Table of Contents
Introduction
How Polyurethane Concrete Raising Works
Benefits of Polyurethane vs. Traditional Methods
Soil, Moisture, and Longevity Considerations
Crack and Joint Sealing After Raising
The Sealant Application Process
Choosing the Right Sealant: Dow vs. Sika
Conditions to Avoid When Sealing
Conclusion
1. Introduction
Polyurethane concrete raising – also known as polyjacking or foam jacking – is a modern solution for fixing sunken or uneven concrete slabs. Rather than demolishing and replacing the slab or pumping heavy mud slurry underneath (traditional mudjacking), technicians inject expanding polyurethane foam through small holes. The foam quickly lifts and stabilizes the slab, cures to a water-resistant support, and allows the surface to reopen within hours instead of days.
Yet long-term success isn’t only about lifting. Controlling water after the repair is just as critical. If moisture reaches the soil beneath a slab, it can erode that soil, create new voids, and undermine the lift. That’s why sealing open cracks and joints is a vital follow-up service. This article explains how polyurethane lifting works, why sealing is crucial, and how Acme Concrete Raising & Repair applies professional-grade sealants to protect your investment.
2. How Does Polyurethane Concrete Raising Work?
Polyurethane concrete raising involves a precise and efficient process that permanently stabilizes uneven slabs. Technicians begin by drilling small access holes, approximately 5/8-inch in diameter, at carefully selected points across the settled slab. Through these holes, they inject a two-part resin—polyol and isocyanate—that chemically reacts upon mixing to form a rapidly expanding closed-cell foam.
As the foam expands beneath the slab, it fills voids, compacts loose subgrade material, and gently lifts the concrete back to its intended position. The foam typically expands 15-20 times its original volume, ensuring thorough void filling and soil compaction. Once the slab reaches its desired elevation, the foam quickly cures to a stable and strong state, usually within just minutes. After curing, technicians patch the drilled holes flush with the surface, leaving minimal evidence of the repair.
Due to its lightweight nature—only 2 to 6 pounds per cubic foot—polyurethane foam does not significantly increase the load on underlying soils, reducing the risk of future settlement. The precise, clean, and rapid nature of this process makes it ideal for addressing residential, commercial, and municipal concrete leveling needs without significant downtime or disruption.
3. What are the Benefits of Polyurethane vs. Traditional Methods?
Polyurethane concrete raising offers numerous benefits compared to traditional mudjacking or slab replacement. Traditional mudjacking uses heavy cement-based slurry that can add excessive weight and further stress weak or unstable soils. By contrast, polyurethane foam is lightweight, reducing this risk significantly. Additionally, the expanding foam can better penetrate and fill small voids, compacting and stabilizing loose soils more effectively.
Another distinct advantage is the minimal invasiveness of the polyurethane lifting process. Rather than large-scale demolition or extensive site cleanup, polyurethane lifting requires only small, discreetly patched holes. The process also provides exceptional speed—most projects are completed within hours rather than days, allowing normal use of the area shortly after the repair.
Furthermore, polyurethane foam is hydrophobic, meaning it does not absorb water or degrade in moist conditions. This property ensures a more durable repair compared to mudjacking slurry, which can erode or wash away over time due to water infiltration. Long-term stability is significantly enhanced when polyurethane lifting is combined with effective drainage and crack sealing measures, often allowing repaired slabs to remain level and stable for decades.
These combined advantages clearly establish polyurethane concrete raising as a superior, modern method for concrete repair, offering both immediate and long-lasting benefits.
4. Soil, Moisture, and Longevity Considerations
While polyurethane foam is waterproof, the subbase soil beneath the slab is not. If water penetrates beneath concrete slabs (through unsealed joints or cracks), it can erode soil, forming voids and weakening the structure. These conditions can cause slabs to settle again or crack under stress. Thus, sealing cracks and joints becomes essential for long-term durability.
5. Crack and Joint Sealing After Raising
After a slab has been raised, sealing cracks and joints is crucial to prevent moisture infiltration. Water intrusion through open joints or cracks can compromise the stability achieved by polyurethane lifting, potentially leading to soil erosion and re-settlement. Professional sealing ensures that moisture is kept away from the subbase, significantly extending the repair’s lifespan.
6. The Sealant Application Process
ealing may look as simple as squeezing material into a gap, but professional installation follows these disciplined steps:
Surface Preparation: Remove debris, loose concrete, old sealant, and vegetation. Clean, dry sidewalls ensure proper bonding.
Backer Rod or Filler: For deeper joints, insert a closed-cell foam backer rod to control sealant depth and create an ideal hourglass shape for maximum flexibility.
Tape Along Edges (Silicone Applications): Durable tape along joint edges keeps adjacent surfaces clean and defines crisp, professional lines.
Sealant Placement: Sealant is dispensed carefully to avoid air pockets. Non-sag silicone stays in place, while self-leveling polyurethane settles into horizontal cracks naturally.
Tooling the Bead: Silicone is tooled smooth for proper adhesion, air removal, and water runoff. Self-leveling polyurethane typically needs no tooling on horizontal surfaces.
Optional Sand Broadcast: Broadcasting silica sand onto freshly tooled silicone can blend the joint visually and add skid resistance.
Tape Removal & Inspection: Remove tape before sealant skins over, verify a neat, continuous seal and complete adhesion to joint walls.
Primary Purpose: Although aesthetics matter, the foremost goal is erosion protection. A watertight seal is key to preventing subbase erosion and ensuring slab stability.
7. Choosing the Right Sealant: Dow vs. Sika
Acme Concrete Raising & Repair carefully selects the appropriate sealant based on specific project needs. Dow Contractors Concrete Sealant is silicone-based and requires tooling. It is ideal for wider or vertical joints due to its non-sag characteristics and offers superior flexibility, durability, and UV resistance. This sealant type provides a neat, concave, professional finish, and sand can be added to enhance visual blending.
On the other hand, Sika Self-Leveling Sealant, polyurethane-based, is used for narrower, irregular horizontal cracks where tooling is impractical. It naturally flows into and fills irregular cracks, curing to a flush surface. While it provides convenience and efficiency, it generally has a shorter lifespan under prolonged UV exposure than silicone sealants.
Acme assesses each project individually, considering joint size, location, exposure conditions, and aesthetic requirements to choose the most suitable sealant product.
8. Conditions to Avoid When Sealing
Sealant performance can be compromised under unsuitable conditions. To ensure long-term durability, Acme adheres strictly to manufacturer guidelines:
Cold Temperatures: Avoid sealing at temperatures below 40°F (4°C), as colder conditions slow curing and weaken adhesion.
Moist Surfaces: Surfaces must be dry; rain, snow, or condensation prevent proper bonding and trap moisture beneath the sealant.
Rapid Temperature Changes: Extreme temperature fluctuations right after application can stress the sealant prematurely.
If conditions are unfavorable, sealing work is postponed to prevent failure.
9. Conclusion
Polyurethane concrete raising effectively stabilizes uneven slabs, and sealing cracks and joints afterward is essential to maintain stability and longevity. Proper sealing prevents water intrusion, protecting the subbase from erosion and freeze-thaw damage. By following disciplined application methods, using the appropriate sealants, and avoiding unsuitable weather conditions, Acme Concrete Raising & Repair delivers robust, durable, and lasting solutions that withstand harsh weather and keep concrete surfaces stable for years to come.