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Subsidence Caused by Weak and Unstable Ground

A Sign of Subsidence

The ground beneath us is constantly moving

Subsidence is the propensity for downward ground movement, which can result in structures moving, sinking in one area or across the entire foundation footprint. Ground subsidence can cause movement of the building or structure, resulting in internal or external wall cracks, inability to open and close windows and doors, sunken floors, and more.

Equally, weak ground cannot adequately support the weight of structures, thereby causing settlement. Uneven floors, fractured floor tiles and wall cracks are all strong indicators of weak ground beneath the structure.

If a building or structure has sunk due to ground movement or weak ground, it is important to fix it right away, or risk further damage and potential hazards.

Ground instability

Weak ground under homes

As the weak ground under houses is strengthened, and sunken floors are brought back towards level, any internal and external wall cracks may close up too. Most importantly, structural damage is resolved and, with a stable foundation, the future of the house is sound.

Our deep resin injection ground improvement and foundation repair solutions are the modern answer to more traditional methods of underpinning. Compared to concrete underpinning, it’s like keyhole surgery, as the injection holes are often as small as the size of a five cent coin. Our alternatives to underpinning are suitable for slabs, strip footings, raft slabs, and ‘waffle-pod’ slabs.

Our Teretek® engineered resin solution is a method used for strengthening foundation ground. The resins and hardeners mix together and expand in the ground to compact the adjacent soils and increase their load-bearing capacity.

Another of our technologies for improving ground compaction and stability is Permeation Grouting, which can create ground cohesion before soil excavation takes place, making it a good option for soil stabilisation for swimming pools, retaining walls etc. It involves filling in cracks, joints, and other small defects in sandy soils or other porous ground with a cement-based grout.

Identifying subsidence

Subsidence is not without warning signs. Some of the most common include:

Internal cracked walls

Wall cracks are common in homes and are often the first sign of foundation subsidence. Inside the house, they appear like steps in the brickwork/blocks or tiles and typically follow mortar or grout lines. The mortar and masonry deteriorates over time due to the movement of the affected wall.

Sinking floors

A concrete floor slab within a home can sink due to weak ground or subsidence. A building can sink at various localised points or can be spread across the entire footprint of the house foundation.

Jammed doors

Doors that don’t open smoothly, have uneven gaps or rub against frames are often a first indication of foundation damage

Exterior cracked walls

Step wall cracks are common in homes and are often the first sign of foundation subsidence. The mortar and masonry deteriorate over time due to the movement of the affected wall. Wall cracks are usually of concern when one side of the wall is higher than the other or cracks are wider than about 5mm.

Sinking & uneven concrete slabs

Sinking and uneven concrete driveways or path slabs can be an indication of unstable ground due to voids beneath the surface. If there is noticeable soil building up around slab joints, the concrete slab can start to crack around the edges as weight is exerted where there is no ground support.

Articulation joints

Usually visible in building extensions where two walls join and in modern buildings at the sides of large window and door openings. The gap is often wider at the top of the joint, exposing the lining.

How to fix subsidence?

Mainmark specialises in ground improvement, re-levelling and void filling solutions. We treat the ground beneath structures to raise, re-level, and re-support.

Mainmark’s Terefil® is the most advanced structural lightweight polymer modified cementitious-based filler. It flows into spaces to fill voids, making it a fast and effective way to stabilise the ground. The patented foam used in Terefil® has increased stability, a greater lift thickness, and can be pumped greater distances. It’s a cost-effective and environmentally-inert option that suits a range of applications such as mass fill for large voids, tanks, and abandoned mines.

Permeation grouting can create ground cohesion before excavation. It’s the longest-established and most widely-used technique, which involves filling cracks, joints, and other small defects in non-cohesive soils, sand, or other porous media. It can stabilise the ground at depths of up to 60 metres.

Alternatively, Mainmark can inject our proprietary Teretek® engineered resin solution into the foundation ground under a building’s footings. The resins expand together chemically, creating pressure. That pressure lifts the building back to its correct level. Then, if there are weak layers in the ground, continuing injection at deeper levels can resolve this by compacting the ground, densifying and strengthening it to increase its bearing capacity. 

In cases of weak ground, Teretek® engineered resin improves sub-grade under existing on-ground structures including buildings, concrete floors, driveways, roads, airport runways, bridge approach slabs, bridge abutments and more. 

What causes subsidence?

There are many different causes of subsidence and various contributing factors.

All involve some change in the ground, which, in turn, generates movement of the soil.

As well, different types of ground are more affected by different conditions.

When ground has been affected, building subsidence is common. Foundations or footings are no longer fully supported, sinking due to weak ground.

Soil Types

Moisture levels in the soil affect reactive clays as they expand and contract.

Oversaturated clays lose their strength resulting in footing subsidence. In loosely packed soils, such as sand and silt, the fine particales in the soil can wash away causing the footing to settle.

Tree Roots

Neighbouring trees and shrubs absorb water using their roots causing movement in the soil as it soaks up moisture in the ground.

Footing Systems

Poor foundation design or inadequate compaction of soil during construction results in movement of the structure as it settles.

Excess Water

Burst or cracked water pipes including blocked sewage and rain gutters  can oversaturate clay soils or wash fine particles from sand and silt soils and cause footings to subside.

Extreme or Seasonal Weather

Natural disasters such as flooding, drought and earthquakes affect soil moisture levels in particular clay resulting in excessive foundation movement.

Renovation or Construction

Vibration caused by nearby construction activity such as drilling or piling, or heavy road traffic causes soil particles to shift and settle, resulting in ground subsidence.

How we get your home back to level in as little as a day.

Features & Benefits

Mainmark’s Solutions & Technologies For Weak & Unstable Ground

Fast, Surgical & Accurate

The process is accurate within a few milimteres and completed within hours compared to traditional methods.

Environmentally Inert

No effect to the surrounding soils.


Repairs are performed without the need for excavation, extensive road closures or traffic disruption.


Compared to traditional methods, our solutions are more cost-effective.

Get a quote

Arrange a site assessment in 3 simple steps:

Step 1

Submit your enquiry using our online form. Include a brief message about the type of foundation issues you are experiencing.

Step 2

Our friendly customer service team will be in touch to schedule a site assessment that suits you.

Step 3

One of the Mainmark experts will visit your home or property, assess the damage, and ascertain the likely cause. They will establish the approach needed, creating a plan specific to the needs of your building and provide you with a detailed quote.

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Mainmark Ground Engineering Pty Ltd
ABN: 51 606 182 503

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