Foam jacking is a concrete slab repair method that uses a high-density polyurethane foam to raise the slab. This process is much the same as mud jacking, an older method that uses a concrete slurry mixture to obtain the same results. The foam process is considered cleaner from an environmental standpoint, though, and leaves less visible marking of the concrete. The method leaves no sign of the foam behind, resulting in a level slab that should remain level for years to come.
Locate the point at which the slab begins to sink into the soil by placing a carpenter's level onto the surface of the slab and moving it from the level section toward the sagging edge. Mark the point at which the slab begins to sag downward with a piece of chalk, then place a second mark at the lowest point of the sag.
Place chalk marks in a row on the slab extending from the low point to the beginning point of the slag, spacing the marks every 6 inches.
Drill a hole vertically through the slab at each marked point using a 5/8-inch masonry bit. Use a low-rpm drill to avoid creating a crack at the base of the slab as the drill penetrates through the bottom surface. Use a shop vac to remove any dust from the holes.
Extend the hose from the mud-jacking pump down the hole at the highest point of the sloping slab until it reaches the level of the soil beneath, without actually running down into the soil. Fill the pimp hopper with the high-density polyurethane mixture.
Place the carpenter's level next to the hole. Start up the pump and begin pumping the mix through the hose and under the slab. The slab will begin to rise. Watch the level for changes in the slope of the slab. When the level reads even, stop the pump and remove the hose.
Repeat the pumping process for the next hole down the line, raising that section of the slab until it's level as well. With each hole covered, the lower ones will begin to rise as well. Continue the process until you reach the lowest point and have raised it level with the others.
Mix a small batch of fast-setting concrete. Add some of the concrete dust removed from the holes after drilling to the mix to tint the mix the same color as the slab. Place the concrete into a grout bag and inject it into the holes, filling them up to the level of the slab's surface. Allow the slab to cure for 48 hours before adding any heavy weight onto its surface.