However, resin injection is not always the right solution for every property. The best repair method depends on the cause of the movement, the soil conditions, the foundation type, the severity of settlement and whether the movement is still active.

For many Australian homeowners, the main concern is simple: “Do I need traditional underpinning, or is there a less disruptive way to repair my sinking foundation?”

Mainmark has provided ground engineering and foundation repair solutions since 1989, helping homeowners address issues caused by ground movement, house subsidence, reactive soils, voids and foundation settlement. Depending on the site conditions, Mainmark’s non-invasive resin injection, ground improvement and house re-levelling solutions may reduce the need for disruptive excavation or traditional underpinning.

Resin injection may be a suitable alternative to underpinning when the problem is related to weak ground, voids, localised settlement, slab sinking or loss of support beneath part of the home.

It can be particularly useful where targeted ground improvement, void filling, slab lifting or house re-levelling is required without major excavation.

The important point is this: resin injection and underpinning do not solve every foundation problem in the same way.

Traditional underpinning generally focuses on adding deeper or stronger support beneath existing foundations. Resin injection focuses on improving the ground beneath the structure, filling voids and, where suitable, helping lift and re-level affected areas.

So, which one is better? The answer depends on what is happening under your home.

Traditional underpinning is a foundation repair method that usually involves excavating beneath existing footings and installing new structural support, often using concrete.

It is commonly used when existing foundations need deeper support or when structural loads must be transferred to more suitable ground.

For some homes, underpinning may be the correct repair method. However, it can involve excavation, access challenges, longer project timeframes and disruption around the property.

Common considerations with traditional underpinning include:

• Excavation around or beneath the home
• Removal of soil near existing footings
• Concrete works and curing time
• Potential disruption to landscaping, paths or driveways
• Engineering design and approvals in some cases
• Longer repair timeframes compared with some non-invasive methods

No. Not every sinking house needs traditional underpinning. Some homes may be better suited to resin injection foundation repair, ground improvement, void filling or house re-levelling, depending on the cause and extent of the movement.

Resin injection foundation repair involves injecting an engineered expanding resin into targeted areas beneath a slab, footing or structure.

As the resin expands, it can help fill voids, improve ground support and, in some cases, lift and re-level settled areas. Mainmark uses advanced resin injection solutions, including Teretek®, for applications such as ground improvement, house re-levelling, slab lifting and void filling where site conditions are suitable.

For homeowners, resin injection is often appealing because it is generally less invasive than traditional excavation-based repairs. Injection points are usually small and targeted, which can help reduce disruption to the home, garden, driveway or surrounding areas.

How does resin injection help a sinking foundation?

Resin injection can help by improving support beneath the affected area. If voids have formed or the ground has weakened, the expanding resin can be injected into the ground to fill spaces, compact surrounding soils and support the structure above.

Both resin injection and underpinning are used in foundation repair Australia-wide, but they work in different ways.

Excavation and disruption

Traditional underpinning usually requires excavation. Resin injection is generally non-invasive and often completed through small injection points.

For homeowners, this may mean less mess, less disturbance and a shorter repair process, depending on the property.

Speed of installation

Underpinning can take longer due to excavation, concrete works and curing time. Resin injection can often be completed more quickly, particularly for localised settlement, slab sinking or void filling.

Suitability

Underpinning may be required where deeper structural support is needed. Resin injection may be suitable where the issue relates to weak ground, voids, localised settlement or loss of support beneath a slab or footing.

Ground improvement

This is where resin injection can be especially useful. Rather than only adding new structural elements, resin injection can help improve the ground beneath the home.

House re-levelling

Where suitable, resin injection may be used to help lift and re-level areas affected by foundation settlement. This can assist with symptoms such as uneven floors, gaps around openings and sticking doors caused by foundation movement.

Resin injection may be a good underpinning alternative when the movement is caused by localised foundation settlement, weak soils, voids, erosion, poor compaction or slab sinking.

