Lifting concrete slabs with foam is a technique that has become popular in recent years as an alternative to more traditional methods of raising settled concrete like mudjacking or slabjacking. The basic premise involves drilling holes into the sunken slab, injecting expanding polyurethane foam underneath, and then allowing the foam to expand and lift the concrete back into place. But does this method actually work? And how effective is it compared to other options? We’ll take an in-depth look at concrete lifting foam, including how it works, the pros and cons, cost comparisons, and situations where it excels versus when other slab lifting methods may be better. Keep reading to get the full low-down on using foam for concrete raising.
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How Does Concrete Lifting Foam Work?
Concrete lifting foam works by injecting an expanding rigid polyurethane foam underneath the slab through drilled holes. As the foam expands, it exerts upward pressure and lifts the settled section of concrete back into place. Here is a step-by-step overview of the process:
Drilling Access Holes
The first step is to drill a series of access holes through the slab where the foam will be injected. Hole spacing and pattern will depend on the size of the project, but holes are typically drilled every 4 to 8 feet. The holes are angled slightly toward the lowest side of the sunken slab. Depth is normally around 80% of the slab’s thickness.
Injecting the Foam
With the holes drilled, the expanding foam mixture is pumped beneath the concrete through the holes. The foam begins expanding immediately upon injection, filling voids, cavities and spaces under the slab. As it expands 30-40 times its liquid volume, the foam exerts upward pressure on the underside of the concrete.
Lifting the Slab
As more foam is injected, the continual expanding action gently lifts the settled portion of the slab back into its original position. Careful monitoring ensures the slab is raised to the proper elevation. The foam is given time to fully cure and solidify before trimming flush with the concrete surface.
Sealing the Holes
Once lifted level, the injection holes are sealed with concrete or other filler material. The access points are made flush with the surrounding slab. The foam remains permanently in place underneath the concrete to provide lasting support and reduce the chance of resettling.
The Pros and Cons of Using Foam for Concrete Lifting
Like any repair method, using foam to lift settled concrete slabs has both advantages and disadvantages. Here is an overview of the key pros and cons:
The Pros
- Less invasive than slabjacking – doesn’t require digging or tunneling under slab
- Lifts many types of settlement – center dips, corner drops, joint lowering, etc.
- Quick injection process takes just hours, not days
- Less materials and equipment needed compared to mudjacking
- Less landscape disruption since no access pits are required
- Effective on uneven settlement with voids under slab
- Permanent solution that doesn’t wash away over time
- Prevents further settling of slab in injected areas
The Cons
- Higher cost than traditional mudjacking or slabjacking
- Limited lifting height, usually up to 3 inches
- Not effective if very large voids exist under slab
- Requires holes drilled through good slab areas
- Not a DIY project – professional equipment/training needed
- May not work well in sandy, shifting soils
- Surface may not be perfectly level if settlement is uneven
Cost Comparison to Mudjacking
One of the downsides of using concrete lifting foam is often the higher cost compared to traditional mudjacking. Here is an overview of cost differences:
- Mudjacking – $2-$8 per square foot
- Slabjacking – $5-$15 per square foot
- Foam injection – $8-$20 per square foot
Mudjacking is usually the most affordable option for lifting settled slab areas. Slabjacking costs more due to drilling access holes. Foam injection is often the most expensive due to the proprietary equipment and chemicals required.
However, costs for any method can vary significantly based on:
- Size of area being lifted – larger areas tend to cost less per sq ft
- Amount of lifting required – 1″ may cost around 50% less than 3″ of lift
- Site accessibility and conditions
- Local contractor rates and competition
It’s best to get multiple bids from qualified contractors to find the most competitive pricing. And keep in mind that foam injection is often faster with less mess, which can offset some of the higher costs.
When Foam Injection Excels vs. Other Methods
While foam lifting may not always be the most affordable choice, there are certain situations where it really excels compared to alternatives like mudjacking:
- Faster lifting when project time is limited – foam takes hours, not days to inject
- Areas with numerous treatment points – foam requires fewer access locations
- Concrete with decorative finishes – foam causes less surface distortion
- Irregular slab settlement – foam fills voids better than grout-based methods
- Elevated slabs – foam injection is less invasive for raised patios or walkways
- Environmentally sensitive areas – foam causes less runoff issues
In contrast, mudjacking and slabjacking may be better choices when:
- Budget is very tight – grout injection is usually most affordable
- Large slabs with minimal access points
- Settlement exceeds 3 inches – foam has limited lift height
- Deep voids exist under the slab
- Soil conditions are very porous or shifting
Assessing the specific characteristics of your project and slab damage can determine which method will provide the most effective, long-lasting repairs. An experienced contractor can recommend the best options.
Example Project Comparison
To illustrate cost and application differences, let’s compare quotes on a sample project:
* Slab: 4-inch thick patio slab, 400 sq ft
* Problem: 2 corners settled 1.5 inches from frost heave
* Goal: Lift settled areas back to level
| Method | Price Estimate | Time to Complete | Notes |
|---|---|---|---|
| Mudjacking | $1600 | 2 days | 2 access pits dug, re-landscaping needed after |
| Slabjacking | $2000 | 1 day | 10-12 holes drilled, some slab damage |
| Foam injection | $2400 | 4-6 hours | 6 holes drilled, less invasive, fastest lift |
In this example, foam injection is the fastest option with minimal disruption, despite being the most expensive. Since speed is critical and there are access limitations, it excels over the other methods.
Finding Certified Foam Lifting Contractors
If you determine foam injection is the best solution for raising your settled concrete slab, it’s essential to hire a qualified professional. This is not a DIY project. Here are tips for finding certified foam lifting contractors:
- Ask about training and certifications – look for approved installers trained by the foam system manufacturer
- Verify necessary licenses and insurance are up to date
- Request references from past jobs lifting concrete slabs
- Review examples of their work through before/after pictures and videos
- Get multiple quotes to compare costs
- Ask lots of questions upfront to ensure the process is fully understood
Reputable foam lifting contractors should offer free site inspections and quotes as part of their bid process. This on-site evaluation is crucial for assessing the current slab condition and making corrective recommendations. Only experienced contractors should be considered for this specialized injection work.
Conclusion
While concrete lifting foam comes at a higher cost than mudjacking and slabjacking, it offers a faster and less invasive process for raising settled exterior slabs. When site conditions and access limitations call for minimal disruption, foam injection can lift concrete back into position within just hours. And the foam provides lasting support to prevent the slab from sinking again. Just be sure to use a certified professional trained in foam lifting applications for optimal results. Considering all repair options before deciding on the best method for your specific concrete slab issues will lead to long-lasting, effective repairs.