Concrete Pressure Lifting

Basics

• Free-floating concrete slabs include sidewalks, slab-on-grade foundations, garage floors, streets and bridge structures. Because of soil movement, frost damage and settling, these can sink, creating trip hazards and, in extreme conditions, destroy the integrity of the structure. Mudjacking and sandjacking avoid a need to replace or break up the slab or floor and replace it. These processes work on the existing slab.

Mudjacking

• If a concrete slab is free-floating and sinking, tilting or settling, it is a candidate for lifting. The mudjacking process begins with a drilled hole about 2 inches in diameter. A high-pressure pump fills the underside of the concrete with grout, usually a sand and concrete mix. This pumping action fills all the underlying voids and then lifts the structure back into place. If this is insufficient, then another hole is drilled in the area that has yet to rise, and the process is repeated. In some cases, such as involving a tilting slab foundation, a chemical that expands adds more lift to the grout mixture. Deep foundations cannot be lifted with this process.

Sandjacking

• Sandjacking, normally not used in residential work, is an alternative to mudjacking. It can be used for sidewalks and streets. In this process, workers drive jacks underneath the sides of the slab. These jacks are hand pumped or connected to hydraulic pumps depending on the size of the slab to be moved. Workers insert a powerful air pump nozzle underneath and spray a mixture of sand and lime underneath the structure.

Comparisons

• Sandjacking has the benefit of being a more even lift than mudjacking, which often creates a “pyramid” of material and uneven lifting. If two sides of the slab are accessible, sandjacking does not need to entail drilling holes in the concrete. If the structure is enclosed, workers need to drill holes and air pump the sand in the same way that grout is pumped in the mudjacking process. Sandjacking also has the advantage of not having to dry, so the dangers of post-jack settling are minimal. Mudjacknig has the advantage of having a stable of chemicals to choose from that can serve to fill voids more effectively and expand, so as to lift the structure with more force than the normal grout.