It may be suitable for homes showing signs such as:

• Sinking slabs
• Uneven floors
• Localised foundation settlement
• Cracks in walls
• Cracks in brick walls
• Sticking doors linked to foundation movement
• Gaps around windows or doors
• Voids beneath concrete
• Loss of support under footings or slabs

Australian homes built on reactive clay soils, slab-on-ground foundations, brick veneer homes and double brick homes can all experience movement due to changing moisture conditions, drought, heavy rain, poor drainage and ground behaviour.

The key question is not simply, “Can resin injection fix a sinking house?”

The better question is, “Is the movement in this home suitable for resin injection?”

That requires a professional assessment.

Resin injection is not always the right repair method.

Traditional underpinning or another structural support solution may still be required where the foundation issue is deeper, more severe, structurally complex or outside the suitable application of resin injection.

Underpinning may be considered where:

• The home requires deeper structural support
• Existing footings are inadequate or damaged
• The movement is severe or widespread
• Loads need to be transferred to deeper, stronger ground
• Structural engineering advice recommends underpinning
• The issue cannot be solved through ground improvement alone

In some cases, a combined approach may be required. This is why it is important to avoid choosing a repair method based only on symptoms or online research.

For suitable properties, resin injection offers several practical benefits.

Reduced excavation

Resin injection usually requires minimal excavation compared with traditional underpinning. This can help protect landscaping, paving, driveways and finished areas around the home.

Faster installation

Because resin injection is targeted and non-invasive, it can often be completed faster than excavation-based repairs, depending on the scope of work.

Minimal disruption

For homeowners living in the property, reduced disruption can be a major advantage. Resin injection may allow foundation repair, ground improvement, void filling or slab lifting to be carried out with less impact on daily life.

Targeted ground improvement

Resin can be injected into specific areas where support has been lost. This makes it useful for localised settlement, sinking slabs and voids beneath structures.

Potential house re-levelling

Where site conditions allow, resin injection may help lift and re-level affected areas of a home. This can improve support beneath the structure and help address symptoms caused by foundation movement.

Foundation movement can show up in several ways around the home. One sign on its own may not mean there is a serious issue, but several signs together can suggest the home should be assessed.

Common signs include:

• Wall cracks in house interiors
• Cracks in brick walls or stair-step brick cracks
• Uneven floors or sloping floors
• Sinking slabs around the home
• Sticking doors or windows
• Gaps around windows or doors
• Cracks returning after patching
• Floors pulling away from skirting boards
• Visible movement around patios, garages or driveways

They can be. Sticking doors may be caused by humidity, paint or normal building movement. However, sticking doors combined with wall cracks, brickwork cracks or uneven floors may indicate foundation movement or settlement.

Learn more about sticking doors. 

Before deciding between resin injection and underpinning, the cause of the movement needs to be understood.

A site assessment helps identify:

• Whether the issue is cosmetic or structural
• Whether the home is still moving
• Soil and ground conditions
• Drainage or moisture-related problems
• The type and extent of foundation settlement
• Whether voids are present beneath slabs or footings
• Whether resin injection, underpinning or another method is suitable

Mainmark’s approach is to assess the site conditions and recommend a solution that suits the property, rather than assuming one repair method is right for every home.

If you suspect foundation movement, avoid focusing only on visible damage.

Patching cracks, repainting walls, replacing tiles or trimming doors may make the home look better temporarily, but these repairs do not address weak ground, voids, foundation settlement or house subsidence.

Avoid:

• Patching cracks before understanding the cause
• Trimming sticking doors without checking the frame movement
• Ignoring poor drainage around the home
• Replacing flooring over a sinking slab
• Assuming underpinning is the only option
• Assuming resin injection is suitable for every home
• Delaying an assessment if symptoms are getting worse

The best first step is to understand what is causing the movement.

Mainmark can assess your property, identify the likely cause of foundation movement and explain whether resin injection, ground improvement, house re-levelling, underpinning alternatives or another structural support solution may be suitable.

If you have noticed wall cracks, brickwork cracks, uneven floors, sinking slabs or sticking doors, contact Mainmark to arrange a site assessment and understand your repair options.