Repair a sinking concrete slab using the mudjacking process. It pumps a slurry of concrete under the slab to fill any voids and lift the slab gently to its original level and prevent further sinking.
The process requires using a concrete saw to cut joints in the slab so it has room to move without cracking. Use a core drill for cutting holes in the concrete that are large enough to accommodate the hydraulic hose for pumping the slurry under the slab. Save the cores for patching the concrete. Extend the holes into the ground beneath the slab another 12 inches using a pneumatic rock hammer.
Mix the slurry by placing Portland cement, silt, sand and water in the auger of the mudjacking machine. Once it mixes, move it to the hopper of the hydraulic concrete pump. Insert the end of the hydraulic hose into the previously drilled holes and slowly pump the mixture under the slab. Once the voids are full, the pressure from the mixture starts to lift the slab. Depending on the depth of the sunken area, it may be necessary to rotate the nozzle through the holes several times so the slab lifts slowly and does not crack. Continue the process until all the pieces of the slab are level.
Clean any excess slurry from the holes in the concrete. Add mortar mix to the hole and replace the plug.