Slab leveling

Slab Leveling: Top Five Most Common Customer Questions

Just like with any construction project, customers are going to have a variety of questions to help them understand how their project is going to go and what to expect from the contractor. This is no different when trying to determine if slab leveling with polyurethane is the right solution for their project. Here are a few common questions that customers have when evaluating the slab leveling process. 

  1. How does slab leveling with polyurethane work?

Slab leveling with polyurethane is a relatively simple procedure to understand.  The polyurethane is a specialized geotechnical system that is formulated to compact and densify soils with enough expansive capacity to lift concrete.When the polyurethane is injected below a slab it reestablishes contact between the slab and the soil, helping to transfer the load of the slab back into the soil.  Once the soil beneath the concrete is fully compacted and densified, injections are continued while closely monitoring the surface for movement.  The expansive force of the polyurethane then pushes upward and lifts the slab.  

  1. Does polyurethane slab leveling require excavation?

No excavation is required with slab leveling. The process works by drilling 5/8″ holes, less than the size of a penny, through the slab to give access for the polyurethane below the slab.  Once injections are complete, the holes are filled with a non-shrink grout to help deal with potential aesthetic issues.  

  1. How long does polyurethane slab leveling take?

Polyurethane slab leveling is a fast process. Geotechnical polyurethanes range in expansion and cure time, but they typically cure up to 95% capacity within 25 minutes. This means you can drive a car over the treated area within 25 minutes after injections are completed. The project length is dependent upon the size and scope of your project, but typical residential projects are completed in less than a day. 

  1. Does polyurethane harm the environment?

Since polyurethane is injected into the soil, it is reasonable to have concerns about the environmental impacts of the polymer.  Our geotechnical polyurethanes are environmentally inert, meaning they do not leach chemicals into soils or water.  In specialized formulations, our polyurethanes meet NSF-61 ANSI safe drinking water standards, meaning the polyurethane can be put in contact with drinking water without concern for contamination.  Polyurethane slab lifting also uses less energy thank rip out and replace and reduces greenhouse gas and landfill waste by extending the useful life of existing concrete.   

  1. What is the cost of polyurethane slab leveling?

It goes without saying that polyurethane slab leveling costs are dependent on the size of your project and site conditions.  However, in most cases when compared to the cost of replacement, polyurethane slab leveling is significantly less expensive.  When comparing with the cost of older slab lifting methods or rip out and replace, ancillary costs such as down time, removal of landscaping or irrigation systems, and interrupted access should be considered. 

If you have additional questions about the slab leveling process, contact us today for a free consultation on your concrete repair project.

Concrete raising with polyurethane foam jacking

Concrete Raising with Foam Jacking

You’ve probably stumbled across uneven concrete slabs in your neighborhood. This is a common problem, especially if the concrete slabs are placed over soft ground. Fixing this issue isn’t as complex it may seem because replacement isn’t the only option. Concrete raising is a cheaper option as opposed to replacing concrete. One of the ways concrete is raised is by using polyurethane foam, a foam that expands instantly. This process is known as polyurethane foam jacking. Read on to learn more about how foam polyurethane can be used to aid in concrete raising.

Soil Load-Bearing Capacity

Another crucial aspect of concrete raising is soil load-bearing capacity. If the soils are weak or unconsolidated the weight-bearing ability of foam polyurethane isn’t effectively distributed into the ground. This is due to the fact that the soil, if not densified, will inevitably slip under the weight of the concrete. This, in turn, causes the concrete to become uneven once again. If soil densification is determined to be a necessary process, it’ll look something like this:

A lengthy inspection will be done to determine where the injections must be done in order to effectively densify the soil. A large 3-5ft square grid pattern will be laid out where the injections will be done at multiple depths.

The initial injections are completed at the top level in order to condense and strengthen the soil and use the concrete slab as a way of consolidating the top layers for the lower injections to work against.

The remaining injections are shot from the top-down, with each lower layer having the capability to densify against the denser top layers. This strengthens the overall weight-bearing ability and ensures that the slab will not slip back down by consolidating the lower soils over time.

Choosing The Right Type

There are two main types of foams that are used for concrete raising. The reactivity and density of the foam need to be determined before moving on with the concrete raising process. Here’s a guide to the two factors that come into play:


A foam that reacts slowly is typically used when a large void needs to be filled. The foam will spread evenly and thicker, allowing for more coverage. A foam that reacts quickly won’t spread evenly and won’t have the same amount of spread that is offered with a slow reaction. Having control allows the workers to ensure that the slab isn’t raised too much and lines up precisely with the other slab. This ensures the success of the concrete raising process.


A foam that is much denser will be used if a larger weight needs to be born. If the slab doesn’t weigh as much and the void is large, a foam with a lower density will be used to fill in the void easier. Density is important to keep in mind as this determines the success of the operation and whether or not the polyurethane will be able to hold the weight of the concrete slab.

For Your Understanding

In short, though concrete raising is based around the environment, there is a basic process to it. Because polyurethane can be used to lift concrete in almost any area including foundation, sidewalks, driveways, steps, garages, pool decks, etc. it’s important to gauge the environment and reasons why the concrete slabs are uneven to begin with. This information will determine what kind of polyurethane will be used and what style of injection will be done. Slow reaction polyurethane is typically used for large voids to increase the spread and ensure an even rise. Density is also a factor that will be determined based on how much weight the polyurethane needs to bear. Polyurethane jacking is the most effective form of concrete raising and is far superior to replacing concrete altogether.

Analysis of Polymer Slab Jacking vs. Mud Jacking

We are often asked about the differences between mud jacking and the use of CST’s polymers for slab jacking. Below is a quick overview displaying what the key differences are between cure time, lift accuracy, footprint and lifecycle.

Production Savings:  Polymer Injection is 4 to 8 times faster than traditional methods and requires smaller crews.

Traffic Control Savings:  Total time required for closure is reduced 4 to 1 because of production savings.  Delay time before traffic may return to treated roadway after completion of injection is approximately 15 minutes.

Life Cycle Savings:  The Polymer Injection process has a minimum 4 to 1 advantage over conventional mud jacking’s life span of 1 to 2 years with a typical polymer 10 year warranty against shrinkage and deterioration.

CST Polymer Injection Traditional Mudjacking
PRESSURE OF INJECTION Low Pressure High Pressure
HOW IT LIFTS Chemical reaction creates expansion of polymer that lifts the slab. Fluid or Hydraulic pressure of grout lifts the slab.
CURE TIME Expands in less than one minute and reaches 90% strength within 15 minutes. Requires additional cure time of 4 hours or more to complete hydration.
ACCURACY OF LIFT Surgical precision lift to desired elevation is accomplished. An “over-lift” is necessary to compensate for water loss in the grout as it cures.
FOOTPRINT/PROPERTY IMPACT Small 5/8” holes, about the size of a penny, are drilled to inject polymer with no damage to existing concrete slab. Large 2 to 3 inch holes are drilled to inject high pressure grout. This can compromise the concrete causing breakout at the bottom of the slab.
LIFECYCLE OF REPAIR Permanent lift & stabilization is standard. Polymer material is guaranteed for 10 years. Longevity of lift/repairs is expected to last for approximately 1 year. University of Illinois Study 1985-1989.
COST IMPACT Savings over tear out and replace. One time cost. Ongoing cost due to need for rework/repair of same area.