A costly problem that residential and commercial property owners face is the development of voids beneath their building structures. These voids can weaken the integrity of foundation slabs and cause ugly and dangerous cracks and breaks in the walls and floors of the buildings.

Cracks in walls, ceilings and floors can open commercial properties up downtime, and are early signs of foundation problems.

This article outlines the common reasons why voids occur and effective foundation repair methods to resolve them.

What Causes Voids under Concrete Slabs?

There are various reasons why voids form underneath concrete slabs. While erosion is a commonly cited culprit, there are also naturally occurring reasons for the presence of voids under slab foundations.

Erosion Due to Poor Water Drainage and Plumbing Leaks

Without proper measures to drain water around slab foundations, there is an increased possibility of erosion of the topsoil. Lack of drain channels and poor foundation sloping will all result in a loss of foundation soil. This frequently leads to the formation of voids beneath concrete slab foundations.

Faulty plumbing can also contribute to the creation of voids. The accumulation of water leaking from the faulty pipes underneath building structures will trigger further soil erosion.

Soil Settlement and Consolidation

These cause voids under concrete slabs. These two processes develop slowly and are worsened by the erosive behavior of poorly drained water.

Potential Effects of a Void under a Concrete Slab

Defects underneath concrete slab foundations will manifest in several ways including:

  • Tilted/leaning building walls
  • Wall buckling
  • Uneven floor surfaces with bowls and dips
  • Total foundation disruption

The occurrence of these features indicates an urgent need for corrective measures to regain structural integrity of the building foundation.

how to fill void under slab foundation - team using URETEK foam

How to Fill Voids Under a Concrete Slab

There are several ways to fill material under a concrete slab and remove voids.

Slab Jacking

This is a means of filling voids underneath concrete slabs by injecting/pumping filler materials into the defective areas. There are several conventional and alternative void filling materials which can be employed to achieve a similar effect.

– Sand-Cement Grout

A sand-cement grout can be used to fill voids under concrete slabs. This mix of sand, cement, and water is pumped through holes drilled to fill up the voids. While this method of slab jacking is cost-effective, there are major drawbacks to opting for this type of repair.

  • Void penetration is not usually extensive, and this will result in the persistence of void effects
  • A significant amount of time is needed to cure the filled concrete (approximately two to three weeks depending on air-flow)

– Expanding Polymer Foam

This newer more innovative method of void filling utilizes a polyurethane foam to achieve slab stability. This high-density material is injected through small holes drilled into the concrete slab. Immediately after injection, the polyurethane will undergo chemical reactions resulting in its expansion to seal off void defects.

Polyurethane foam void filling has the following advantages:

  • It is stable and non-erosive
  • Repaired slabs are usable almost immediately after the repair
  • Polyurethane foam can consolidate both organic and inorganic material which increases the stability of the soil beneath building foundations
  • Penetrates hard to reach void areas (small fissures, crevices)

Sectional Slab Repair

As an alternative to slab jacking, discrete sections of damaged concrete slabs can be repaired.

The concrete over the defective area can be broken up to access the void which is then filled with sand and sealed with a concrete mixture. Ensure sand filling is properly compacted because a poorly filled void has a high tendency to reform.

In extreme cases where there is extensive damage to the slab, neither the use of slab jacking nor sectional slab repair techniques will be enough. The entire slab might need to be replaced.

To prevent the need for this financially tasking last resort, installation of proper drainage systems.

Contact URETEK Today for Void Filling in Houston

URETEK is dedicated to providing the highest quality Houston foundation repair services. With our unique foam foundation repair technology for filling voids, you can rest assured that we’ll meet and exceed your foundation repair and maintenance needs.

To learn more about our highly effective foundation repair techniques, please contact us online today to schedule a free estimate!