Concrete Lifting: High-Density Geotechnical Polyjacking
Concrete lifting is the process of injecting high-density, closed-cell polyurethane foam beneath sunken concrete slabs (driveways, warehouse floors, sidewalks) to level them. By utilizing the same high-pressure “proportioner” technology used for insulation, we can exert thousands of pounds of lifting force with surgical precision.
1. How the “Lift” Works
Unlike traditional “mudjacking” which uses a heavy slurry of sand and cement, polyjacking uses the expansion of the foam itself to do the work:
- Small-Bore Access: Holes as small as 5/8-inch are drilled through the concrete.
- Injection: The two-part geotechnical foam is injected. It initially flows like a liquid, seeking out the “voids” or soft spots in the soil.
- Expansion: Within seconds, the foam expands and hardens. Because it is high-density (2.5 to 6.0 lbs), it creates enough upward pressure to lift the slab.
- Seal: The foam is hydrophobic (waterproof), meaning it won’t wash away or erode like soil or mud.
2. Fire Safety & Utility Penetrations
When lifting slabs inside a building or against a foundation, fire code compliance remains a priority:
- The “Void” Risk: Voids under a slab can act as a horizontal plenum for gas or smoke. Filling these with high-density foam eliminates those pathways.
- Proximity to Utilities: Often, concrete settles around floor drains or conduit penetrations. When lifting these areas, ensure the geotechnical foam does not compromise the existing through-penetration firestop assemblies.
- Internal Applications: If used to lift an indoor warehouse floor, the foam must be assessed for its contribution to the “fire load” of the building, though it is typically protected by the non-combustible concrete slab above.
3. Material Specifications: Geo-Foam vs. Insulation Foam
You cannot use standard wall insulation for concrete lifting. The “Geo-Foam” used in polyjacking has different chemical properties:
| Property | Geotechnical Foam | Insulation Foam |
| Compressive Strength | 60–100+ psi (Structural) | 15–25 psi (Thermal) |
| Reaction Time | Very Fast (5-10 seconds) | Moderate (20-30 seconds) |
| Hydrophobicity | 100% Waterproof | Water-resistant |
| Fire Rating | Class A / Class 1 (Usually) | Class A / Class 1 |
Export to Sheets
Frequently Asked Questions (FAQ)
Is the foam used for concrete lifting flammable?
Geotechnical foam contains fire retardants and is typically rated Class A (per ASTM E84). However, its primary “protection” is its location. Being encased under a 4-inch thick non-combustible concrete slab provides an inherent “thermal barrier” that protects the foam from ignition.
Can polyjacking foam damage underground gas or electric lines?
If installed by a professional using a monitored spray foam machine, the risk is low. The foam follows the path of least resistance (voids). However, before any lifting near a building, “Call Before You Dig” (811) and utility mapping are essential to ensure the foam doesn’t encapsulate and potentially stress utility lines.
Does the foam produce toxic fumes?
Once the foam is cured (which takes about 15–30 minutes), it is inert and environmentally safe. It does not off-gas or leach chemicals into the soil or groundwater, making it safe for use near building foundations.
Will the foam melt if there is a fire on top of the concrete?
Concrete is an excellent insulator. For the heat of a fire to reach and melt the foam beneath a standard slab, the fire would have to be intense enough to cause structural failure of the concrete itself.
Can this foam be used to seal fire-rated floor penetrations?
No. While geotechnical foam is dense and flame-retardant, it is not a “Firestop.” If a pipe passes through the slab you just lifted, you must use a UL-listed firestop sealant or collar at the surface to maintain the floor’s fire rating.
Why Trust Firestopping.com for Structural Repairs?
We understand the chemistry of polyurethane. Whether we are stopping fire in a wall or lifting a 10-ton slab, we use only the highest-grade, fire-rated resins and precision-calibrated equipment.