Techniques to Level a House on a Slab

Mud Jacking

• With mud jacking, the contractor drills a number of holes or cores downward through the concrete slab from the top, strategically located at the lowest points of the slab. The holes are pumped full of a cementitious group, a substance made up of Portland cement, fly ash, sand and additives to prevent shrinkage. Pumped under pressure, the substance fills any gaps under the concrete slab and compacts the soil with which it makes contact. Thereafter, it spreads under the slab, gradually raising it. The holes or cores are refilled and sealed to ensure bonding of the substance under the slab.

Modern Slab Jacking

• Since the discovery of polymers and their varied uses, slab jacking has evolved to the point that slab jackers now use high-density, closed-cell polyurethane foam to level residential concrete slabs. Holes of 2 to 3 inches in diameter are drilled in the concrete, and the contractor drills the foam substance through the holes under pressure.

Polyurethane Substance

• The polyurethane substance used in modern slab jacking consists of two components. One is a combination of polyhydroxy compound, water and catalysts, while the other is an isocyanate compound. When both substances are injected into the holes together, they foam up to several times their original volume. As the substance sets, it forms a rigid foam material that lifts the concrete slab. The polyurethane is moisture resistant and repels water.

Equipment

• Mud jacking takes place using a hydraulic power mud pump. The pump is self-propelled with a remote control and has a second pumping cylinder to double the speed at which it can pump the jacking material. Modern technology has produced power pumps capable of pumping concrete containing pea gravel for greater stability. Polyurethane injection slab jacking is done using a pumping unit mounted on a truck; the unit has a meter that measures the quantity of foam pumped.