Understanding the Material Behind Modern Concrete Raising
Polyurethane is a versatile, high-performance material used in a wide range of applications, but when it comes to raising and leveling sunken concrete, it becomes something even more remarkable. At Acme Concrete Raising & Repair, polyurethane foam is the key component in our concrete lifting service—a method that’s cleaner, faster, and longer-lasting than traditional mudjacking. But what exactly is polyurethane? And why is it so effective for lifting concrete?
This article answers those questions in detail, focusing on polyurethane as it’s specifically used for concrete raising. We’ll cover how it’s formulated, how it works, what makes it safe and effective, and why it’s become the gold standard for modern concrete repair.
What Is Polyurethane and How Is It Used in Concrete Raising?
At its core, polyurethane is a polymer—a type of plastic—created when two liquid chemical components (known as “A-side” and “B-side” materials) are mixed together. The resulting reaction forms a rigid foam that expands quickly and cures into a durable, high-strength material.
In concrete raising, this reaction happens at the point of injection and beneath the concrete slab, where the expanding foam gently lifts the sunken surface back to its original level. Unlike older techniques like mudjacking, which involve pumping in heavy soil-based slurries, polyurethane foam is incredibly lightweight yet strong.
What Are the A-Side and B-Side Materials Used to Make Polyurethane Foam?
Polyurethane foam used in concrete lifting is created by combining two components at the point of injection:
A-Side (Isocyanate): This is typically a mixture of diisocyanates, the reactive component that begins the polymerization process. It plays a critical role in forming the cellular structure of the foam.
B-Side (Polyol blend): This part includes polyols, blowing agents, catalysts, and surfactants. The polyols help form the foam matrix, while the blowing agents and catalysts control the rate of expansion and cure.
When mixed in the proper ratio, these components react within seconds, generating heat and expanding rapidly into a high-density foam. Once cured, the foam forms a rigid, water-resistant material capable of supporting significant weight.
Importantly, while isocyanates are hazardous in their raw form, the final cured polyurethane foam is non-toxic, chemically inert, and classified as non-hazardous. In fact, the cured foam can be disposed of in standard municipal landfills that accept construction debris.
How Is Polyurethane Foam Injected During the Concrete Raising Process?
Injecting polyurethane foam under concrete requires specialized equipment and precise control over temperature, pressure, and flow. Here’s a basic overview of how the process works:
Preparation: Small holes—usually around 5/8 inch—are drilled through the sunken concrete slab.
Preheating: The A-side and B-side materials are stored in separate tanks inside a heated rig. Both materials are preheated to optimal temperatures to ensure proper reactivity and flow.
Heated Lines: The two components are pumped through separate heated hoses to maintain temperature as they travel to the injection point.
Mixing at the Point of Injection: The materials are combined only at the nozzle or injection port, ensuring the reaction occurs precisely under the slab, not inside the equipment. The reaction forms a closed-cell structure that is moisture-resistant and structurally stable. Acme’s specialized injection equipment also features pressure gauges mounted at the injector itself, allowing our technicians to monitor and verify that the A-side and B-side components are being mixed in the correct ratio. This ensures consistent performance and the creation of strong, properly cured foam with every injection.
Expansion and Lift: As the foam reacts and expands, it gently lifts the slab from below, filling voids and stabilizing the soil in the process.
The entire process is fast and minimally invasive. Most residential jobs can be completed in a few hours, and the concrete is ready to use shortly after.
How Does Polyurethane Foam Form and How Long Does It Take to Cure?
Polyurethane foam forms through a rapid chemical reaction between two liquid components—A-side (isocyanate) and B-side (polyol blend)—when they are mixed at the point of injection. This exothermic reaction generates heat, causing the foam to expand and fill voids beneath the concrete slab. Within seconds, the foam typically reaches 90% of its final volume.
As the reaction completes, the material transitions from a fluid to a solid, forming a rigid, closed-cell structure. This foam begins to harden almost immediately and achieves full curing within 15 to 30 minutes, depending on environmental conditions and formulation.
The result is a durable foam that resists water, supports heavy loads, and remains dimensionally stable. The foam used by Acme Concrete Raising & Repair has a compressive strength of approximately 100 PSI, with a typical foam density of 4 lb/ft³, making it ideal for residential, commercial, and even highway-grade lifting applications.
Is Polyurethane Foam Safe and Environmentally Friendly for Concrete Raising?
Polyurethane foam used in concrete raising is engineered for environmental safety:
Non-toxic and Inert: Once cured, the foam is chemically inert and does not release harmful substances into the soil or air.
Water-Resistant: Its closed-cell structure makes it highly resistant to water infiltration, preventing further soil erosion and slab movement.
Classified as Non-Hazardous Waste: Cured foam can be disposed of in landfills that accept general construction materials.
Minimal Site Disturbance: The small injection holes and fast cure time mean less mess, less noise, and less downtime for the property owner. Our process does not disturb surrounding landscaping or structures and is considered safe for both indoor and outdoor use.
One caveat: polyurethane foam is not UV-stable. Direct exposure to sunlight will degrade the material over time, which is why it must always be injected under concrete or soil and not left exposed.
Where Else Is Polyurethane Commonly Used in Everyday Life?
Polyurethane is not a niche or experimental material—it’s something most people interact with daily without realizing it. Its versatility makes it one of the most commonly used polymers in modern manufacturing. You’ll find polyurethane in:
Furniture cushions and mattresses
Car seats and interior trim
Refrigerator and freezer insulation
Footwear soles
Coatings, adhesives, and paints
Its use in concrete raising is just one example of how this remarkable material combines strength, flexibility, and longevity.
What Types of Polyurethane Foam Are Used for Different Concrete Projects?
Not all concrete repair situations are the same—and neither is the foam. At Acme Concrete Raising & Repair, we don’t believe in a one-size-fits-all approach. We select the right polyurethane formulation based on the needs of each project, using our technical expertise to ensure long-term performance and cost-effectiveness.
401: This is our go-to foam for most standard lifting projects, from sidewalks and driveways to garage floors. It provides excellent expansion characteristics and a quick cure, making it ideal for general-purpose concrete raising.
501: We use this formulation for void filling and soil stabilization. It expands less aggressively than 401 but offers superior penetration into loose soils and larger voids. It’s ideal for filling subsurface gaps and stabilizing weak subgrades.
401G: Specially designed for wet environments such as seawalls, retention ponds, or areas with high water tables. 401G resists washout and maintains its integrity in constantly damp conditions.
This variety of options allows us to solve a wide range of problems with precision. Unlike many companies that rely on a single foam for every job, we tailor each solution using the formulation that best suits the application. Our Foamjection-certified team has the engineering knowledge to diagnose underlying issues and match them with the right material—ensuring better results and longer-lasting repairs.
When it comes to lifting and leveling concrete, polyurethane foam checks every box:
Lightweight: Doesn’t add extra stress to already weak soil
Strong: Withstands heavy loads (100 PSI+ compressive strength)
Fast-Acting: Sets up quickly, minimizing downtime
Water-Resistant: Prevents future erosion and settlement
Environmentally Friendly: Non-toxic and safe for residential, commercial, and municipal use
At Acme Concrete Raising & Repair, we’ve used polyurethane foam to raise thousands of slabs throughout Chicagoland. Our technicians are Foamjection-certified, and our proprietary process delivers lasting results with minimal disruption.
