Uneven or sunken concrete can create serious safety problems, affect drainage and interrupt daily operations in warehouses, factories, driveways and other areas. Although replacing the entire concrete slab is an option, it can be expensive, time-consuming and disruptive.
PURL-SJ40 polyurethane slab-lifting foam provides a faster and more practical way to restore uneven concrete slabs. The foam is injected beneath the concrete, where it expands to fill empty spaces and carefully lift the slab back into position. In this article, we explain how PURL-SJ40 works, its main benefits and why it is a reliable concrete-lifting solution for Australian projects.
For Australian builders, civil contractors, engineers, facility managers and specialist applicators, PURL-SJ40 offers a practical option when a project requires concrete levelling with minimal demolition and disruption.
Concrete is strong, but its long-term performance depends heavily on the material supporting it. When the ground or fill beneath a slab changes, an unsupported area or void may form. Loads that were previously distributed across a stable base can then contribute to movement, cracking or settlement.
Common causes of uneven concrete slabs include:
Australia has a wide range of soil and environmental conditions. Periods of heavy rain, drought and changing groundwater conditions can all influence the ground supporting concrete. However, a lowered slab does not automatically reveal the cause. Before selecting a repair method, the site should be assessed to determine why movement has occurred and whether drainage, leaking pipes, unstable ground or another contributing issue also needs attention.
Repairing the level without understanding the underlying cause may leave the original problem unresolved. A professional assessment is therefore an essential first step in any sunken concrete repair project.
Polyurethane slab lifting also called foam jacking, poly jacking, resin injection or polyurethane concrete lifting is a process used to fill voids and raise settled concrete. Instead of removing the complete slab, an applicator creates a planned series of injection points and delivers a two-component polyurethane system beneath the concrete.
Once the components mix, the polyurethane begins to react and expand. The expanding material travels into accessible voids beneath the slab. With carefully controlled injection, the reaction can provide support and gradually lift the concrete.
The process generally involves:
The exact design, injection depth, spacing, material quantity and equipment settings depend on the project. Slab lifting is specialist work and should be performed by trained contractors who understand both the material and the behaviour of the structure and supporting ground.
PURL-SJ40 is a two-part, closed-cell polyurethane foam system designed for slab lifting and structural support applications. It is formulated with high crosslink density, heat stability, compressive strength and structural properties suited to lifting applications.
During installation, the two components are processed at a 1:1 ratio through compatible high-pressure plural-component equipment. The mixed liquid is injected beneath the affected concrete rather than sprayed onto its surface. As it reacts, it expands within available spaces below the slab.
This reaction supports the repair in two connected ways:
The foam expands into accessible gaps beneath the concrete. Filling these voids helps re-establish contact between the slab and the supporting area below it. This is important because simply lifting a slab without supporting the space beneath it would not provide a complete repair.
After filling available space, continued controlled injection can generate upward pressure. A skilled applicator monitors the slab throughout the process and introduces material in stages, allowing the concrete to be moved gradually towards the specified level.
The goal is controlled correction—not uncontrolled expansion. Levels, joints, cracks, nearby structures and service connections all need to be observed during injection. Product knowledge and applicator experience are critical to achieving an accurate result.
Concrete replacement normally requires breaking up the existing slab, removing rubble, preparing the base, installing reinforcement where required, pouring new concrete and waiting for the replacement to reach the necessary condition for service. Polyurethane concrete lifting works through comparatively small injection points, allowing much of the existing concrete to remain in place.
This can reduce demolition noise, waste, dust and interruption around an active property. For factories, warehouses, car parks and commercial facilities, avoiding unnecessary closure can be a major project advantage.
PURL-SJ40 is a fast-reacting system. According to Liquimix product information, it gels at approximately 20 seconds and expands within about 50 seconds. These figures are indicative product characteristics and actual site performance can be influenced by application conditions and equipment setup.
The rapid reaction allows trained applicators to observe the lifting response and proceed in controlled stages. It may also help projects return to service sooner than demolition and full concrete replacement, subject to the condition of the slab, the repair design and the applicator’s approval.
Once cured, PURL-SJ40 forms a closed-cell polyurethane structure. A closed-cell foam has cells that are largely enclosed rather than openly interconnected. This structure helps the cured material resist water ingress and maintain support beneath the slab.
Water management still matters. Slab lifting foam should not be treated as a substitute for repairing broken drains, managing surface water or correcting ongoing erosion. Those issues should be investigated and addressed as part of the overall remediation plan.
Although it is described as foam, PURL-SJ40 is designed as a rigid structural material for slab lifting. Its compressive strength and high-crosslink formulation allow it to support loads beneath concrete in suitable applications.
The required material and system design will depend on anticipated traffic, slab thickness, ground condition, void size and other engineering considerations. Technical advice should be obtained before specifying polyurethane slab lifting foam for critical infrastructure or heavily loaded areas.
