

Call (770) 285-5619. The line is answered 24/7, and we connect you with an independent local plumber who handles leak detection and slab leaks. The plumber does the work and gives you the price. For other water bill mysteries, see why your water bill is suddenly high.

Frequently Asked Questions

What causes a slab leak?

Mostly corrosion of the supply lines, soil movement stressing the pipe, abrasion where pipe rubs against concrete or gravel, poor original installation and high water pressure. In this part of Georgia, shifting red clay is a big factor.

Why do hot water lines leak under slabs more often?

Heat speeds corrosion and makes lines expand and contract more, so hot lines wear faster than the cold ones next to them. That is why a warm spot on the floor is such a useful clue.

Does soil type affect slab leaks?

Yes. Georgia red clay swells when wet and shrinks when dry, and that movement puts stress on pipes in and under a slab.

Can high water pressure cause a slab leak?

It can contribute. Pressure that sits very high strains every joint. A screw-on pressure gauge at an outdoor spigot shows your house pressure, and a plumber can advise on a pressure reducing valve.

How long can a slab leak go unnoticed?

Weeks or months is not unusual, since the water soaks into the soil under the house instead of showing up on the floor. A jump in the water bill or a warm spot is often the first clue.