Cracks in the walls near windows and doorways, or sinking and sloping floors, may be early indicators that you are experiencing problems with your home's foundations.
Underpinning can help to address this building issue, which can occur when soil becomes too wet or dry, affecting the foundation structure. The process of underpinning strengthens a building's foundations and there are several methods to consider.
Two of the most popular methods include concrete underpinning and resin injection. Both are proven, yet very different, engineering procedures. In this blog post, we explain the difference.
This traditional method has been around for more than 100 years. The basic premise of concrete underpinning is to increase the depth of the foundation to extend it to stonger soil.
It involves digging holes beneath the home or building and pouring concrete into the spaces in accordance with the project specific plan. The concrete is then left to set, essentially creating a new foundation beneath the existing one.
Benefits of concrete underpinning:
- This is a proven engineering technique
- It is commonly used for small underpinning jobs
Disadvantages of concrete underpinning:
- It can be a slow process
- It involves excavation, which can be messy. If excavation is required under the existing foundation, you may be unable to use parts of your home
- It is labour intensive, which can increase costs for larger jobs
- The deeper soil is not always stronger. Combined with this, the area of the concrete underpins is often less than the area of the strip footing – which might support a longer wall, for example. So the actual bearing capacity of new underpins can be less than that of the building's original footing
- In reactive clay soils, the use of traditional underpins creates differential movement between the underpinned sections of the structure and the rest of the structure. AS2870, the Australian Standard for Residential slabs and footings, advises traditional underpinning should generally be avoided when the problem is related to reactive clays.
Resin injection underpinning
This is a more modern but still proven method of underpinning and strengthening building foundations. It involves injecting environmentally-friendly resin into the foundations through small holes. The resin flows into the soil and expands as it gels, placing pressure on the ground and compressing the surrounding soil. It also fills voids and cracks. As more resin is injected, it will eventually lift the house or structure above.
The process is closely controlled by practised technicians who monitor injection using special precision instruments, usually laser levellers. The resin formula is carefully mixed to suit unique weather and soil conditions.
Benefits of resin injection:
- It's clean – there's no need to excavate, which means no dust or water
- It's quick, with most projects completed in a day or two
- You can usually stay in your home and won't need to move much furniture
- It's a 30 year world-wide proven method for strengthening foundations and protecting the future of your most important asset.
Learn more about Mainmark's patented Uretek® structural resin injection technology here.
James O'Grady is the Sales and Business Development Manager at Mainmark. He is a civil engineer with 25 years' experience in structural engineering, construction materials and ground treatment.