Raising and leveling concrete that has settled or sunk over time is a common need for many homeowners and contractors. Spray foam is one method that can be used to lift concrete slabs back to their proper elevation. Spray foam works by expanding under the slab when applied, gently raising the concrete back into place. When cured, the foam provides a permanent, structural support and insulation. There are several types of spray foam that can be used for concrete raising, each with their own advantages and best uses.
In this article, we will look at the most common types of spray foam used for concrete lifting and examine the benefits and ideal applications of each. We will overview polyurethane foam, polyurea foam, and low-density polyurethane foam. With the right information, you can determine the best spray foam option for your concrete raising needs.
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Overview of Spray Foam Types for Concrete Lifting
There are three main categories of spray foam used to lift and reinforce sunken concrete slabs:
Polyurethane Foam
Polyurethane foam, also referred to as PU foam, is a two-part spray foam created from the mixing of an isocyanate and a polyol resin blend. It cures into a rigid plastic. Polyurethane foam offers high compressive strength and low permeability. It provides structural reinforcement and insulation. Polyurethane is available in a range of densities from 1.5 to 2.5 pounds per cubic foot. Lower density options work well for concrete raising applications.
Polyurea Foam
Polyurea foam is formed by the reaction of an isocyanate component and an amine-terminated resin blend. Polyurea cures more rapidly than polyurethane and forms a flexible, rubber-like material. It has excellent adhesion, high tensile strength, and low water absorption. Polyurea is well-suited for concrete lifting and void filling applications. It is available in foam or liquid spray grade options.
Low-Density Polyurethane Foam
Low-density polyurethane foams with densities around half a pound per cubic foot are also used for concrete slab lifting. This lightweight, expansive foam can gently raise concrete back to level. Low-density polyurethane provides excellent lift capacity combined with thermal insulation.
Factors to Consider When Choosing a Spray Foam
When selecting the right type of spray foam for raising concrete slabs, there are several important factors to take into account:
Lift Capacity
The amount of lift needed will influence the best foam choice. In general, polyurethanes and polyureas can achieve 1 to 4 inches of lift. Ultra low-density polyurethane can provide 4 inches or more of lift capacity.
Foam Rigidity and Strength
The stiffness and durability requirements of the application should be considered. Polyurethane provides very high compressive strength for structural reinforcement. Polyurea is flexible but offers excellent tensile strength.
Foam Density
Higher density foams like polyurethane provide more structural strength. Lower density options such as half-pound polyurethane foam maximize expansion and lift height.
Water Resistance
Since rising moisture can impact unsealed concrete, the foam’s water absorption properties are important. Closed-cell polyurethane and polyurea resist water intrusion better than more permeable, low-density foams.
Adhesion Level
The foam needs to bond tightly to the underside of the concrete slab. Polyurea provides superior adhesion to the underside of concrete slabs. Polyurethane also bonds well.
Cure Speed
Faster-curing foams like polyurea gain structural strength more quickly after injection. Slower-curing options like polyurethane can allow more time to fill voids thoroughly under slabs.
Insulation Value
If insulation under the slab is desired, polyurethane and low-density polyurethane foam provide thermal insulation. Polyurea has minimal insulation value.
Concrete Condition
For structural reinforcement of cracked or deteriorated slabs, higher strength polyurethane is recommended. Polyurea works well for less damaged slabs requiring lift and void filling.
Cost
Material cost can also be a factor. Polyurethane is generally the most affordable option. Polyurea has a moderately higher cost. Low-density polyurethane is often the most expensive.
Best Spray Foam Options for Concrete Lifting
Now that we’ve compared the performance characteristics and costs of the main spray foams, we can recommend the best options for various concrete raising applications:
Polyurethane Foam
Polyurethane is the best choice when high compressive strength and structural reinforcement are needed in addition to slab lifting. The rigid foam adds durability to deteriorated, cracked concrete. It works well when 1 to 3 inches of lift is required. Polyurethane provides long-lasting support at the most affordable price point.
Low-Density Polyurethane
For maximum lift height, low-density polyurethane is ideal. This ultra-light foam can gently raise slabs up to 4 inches or more. Low-density polyurethane also insulates effectively. The foam is best for slabs in generally good structural condition requiring leveling back to position.
Polyurea Foam
Polyurea is optimal for fast curing, rapid turnaround projects. It bonds tenaciously to clean concrete for reliable support. The flexible foam conforms well to voids beneath slabs. Polyurea works well for both partial and full slab lifting. It provides long-lasting lift at a moderate cost.
Case Studies: Polyurethane vs Polyurea for Concrete Raising
To further compare performance, let’s examine two real-world case studies where polyurethane and polyurea were used to lift sunken concrete slabs:
Case Study 1: Polyurethane
Project: Lifting and leveling a 2500 square foot industrial warehouse concrete slab
Original Problem: The large reinforced concrete slab had sunk 2 inches unevenly due to soil settling.
Foam Used: 2 pound per cubic foot density closed-cell polyurethane
Application: Holes were drilled on a grid pattern across the slab every 4 feet. Polyurethane foam was injected through the holes.
Results: The polyurethane expanded gradually over 24 hours, lifting the entire slab back to its original elevation. The rigid foam reinforced the structural integrity of the concrete.
Case Study 2: Polyurea
Project: Raising a sunken section of concrete driveway
Original Problem: A portion of the driveway had settled 1.5 inches due to erosion under the slab.
Foam Used: Semi-rigid, medium-density polyurea foam.
Application: Polyurea was injected under the affected section of the driveway through holes drilled every 3 feet.
Results: The polyurea lifted the driveway completely back into alignment within 2 hours. It filled voids, stabilized the soil, and created a durable repair.
Installing Spray Foam for Concrete Lifting
Once the best type of spray foam is selected, proper installation is critical for successful concrete raising. Here is an overview of installation best practices:
– The underside of the concrete slab should be cleaned and prepared to promote adhesion. Surface debris and loose particles are removed.
– Access holes are drilled into the slab, spaced evenly apart. Hole pattern and spacing is optimized based on project size and lift height required.
– Perimeter holes may be drilled to allow air or moisture to escape during foam application.
– Spray foam is mixed on site per the manufacturer’s directions and injected into the holes using specialized equipment. Rising foam fills voids and lifts the slab.
– Multiple foam passes are made until the slab is lifted to the desired elevation. Foam left to cure completely, normally within 24 hours.
– Holes are then plugged neatly to create an even surface. The raised slab can be put back into use once cured.
– A polyurea protective coating is often applied to the lifted slab for added moisture, abrasion, and corrosion resistance.
Conclusion
Raising and stabilizing sunken concrete slabs can be accomplished effectively and affordably using the right spray foam solution. Polyurethane foam provides robust structural reinforcement combined with reliable lift capacity and insulating value at an economical price point. Polyurea fills voids quickly and bonds tenaciously to lift and stabilize slabs. Ultra low-density polyurethane maximizes lift height for completely sunken slabs. By selecting the optimal foam for your specific project requirements, you can achieve successful long-term concrete raising results. Reach out to leading spray foam suppliers to discuss your unique application challenges and get expert recommendations. With professional installation, spray foam can restore stability, strength, and level positioning to settled, uneven concrete slabs.