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What Causes a Slab Leak and How to Fix It

What Causes a Slab Leak and How to Fix It

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slab leak - Laying cement over sewer lines - workers smoothing fresh cement

A slab leak is a type of foundation failure. It usually occurs when water seeps through the walls or flooring in a building and travels under the floor. 

They can appear in any building, like homes, commercial, and industrial buildings. But generally, slab leaks tend to occur in buildings with a concrete or masonry foundation.

It is important to identify warning signs of water leaks before they cause any problems with the building. However, slab leak detection is not always easy, but there are some signs to look for:

  • Spongy floors or hollow underfoot
  • Discoloration on the ground 
  • Wet spots near an outside wall

Causes of Concrete Slab Leaks: Slab Leak Detection

Slab leaks usually appear as pinhole leaks or cracks in the ground beneath or in the concrete foundation. They are often caused due to the expansion and contraction of concrete.

slab leak - Slab leak repairs - cracked dry cement with boot imprints

Many factors cause a home concrete slab foundation to leak, including:


  • Earthquakes can cause slab leaks, which means buildings will be at risk of collapse. Once the ground is saturated with water, it becomes difficult for gravity to hold up the weight of the soil above it. Concrete slab leaks can also lead to soil erosion, which causes landslides.
slab leak - earthquakes cause slab leak - heavily damaged exterior wall

Improper Construction

  • Slabs are typically built by pouring concrete over a steel mesh or wire grid. When the slab is first poured, it’s usually allowed to cure for a few days before the concrete is troweled smooth, and any imperfections in the mesh or wire are removed.
  • This process helps prevent water infiltration into the masonry wall system below. The problem arises when imperfections in the mesh or wire grid during construction allow moisture or water leak to penetrate the concrete and reach an underlying masonry wall system.
slab leak - high water pressure causes slab leaks - water from high pressure hose with soapy bubbles

High Water Pressure

  • One of the most common causes of a slab leak is high water pressure. The higher the water pressure, the more likely a slab leak will happen. 
  • The pressure of the water causes the water line to expand and push the ground against the foundation. Moreover, a slab leak can cause damage to other parts of your plumbing system.


Deteriorating Copper Pipes in Plumbing System

  • Slab leaks occur when the copper pipe used for the water supply becomes corroded and starts to leak. No coating on the pipe promotes corrosion due to contact with ground moisture and oxygen in the air. Eventually, it leads to leakage from joints and cracks in the pipe that are difficult to detect.
slab leak - acidic water causes slab leaks - hose with spraying water from leaks

Highly Acidic water

  • Slab leaks also occur in the foundations when exposed to highly acidic substances such as acids and other chemicals. It happens when the slab is not properly protected from these substances. 
  • Highly acidic water also causes slab leaks in residential buildings by weakening mortar bonds. This damage weakens the bond between the slabs and allows water to seep through from below.

Ways to Fix a Slab Leak

Slab leaks can lead to structural damage, property damage, and mold growth. If you are a homeowner and your house has a slab leak, it is important to take immediate action to avoid further damage. There are various ways to repair slab leaks. Here are some of them:

slab leak - replacing pipes to fix slab leaks - interior plastic pipe system

Replacing Pipes

  • One way is to re-pipe your home with the help of a professional plumber. It is a process that involves replacing the abrasion pipes with new ones. This process usually takes several hours and requires specialized equipment to fix underground pipes. 
  • However, you can replace any damaged section in your existing piping with new pipe sections that match your existing home plumbing systems.


Installing Pipe Lining

  • Pipe lining can fix slab leak issues for you. It involves installing a metal pipe underneath your slab, and it will stop the leaking water from seeping into your basement and causing water damage to the floor below it. 
  • Some people prefer filling the epoxy coating within the water pipes to avoid poor installation of new pipes. The coating hardens and covers the cracks and holes and prevents slab leaks.
slab leak - trenchless repairs to fix slab leaks - person using drill to make hole in cement wall

Trenchless Repair

  • Drilling holes in the water pipes is easy for plumbers to fix slab leaks in the home’s foundation and save on expensive repairs. 
  • The process involves drilling multiple small holes into the water lines before connecting them with threaded rods attached to a valve stem. 
  • It requires minor demolition and is considered the most non-destructive method to fix slab damage.


Although a slab leak is a serious problem for many homeowners, it is possible to fix it. In most cases, the source of the leakage is identified first and then repaired. 

However, if you cannot find where the leak is coming from, you can use a water detection kit to identify where there is moisture in your home or business. 

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