The Causes of Slab Leaks
Wednesday, October 7, 2020
by: Elvira Ocampo, ASAP Drain Guys & Plumbing

Section: Member News

Slab leaks are leaks in plumbing that runs underneath a concrete floor slab. Most residential and small commercial buildings have a slab-on-grade foundation.  It is more stable, less expensive, and faster to build. But when pipes run underneath the slab, leaks are hard to detect, and often expensive and disruptive to repair.  Until they are found and fixed, the resulting dampness can cause mold and other water damage.  Larger leaks can even lead to erosion that weakens the foundation resulting in structural damage to floors, walls, and even ceilings.

All plumbing, regardless of where it is located, can potentially suffer from leaks for a variety of reasons such as:
  • Corrosion from oxygen, alkali, or acidic traces in water chemistry.  This is especially true for the galvanized iron pipes used through the 1950s.
  • Faulty installation (such as poorly soldered or otherwise weak joints) or accidental damage during building construction.
  • Poor quality materials.
  • Excessive water pressure, particularly water hammer (the physical shock and vibration from flow suddenly stopping).
Slab leaks typically occur because of one or more of the following reasons:
  1. As the soil shifts and settles it can displace pipes, putting them under mechanical strain.  Earthquakes can worsen the problem. According to The American Society of Civil Engineers, a quarter of all US homes suffer some damage to plumbing or direct structural damage from expansive soil shift.  That is more than earthquakes, floods, hurricanes, and tornadoes combined!  That is why understanding soil conditions and proper foundation design and construction are so important.
  2. Many types of soil expand with water, bending pipes and weakening connections.
  3. The surrounding soil can have particularly abrasive particles such as a large amount of sand or gravel.  As hot water pipes heat up and cool down, they expand and contract, rubbing against abrasive soil.  Vibration from appliances and water usage shutting on and off can affect both hot and cold-water pipes.
  4. Alkalis from concrete can pose a direct risk, and there are certain types of pipes that should not be used within or immediately adjacent to concrete.  Some types of soil also have high alkali content.
  5. In colder climates, freezing soil expands and can exert tremendous pressure.
The likelihood of a slab leak increases over time.  Plumbing pipes, whether metal or plastic, have an expected lifetime of no more than 50 years.  Re-piping is often the solution to broken pipes.
Thank you to ASAP Drain Guys & Plumbing, a 2020 BOMA San Diego Annual Supporting Partner, for providing this educational content.