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Underpinning versus resin injection: choosing the right underpinning solution for foundation issues

Underpinning vs. Resin Injection. What is the Best Foundation Solution

With unique climates and landscapes, homes in Australia and New Zealand face diverse ground conditions that can cause subsidence, affect building foundations and result in structural issues.

While most issues are due to unstable ground, extreme weather conditions, including drought and floods, can be common contributors to subsidence.  Other factors, such as leaking pipes or inferior concrete foundations, can also be a cause.

The first tell-tale signs of subsidence often appear in the home as cracks in walls, sinking or sloping floors, or doors and windows that won’t close.  While minor cracks are not usually caused for concern, large cracks and misaligning doors and windows can be signs of something more serious and should not be ignored. Cracks that are wider than 5mm or big enough for you to insert your little finger in them or zig-zag/stepped cracks in the brickwork which usually follow the mortar lines, are big indicators of possible structural problems.

While the anticipated cost to rectify foundation damage may seem prohibitive, the rectification costs do increase over time as the situation gets worse and not addressing the issue can significantly devalue the property.  There are several solutions to consider, including traditional methods like concrete underpinning and the more cost-effective, non-invasive resin injection solution to help resolve structural problems.

Concrete underpinning: an expensive, labour intensive process

Historically, concrete underpinning has been the go-to solution for strengthening foundations affected by soil subsidence. This tried and tested method has been used for more than 100 years, however, it is a costly and time intensive process that can take weeks to complete.  It’s also inconvenient for homeowners who are generally required to vacate their home while the work is being completed.

Depending on the extent of the issue, homeowners may also need to consult with external engineers and gain appropriate council permits before commencing the underpinning work which can add weeks to the project.  Once work begins, cement trucks and other heavy vehicles will need to transport concrete, tools and machinery onto the site, adding further disruption and chaos.  Homeowners may also find that existing plants and landscaping are damaged around the home’s perimeter.

THE UNDERPINNING PROCESS:

  • Excavation: heavy machinery is required to dig large holes under the home, with extensive digging to depths often up to 3 metres.
  • Soil removal: large quantities of dirt and rock are loaded onto dump trucks and transported away from the site.
  • Pouring concrete: filling the holes or “piers” with concrete can be complex and logistically challenging depending on the site (a typical suburban home may require as many as 24 concrete pours to fill the piers), and concrete mixers will need access to the site.
  • Curing time: concrete can take several days to set, depending on circumstances including the weather, adding more days to the project timeframe.

Resin injection: a faster, smarter, less-invasive solution

If concrete underpinning sounds logistically and economically unfeasible, there is good news for homeowners concerned about the structural integrity of their home.  Modern resin injection solutions can be used to successfully remediate homes affected by subsidence in significantly less time than it takes for traditional concrete underpinning.

Mainmark’s proprietary Teretek® engineered resin injection solution is a proven, cost-effective and quick alternative to more invasive methods. Using a process similar to keyhole surgery, the work can often be completed in one day.  It is widely used to strengthen foundations, re-level buildings and remediate issues for residential, commercial, industrial, mining and infrastructure projects.

THE RESIN INJECTION PROCESS INCLUDES:

  • Initial site inspection: The Mainmark expert arrives on site for an initial consultation to carefully assess the property, identify the optimum resin injection points and provide a quote.
  • The Mainmark ‘rig’: On the day, Mainmark technicians arrive on site, typically in a single truck or ‘rig’ which contains all the equipment required to complete the project.  There is no need for messy excavators or concrete trucks on site and the team work quickly and discreetly.
  • Resin injection: Once the home’s services have been located and resin injection points have been determined, Teretek® is applied through tiny holes, typically 6mm to 16mm in diameter. The resin expands in the ground within minutes, instantly placing pressure on the ground and compressing the surrounding soil. The home is constantly monitored using laser levels. Once the resin is in the ground, it remains inert and does not break down. The process is clean and quiet, has minimal impact on homeowners or neighbours, and leaves gardens and landscaping undisturbed.

Resin injection strengthens and improves the ground beneath a structure. By using Mainmark’s Teretek® resin injection solution homeowners will experience immediate results:

  • Windows and doors will work properly again
  • Gaps between skirting boards and sunken floors will realign

The key thing to remember is that only underpinning experts are qualified to treat structural issues. Always choose a professional that is willing to work with you to ensure the fix does not cause more extensive damage than the original problem.

Typical Costs of Underpinning

The average cost of underpinning a house in Australia varies.

The final price will depend on the abovementioned factors, including the property size and the damage’s extent.

