What causes slab leaks in house pipes?

Pipes under a slab can fail for several reasons: corrosion, poor initial installation, shifting soil, freezing and thawing, or chemical reactions between the pipe material and surrounding soil. Metallic pipes may corrode over time while some plastics can become brittle or suffer from abrasion from rocks and movement. Hydrostatic pressure changes and settling of the foundation can stress joints and fittings. Understanding the specific pipe material and local soil conditions helps narrow likely causes and influences the repair method selected.

How to detect hidden water under a slab?

Signs of an active leak under a slab include unusually high water bills, persistent damp spots, warm areas on the floor (near hot water lines), unexplained mold or mildew, and sounds of running water when no fixtures are in use. Professionals use tools such as acoustic listening devices that pick up the sound of escaping water, infrared cameras to find temperature anomalies, and electronic leak detection to pinpoint underground moisture. A systematic inspection reduces unnecessary concrete removal and helps locate the exact pipe segment needing attention.

Can spray or moisture tests locate leaks?

Spray tests and surface moisture meters can help indicate elevated dampness on floors but are rarely sufficient to locate a slab leak precisely. Spraying a surface to look for water ingress is more suited to finding exterior entry points or testing waterproofing. For slab leaks, technicians commonly combine noninvasive methods—acoustic sensors, thermal imaging, and tracer gas or dye tests—to triangulate the leak. Surface spray tests may be used as a preliminary check but should be followed by specialized detection for a reliable diagnosis.

How is a slab floor repaired after a leak?

Repair options vary with the leak’s size, location, and pipe material. Spot repairs involve cutting the slab and replacing or patching the affected pipe segment, then repouring concrete. Trenchless approaches, such as pipe relining or epoxy coatings applied inside the existing pipe, reduce or eliminate concrete removal and can be suitable for many pipe types. In severe cases where pipes are extensively damaged or inaccessible, full repiping or partial slab replacement may be necessary. After plumbing repairs, the slab and floor finishes are restored, and any moisture-related damage (insulation, framing, flooring) is repaired to prevent mold or structural issues.

When should you call a licensed technician?

If you suspect a slab leak—indicated by higher water usage, visible floor damage, or persistent dampness—contacting a licensed plumbing technician is advisable. Professionals experienced in slab leak detection can use calibrated equipment and follow diagnostic steps to avoid unnecessary demolition. A technician will evaluate pipe material, access options, and the most appropriate repair methods for your local conditions. Look for technicians familiar with local building codes and who can coordinate any required permits or inspections.

Conclusion

Slab leaks present a challenging problem because pipes are concealed beneath concrete, but modern detection tools and a range of repair methods make accurate diagnosis and targeted repairs possible. Prompt identification minimizes water waste and reduces the risk of structural or mold damage. When in doubt, rely on experienced local services to assess the situation and recommend a repair strategy suited to the specific pipe type, floor construction, and site conditions.