A sunken concrete slab isn’t just an eyesore—it’s a structural red flag. Whether it’s a driveway with a dangerous trip hazard, a warehouse floor causing forklift instability, or a residential patio pulling away from the house, uneven concrete compromises safety, function, and asset value.
The good news? You don’t need full demolition and replacement. Modern remediation techniques allow you to lift and level a sunken concrete slab efficiently, cost-effectively, and with minimal disruption.
But not all methods are created equal. Choosing the wrong approach can lead to re-settlement, cracking, or even structural failure.
At Perfect Remediation and Refurbishment, we’ve restored hundreds of slabs across residential, commercial, and industrial sites in NSW—from Albright & Wilson’s storage yards to retail tenancies in Sydney CBD. Our engineers evaluate every job on technical merit, not convenience.
In this detailed guide, we’ll compare the three primary methods used to lift and level concrete slabs in Australia:
- Mudjacking (Slab Jacking)
- Foam Injection (Polyurethane Lifting)
- Structural Underpinning & Re-slabbing
We’ll break down:
- How each method works
- Pros and cons
- Ideal use cases
- Cost and timeline comparisons
- Real project examples
- How to choose the right solution for your site
By the end, you’ll know exactly which method suits your sunken slab—and how to ensure it’s executed to the highest standard.
Why Concrete Slabs Sink: Understanding the Causes
Before comparing solutions, it’s essential to understand why slabs settle in the first place. In Australia, common causes include:
Poor Drainage & Water Erosion
Water washes away soil beneath the slab, creating voids. This is especially common after heavy rain or near downpipes, garden beds, or leaking pipes.
Inadequate Subgrade Preparation
If the soil wasn’t properly compacted before pouring, it compresses over time—especially in clay-rich areas like Western Sydney.
Tree Roots & Vegetation
Roots can displace soil or draw moisture, causing shrinkage and settlement.
Vibration & Load Changes
Heavy machinery, nearby construction, or increased storage loads can accelerate settlement in industrial zones.
Real Example: At Albright & Wilson in Wetherill Park, a new chemical storage slab began sinking due to poor compaction and drainage. We delivered a concrete slab extension with engineered subgrade to prevent recurrence. (Project: Concrete Slab Extension )
Ignoring a sunken slab risks:
- Trip hazards (liability under WHS laws)
- Water pooling (leading to leaks or concrete cancer)
- Structural stress on connected walls or foundations
- Reduced property value
Method 1: Mudjacking (Slab Jacking)
How It Works
Mudjacking involves drilling small holes (25–50mm) through the slab and pumping a cementitious grout (typically sand, cement, and water) into the void below. The pressure lifts the slab back to level.
Pros
- Lower material cost
- Proven technology (used for decades)
- Suitable for heavy loads (e.g., industrial floors)
Cons
- Heavy grout adds significant dead load (up to 100kg/m²)
- Large injection holes require patching
- Longer cure time (24–72 hours before use)
- Less precise control—can over-lift or crack brittle slabs
- Not ideal for clay soils (grout can wash away)
Best For
- Thick slabs (>150mm)
- Industrial yards, warehouse floors
- Areas with stable, non-expansive soil
Note: Mudjacking is rarely used by Perfect Remediation today due to its limitations in precision and sustainability.
Method 2: Foam Injection (Polyurethane Lifting)
How It Works
Also called polyurethane foam lifting, this method injects a two-part expanding foam through small holes (10–16mm). The foam expands 20–30x its volume, filling voids and gently lifting the slab.
Pros
- Lightweight: Adds almost no load (<2kg/m²)
- Precise control: Lifts in 1–2mm increments
- Rapid cure: Walkable in 15–30 minutes
- Minimal disruption: Small holes, no heavy equipment
- Water-resistant: Foam seals against future erosion
- Eco-friendly: Closed-cell, non-toxic, inert after cure
Cons
- Higher material cost
- Not suitable for very heavy loads (e.g., bridge abutments)
- Requires skilled technicians to avoid over-expansion
Best For
- Residential driveways, patios, pool surrounds
- Commercial lobbies, retail floors
- Heritage sites (minimal vibration)
- Areas with expansive clay soils (common in Sydney)
Real Example: At a Beaconsfield rooftop garden bed, foam injection lifted and stabilised a sunken planter slab without damaging waterproofing membranes below. (Project: Rooftop Garden Bed Remediation )
This is the most common method we recommend for light to medium-duty applications across NSW.
Method 3: Structural Underpinning & Re-slabbing
How It Works
When a slab is severely cracked, broken, or the subgrade is fundamentally unstable, full replacement may be necessary. This involves:
- Demolishing the existing slab
- Excavating and re-compacting the subgrade
- Installing drainage (e.g., agi-pipe)
- Pouring a new reinforced slab
Pros
- Permanent solution
- Opportunity to upgrade thickness, reinforcement, or slope
- Full control over materials and design
Cons
- High cost (3–5x more than lifting)
- Long timeline (1–3 weeks)
- Major disruption: Dust, noise, access restrictions
- Waste generation: Demolition debris (contradicts sustainability goals)
Best For
- Slabs with extensive cracking or spalling
- Sites with chronic drainage issues
- New builds or major renovations (via Early Contractor Involvement) (ECI Service )
Real Example: At YMCA Camden, we replaced a failing gym slab as part of a broader refurbishment—integrating new drainage and reinforcement. (Project: Gym Refurbishment )
Head-to-Head Comparison
| Cost (per m²) | $80–$150 | $120–$250 | $300–$600+ |
| Time to Use | 24–72 hrs | 15–30 mins | 7–28 days |
| Disruption | Moderate | Low | High |
| Precision | Low | High | N/A (new slab) |
| Load Capacity | High | Medium | Very High |
| Sustainability | Medium | High | Low (waste) |
| Warranty | 1–2 years | 5–10 years | 10+ years |
Key Insight: For 80% of sunken slab cases in Australia, foam injection offers the best balance of speed, cost, precision, and sustainability.