Resin injection underpinning is typically more cost-effective compared to traditional methods, and it can often be completed within a day, making it a popular choice for homeowners looking for a quick and efficient solution.

The cost of underpinning varies based on factors like the method used, soil conditions, and project size. Here’s a general breakdown:

  • Mass Concrete Underpinning: $1,000 – $3,000 per meter.
  • Beam and Base Underpinning: $1,500 – $3,500 per meter.
  • Mini-Piled Underpinning: $10,000 – $20,000 per pile (depending on depth).
  • Resin Injection: The cost of underpinning a house using resin injection varies based on the size of the property and the extent of foundation damage. However, resin underpinning is generally more cost-effective compared to traditional methods due to its efficiency and lower labour requirements.

Mainmark provides underpinning services in SydneyMelbourneBrisbanePerthAdelaideCanberraHobartTasmaniaNSWQueenslandVictoriaSouth AustraliaWestern Australia.

 

Refer to this page for price inquiries.

Underpinning Frequently Asked Questions
What is underpinning?

Underpinning a house foundation is the process of strengthening an existing foundation, usually when it has become unstable or is no longer capable of supporting the structure. This process is typically performed when there are signs of foundation settlement or shifting, such as cracks in the walls, uneven or sinking floors, or doors and windows that no longer close properly. Mainmark provides underpinning in, Canberra, Hobart, Townsville  NSW, QLD, SA, WA, Tasmania, Victoria plus the major cities of Sydney, Melbourne, Perth, Adelaide, Brisbane, Newcastle

What is chemical underpinning?

Chemical underpinning, also referred to as resin injection and is an innovative non-invasive solution used to provide ground improvement and enhance the load-bearing capacity of a structure’s foundation.

This method is particularly useful in situations where the foundation soil has insufficient strength or when the soil’s characteristics have changed over time, reducing its ability to support a structure.

What is the underpinning procedure?

The underpinning procedure involves a series of steps designed to strengthen or stabilise the foundation of an existing building. The exact procedure can vary depending on the method of underpinning chosen (e.g., mass concrete, mini piles, etc.) and the specific needs of the building.

What does a house need underpinning?

Underpinning is a method used to strengthen  the foundation of a building, often when it has been compromised due to soil movement, settling, or other structural issues. Identifying the need for underpinning early can prevent further damage and more expensive repairs. Here are the key signs that may indicate the need for underpinning:

1. Visible Cracks in Walls or Foundation

  • Large or Growing Cracks: If you notice large cracks, especially those wider than 1/8 inch, that continue to grow over time, this could indicate a shifting or settling foundation. Cracks may appear in walls, ceilings, floors, or the foundation itself.
  • Diagonal Cracks: Cracks that appear at an angle, especially near doors, windows, or corners, may be a sign of foundation movement, requiring underpinning to stabilize the foundation.
  • Step Cracks: Cracks that follow the mortar lines in brick or masonry walls can signal a shifting foundation, often seen in older buildings.

2. Uneven or Sloping Floors

  • Sagging or Sloping Floors: If you notice that floors are uneven, sagging, or slope in certain areas, it could indicate that the foundation is settling unevenly, which may require underpinning to correct.
  • Bouncing Floors: Floors that feel bouncy or unstable, especially in areas near walls or corners, can be a sign that the foundation is not providing proper support.

3. Sticking Doors and Windows

  • Difficulty Opening or Closing Doors and Windows: If doors or windows start to stick or fail to close properly, this could indicate that the house is shifting or settling, causing misalignment of door frames or window frames.
  • Gaps Around Doors/Windows: If gaps develop around doors or windows (for example, at the top or bottom), it can also signal that the foundation is moving, which may require underpinning.

4. Cracking or Bowing Walls

  • Bowling Walls: If interior or exterior walls start bowing, bulging, or leaning, this could suggest that the foundation is not providing enough support, especially in cases of moisture-related expansion or soil instability.
  • Severe Wall Cracks: If the cracks are large and running horizontally across walls, this is often a serious sign of foundation instability, indicating the need for underpinning.

5. Gaps Between Walls and Ceilings or Floors

  • Separation Between Walls and Ceiling/Floor: If there is noticeable separation between walls and the ceiling or floor, it may indicate that the foundation is shifting or settling unevenly, which could require underpinning to stabilize the structure.

6. Sinking or Settling of the Structure

  • Uneven Settlement: If different parts of the house are sinking or settling at different rates, it can cause the structure to become unlevel and may be a sign of foundation issues.
  • Visible Foundation Movement: You may notice that the foundation itself has settled, cracked, or shifted, which can be a clear indication that underpinning is necessary to restore stability.

