How polyurethane foam lifts a concrete slab
The chemistry, the expansion ratio, the lifting force — and why structural foam is the best material in the world for raising sunken concrete.
It's a two-part chemical reaction
Polyurethane lifting foam is created on-site by mixing two liquid components — an isocyanate (Part A) and a polyol resin (Part B) — at the injection nozzle. Within seconds of contact, they react exothermically, releasing CO₂ that creates millions of closed cells.
That expansion is what does the lifting. The foam pushes outward in every direction with thousands of pounds of force, finding voids, filling them, and then transferring force upward into the slab.
The numbers behind the lift
- • Expansion ratio: 15–25× the liquid volume — a few cups of resin become a hockey-bag-sized block of structural foam.
- • Lifting force: 4,000–14,000 lbs/ft² depending on density.
- • Cure time: 90% of full strength in ~15 minutes.
- • Density: 2.5–6.0 lbs/ft³ — about 5% the weight of mudjacking slurry.
- • Water resistance: Closed-cell, hydrophobic, will not absorb moisture or wash out.
Why it doesn't damage your slab
Lifting force is distributed over the entire underside of the slab — not concentrated at one point. Trained crews use real-time laser monitoring to inject in small bursts, watching the slab rise mm-by-mm. The slab moves as a single rigid plate, exactly the way it was poured.