Raising a concrete slab is not exactly the same, but close enough for our comparison. You may have a concrete slab patio, driveway, or portion of a house foundation that has sunken or tilted over the years.
In the example of the house foundation, if the house was built over a crawlspace or basement, it is possible to get into the crawlspace or basement to insert jacks and raise the foundation. But it is impossible to get under concrete slabs. So, a cement "cocktail" is squirted through holes in the concrete, which raises the foundation. Caution: slab jacking is not intended to raise or re-level entire houses. It is more intended for portions of slab foundations, garage floors, sidewalks, patios, driveways, etc.
Why Concrete Slabs Sink or TiltBefore understanding slabjacking, you need to understand why concrete slabs fail. Traditionally, houses were built over a crawlspace or basement--the flooring was raised over ground-level. But as concrete became a predominant building material, concrete slabs became the vogue. In simple terms, sheets of concrete were poured at grade, and this became the level for the house's flooring.
Soil is not a stable thing. Other materials--rock, gravel, ash, sand, etc.--are far more stable. Also, soil can have empty spaces within it. If you have ever worked in a garden, you know this. As the years go by, those empty spaces allow the soil base to shift and compact. But often in ways that you don't want.
Slab Jacking to Repair Concrete SlabsHere's how concrete slab jacking works.
- A series of holes, about a half-inch in diameter, are drilled in the concrete slab. If you have ever injected insulation into your walls, or at least know the process, you will know that many holes are required. It's the same thing with slabjacking. One hole will not suffice.
- A "cocktail" of stable materials, such as sand, gravel, and ash, along with water, is injected into the holes.
- The slab slowly raises.
- The holes are plugged.
Uretek and Polyurethene Concrete Lifting MaterialsNewer methods of slabjacking dispense with the natural elements (the sand and gravel slurry), relying instead on polymers. Uretek is the most visible manufacturer of these polymer resins.
While Uretek is more expensive than traditional slab jacking materials, its chief distinction is that pumping pressure does not lift the slab--expansion of the polyurethane creates the "lift."
Special Note: For further information on Uretek, I urge you to read the report from the Oregon Department of Transportation (link attached), where they objectively tested Uretek. Unlike most government reports, the Oregon DOT's report is clear, concise, very readable, and applicable even to residential homeowners considering slabjacking with polymers. You will also want to note the $42,260 cost for 10.5 hours of Uretek work.