Polyurethane foam can fill subsurface spaces without introducing the same volume of heavy cementitious material that may be used in some traditional slab-jacking methods. Where weak or settled ground is part of the concern, limiting added repair weight may be beneficial. The most appropriate repair method must still be determined from the conditions and requirements of the individual site.
PURL-SJ40 is manufactured in Australia by Liquimix under an ISO 9001-certified quality management system. Local supply and technical support can help Australian applicators discuss product selection, compatible processing equipment and project requirements with a team familiar with local construction and infrastructure conditions.
Different concrete lifting and void-filling projects require different foam systems. The recommended product depends on the slab, expected load, ground conditions, void size and project requirements.
| Application | Recommended foam |
|---|---|
| Warehouse and factory floors | PURL-SJ40 |
| Concrete driveways and access areas | PURL-SJ40 / PURL-SJ80 |
| Footpaths and pavements | PURL-SJ40 / PURL-SJ80 |
| Car parks | PURL-SJ40 / PURL-SJ80 |
| Concrete roads | PURL-SJ80 |
| Airport tarmacs and runways | PURL-SJ120 |
| Highways and transport infrastructure | PURL-SJ80 / PURL-SJ120 |
| House or building foundation slabs | PURL-SJ40 |
| Slab-on-grade structures | PURL-SJ80 / PURL-SJ120 |
| Industrial yards and loading areas | PURL-SJ40 / PURL-SJ80 |
| Void filling beneath suitable concrete structures | PURL-GP42 |
These recommendations provide general guidance only. Not every cracked, damaged or uneven slab is suitable for foam lifting. Product selection should be based on a professional site assessment, including the slab condition, expected loads, ground stability and the cause of settlement. An engineer or qualified contractor should confirm the appropriate repair method and foam system for each project.
Choosing between concrete lifting and replacement is a project-specific decision. Replacement may be appropriate when the slab itself has failed, reinforcement is badly deteriorated, extensive reconstruction is planned or the concrete cannot be returned to service safely.
When the slab remains suitable for retention and the main problem is loss of support or settlement, PURL-SJ40 slab lifting may offer several practical differences:
| Consideration | PURL-SJ40 polyurethane lifting | Full concrete replacement |
|---|---|---|
| Existing slab | Retained where suitable | Demolished and removed |
| Access | Small planned injection points | Large work area required |
| Waste | Generally less demolition waste | Broken concrete must be removed |
| Disruption | Often lower | Usually greater |
| Project time | Rapid injection and reaction | Demolition, preparation, pouring and curing |
| Main limitation | Requires specialist assessment and application | More extensive but replaces failed concrete |
Cost should not be judged by material price alone. Australian asset owners and contractors should also consider access restrictions, waste disposal, labour, traffic management, shutdown time and the value of keeping a facility operational. A site-specific quotation provides a more meaningful comparison than a generic price per square metre.
A successful slab lift depends on more than selecting a foam. Before work begins, applicators should review the complete site and application system.
Identify whether settlement is connected to erosion, water leaks, insufficient compaction, soil movement or another factor. Where possible, correct ongoing causes so they do not continue affecting the repaired area.
Assess slab thickness, reinforcement, crack condition, joints, loads and connections to surrounding structures. A slab that is badly fragmented may not respond as one controllable unit during lifting.
Injection work can interact with underground utilities, drainage and other concealed infrastructure. Applicable plans, detection procedures and site controls should be used before drilling or injecting.
Hole locations, injection depth, staging and monitoring should be planned for the actual void and lifting objective. Liquimix publishes general guidance, but fixed spacing or depths should not be copied from one project to another without site-specific assessment.
PURL-SJ40 is processed as a two-component material at a 1:1 ratio and requires suitable high-pressure plural-component proportioning equipment. Liquimix identifies compatible Graco Reactor configurations, including the E-10HP and E-XP2, for consideration. Applicators should confirm the complete machine configuration, temperature, pressure and handling requirements against the current technical data sheet and equipment guidance.
Fast reaction is useful, but it also demands precision. Injecting too much material in one location can over-lift the slab or create unwanted stress. Small, controlled injections with continuous level monitoring help the applicator manage movement.
Polyurethane components are industrial chemicals and require appropriate training, personal protective equipment, ventilation, storage and handling. Applicators must follow the current safety data sheets, technical data sheet, equipment instructions and Australian workplace requirements.
PURL-SJ40 provides a fast and practical way to lift uneven concrete and fill underground voids. By retaining the existing slab where suitable, the system can reduce demolition, waste and disruption across residential, commercial, industrial and civil projects.
Every site is different, so the cause of the concrete movement should be identified before work begins. Professional assessment, compatible equipment and trained application are essential for achieving a safe and reliable result.
Want to know whether PURL-SJ40 is suitable for your project? Contact Liquimix today for product information, technical advice and applicator support.
