Originally posted 1/9/20; updated 9/21/23
Concrete slabs are a universal component in housing. No matter where you live or what kind of home you have, there’s a concrete slab somewhere on your property. It could be the base of your porch, the patio, or even your home’s floor. Another universal truth is that concrete slabs move and create problems for homeowners. You may think you have to tear out and replace an uneven or sinking slab — but that’s not always true. Often, the best way to repair a concrete slab is through a process called slab jacking.
Acculevel was founded in 1996 and is well known in the industry for repairing foundations, basements, and crawl spaces. We raise and repair slabs for hundreds of customers per year. In this article, we’ll review what causes slabs to sink, how slabjacking works, and the benefits slabjacking offers.
What is Slab Jacking?
Slabjacking is a type of concrete lifting or leveling. Both of these terms refer to a process meant to return the slab to its original position. It’s an effective method of concrete raising that can be used on all major types of slabs, including:
What Causes A Concrete Slab to Move?
Concrete slabs move as the soil below them shifts. As the dirt settles, it can create voids or gaps below the slab, reducing the support it needs to hold firm. The ground around your home sinks for a variety of reasons, but the three most common issues are erosion, uneven weight distribution, and fluctuating soil conditions.
Before & After: The porch has cracked across the center, with the sunken slab portion next to the home. (Both photos were taken by Acculevel employees)
If you remember science classes from school, then you know that rainwater saturates the earth, mixing water into the soil. Then, when the water drains away, it takes part of the soil with it. This erosion can happen gradually as a natural process or suddenly if it’s caused by a broken pipe or ruptured drain. If the soil under a slab is eroding quickly or seems loose, evaluate your home’s guttering and plumbing systems. It’s possible the downspouts or water leaks are draining under the slab and washing out the soil.
Uneven weight distribution is a common issue in garages or driveways since vehicles are routinely parked in the same locations every day. The pressure your car or truck exerts on slab foundations or parking slabs gradually wears down the concrete until cracks form. Once the concrete slab cracks, the added weight of your vehicle causes separation and sinking to occur.
This photo was also taken by an Acculevel project advisor during a home evaluation. The crack in this garage has formed directly under the tires of the SUV.
Climate and Soil Type
It’s also possible the earth itself moves around below the concrete slab. It could be from improper installation; if the dirt wasn’t thoroughly compacted before the concrete was poured, it’s going to be uneven from the start.
But in our service area (the U.S. Midwest), the weather cycle is often to blame. Your yard floods in the spring, which leads to erosion. Then the soil dries out and contracts during a summer dry spell or drought, causing uneven support below the concrete. And then there’s the fluctuating freeze-and-thaw pattern we endure in the winter. Any one of these weather conditions could produce voids or gaps to form below the concrete.
How Exactly Is Concrete Leveling Done?
In order to lift the concrete slab, you need to access and fill the void that has formed below it.
Slab lifting is done by injection. Small holes are drilled through the concrete slab, and fill material is injected through the drill holes into the void beneath the concrete.
As the material fills the empty spaces below the concrete, it gradually accumulates until it pushes against the uneven concrete, creating lift.
Once the concrete slab is lifted, the drill holes are patched and the cracks are sealed.
What Does Slab Jacking Use As Void Filler?
There are two major types of injection material used in the concrete raising process: a concrete slurry mixture called “mud” and polyurethane foam.
When concrete lifting was first developed, contractors used a grout mixture they called “mud.” It’s usually a combination of concrete, water, limestone, and/or sand. (You may have heard of mud jacking as a repair type; this was the precursor to slab jacking.) As the concrete portion of the slurry sets up and hardens, it creates lift.
Slab Jacking Is the Upgraded Version
When Acculevel began in 1996, we also used mud jacking as a concrete repair method. But over time, technology developed a new variation. After extensive research and experimentation, we switched to the new fill material, which is a polyurethane foam.
In our experience, slab jacking provides a better, more reliable, and often permanent repair. As soon as the foam components are injected, a chemical reaction begins. This creates a foam that expands and sets up almost immediately.
Why is Slab Jacking Better?
Injecting a polyurethane foam is more convenient, takes less time, and lasts much longer than a mud fill.
Curing Time is Minimal
Polyurethane foam sets up quickly and cleanly; it solidifies within minutes. This means you can walk across a repaired patio within minutes and drive on a garage floor within an hour.
Because “mud” uses a concrete mixture, it needs to cure for a minimum of several hours before it’s “usable,” depending on the use of the slab, ground and air temperature, and the amount of moisture in the soil. (Temperature and moisture influence the cure time.)
Before & After Slab Jacking (both photos were taken by Acculevel employees)
Foam is Cleaner and Less Invasive
Slab jacking uses specialized equipment, but it can usually be installed in a standard-sized service truck. This means concrete leveling repairs rarely require one of our Acculevel crews driving across your lawn or disturbing your landscape. Our designated slab jacking vehicles have a 250-foot injection hose to maximize our reach to the repair section.
In fact, there is usually very little mess generated at a slab jacking job site. Generally, crews only need to clean the dust generated from drilling holes through the concrete, plus some trace amounts of foam from the injection holes.
Do you want to know more about slab jacking?
- Costs: We break down the costs of slab jacking and how it compares to other concrete raising methods.
- Garage Repairs: We address specific concerns about slab jacking and how it can repair garages.
- Slab Foundation Concerns: If your home is built on a slab and your floor is sloping, slab jacking may be the solution you need.
Need an Estimate on Repairing Your Concrete Slab?
Your first step will be to find an experienced specialty company that provides the service you prefer and make an appointment. Before you sign a contract for any service, you should always verify the company is reputable, insured, and accredited by the Better Business Bureau.
If you live in Indiana or the surrounding states, contact Acculevel. Established in 1996, we specialize in foundation repairs. If you have noticed sinking or cracking on any of your concrete slabs, call us for a free estimate! We’ll schedule an appointment for you with an experienced project advisor who will evaluate your home and the sections of concern, then we’ll help you choose the best course of action for you and your home.
If you don’t live in our area, or you’re not sure how to hire a contractor, we encourage you to use our free guide, Questions to Ask a Contractor. The article explains why we recommend these questions, provides Acculevel’s answers, and comes with a downloadable version you can use to interview any contractor.