What Is Polyurethane Foam Injection?
Polyurethane foam injection is a versatile solution used by APS Foundation for two distinct applications: sealing actively leaking foundation cracks and lifting settled concrete slabs. Unlike rigid epoxy, polyurethane foam expands on contact with moisture, creating a flexible, waterproof seal that accommodates minor movement without cracking. For slab lifting, high-density polyurethane foam is injected beneath the settled concrete through small drilled holes, expanding to fill voids and raise the slab to its original elevation. APS does not use mudjacking. Polyurethane foam injection is a cleaner, faster, longer-lasting alternative.
How Polyurethane Foam Injection Works
Polyurethane foam is a two-component material: when the two liquid components mix at the injection tip, a chemical reaction begins that causes the foam to expand rapidly. This expansion is what gives the material its unique properties for both crack sealing and slab lifting. For crack sealing, low-pressure ports are installed along the leaking crack, and the foam is injected into the crack from the lowest port upward. As the foam expands, it fills the crack from face to face, and its expansion force drives it into hairline voids and irregular crack surfaces that would be difficult to fill with a rigid material. The cured foam is flexible, meaning it accommodates minor foundation movement without re-cracking and re-leaking. This makes polyurethane injection the correct choice for cracks with any moisture present, where epoxy bonding would be compromised. For slab lifting, a denser formulation of polyurethane foam is used. Small 5/8-inch holes are drilled through the slab at strategic locations calculated to lift the slab uniformly. Foam is injected and begins expanding immediately beneath the slab, filling any void space and exerting upward pressure on the concrete. The crew monitors elevation continuously and stops injection when the target elevation is achieved. Walk-on strength is reached within 30 minutes of injection, and there is no cure period before the slab can bear full loads. Polyurethane foam used for slab lifting is inert, non-biodegradable, and unaffected by water. It does not wash away over time, degrade in wet soil conditions, or compress under normal structural loads, making it a far superior long-term solution compared to traditional soil-cement slurry methods.
“The foam is working for you from the moment it hits that crack. It expands, forcing itself into every void, and it uses the moisture in the crack to do it. That is why we use it for leaking cracks and not epoxy.”
How APS Installs Polyurethane Foam Injection
- 1
Free On-Site Assessment
An APS inspector evaluates the crack or slab condition and determines whether polyurethane foam injection is appropriate. For slab lifting, the cause of settlement is assessed to ensure foam injection will provide a lasting result.
- 2
Port Installation or Hole Drilling
For crack injection, ports are installed along the crack. For slab lifting, 5/8-inch holes are drilled through the concrete at calculated injection points that will lift the slab uniformly.
- 3
Foam Injection
Polyurethane foam is injected through the ports or drilled holes. The foam expands on contact with moisture, filling voids and cracks or lifting the slab as it cures. The crew monitors progress in real time.
- 4
Elevation Monitoring and Completion
For slab lifting, elevation is measured continuously. Injection stops when the target grade is achieved. For crack sealing, injection continues until foam emerges from the next port above, confirming full fill.
- 5
Port or Hole Finishing
Injection ports are removed from sealed cracks. Drilled holes in lifted slabs are patched flush with the slab surface. The repaired area is ready for use within 30 minutes.
What Polyurethane Foam Injection Costs and What Is Covered
Cost Range
Crack injection: $200 to $800. Slab lifting: $800 to $4,000 depending on slab size and void volume.
Frequently Asked Questions
Why does APS use polyurethane foam injection instead of mudjacking?
Polyurethane foam injection outperforms mudjacking in every meaningful way. Foam is lightweight (mudjacking slurry can weigh as much as 100 pounds per cubic foot, adding load to already stressed soil), cures in 30 minutes vs. 24 to 48 hours for mudjacking, and is inert and non-biodegradable so it does not wash away or degrade over time. The small injection holes (5/8 inch) are also far less disruptive than the larger holes required for mudjacking equipment.
Can polyurethane foam injection fix my leaking basement wall crack?
Yes. Actively leaking cracks are the primary application for polyurethane foam injection in wall repairs. The foam expands on contact with the moisture in the crack, filling the void and creating a flexible waterproof seal. Unlike epoxy, which requires a dry surface for proper bonding, polyurethane actually uses the moisture present in the crack to initiate and sustain its expansion.
How long will the slab lifting last?
High-density polyurethane foam used for slab lifting is inert and non-biodegradable. It does not wash away, compress, or degrade under normal conditions. The longevity of the lift depends more on whether the underlying soil conditions that caused the original settlement have been addressed than on the material itself. APS inspectors will advise on any drainage or soil improvement steps that should accompany the lift.
Is polyurethane foam safe in areas near landscaping or well water?
Yes. Once cured, polyurethane foam used for construction applications is chemically inert and does not leach harmful substances. It is routinely used in environmentally sensitive applications and is considered safe for contact with soil and water.