RESIDENTIAL SOLUTIONS

Chemical Underpinning

What is Chemical Underpinning?

Engineering the Ground Beneath Your Home

Chemical underpinning is an advanced ground stabilisation method that improves weak or unstable soils beneath existing foundations.

Also known as polyurethane underpinning is the process of injecting a 2-part resin under the affected area of the slab, causing a rapid expansion which fills any empty spaces (or voids) in the soil. This strengthens the soil and creates a strong base which ensures that the property will no longer sink. Using this solid base, more resin is then injected on top causing the property to lift back into the original position and returning it to a near new state.

Rather than excavating beneath your home, specially engineered expanding polyurethane resin is injected into carefully selected locations beneath the slab.

As the resin expands, it:

Fills underground voids
Densifies weak soils
Improves load-bearing capacity
Restores uniform support beneath the foundation
Can carefully re-level sections of the structure where appropriate

The result is a stronger, more stable foundation with minimal disruption to your property.

Common Signs You May Need Chemical Underpinning

Many Australian homes are built on reactive clay soils that naturally expand and contract as moisture levels change. Over time, this movement can place stress on your home's foundation, leading to structural issues that become more costly if left untreated.

If you've noticed one or more of these issues, an inspection can determine whether foundation movement is the underlying cause.

Cracks appearing in internal or external walls

Doors and windows becoming difficult to open or close

Uneven, sloping or sinking floors

Gaps forming around skirting boards, cornices or ceilings

Exterior brick cracking

Windows sticking

Visible slab settlement

Chemical Underpinning Can Be Used For

Residential Homes

House Extensions

Settlement Caused by Reactive Soil

Raft Slab Foundations

Waffle Slab Foundations

Garage

Void Remediation beneath Foundations

Internal Floor Slab

Why Choose Rectify

Engineering-Led Solutions

Every project begins with understanding the cause of the problem, ensuring the right solution is delivered—not just a temporary fix.

Proven Structural Expertise

Trusted to deliver engineered solutions across residential, commercial and infrastructure projects.

Non-Invasive Technology

Our advanced, non-invasive technologies restore structural stability with less excavation, less mess, and minimal interruption.

Long-Term Confidence

We don’t just repair today’s problem—we strengthen your asset for long-term performance and lasting value.

Whatever the cause, our underpinning services can help.

Structural Assessment

We inspect your home to identify the cause of movement and determine whether chemical underpinning is the appropriate solution.

Site Preparation

Our team identifies treatment zones, completes pre-condition surveys, verifies underground services and prepares the work area before injection begins.

Precision Resin Injection

Small injection ports are installed through the slab and engineered resin is injected at carefully controlled depths and pressures to improve the supporting soils.

Continuous Monitoring

Throughout the injection process we monitor floor levels and structural movement using precision laser equipment to ensure accurate control.

Completion & Verification

Injection points are sealed, floor levels are rechecked where applicable and comprehensive project documentation is completed.

Causes of damage:

Founding in Reactive Clay Soil

Clay soils has the ability to absorb or dispel moisture. In a wet environment, clay will absorb moisture increasing its plasticity and expanding. This causes heave in footings and structures. In contrast, in hot and dry environments, it becomes hard, brittle and non-plastic shrinking in the process. During periods of prolonged drought, the clay shrinks to the extent that the structure supported by it subsides significantly. Any other cause for loss of moisture in clay will cause subsidence and settlement, this includes trees and vegetation, or the construction of a new structure which affects the impermeability of soil beside structure.

Flooding and Water Erosion

Poor site drainage can lead to water ponding against and seeping below a concrete structure, be it a house or a warehouse slab. The water weakens soil and washes away the silt/sands from silty and sandy clays. This leads to voids and weakening of soil causing subsidence. Cracked or leaking pipes (drainage or sewer) is another cause of poor site drainage. Therefore, we recommend regular checks of all pipes for any signs of leak.

Undermining or Due to Adjoining Footing Construction

If the adjoining land to your property is vacant, and during slab preparation your footing is undermined, that is the adjoining cut is below the bottom of your footing, this may loosen soil and cause subsidence.

Load Exceeds Concrete Strength and Soil Bearing Capacity

A 150mm thick concrete slab can typically support a weight of 860kg/m2. However, the soil supporting the slab can have less support weight/bearing capacity. Once a structure or another type of load, such as a heavy vehicle, overloads this limit, the concrete begins to weaken and cracks can begin to form and soil underneath starts to settle. This creates openings for moisture to enter; weakening the underlying soil. A crack that is 5mm wide has the potential to reduce the weight capacity by up to half of its initial strength.

Poor Workmanship and Inadequate Founding

Waffle slab footing (edge and internal beams) can be supported on up to 300mm of "controlled fill". The controlled fill has a strict method of laying, and is required to be of clayey materials with 97% of moisture. We recommend that all edge ribs are trenched through this fill and founded into natural clay. However, when the ribs are founded on fill, if it hasn't been prepared as per requirements set out in AS2870 - Residential Slabs and Footings, then the fill will settle over time and the slab will subside and show signs of distress.

Protect Your Home Before Foundation Movement Gets Worse

Foundation movement rarely improves without intervention.

If you've noticed cracks, settlement or uneven floors, our specialists can determine the underlying cause and recommend the most appropriate solution for your home.