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Understanding the cause requires consideration of a large number of factors, and is the first step in making any assessment as to the seriousness and cost of repairing wall cracks.

Some of the most common causes of cracking are:

The impact of foundation soils

Some level of soil excavation is usually required when a home is first built. Depending on the type of home you have, will determine how much excavation work needs to be carried out. Some types of homes require more disruption to the soil than others in the course of their construction.

Disturbed soil will compact and settle with time, which can cause a wall to crack. This process can take months or even years to occur. Natural settling will often cause narrow vertical cracks as opposed to big jagged cracks.

Minor settling is a normal process that occurs over time. However, significant downward motion in the soil under a wall may create more serious structural faults. Significant faults can occur when soil is washed away (an example is sudden flooding or slowly over time during a gradual leak), when soil compacts too much or collapses. A powerful example of this is sink holes.

Reactive Soils

A reactive soil is a type of soil that contracts when it is dry and dramatically expands when moist. A good example of a reactive soil is clay. Examples of non-reactive soil types include bedrock, gravel and sand. To assist in identifying whether the soil on your property is reactive and could be a contributing factor to cracking, soil testing should be undertaken.

Changes occurred by nature and the environment

Intense climate and seasonal changes, such as flood and drought, can cause dramatic contraction and expansion of the soil. Wall cracking can also occur when the water table changes deep below a property.

While earthquakes and earth tremors are infrequent events in Australia, these can also contribute to wall cracks appearing.

Construction and excavation work in your area

If you live in an area where there is a lot of construction work happening, such as a new housing estate, or if you live in close proximity to a quarry then this can be the cause of wall cracking.

The vibration of heavy machinery, excessive mechanical compaction of the soil or blasting (the use of explosives to excavate) can all cause your walls to crack.

If the wall cracking appears during or following construction in your area, you should seek an urgent assessment of the cracks and legal advice.

Design or extension work

If your property was poorly designed (whether it is the initial construction or an extension which has been added), this can cause wall cracking.

The cracking can occur because of too much weight on a load-bearing wall, inferior or faulty building materials, or under-engineered footing design.

Surrounding the property

Blocked or leaking pipes, garden sprinklers or blocked gutters can all cause wall cracks as they can have the effect of saturating or even washing away soil.

Trees can also have invasive root structures that can contribute to wall cracking. It is best to only have small bushes or shrubs in close proximity to your walls. Apart from destructive roots, trees can also contribute to wall cracking by removing water from the soil and affecting the soil’s moisture content.

If you remove a large tree from an area in close proximity to your walls, this can also cause cracking as it can destabilise the soil in the space previously occupied by the root system. It can also lead to changes in the moisture levels of the soil or settling over time.


Nothing lasts forever, and building materials are no exception. Weathering, gravity, poor maintenance or rotting can all take their toll on building materials.

When building material starts to age, its structural integrity might be undermined causing it to succumb to gravity. This can cause wall cracks to appear. If steel reinforcements in concrete starts to rust and degrade following exposure to moisture and salt, this can also cause cracking.

Next steps

Don’t be complacent. Take photos and document wall cracks. We recommend including a ruler in the frame of the photo so you can easily compare and track the progress of any cracks over time.

According to QBCC Standards & Tolerances Guide 2016 and Australian Standard AS2870, cracks in concrete slabs 2mm or greater and those in masonry or plasterboard walls 5mm or greater (3mm or greater when in groups) may be deemed to be defects.

If the cracks in your walls are the sizes mentioned above, or if you have any concerns about smaller cracks, we recommend that you contact a qualified building inspector for an assessment of the possible cause and severity of the cracks in your walls. They will be able to provide you with a plan of attack and estimate the possible costs of repairs.

Protecting your family’s safety and your financial investment is paramount, and it is important that you take their advice seriously and follow through within the recommended timeframes.

Need to identify the cracks in your wall? Read our article on “Cracks in Buildings. How Serious Are They?”

Concerned about cracks in your walls? Contact BeSafe Property Inspections to discuss your wall crack concerns on(02) 9410 3740 or via our website.

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The sight of cracking can set off alarm bells in anyone considering purchasing a property, although, most properties will exhibit cracking at some point in their lives. As materials age and settle to accommodate changes in the building's environment, cracks can appear if the builder has not allowed for this environmental change by installing control or expansion joints.

While cracking is often not a great cause for alarm, affecting only the appearance, some cracking can also be a sign of a serious problem, such as the stability of the building being under threat.

Because of this, all cracking, insignificant or otherwise, should be considered seriously and checked by an expert.

What To Look Out For

Wall cracks fall into three main categories:

  • Interior wall cracks which occur in plasterboard or gyprock;
  • Exterior wall cracks such as cracks in the surface, brickwork, or in the rendering of external walls;
  • Cracks in foundation walls.

All three can be serious and signs of structural failure.

In order to assess how serious the problem really is, you need to look at the location, the type of crack, and whether there is a separation in the materials used to construct the wall or if a separation has appeared between the wall and the framework.

Cracks should also be monitored over time to see if they are smaller or bigger, or staying the same size. A crack that starts off small in size may change into a larger crack, being an indication of more significant movement to the building’s structure that will require remediation.

