Cracking, sinking, and unstable concrete can be significant concerns for homeowners and property owners. These issues not only affect the aesthetics of the concrete but also pose safety risks and can lead to further structural damage if left unaddressed.

Understanding the causes and solutions of cracking, sinking, and unstable concrete will help you effectively tackle these problems and ensure the longevity and stability of your surfaces.


The Cause of Unstable Concrete: Sub-Slab Voids

One of the common causes of unstable concrete is the presence of sub-slab voids. Sub-slab voids are empty spaces or gaps beneath the concrete surface, typically caused by soil erosion, inadequate compaction during construction, or water infiltration.

These gaps beneath your concrete can lead to sinking, cracking, and unevenness, making it unstable and compromising its structural integrity. Identifying the presence of sub-slab voids is crucial for implementing appropriate repair solutions.


Testing for Sub-Slab Voids

Various testing methods can be employed to determine the presence and extent of sub-slab voids. One is ground penetrating radar, which uses electromagnetic waves to create a subsurface image of the concrete and identify empty spaces or anomalies.

Another method is coring, where small cores are drilled into the concrete to inspect the underlying soil conditions and identify voids. Additionally, engineers may perform dynamic cone penetrometer tests or use laser levels to measure floor flatness and detect sinking or unevenness.

These testing methods help determine the severity and location of your sub-slab voids, allowing for accurate repairs.


Repair Options for Sub-Slab Voids

Once sub-slab voids have been identified, several repair options are available to stabilize the concrete and prevent further sinking or cracking.

The most popular repair method is slab or mud jacking, which is injecting a specialized grout mixture into the voids to raise the concrete back to its original level. The grout fills the gaps, compacts the soil, and provides a stable base for the concrete.

Another option is polyurethane foam injection, where expanding foam is injected into the voids, filling them and lifting the concrete. Both methods offer long-lasting solutions by addressing the underlying cause of the instability and restoring the concrete’s integrity.

Sub-Slab Void Repair Process

The repair process for sub-slab voids typically begins with drilling small holes into the concrete surface. These holes are strategically placed to access the empty spaces beneath.

The grout or foam mixture is then injected into the voids through the holes, filling them and raising the concrete. Once the repair is complete, the holes are patched, and the surface is restored.

The repair process is efficient, minimally invasive, and provides a permanent solution to stabilize the concrete and prevent further sinking or cracking.


Outlook for Repaired Sub-Slab Voids

With proper repair techniques and materials, the outlook for repaired sub-slab voids is generally positive. The concrete becomes stable, level, and structurally sound, restoring its functionality and appearance.

Repaired areas should be monitored periodically to ensure no further issues arise. Maintaining proper drainage around the concrete and addressing water infiltration help prevent future sub-slab voids and prolong the life of the repaired concrete.