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Published on 18th January 2017

Author: Buildfix

Why do walls crack?

They're many reasons why walls crack and move. Understanding and removing the cause is an important step in tackling wall cracks.


Together with building owners, Buildfix works to solve the cause of the problem and if required, suggest remedies to put the issue right before undertaking structural repairs. 

The leading 3 causes of wall cracks

Reactive clay soils


Building movement problems leading to cracked walls can result from many factors, and a common cause is a result of differential soil movement from reactive clay and in Australia, many buildings are located on these expansive clay soils.


Reactive soils respond in a like manner to a sponge, increasing in volume with moisture gains and shrinking with moisture loss.  As long as all soils supporting your foundation experience the same volume changes, problems may not develop.  However, when a portion of these soils move differently to those under the rest of the foundation, stress can develop in the structure causing walls to crack and become unstable. 


Continual movement can cause additional structural damage elsewhere in your building and can result in costly repairs if the problem is not dealt with and movement controlled.


Tree roots


Tree roots most often do not affect buildings physically due to the location of the building, and as foundations pose too much of an obstacle there are far easier water sources elsewhere.


A Large tree nearby can have an impact on a building structural integrity by withdrawing moisture from soils below foundations causing shrinkage, especially during times of drought. This, in turn, creates voids and deteriorates soils under foundations allowing movement to occur to the foundations and in turn causes structural movement and cracked walls above.


To avoid expensive repairs it is important to remove the cause of movement and repair structural problems as they become apparent.


Poor drainage and soil erosion


Sometimes the silent assassin, water can create havoc with a building's foundation.


Water seeks the easiest way to the ocean and creates underground channels that remove and aerate soil under foundations.


As soils below the foundation become weaker gravity always wins and foundations are forced downwards causing subsidence.


To avoid the problem getting worse it is essential that drainage in and around buildings are fixed ASAP, sub-soils are stabilised, voids under foundation are filled and all structural wall cracking above ground is repaired. 

Reactive Clay Soils

Tree Roots

Poor Drainage

Other leading causes of wall cracks in Australia


  • Thermal Movement

  • Water Erosion

  • Settlement

  • Poor Workmanship

  • Vibrations from Traffic and Construction Sites 

  • Additional Loads

When & why should I repair building cracks?

Wall cracks should be repaired within 6 months of first being discovered. Delaying repairs can lead to the further movement as the direct load can add additional stress to the foundation and other areas of the building.


If movement is allowed to progress and underlying cause not rectified costly repairs such as underpinning or rebuilding walls may be required.

Concerned your house wall cracks?

If you're worried about your house cracking and need more information, we’d be happy to help.

Call Buildfix on 1300 854 115 or book a FREE inspection today.

* If you reside in NSW, ACT or southern QLD.

Head Office:

259 Darling Street, Balmain NSW 2041

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*Locations throughout NSW, ACT & southern QLD.

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