Concrete raising is a specialized repair process used to lift and level sunken concrete slabs. Over time, surfaces like driveways, sidewalks, and patios can become uneven due to soil shifting or erosion. Instead of tearing out the old concrete and pouring a new slab, concrete raising offers a faster and more affordable solution.
This guide will explain how concrete raising works, the different methods available, and why it is often the best choice for homeowners. By understanding the process, you can make an informed decision about maintaining your property’s safety and curb appeal.
Why Concrete Slabs Sink
Before exploring the solutions, it is helpful to understand why concrete settles in the first place. Most concrete issues are caused by the soil beneath the slab rather than the concrete itself.
One common cause is soil erosion. Water from heavy rain or poor drainage can wash away the dirt under a sidewalk or driveway, creating empty pockets called voids. Without support, the heavy concrete eventually drops into these gaps.
Another factor is soil compaction. If the ground was not properly packed down before the concrete was poured, the weight of the slab will eventually cause the soil to compress. Environmental changes, such as extreme drought or freezing and thawing cycles, also cause the ground to shift and settle.
The Two Primary Methods of Concrete Raising
There are two main techniques used by professionals to level concrete: mudjacking and polyurethane foam injection. Both methods involve drilling small holes into the slab and injecting a filler material to create upward pressure.
1. Mudjacking
Mudjacking is the traditional method of concrete raising. It uses a “slurry” mixture made of water, dirt, sand, and cement. This thick mixture is pumped under the slab through holes that are typically about one to two inches in diameter.
As the slurry fills the voids, it creates enough pressure to lift the concrete back to its original height. Once the slab is level, the holes are filled with a concrete patch. Mudjacking is known for being very strong and is often the most budget-friendly option for large projects.
2. Polyurethane Injection (Polyjacking)
Polyurethane injection, often called polyjacking, is a more modern approach. Instead of a heavy slurry, professionals inject a high-density expanding foam through much smaller holes, usually about the size of a penny.
When the two-part foam is injected, it undergoes a chemical reaction that causes it to expand rapidly. This expansion fills every crevice in the soil and lifts the slab with incredible precision. Polyurethane is waterproof and very lightweight, meaning it does not add significant weight to the soil below.
Comparing Mudjacking and Polyjacking
Choosing between these two methods depends on your budget, the location of the concrete, and your long-term goals. Both are effective, but they offer different advantages.
- Hole Size: Polyjacking uses much smaller holes, making the repair nearly invisible once finished. Mudjacking requires larger holes that are more noticeable.
- Weight: The slurry used in mudjacking is heavy, which can sometimes cause further settling if the soil is very soft. Polyurethane foam is light and puts less stress on the ground.
- Curing Time: Polyurethane foam hardens almost instantly. You can usually walk or drive on the surface within 15 to 30 minutes. Mudjacking requires 24 to 48 hours to fully cure.
- Durability: Mudjacking material can eventually erode if water gets under the slab again. Polyurethane foam is waterproof and will not wash away or degrade over time.
- Cost: Mudjacking is generally cheaper upfront. Polyjacking has a higher material cost but often lasts longer and requires less cleanup.
Signs You Need Concrete Raising
Identifying concrete issues early can prevent more expensive repairs down the road. You should inspect your outdoor surfaces regularly for specific warning signs.
The most obvious sign is a trip hazard. If one section of a sidewalk is higher than the one next to it, it poses a safety risk for pedestrians. You should also look for pooling water. If water sits on your driveway or near your home’s foundation after a rainstorm, it indicates the slab is no longer sloped correctly for drainage.
Large cracks are another indicator of settling. While small hairline cracks are common in concrete, wide gaps usually mean the slab is tilting or sinking. Addressing these issues early prevents the concrete from cracking further or breaking into smaller, unrepairable pieces.
The Concrete Raising Process Step-by-Step
If you hire a professional for concrete raising, the process is usually straightforward and can be completed in just a few hours. Here is what you can expect during the appointment.
Preparation
The technician will first inspect the area to determine the best points for injection. They will identify where the voids are located and calculate how much lift is needed to make the surface level with the surrounding slabs.
Drilling
Small holes are drilled into the concrete in a strategic pattern. The number of holes depends on the size of the slab and the severity of the sink. For polyjacking, these holes are very discreet.
Injection and Lifting
The chosen material (slurry or foam) is pumped through the holes. The technician monitors the lift carefully, often using levels or laser sights to ensure the slab returns to the exact height required. This part of the process happens slowly to avoid over-lifting or cracking the concrete.
Sealing and Cleanup
Once the slab is level, the injection equipment is removed. The holes are cleaned out and filled with a durable concrete grout that matches the existing surface as closely as possible. Any mess from the drilling or injection process is washed away.
Cost Factors for Concrete Raising
The cost of concrete raising is typically 50% to 70% less than the cost of replacing the concrete entirely. However, several factors will influence the final price of the project.
The size of the area is the most significant factor. Larger slabs require more material and more time to level. The amount of “drop” also matters; a slab that has sunk four inches will require more filler than one that has only sunk one inch.
Accessibility can also play a role. If the equipment can easily reach the site, the labor costs may be lower. If the technicians have to move heavy hoses through tight spaces or around complex landscaping, the price might increase slightly.
Maintaining Your Level Concrete
After your concrete has been raised, taking a few maintenance steps will help ensure it stays level for years to come. The goal is to keep water from getting underneath the slab again.
First, seal any cracks in the concrete. Using a high-quality concrete caulk prevents rainwater from seeping through the cracks and eroding the soil or the repair material. You should also ensure that your gutters and downspouts are directing water at least five feet away from your concrete surfaces.
Finally, keep an eye on the joints between the concrete and your home’s foundation. If these joints open up, they should be filled to prevent water intrusion. Proper drainage is the most effective way to protect your investment in concrete repair.
Conclusion
Concrete raising is a practical, efficient, and cost-effective way to fix sunken surfaces around your home. Whether you choose the traditional strength of mudjacking or the modern precision of polyurethane injection, you can restore your property’s safety and appearance without the hassle of a full replacement.
By addressing uneven slabs early and maintaining proper drainage, you can extend the life of your concrete for decades. For more tips on maintaining your home’s exterior, explore our articles on driveway sealing and foundation care.