Concrete Leveling Systems Inc. (CLEV)

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Concrete leveling is a procedure that attempts to correct an uneven concrete surface by altering the foundation that the surface sits upon. It is a cheaper alternative to having replacement concrete poured, and commonly performed at small businesses and private homes.
[edit] Problem cause

Sidewalks, patios and garage floors are most often made of concrete. When the concrete is a few inches thick and poured on insufficient foundation and/or without steel reinforcement it may crack and subside. Sometime water run off from rain or flood can wash away dirt upon which the concrete slab is resting leading to cracking and subsiding. In addition tree roots and other subsurface obstructions can make concrete slabs rise making them not align to the adjacent slabs.
[edit] Slabjacking

Slabjacking can both raise the old cracked slab back to its original position and create a new foundation of cement mortar or sand mix by injecting the mortar under the slab through a hole, under pressure. The viscosity of the mortar will keep it from flowing back through the hole until it sets.

Accounts of raising large concrete slabs through the use of hydraulic pressure go back almost a century. Mudjacking or slabjacking has been in common use for about 50 years. Generally a portable pump is carried to the location of the block to be raised. A hole of up to 3 inches in diameter is drilled into the block. Varying combinations of soil, sand, cement, or other materials, are mixed and then injected under the sunken concrete block, causing it to rise.

Problems associated with slabjacking involve: containment of the mess caused by excess mud or cementeous material in the area to be raised; drilling of large holes that can weaken the block, and allow material to flow too quickly causing cracking of the slabs. HMI is not conducive to filling large void areas.

Modern methods use smaller holes to avoid weakening the concrete slab, or raising the blocks too quickly. A highly dense crushed limestone is sometimes mixed with moderate amounts of cement, and can be pumped slowly and safely through hoses that are connected directly to the pumping truck, with little or no destruction of landscaping or surrounding structures.