3 Must-Know Causes Of Slab Leaks

Prevent costly damage and discover the 3 common causes of slab leaks and how to manage them

In areas with unstable soils or homes built on a concrete slab, slab leaks are a common problem. However, if the pipes beneath a slab crack or plumbing joints leak, this is the cause of concern. This article will walk you through the different causes of slab leaks.

Expansive Soil Shift

  • The primary cause of slab leaks is the movement of expansive soils, which is responsible for most of the damage to homes. Although slab leaks can be attributed to factors such as the type of materials used and the installation method, soil shifting is the most significant contributor. The American Society of Civil Engineers has reported that approximately 25% of homes in the United States are damaged by expansive soils, resulting in $2.3 billion in annual damage costs.

A slow slab leak can cause water to penetrate the ground beneath the home, leading to further soil expansion and significant damage over time. As hydraulic pressure builds beneath the slab, it seeks out any weaknesses or cracks, resulting in upward pressure that eventually causes damage. In severe cases, water may seep through the hardwood flooring or carpeting, leading to flooding within the home.

Plumbing System Failure

  • Slab leaks are typically caused by plumbing system failures, which can arise from various factors, such as poor installation, deteriorating water lines, chemical reactions between earth metals and plumbing materials, and soil movement beneath the slab.

Materials Used in Plumbing System

The materials used in plumbing systems can be a critical factor in slab leaks and are often linked to the system’s age. The commonly used plumbing materials include:

Cast Iron Pipes

  • Cast iron pipes were commonly used in homes built before the 1960s, but plastic pipes have become more popular. Unlike plastic pipes, cast iron pipes have a quieter operation due to less vibration and high durability that resists fire damage.

However, unprotected cast iron pipes installed underground are susceptible to corrosion from minerals and water in the soil. A cracked pipe can burst over time to cause slab leaks.

Galvanized Steel Pipes

  • Like cast iron, they are solid but prone to corrosion. These pipes are also more likely to become clogged due to rust, mineral buildup, and waste matter. As a result, a cracked pipe can lead to slab leaks.


  • ABS, or acrylonitrile butadiene styrene, was the first plastic pipe used in residential plumbing. However, some issues have been with keeping ABS joints together, leading some municipalities to disallow it in new construction. Additionally, ABS may deform when exposed to direct sunlight, making it unsuitable for some above-ground installations. A failed joint beneath a slab can result in costly slab leaks.

Durable Alternatives

  • Plastic pipes are corrosion-resistant, durable, and versatile for above and below-ground plumbing applications. In addition, they are relatively easy to work with and prevent cracks and leakage. They come in several standard types, including:


  • Polyvinyl chloride pipes are now more commonly used in plumbing applications. PVC pipes come in different colors that indicate their intended usage, such as white for drain lines and irrigation, blue for potable water, green for sewer water, purple for reclaimed water, and gray for electrical conduit.


  • causes of slab leaksChlorinated polyvinyl chloride pipes are similar to PVC pipes, but the chlorination process gives CPVC different physical properties. CPVC pipes can withstand higher temperatures than PVC, making them more suitable for hot water lines.

If you notice signs of slab leaks, seek immediate professional help. Call us at 877-727-2259. Our experts at Crack-X will inspect your property and take the necessary measures to fix your leaking pipes. Crack-X is a civil structures repair company operating in Maine and New Hampshire.

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