Shapes Of Cracks

The form and size of the crack can sometimes indicate the underlying problem. Cracking can be horizontal, vertical, stepped, cogged or a combination of all these. When assessing cracks, the width of the crack is often more important than the length of the crack.

Stepped cracks tend to follow the lines of horizontal and vertical joints in buildings, such as beds of mortar between bricks or blocks and may indicate structural movement.

Vertical cracks may indicate that structural components such as bricks or blocks have failed and so can be a sign of significant stresses within the building structure.

Cracks that are wider at the top or at the bottom may indicate that there has been foundation movement, with the direction of the widening giving an indication of the likely direction of the movement.

Horizontal cracks may indicate that an element such as a wall is failing and this may present a safety concern.

As a general rule, the following sizes and descriptions apply:

Damage to Walls caused by movement of Slabs and Footings, and other Causes*

Crack Width Limit Typical Description and Repair
< 0.1 mm Hairline cracks
< 1 mm Fine cracks that do not need repair
< 5 mm Cracks noticeable but easily filled. Doors and windows stick slightly.
5 mm to 15 mm (or a number of cracks 3 mm or more in one group) Cracks can be repaired and possibly a small amount of wall will need to be replaced. Doors and windows stick. Service pipes can fracture. Weather tightness often impaired.
15 mm to 25 mm but also depends on number of cracks Extensive repair work involving breaking-out and replacing sections but also depends on walls, especially over doors and windows. Window and door frames distort. Walls lean or bulge noticeably, some loss of bearing in beams. Service pipes disrupted.

* Guide to Standards & Tolerances 2015, Building Commission


Cause And Action

Cracks fall into 3 main categories.

Category 1: Small (Minor) Cracks - includes hairline cracks <.1 mm and fine cracks <1 mm including cornice cracks


The most common cracks you will find in buildings are hairline cracks, particularly in plaster, which is prone to shrink and is very sensitive to movement.

The main cause is often settlement of the walls onto the foundations or movement in the building associated with changes in moisture and/or temperature.


Most of the time small cracks don’t require any specific repair, as the issue is likely to only be cosmetic.

If required, you can engage a contractor to do the job but most hairline cracks can be resolved with a DIY job.

It might seem counter-productive, but first you should create a deeper hairline crack (using a screwdriver, scraper or utility knife) before starting the repair work. This “opens up” the crack so that you can clean out the loose paint, debris, concrete or old filler (using a dry brush, cloth or vacuum) before mending. This also helps the filling solution to properly fill the insides of the crack.

After cleaning the crack, fill it with filling solution/joint compound. Make sure the filler covers the entire crack.

Even out the surface with your scraper and let the filling dry out for a day. Don’t rush the process!

Once the surface has dried, sand it down so the surface is completely smooth and even.

Then apply paint. If you are applying two coats, always make sure the first coat has properly dried before applying the second coat.


Category 2:  Medium Cracks – includes cracks from 1 mm to 5 mm


Whilst aesthetically concerning, cracks up to 5mm can generally be patched and painted. In newer homes the cracking almost inevitably relates to settlement and or vibratory action from within or adjacent properties. With older properties it can be the onset of one of the key contributing factors associated with Category 3 cracking (see below).

In addition, one of the major contributors to wall cracking is when downpipes are not connected to soak wells, the concentration of water around the footings at the downpipe positions can lead to subsidence of the footings and cracking of the house walls.


The key issue with category 2 cracks is to determine significant changes over a relatively short period of time, say 6 – 12 months (or even shorter). If the cracking gets worse, preventative action should be taken sooner rather than.

If there are any significant contributory causes to the cracking, like rusting lintels or significant cracking to concrete which is facilitating water ingress, preventative action should be taken immediately. While the cracking may only be minor now, unless the underlying issue is addressed it will only get worse. Taking care of the cause is more important than fixing the crack itself.

It is also very important to monitor any changes in the crack over time. Once you become aware of a crack, your eyes will constantly be drawn to it and it can often seem like the crack is getting bigger. Photography can greatly assist with monitoring cracks. By using your smart phone or digital camera (ensuring the date stamp is turned on), you can take regular pictures of the cracking and monitor changes. It is a good idea to place a coin or ruler next to the crack as a point of reference to properly determine whether the crack is growing.


Category 3: Large (Moderate to Severe) – includes cracks from 5 mm to 25 mm


Category 3 cracks are important to address immediately as there could be a significant safety issue. There can be a range of issues which can cause severe cracking, such as:

  • Issues with footings and or concrete pads (subsidence)
  • Water ingress, moisture/damp in the walls
  • Concrete cancer and rusting lintels
  • Impact damage
  • Issues associated with the roof frame or other load bearing problems
  • Concentration of water around the footings


As a general rule, cracks within this category shouldn’t be ignored and left untreated. At the smaller end of the scale, the crack needs to be filled to avoid any potential water ingress, particularly if it is an external wall. At the other end of the scale, the wall may need to be inspected by a structural engineer to determine what remediation work is required. There is a possibility that a section of a wall needs to be rebuilt.

At the very least, an inspection by a professional and a plan of action needs to be determined – and acted upon as soon as possible.

Do you want to better understand what causing cracking? Read our article on “The Cause Of Wall Cracks”.

Concerned about cracks in your walls? Contact BeSafe Property Inspections to discuss your wall crack concerns on (02) 9410 3740 or via our website.

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