Technical Considerations: Soil, Slab Condition & Environment
Soil Type Matters
- Sandy soils: Drain quickly—voids form easily. Foam injection works well.
- Clay soils: Expand when wet, shrink when dry. Requires long-term moisture control—foam + drainage is ideal.
- Fill soils: Unstable. May need geotechnical assessment before lifting.
Slab Integrity
- Intact but sunken: Ideal for lifting.
- Cracked or broken: May need stitching with carbon fibre reinforcement before lifting. (Service: Cathodic Protection & Carbon Fibre )
- Spalling or concrete cancer: Must be repaired first. (Concrete Repairs Service )
Weather & Timing
- Avoid lifting during heavy rain (soil too soft)
- Best done in dry, mild conditions (10–30°C) for foam cure
Safety, Compliance & Environmental Impact
OH&S Compliance
All methods require:
- Edge protection (if near drop-offs)
- Dust control (especially during drilling)
- Site induction
As an AS/NZS 4801-certified company, we enforce strict safety protocols. (Certifications )
Sustainability Advantage
- Foam injection generates 95% less waste than re-slabbing
- Supports our 60%+ recycling target and Excellence in Sustainability Award (Sustainability Commitment )
- Reduces embodied carbon (no new concrete)
“We are committed to reaching our goal… by recycling over 60% of the waste material we remove.”
— NSWBC Sustainability Award
Real-World Applications from Perfect Remediation
Beaconsfield Rooftop Garden Bed
Challenge: Sunken planter slab causing drainage issues on a waterproofed roof.
Solution: Polyurethane foam injection through 12mm holes—lifted 25mm with zero damage to membrane.
Result: Restored slope, no leaks, completed in one day.
Project Details
Albright & Wilson Storage Yard
Challenge: New external slab settled due to poor compaction.
Solution: Engineered re-slabbing with compacted subgrade, drainage, and reinforced concrete.
Result: 25-year design life for chemical storage.
Slab Extension Project
City of Sydney Tenancy Make-Good
Challenge: Uneven retail floor after tenant fit-out removal.
Solution: Foam injection to level without disrupting neighbouring businesses.
Result: Floor restored to <3mm tolerance in 4 hours.
Tenancy Make-Good
These projects reflect our tailored approach—never one-size-fits-all.
How Perfect Remediation Delivers Superior Results
Engineer-Led Assessment
We start with:
- Laser level survey (to map settlement)
- Void detection (using ground-penetrating radar if needed)
- Soil and slab evaluation
No guesswork—just data-driven decisions.
Tier 1 Equipment & Expertise
- Hilti, Tyrolit, and Husqvarna for precision drilling
- Certified foam injection systems (e.g., URETEK, NCFI)
- Three workshops and 25/8 mobile technicians for rapid response (Our Approach )
“Reliability can make or break a deadline… and eventually—a relationship.”
— Equipment Philosophy
Transparency & Warranty
- Fixed-price quotes with no hidden fees
- Digital reporting with before/after photos
- 5–10 year warranties on foam injection works
FAQs: Your Sunken Slab Questions Answered
Q: Can I DIY slab lifting?
A: No. Foam and grout injection require specialised equipment and training. DIY kits often fail or cause damage.
Q: How much does it cost to lift a driveway?
A: Typically $1,200–$3,500 for a standard 40m² driveway using foam injection. (Get a Quote )
Q: Will the slab crack during lifting?
A: If done correctly—no. We lift slowly (1–2mm at a time) and monitor in real time.
Q: How long does it last?
A: 10–25 years, provided drainage and soil issues are addressed.
Q: Do you service all of NSW?
A: Yes! 12-hour response in Sydney, 24 hours elsewhere. (FAQ )
Final Recommendation: Choose Smart, Not Cheap
- For minor settlement (<50mm) on intact slabs: Foam injection is your best bet—fast, clean, and durable.
- For heavy industrial floors with stable soil: Mudjacking may suffice (though we rarely recommend it).
- For broken, spalling, or chronically wet slabs: Re-slabbing is the only long-term solution.
At Perfect Remediation and Refurbishment, we don’t push one method. We diagnose first, then prescribe—backed by 12+ years of Tier 1 experience, ISO-certified processes, and a team that “goes above, goes beyond, does more, and is better.”
Don’t let a sunken slab become a safety hazard or financial drain. Act now—before it’s too late.
Contact us today for a professional slab assessment:
Email :- info@perfectremediation.com.au
Contact us :- (02) 7912 3054 | 1300 737 332
Concrete Repairs & Remediation Services
Perfect Remediation and Refurbishment acknowledges the Aboriginal and Torres Strait Isander people as Traditional Custodians of the country on which we live and work. We pay our respects to the Traditional Custodians and Elders past, present and future, and honour their connection to the land and ongoing contribution to society.