Slabjacking appears simple and homeowners believe it is the solution to their foundation problems.
Slab jacking is the act of lifting one side of a concrete slab below in order to level it. This sounds appealing, as there is no need to break up or dispose of concrete. However, it is not as easy as it seems.
Consult a structural engineer to ensure the integrity of concrete and structure. Slab jacking is not recommended if the concrete or structure are unstable.
Analogy of Dry-Dock Boats
Think of something large, like a boat in dry-dock. It weighs in excess of a thousand pounds when it is resting. It is your goal to raise it 3 feet. You don’t have a crane so you can simply put water underneath it. You can raise it, then it floats. You have lifted a large object hydraulically.
Although raising a concrete slab may not be exactly the same as raising a brick, it is close enough to allow for comparison. Concrete slab patios, driveways, and other parts of house foundations may have sunken or been tilted over time.
If the house foundation was built on top of a crawlspace, or basement, it’s possible to enter the crawlspace to install jacks or raise the foundation. It is not possible to reach under concrete slabs. A cement “cocktail” is used to raise the foundation by squirting cement through the concrete. Attention: Slabjacking is not designed to raise or level entire houses. This is used to jack slab foundations, garage floors and sidewalks.
Why do slabs sink or tilt?
Understanding slab jacking is essential before you can understand why concrete slabs often fail. The foundation of houses was built on top of a basement or crawlspace. The flooring was then raised above the ground. Concrete slabs were popularized as concrete became a more common building material. Concrete slabs were simply poured at grade and used as the floor for the house.
The soil is not stable. Rock, gravel, ash and sand are far more stable. It is possible for soil to have empty spaces. This is something you’ve probably experienced if you have worked in a garden. These empty spaces let the soil base shift and become more compact over time. Of course, sometimes in ways you don’t like.
How the Process Works
This is how concrete slab jacking works.
- In the concrete slab are drilled a series of holes measuring about a half inch in diameter. You will be familiar with the number of holes required if you have ever injected insulation in your walls. The same applies to slab jacking. A single hole is not enough.
- The holes are injected with a “cocktail” of stable material, including sand, gravel and ash.
- Slowly, the slab rises.
- All the holes have been plugged.
Uretek and Polyurethane Concrete Lifting Material
Modern slab jacking methods no longer use natural elements like gravel slurry and sand, but instead use polymers. Uretek is the most prominent manufacturer of these polymer resins. However, Uretek’s main distinction is that Uretek does not lift the slab. Instead, the pump pressure causes the polyurethane to expand and create the “lift”.