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How to Repair a Sinking Garage Slab?

How To Repair A Sinking Garage Slab?

When your garage floors start cracking, know it is a foundation issue. These cracks appear because of failure in structural support. Don’t think the cracks have spoiled the look of your garage or house look. The problem is bigger than that. If you don’t resolve the problem timely, your house could be at risk.

Cracks are of different sizes. The small ones are normal to be seen on garage floors. A concrete repair contractor can easily seal such cracks. These contractors are also experts at repairing sunken garage floors.

However, in some cases, you may need to replace the garage floor. This usually requires when the structural integrity of the concrete is failing. But this is an extreme situation. So, don’t assume anything by seeing the cracks on your garage floor.


Repair a Sinking Garage Slab

The Causes of Sinking Garage Slab

Do you want to know why your concrete slab is sinking? The common reasons are:

Water Damage

Water damage can be a significant contributing factor to the sinking of a garage slab. Water seeping into the soil beneath the slab can lead to soil erosion and instability. Excessive moisture causes the soil to become saturated and lose its load-bearing capacity, gradually sinking the garage slab. Poor drainage systems, improper grading, or nearby water sources such as leaky pipes or inadequate gutter systems often accelerate this process.

As the soil beneath the slab weakens, it can no longer adequately support the weight of the garage structure, causing it to settle and sink unevenly. Continuous exposure to water exacerbates the problem, potentially leading to cracks, tilting, or even structural failure. Addressing water damage promptly and implementing effective drainage solutions are crucial to preventing further deterioration and maintaining the stability and integrity of the garage slab.

Extreme Temperatures

Extreme temperatures can indeed contribute to the sinking of a garage slab. Fluctuations between hot and cold temperatures can cause the soil beneath the slab to expand and contract repeatedly. During periods of intense heat, the soil expands as it absorbs moisture and expands, exerting pressure on the underside of the slab. Conversely, when the temperature drops, the soil contracts, creating voids and empty spaces beneath the slab. This continuous cycle of expansion and contraction weakens the soil’s stability and can lead to the sinking of the garage slab over time.

Additionally, freezing temperatures can cause water within the soil to freeze and expand, further compromising the structural integrity of the soil and contributing to sinking. Proper insulation, adequate drainage, and maintaining a consistent temperature within the garage can help mitigate the effects of extreme temperature changes and reduce the risk of a sinking garage slab. Regular monitoring and maintenance are essential to promptly identify and address any issues, ensuring the garage structure’s long-term stability and safety.

Soil Displacement 

Soil displacement can be a significant factor in causing a sinking garage slab. Various factors can contribute to soil displacements, such as changes in moisture content, poor compaction, and natural settling over time. When the soil beneath the garage slab shifts or moves, it can create voids or empty spaces, leading to uneven weight distribution. As a result, the garage slab may sink or settle into these areas of soil displacement. This displacement can occur due to factors like erosion from water flow, the presence of tree roots, or soil compaction issues during construction.

Additionally, changes in the water table level can impact the soil’s stability, leading to further soil displacement and subsequent sinking of the garage slab. Proper grading, drainage systems, and soil stabilization measures can be implemented during construction or as part of regular maintenance to prevent or mitigate soil displacement-related issues. Regular inspections and timely repairs can help identify and address soil displacement concerns before they lead to significant structural damage.

Low-Quality Concrete Mix

Using low-quality concrete mix can harm the stability and integrity of a garage slab, ultimately leading to sinking. When substandard concrete is used in slab construction, it lacks the strength and durability to withstand the weight and stress placed upon it. Over time, the concrete may begin to crack, crumble, or deteriorate, compromising the slab’s structural integrity. This degradation can result from improper ratios of cement, aggregates, and water, inadequate curing, or the inclusion of impurities in the concrete mix.

As the concrete weakens and deteriorates, it becomes susceptible to settling and sinking, especially if exposed to heavy loads, temperature fluctuations, or moisture. It is crucial to prioritize the use of high-quality concrete mix and ensure that proper construction practices, including adequate curing and reinforcement, are followed during the garage slab installation. Regular inspections and maintenance can help identify any signs of concrete degradation early on, allowing for timely repairs and preventing further sinking or structural issues.

