Fix Foundation Heave Caused by Wet, Expanding Soil

Heavy water buildup near concrete slab.Foundation heave is the uplift of the foundation caused by wet, expanding soil beneath a slab floor. This uplift occurs when it is dry outside your foundation and wet underneath it.

Foundation heave and settlement have very similar symptoms.

Here is what to look for:

  • Stair-step cracks in brick or concrete block foundation walls.
  • Leaning, tilting chimneys.
  • Cracks around doors and windows.
  • Jamming, sticking doors and windows.
  • Cracks in a concrete slab floor.
  • Cracks in drywall.

Concrete is poured with an excess of water, typically called water of convenience, that does not bind with the cement particles. This excess water takes many years to remove itself. In addition, there are number of mechanisms that bring water under the slab. One such mechanism is clay suction from around the perimeter of a foundation. In addition, through the “stack effect”, water vapor along with other gases is pulled in from around the perimeter of a structure to replace gases that are transmitted up through the foundation into the structure and by heat convection drawn up into the attic. This is a well-documented process for one of those gases, radon. To learn more about radon mitigation, click here

Air-conditioning dries the surface of the slab promoting vapor transmission as well as condensation of water vapor as it is pulled through the slab. As water condenses the pH level is usually around seven, which can promote dissolution and attacking of cement particles causing great greater voids in the concrete thus exacerbating the problem. Once this process has begun de-bonding of most surface treatments becomes more problematic over time.

Most solutions to this problem involve installing sealers on the surface of the concrete.

This is problematic at best for the following reasons:

  • Hydrostatic pressure can be a very powerful force and is likely over time to build up and become strong enough to the bond almost any coating or floor treatment.
  • In order for sealing to be effective all floor coverings and all fixtures must be removed including kitchen, baths, built-in desks, and all cabinets. If this is not done than the vapor transmission becomes concentrated where it is not applied creating mold problems.
  • The inconvenience of removing everything necessitates full move out and accommodations to live and or work somewhere else until the project is done.
  • The cost of such a project is very expensive.

The problem is exacerbated by the reluctance of installers to install a vapor barrier under the slab. Because of the arid hot curing conditions, placing a vapor barrier underneath a slab promotes extreme slab curling due to the difference of evaporation on the sealed bottom versus the open top.

Fortunately, there is a solution that offers some foundation heave protection. A smart foundation system dries out expansive clay soils beneath the foundation slab and corrects foundation heave. It alleviates expansive soil problems beneath concrete slab foundations. This foundation repair technique borrows from reliable radon mitigation technology, using a vacuum and ventilation pipe to create air movement as well as suction on the under-slab soil. Introducing outside air to the damp soil causes evaporation to take place, making it possible to reduce soil moisture content and (as a result) damaging soil expansion.


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