Slab Leaks & Slab Mold Growth: The Hidden Danger

Mold growth on a wall

Slab Leaks & Mold

Slab leaks occur in the water or sewer lines the under the concrete foundation of your home.

They often go unnoticed until they’ve caused significant damage, including mold growth which can threaten your family’s health.

Mold grows in moist areas — and slab leaks create perfect conditions for it.

What Causes a Slab Leak?

Slab leaks aren’t common, but that’s hardly reassuring when your living room floods and you have no idea where the water is coming from. The leading causes of slab leaks include:

  • Corrosion or decay in older pipes, often from acidic or alkaline water
  • Faulty plumbing installation
  • Construction errors, resulting in an uneven or weak foundation
  • Earthquakes or shifting soil due to drought or flooding
  • Natural wear and tear of pipes over time
  • Tree root invasion that creates openings for water leaking into the slab
  • Natural wear and tear caused by shifting temperatures, vibrations, and other factors
  • High pressure inside a buried water or sewer line
  • High pressure exerted on a buried water or sewer line

What Is Mold?

And now, we move from plumbing to biology.

Mold is the common name for fungi that occur naturally in the environment. They can exist outdoors and indoors but thrive in warm, moist conditions — precisely what you get with a slab leak.

Some mold is beneficial (but not in your home!). It can break down organic material; we use it to produce foods, medicines, and more. But when mold grows into your walls or furniture and releases spores into the air, it creates a very unhealthy environment.

Toxic black mold or Stachybotrys chartarum (aka atra) grows on concrete slabs.

Black mold can cause myriad health issues, including:

  • Coughing, sneezing, and wheezing
  • Lung and eye irritation
  • Headaches
  • Fatigue
  • Skin rashes and hives
  • Asthma attacks
  • Unexplained body aches and pains
  • Memory disruptions
  • Mood changes

Are Mold & Mildew the Same?

No. Mildew is a fungus with a gray or white texture that grows on paint, fabric, wood, or other organic surfaces (including interior walls). It usually forms in warm, humid climates and is easy to spot.

Mold can be any color — black, green, yellow — and proliferates in damp parts of your home. It releases spores into the air that can cause allergic reactions. Mold often grows below the surface of walls, so you may not detect it until it’s too late for easy treatment.

How a Slab Leak Leads to Mold Growth

Slab leaks may appear a short distance from drywall, made of gypsum and paper that act as sponges. It’s a near-perfect breeding ground for mold, which rapidly spreads throughout the drywall and other organic surfaces.

Unless you catch mold early, you may need to replace the drywall, insulation, flooring, and other materials — a costly repair — and, worst-case scenario, abandon or rebuild your home.

How Can You Tell You Have a Slab Leak?

In a building with a concrete foundation, mildewy smells or visible mold spots point to a possible slab leak.

Other clues include:

  • Puddles of water on the floor
  • Warped hardwood flooring
  • Damp carpeting
  • Wet or stained baseboards
  • “Hot spots” on the floor (from hot water leaks)
  • An unexplained loss of water pressure
  • A continually running water heater
  • Unexplained increases in your water bill

How to Correct & Prevent Slab Leak Mold

Plumbers have diagnostic equipment to detect slab leaks and pinpoint the break. Your plumber can outline repair options, which will vary depending on the severity of the leak.

For minor leaks, the plumber may replace a small section of pipe and seal it with epoxy.

Cure-in-place piping (CIPP) is a cost-effective way to repair a damaged line. CIPP creates a new pipe within the old one by applying epoxy resin onto the interior walls. This patching method seals any holes and prevents mold growth. It’s also less disruptive than excavation and repiping.

Trenchless repair may be another option — where new piping is pulled through an access port next to old pipe to create a new line.

Otherwise, you may have to tear up a section of concrete and replace the plumbing. Before you replace your slab, check for mold growth and other signs of damage.

Mold remediation is a lengthy process, but it’s necessary to ensure the air in your home is free from spores and allergens. Professional mold removal companies can identify affected rooms, remove infested materials, and thoroughly clean the areas with special chemicals.

How to Prevent Slab Leaks & Mold

  • Schedule a plumbing inspection every few years to locate potential issues in your pipes and slab.
  • Replace outdated or corroded pipes, especially galvanized steel or lead piping.
  • Consider installing an automatic shut-off system that immediately stops water flow if it detects a leak.
  • Inspect the area around your foundation for signs of moisture — damp carpeting, puddles on the floor, etc. If you detect a musty smell or see patches of mildew forming, contact a plumber immediately for an inspection.



Related Links

Servicing Southern California

We at Orange Coast Plumbing, Heating & Air Conditioning can work around your busy schedule. 


(714) 953-1111



1506 N Clinton St., Santa Ana, CA 92703
Service offices located throughout Orange County

*No walk-ins permitted | CA License #596002

service technician assisting residential homeowner signing on tablet

Get $25 off any service when you schedule online or by phone