Pitting and Settling

Pitting and settling are common causes of a sinking garage slab. Pitting refers to the formation of small, localized depressions or craters on the slab’s surface, often caused by the erosion of the underlying soil. This erosion can occur due to water penetration, poor drainage, or soil compaction issues. As the soil erodes, it creates voids beneath the slab, causing it to sink into these depressed areas. Settling, however, refers to a more general sinking of the entire slab. This can be attributed to the natural settling of the soil over time, inadequate soil compaction during construction, or changes in moisture content. As the soil settles or compacts unevenly, the garage slab may follow suit, sinking or tilting in various areas.

Both pitting and settling can compromise the structural stability of the garage slab, leading to uneven surfaces, cracks, or even complete failure if left unaddressed. Implementing proper drainage systems, conducting regular inspections, and addressing any signs of pitting or settling promptly is crucial for maintaining the longevity and stability of the garage slab.


Sinking Garage Slab

How Can You Repair a Sinking Garage Slab?

The entire garage may settle if a sinking slab is connected to the perimeter foundation. Large cracks, a slanted garage floor, or an obviously out-of-level garage header indicate this may be the case. In this instance, polyurethane injection would be used to fix the sinking garage slab. Push piers would be used to fix the perimeter foundation.

Of course, a house will experience tension and settle if a settling garage is adjacent to it.

Use Polyurethane Foam Injection

A technique called “mudjacking” lifts the slab using a cement slurry rather than lightweight polyurethane. It can be replaced with polyurethane foam injection. The outcomes are comparable. A larger, 2-inch hole must often be drilled in the slab for mudjacking. This is because cement slurry weighs significantly more than polyurethane foam.

Repair a Sinking Garage Slab

Step-by-Step Guide for Garage Sinking Slab Repairing

If your garage has no linkages to the perimeter foundation, it can be re-leveled easily. This is true for most cases. The issue can be solved using polyurethane foam injection. The process is called “slab jacking.”

  • First, small holes (about 5/8 9 inches) are drilled into the slab. Polyurethane is injected into the holes.
  • The polyurethane foams spread and expand. It fills all the voids to lift the slab to its usual place.
  • However, if your sinking garage is connected to the perimeter foundation, it can be re-leveled with the help of steel push piers. This is how it works:
  • The foundation footing in the affected area is attached to the push pier brackets.
  • Steel piers penetrate the brackets until they reach the load-bearing material.
  • The foundation and sinking garage slab may now be lifted and leveled using hydraulic jacks and steel push piers.
  • The space under the garage slab is filled with polyurethane foam to offer additional support.

When a slab in a sinking garage is in extremely poor condition, it may occasionally need to be completely replaced. In this situation, we would merely demolish the damaged concrete slab, compact the subgrade, and lay a fresh reinforced concrete slab.


It is important to know when your garage needs replacement or repair. However, homeowners cannot tell that just by looking at the cracks.

They are multiple factors that need to be considered. These factors also vary from garage to garage. We have explored some common issues in garage floors and addressed their solutions in this article!


How do you fix a sinking concrete slab?

The hollow section can be raised in one of three ways: by mudjacking. It involves raising the sunken section with expanding polyurethane foam. You can also do it by covering it with a layer of sand and cement to elevate the surface. The safety problem can be easily fixed by patching, but the change will be obvious.

How do you raise a sunken garage?

Slabjacking is the finest technique for lifting the concrete back into place if your garage floor has a void underneath it. Polyurethane foam is injected through the concrete slab during slab jacking. The fill is injected, and as it foams and solidifies, it raises the concrete.

Can a sinking slab be fixed?

Concrete lifting, removing, and replacing the concrete slab can be used to fix any concrete slabs that have sunk around your property. The soil directly beneath a concrete slab is the main cause of sinking concrete slabs.

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