7. Water Damage or Drainage Issues

  • Water Pooling Around the Foundation: If water is pooling around the foundation or basement, it could indicate that the soil is moving or shifting, which can weaken the foundation and may lead to further settling. Proper drainage and underpinning may be needed.
  • Flooding or Dampness in the Basement: Excessive moisture in basements, whether from leaking pipes or poor drainage, can cause soil erosion around the foundation, resulting in structural problems that may need underpinning to address.

8. Foundation Settling Due to Soil Issues

  • Expansive Soils: If the foundation is built on expansive soils (clay soils that expand when wet and shrink when dry), these can cause significant foundation movement. If the soil under the foundation is unstable, underpinning may be required to prevent further damage.
  • Erosion or Soil Compaction: Soil erosion or inadequate compaction during construction can lead to uneven settling of the foundation. If the foundation is no longer resting on solid soil, underpinning may be necessary to provide stability.

9. Cracks in Exterior Features

  • Cracks in Brickwork or Masonry: Cracks in the exterior brickwork, especially vertical or diagonal cracks, can be a sign that the foundation is shifting, requiring underpinning to prevent further structural damage.
  • Misalignment of Exterior Elements: If exterior elements like chimneys, porches, or patios begin to lean, shift, or crack, it may indicate foundation issues that underpinning can address.

10. Soil Settlement or Foundation Inspection Reports

  • Professional Foundation Inspection: If a structural engineer or foundation expert has examined your home and recommended underpinning, this is a clear sign that action is required.
  • Soil Movement: If there is evidence of soil settlement in the surrounding area (such as soil erosion, soil shrinkage, or noticeable soil displacement), underpinning may be necessary to ensure the foundation remains stable. 
What are the different types of underpinning?

There are several methods of underpinning, each suited to different types of foundation problems, soil conditions, and the overall structure of the building.

The main types of underpinning are designed to strengthen a foundation, usually by extending or deepening it to more stable soil layers.

1. Mass Concrete Underpinning

2. Beam and Base Underpinning

3. Mini-Piled Underpinning

4. Screw Pile Underpinning

5. Underpinning Using Concrete Pilings

6. Resin Injection Underpinning (Chemical Injection)

7. Jet Grouting Underpinning

8. Pile and Slab Underpinning

9. Underpinning by Structural Slab Extension

What are the alternatives to underpinning a house?

The main alternatives to traditional underpinning are resin injection and screw piles.

Resin injection strengthens the soil beneath the footing by compacting the ground. Screw piles extend the footings to a deeper layer of soil.

What is the cheapest method of underpinning a foundation?

The cost to underpin a footing can vary significantly, and depends on the method adopted, soil condition, accessibility to the failed footing and proximity of other buildings and pavements to the work area.

Traditional underpinning is labour intensive and involves large excavations, so its price does depend on how busy the contractor is. Resin Injection and screw piling have more stable prices.

How much does underpinning cost?

The cost of underpinning a house using resin injection varies based on the size of the property and the extent of foundation damage.

However, resin underpinning is generally more cost-effective compared to traditional methods due to its efficiency and lower labour requirements. You can expect the average residential underpinning job cost to be anywhere between $4,000 and $15,000*. 

Contact us for a personalised quote based on your property’s needs.

How long does it take to underpin a house?

Traditional underpinning required digging holes next to the footing and then filling them with concrete.

The excavation of the holes can take some time and will impact gardens and paths as they will be removed.

Traditional underpinning could take a few days for a single underpin to several weeks.

How long does underpinning last?

Concrete underpins if well-constructed using sound concrete should last more than 50 years.

Is resin injection as good as underpinning?

Resin injection is different to underpinning.

Resin injection involves strengthening the ground beneath the footing, whereas underpinning involves extending the footing to a deeper layer of soil. See the following  news article for a more detailed explanation. What’s the difference between concrete underpinning and resin injection?

What are the dangers of underpinning?

There are several pitfalls when using concrete underpins.

In reactive clay soils, if only part of the footing is underpinned then there will be differential seasonal movement between the underpinned sections of the footing and the rest of the footings.

This difference in seasonal movement will result in large cracks forming in the walls adjacent to the areas that have been underpinned.

Another problem that arises with traditional underpinning is poorly compacted soil adjacent to the underpin acts as a water path to the underside of the underpin and can undermine the underpin.

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© 2025 The Mainmark group of companies. ‘Mainmark®’, ‘Terefil®’, ‘Terefirm®’ and ‘Teretek®’ are trademarks of the Mainmark group of companies.

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