How To Lift a Sinking Concrete Slab

A sinking concrete slab is more than just an eyesore—it’s a potential safety hazard. Fortunately, there’s a solution that doesn’t involve tearing out and replacing the entire slab: mud jacking. This technique, also known as slab jacking, can effectively lift and level sunken concrete.

In most cases, we recommend hiring a professional concrete lifting service for this project. Though mud jacking may seem straightforward, it requires specialized equipment and expertise. Attempting to lift a concrete slab without the necessary tools and knowledge can lead to further damage or injury.

If you’re curious about the process, This Old House landscape contractor Roger Cook demonstrates how to lift a sinking concrete walkway using this method in the video above. We’ll provide an overview of the process and answer other common questions in our guide below.

What Is Mud Jacking?

Mud jacking is a cost-effective and efficient way to raise sunken concrete slabs. This process involves pumping a grout mixture beneath the slab to lift it back to its original position. It’s a less invasive alternative to replacing the entire concrete structure and can often be completed in a single day. Mud jacking is an ideal solution for many concrete problems, such as these:

• Sunken driveways
• Uneven sidewalks
• Tilted patios
• Uneven poolside concrete
• Sloping garage floors

If your concrete slab has sunk no more than eight inches and is otherwise in good condition (not cracked or broken), mud jacking could be the right fix.

Preparing for the Mud Jacking Process

Some preparation is necessary before the actual lifting begins. To successfully complete a mud jacking project, several specialized tools and materials are required:

• Diamond-tipped core drill
• Gas-powered saw with a 12-inch diamond blade
• Grout mixture (sand, silt, and Portland cement)
• Hydraulic concrete pump with pressure gauge
• Mobile grout mixer
• Mortar mix
• Pneumatic rock drill
• Sponge for cleanup

Assessing the Slab

Before starting the repair, assess the slab’s condition. Look for any cracks or severe damage that might make the slab unsuitable for mud jacking. Measure how much the slab has sunk—if it’s more than 8 inches, you might need to consider other options. 

Creating Space for Movement

As seen in the video, the first step is to create space for the slab to move upward. This is done by cutting through the slab where it meets any fixed structures, such as stairs. A contractor will use a gas-powered saw with a 12-inch diamond blade for this purpose. 

Drilling Access Holes

The next step is to create access points for the grout mixture. Your contractor will use a diamond-tipped core drill to bore several large-diameter holes through the slab. These holes serve two purposes: They allow for grout injection and help evenly distribute the lifting force across the slab. The core drill allows you to save the concrete pieces to plug the holes later.

The Mud Jacking Process

With the preparation complete, your contractor begin mud jacking. This involves mixing and pumping the grout, lifting the slab, and finishing the job.

Mixing the Grout

The grout mixture used in mud jacking is a blend of sand, silt, and Portland cement. This mixture is prepared in a mobile mixer, which combines the dry ingredients with water in an auger. The resulting grout is fluid enough to be pumped but sturdy enough to provide lasting support once it sets.

Pumping the Grout

Your contractor will inject the grout mixture through the core-drilled holes using a hydraulic concrete pump. The pump is equipped with a pressure gauge, which is crucial for monitoring the force being applied. Too much speed or pressure could crack the concrete, so take your time and keep an eye on the pressure.

Lifting the Slab

As the grout is pumped beneath the slab, it fills voids and exerts upward pressure. The slab is lifted gradually, a little at a time, to prevent cracking. In the video, Cook and his team work their way up the walkway, carefully lifting each section until it’s level with the stairs. They return to the trip point at the stairs and add more grout there for added safety.

Finishing Up

Once the slab is level, your contractor can seal the holes and clean up. Cement the concrete plugs from the drilling process back into the holes using a mortar mix with Portland cement for added strength. Push the plugs flush with the slab surface, and clean away any excess mortar with a sponge.

Advantages of Mud Jacking to Lift a Sinking Concrete Slab

Mud jacking offers several benefits over complete concrete replacement.

• Cost-effective: Mud jacking typically costs less than half the price of replacement.
• Less disruptive: You shouldn’t have much damage to your surrounding landscaping.
• Long-lasting: Results can last for years when done correctly.
• Time-efficient: You can often complete a mud jacking project in a single day.

Potential Drawbacks

While mud jacking is a good solution in many cases, it’s not without its limitations. It may not be suitable for severely damaged slabs or slabs that have sunk more than 8 inches. The job requires some specialized equipment and skill, which not every homeowner has. Mud jacking may need to be repeated if soil conditions continue changing.

Alternatives to Mud Jacking

Mud jacking is often effective, but in some situations, you may want to consider these other methods for lifting or leveling sunken concrete.

Polyurethane Foam Injection

Similar to mud jacking, polyurethane foam injection involves injecting a foam mixture beneath the slab. The foam expands to lift the concrete. This method is highly precise and typically quicker than mud jacking. It’s more lightweight and can be a better choice for certain applications. However, it’s often more expensive than traditional mud jacking.

Concrete Replacement

You may need to fully replace concrete slabs if they’re severely damaged or have sunk more than 8 inches. This involves removing the old slab, preparing the ground, and pouring new concrete. While more disruptive and expensive, this method provides a more long-lasting solution for extensive damage.

Installing Piers

You can install concrete or steel piers to support the slab from beneath. This is often used for larger structures, such as foundations or large patios. Piers provide a strong, stable base, but installation is more complex and usually requires professional expertise.

Our Conclusion

Mud jacking is an effective and efficient method for lifting sunken concrete slabs. It’s cost-effective and involves minimal property disruption. While it’s not a DIY project for most homeowners, understanding the process can help you make informed decisions about repairing sunken concrete. Whether you opt for mud jacking or another lifting method, addressing the issue promptly will enhance the safety and appearance of your concrete surfaces.