Cracks in walls are most commonly caused by foundation movement. In New Zealand, this movement is typically driven by ground subsidence, earthquake and seismic activity, reactive clay soils, moisture changes from rainfall or drought, poor drainage, or weakened supporting ground beneath the home.

When the ground shifts or settles, the foundation moves, and the walls above respond by cracking.

Some minor hairline cracks can occur as a home ages, but progressive, widening, or recurring cracks often indicate underlying foundation movement.

If left untreated, foundation-related wall cracks can worsen over time, leading to uneven floors, sticking doors and windows, and potential structural damage. Early assessment helps prevent more costly repairs later.

Structural cracks usually:

• Reappear after being patched

• Grow wider over time

• Run diagonally from doors or windows

• Appear alongside sloping floors or jammed doors

Cosmetic cracks are often thin, shallow, and stable. A professional foundation assessment is the best way to determine the cause.

Mainmark addresses the cause of the cracks, not just the surface damage.

We inject our proprietary Teretek® engineered resin beneath and around the foundation to:

• Fill voids

• Strengthen weak ground

• Lift and re-level the foundation

Once the foundation is stabilised, wall cracks can be permanently repaired cosmetically.

Yes. In most cases, Mainmark’s resin injection solution eliminates the need for traditional underpinning.

Our non-invasive method requires no excavation or demolition and is significantly faster and more cost-effective than underpinning.

Most Mainmark foundation repair projects are completed within a single day, depending on property size and conditions.

You can usually remain in your home during the works.

Yes. By stabilising and re-supporting the ground beneath your home, Mainmark treats the root cause of wall cracking. This prevents ongoing movement, helping stop cracks from returning.

Mainmark re-supports the foundation and restores structural support. After this, a builder or plasterer can repair the cosmetic cracks, knowing the movement has been resolved.

Absolutely. Reactive clay soils expand during wet periods and shrink in drought, causing homes to lift, twist, or sink,  leading to cracking both inside and outside the home.

Yes. Teretek® resin is engineered for ground improvement, environmentally inert, and used across residential, commercial, and infrastructure projects throughout New Zealand and globally.

Costs vary depending on the extent of foundation movement and ground conditions. However, resin injection is typically significantly cheaper than underpinning.

Mainmark offers professional site assessments to determine the most cost-effective solution.

No. Some cracks form from minor shrinkage or temperature changes. But significant cracks — diagonal, stepped, widening, or repeated cracks — usually point to sinking or unstable ground.

Book a professional foundation assessment with Mainmark NZ and find out what’s causing your cracks — and how we can fix them fast.

Request an Inspection Today