Slab jacking is a process for raising and supporting settled, uneven concrete using a cement-based grout which primarily consists of lime or sand. The process, material and good applications are detailed below. CJGeo has completed thousands of slab jacking projects throughout the Mid-Atlantic. Our slab jacking crews are friendly, experienced, and work with the most efficient and safe equipment.
What Slab Jacking is Good For
Slab jacking is best for repairing exterior concrete which has settled, such as sidewalks, porches and pool decks around vinyl-lined, fiberglass, and other non-concrete/gunite pools. Slab jacking works well for small slabs, but can be used for large slabs, like driveways and garage floors, too. Slab jacking is the only concrete lifting process which may be used around pools with vinyl liners, because the grout can be mixed to be very thick, which helps prevent damaging the liner.
Slab jacking is generally not recommended for lifting floors inside of buildings, because the process can be kind of messy. Cleaning up after slab jacking outside is easy, and just takes a water hose, but that’s not always possible inside of a house. Therefore, we recommend polyurethane grouting for lifting most interior slab floors and slab foundations.
We have lifted everything from sidewalks to interstate highway bridge approaches using slab jacking. Our estimators are familiar with the advantages of both processes, so are capable of recommending which is most appropriate for your situation. The project profiles below have more information about some of our specific slab jacking projects we’ve completed.
How Slab Jacking Works
CJGeo’s skilled technicians are experts at slab jacking, a process that has been around since the 1930’s, and which works by injecting grout material under sunken or unsupported concrete to raise it back to its original levels. After being injected under the concrete, the grout dries out and stiffens to permanently support the affected areas. Slab jacking works on almost any type of flat concrete, whether it be inside of a house, around a pool, on the top of your front porch or slabs of your sidewalk or driveway.
It doesn’t take much pressure to raise concrete, our employees are careful and our concrete leveling equipment is compact, so we can work in almost any environment, safely and effectively. There are three easy steps to slab jacking:
Slab Jacking Material
Depending on the application, CJGeo uses a lime or sand-based grout for slab jacking. We add Portland cement to the sand-based grout to dry it out a bit. Sometimes, we put enough Portland in the grout that it will harden, however for almost all applications, just letting the grout slowly dry out to the moisture content of the surrounding soil is sufficient for the loads which a slab will see. Because slab jacking is used to repair slabs that are in good condition, the slab jacking grout isn’t used for load distribution. Therefore, in most cases, the grout only needs to be slightly stronger than the underlying soil, which rarely requires significant quantities of cement.
Concrete slabs around homes and most businesses are only 3.5 to 6 inches thick, so they only weigh a few pounds per square inch. Even with no cement in CJGeo’s slab jacking grout, the grout has sufficient strength to hold up the concrete, even if the grout is moist enough that you can push your finger into it. Keeping the grout from curing (getting really hard) makes it easy for you to do things like run sprinkler lines, electrical lines or drainage pipes under repaired areas in the future.
A common misconception about slab jacking is that concrete (a mix of Portland cement, sand, stone and water) is pumped under the areas being repaired. Concrete is a very poor choice for a slab jacking material; it is relatively expensive, doesn’t move well through the voids below slabs, and if you ever want to tear out the original concrete, it makes that process much more difficult.
Other materials are used for processes similar to slab jacking. polyurethane grouting involves pumping high density polyurethane foam under the concrete, and sometimes cellular concrete is used to fill large voids below concrete.
History of Slab Jacking
Slab jacking, which was originally called mud jacking (and is still called mud jacking in many areas of the US), was started in the 1930s in Iowa to correct settlement and frost heave of roadway slabs and curb & gutter. The earliest pumps, like the one in this photo, were somewhat primitive. Today’s slab jacking pumps are mobile, powerful and hydraulically powered. CJGeo’s pumps are capable of pumping pressures up to 500 psi, and depending on the grout mix can pump up to 100 feet.
The trucks used for slab jacking have also evolved a lot. CJGeo’s original trucks required shoveling dry grout mix into a mixer and adding water and Portland cement manually. Now, we run automatic trucks which batch the slab jacking material, Portland cement and water in a horizontal hydraulic mixer, no shoveling required. This makes CJGeo’s operation safe and reliable, and enables us to mix and place up to 10 cubic yards an hour of material with each truck.