Teretek® | Voiding and subsidence


Single storey brick home | Warner, QLD

A single-storey brick residence in Warner, Queensland, was suffering from serious subsidence. The 20-year-old home on a battle-axe block was built on loosely compacted reclaimed land with reactive clay soils and its concrete slab floor had dropped up to 120mm.

The property had recently been sold to a new owner who noticed the home’s floors were uneven after moving into the property. While a building inspection report was commissioned prior to purchasing the property, the report failed to identify the uneven floors.

The owner contacted Mainmark on the recommendation of a neighbour, after learning that other homes in the area were suffering from similar subsidence and some homeowners had used Mainmark’s Teretek® resin injection technology to successfully rectify their issues.

Door frame separating from wall due to subsidence
Door frame separating from wall due to subsidence

As the property backed onto a council owned reserve where a cluster of large gum trees had been planted close to the property’s boundary, Mainmark initially suspected that the trees could have been the primary cause of the subsidence. Large tree roots are a common cause of subsidence as the roots draw out moisture from the soils, which can create voids and ground movement.

However, once Mainmark technicians began injecting the Teretek resin into the home’s concrete floor slab, they discovered significant inconsistencies of up to 300mm in the thickness of the concrete slab. The variation in the thickness of the floor slab, combined with the loosely compacted reclaimed soils and aggressive tree roots, were all found to be contributing factors that led to the severe ground subsidence.


Mainmark was required to help stabilise the home by consolidating the loose soils, fill the voids beneath the home’s concrete foundations, and subsequently lift the home’s concrete floor slab as close to level as possible.

Concrete slab separating from wall caused by settlement of loose soils and voiding
Concrete slab separating from wall caused by settlement of
loose soils and voiding


Mainmark’s Teretek Resin Injection solution, a two-in-one ground improvement and re-levelling solution, was identified as being an ideal product to address both the settlement of the loose soils and the voiding that had formed underneath the home’s concrete slab.

Teretek is an expanding polyurethane resin mix that is a highly effective solution to consolidate soils and fill voids. After injection into the ground, the components mix together and quickly expand by chemical reaction to strengthen the ground and re-level building foundations with minimal disruption. The application maximises ground support as the structure is lifted by using the controlled force of the expanded resin.

The excessive voiding under the concrete slab and the significant floor slope presented challenges for Mainmark. The substantial quantity of Teretek polyurethane resin material required was injected and the lifting process carefully monitored by the Mainmark crew. Despite the project’s complexities, a successful outcome was achieved with Mainmark strengthening the home’s foundations and filling the voids under the concrete slab, bringing the floors back to level by more than 100mm in some areas.


The Mainmark site crew did a great job to bring our home back to level. The team clearly communicated what was happening throughout the process and was meticulous in monitoring the degree of lift to minimise the risk of damage to our walls and ceilings, which we had anticipated given the degree of subsidence that had occurred.

The homeowner was relieved to know that the ground under the home is now strengthened, commenting