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What Causes Concrete to Sink and How to Fix It

Published: June 2, 2025

Sunken concrete is more than just an eyesore—it’s a safety hazard and a sign that something’s gone wrong below the surface. Whether it’s your driveway, walkway, patio, or garage floor, uneven concrete can trip up guests, damage vehicles, and lead to bigger structural issues if left untreated. In this article, we’ll explain why concrete sinks, what signs to look for, and the best repair methods to restore stability to your property.

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Why Concrete Sinks: Common Causes

  1. Soil Erosion
     Heavy rain, poor drainage, or leaking pipes can wash away the soil beneath your concrete, leaving a void that causes slabs to settle or collapse.
  2. Poor Compaction
     When the soil beneath a concrete pour isn’t properly compacted during construction, it may compress over time under the weight—leading to sinking.
  3. Freeze-Thaw Cycles
     In Ontario’s harsh winters, water trapped beneath concrete freezes and expands, lifting the slab. When it melts, the voids remain, causing it to sink.
  4. Organic Material Decay
     If the ground under your concrete contains roots, mulch, or construction debris, it may break down over time, creating empty pockets.

Signs You Have a Sinking Concrete Problem

  • A visible drop or tilt in your driveway or walkway
  • Cracks that widen or appear uneven across the surface
  • Water pooling around concrete edges
  • Doors or garage doors that no longer close smoothly

How to Fix Sunken Concrete

1. Slabjacking (a.k.a. Mudjacking or Foamjacking)

This non-invasive repair method involves drilling small holes in the slab and injecting a stabilizing material (grout or polyurethane foam) to lift it back into place.

Pros: Quick, affordable, minimal downtime
 Cons: Not ideal for severely cracked or crumbling concrete

2. Replacing the Slab

In cases where the concrete is too damaged or the subsoil is unstable, full replacement might be the best long-term solution.

Pros: Permanent, great for aesthetics
 Cons: Higher cost, more time-intensive

3. Improving Drainage and Soil Conditions

To prevent future sinking, consider grading your property, installing proper drainage systems, or using compacted gravel under new slabs.

Don’t Wait Until It Gets Worse

Ignoring sunken concrete will only lead to more extensive—and expensive—repairs. Fortunately, most issues can be addressed quickly if caught early. Whether it’s a subtle slope or a serious dip, SVD Restoration offers reliable assessment and repair options to keep your surfaces level and safe.