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A sinking concrete slab creates more than an eyesore—it’s also a safety hazard. Mud jacking, also known as slab jacking, offers a practical way to lift and level sunken concrete without replacing the entire slab. This method restores stability while saving time and money compared to full concrete slab replacement.
We recommend that most homeowners hire a professional concrete lifting service for this job. The process requires specialized equipment and technical skill. Mistakes by an untrained homeowner can cause additional damage to your concrete or even injury. In this guide, This Old House landscape contractor Roger Cook demonstrates the technique in the video above, explains the process, and answers common questions.
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, says Cook. 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, so 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
Core drill
pneumatic rock drill
Hydraulic concrete pump with pressure gauge
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.
Tip: Before reaching out to contractors, hire a structural engineer to assess the severity of your sinking concrete slab, advises Norm Abram, the master carpenter for This Old House. “That way, all the contractors [you gather quotes from] can base their bids on the same analysis,” Abram adds.
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. 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.
Tip: Cook emphasizes the importance of patience during the lift: “We want to raise [the slab] little by little. We don’t want any cracks.” Rushing the process can fracture the very slab you’re trying to save, he added.
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. When pressing the plug back into the hole, you want the mortar to ooze out around the edges, says Cook. That’s how you know you have a solid bond and no voids beneath the plug, he added. 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 do-it-yourself (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.
