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Finding cracks in walls can be worrying, especially when you don't know whether you're looking at a simple plaster issue or movement elsewhere in the home. A wall crack can develop because of normal settlement, moisture, soil movement, changes in temperature or problems with plaster and Gyprock installation. Sydney homes can also face local conditions such as reactive clay soils, particularly across parts of Western Sydney, which can contribute to foundation movement. The key is to look at the damage location, direction, width and whether it's changing over time.
Yes, some wall cracks are normal, particularly fine cracks caused by small movements in building materials or normal settlement. NSW Fair Trading's Guide to Standards and Tolerances describes hairline cracks under 0.1 mm as negligible and cracks under 1 mm as very slight when assessing wall movement. However, width isn't the only factor, because the damage location, pattern and whether it's growing also matter.
If you notice body cracks in house walls, focus on what the crack is doing rather than the label used to describe it. "Body cracks" isn't a standard Australian building term, so a professional will usually assess the wall material, crack direction and surrounding movement instead.
The main types of cracks in walls include vertical, horizontal, diagonal, stair-step and hairline cracks. Vertical cracks can relate to shrinkage, joints or general movement, while diagonal cracks often appear around doors and windows where building movement creates stress. Stair-step cracks follow mortar joints in brickwork, while horizontal cracks may require closer inspection when they appear in masonry or load-bearing walls. Masonry can also crack around weaker points such as window and door openings when uneven foundation movement occurs.
No crack shape alone proves that a home has structural damage. However, diagonal or stair-step cracking in masonry, significant horizontal cracking, visible wall splitting, bulging or displacement deserve professional assessment. NSW Fair Trading classifies wall damage of around 5 mm to 15 mm as moderate and recommends investigation, stabilisation and monitoring in this category. An interior specialist will consider the crack pattern together with the condition of the wider building before determining the cause.
Foundation movement happens when one part of the ground beneath your home moves differently from another. This uneven movement can transfer stress through the building and create structural cracks in walls, brickwork, plaster or Gyprock. Differences in soil moisture, compaction, erosion and saturation can all contribute to uneven footing movement.
Cracks that keep widening, diagonal cracks around windows or stair-step cracking through mortar should receive closer attention. If foundation movement is the cause, you need to address the underlying issue before completing cosmetic plastering repair works.
A house can settle slightly after construction as the foundations and soil adjust to the building's weight. This movement doesn't always indicate a serious problem, especially when the resulting damage remains small and stable. Settlement can occur unevenly because soil beneath different parts of a building may vary in compaction and moisture. Once normal construction settlement stops, related cracking should generally stop changing as well.
A fine crack in the wall that remains unchanged may only need cosmetic repair. A damage that continues opening, however, may indicate that movement is still active and needs further investigation.
Moisture can contribute to cracking in walls by damaging plasterboard, affecting timber framing or changing soil conditions beneath the home. Roof leaks, failed waterproofing and plumbing problems can allow water into wall cavities and weaken the surrounding materials. Moisture inside a wall cavity can also be one reason Gyprock cracks continue returning.
Water can also affect clay soils around foundations, particularly when one area becomes much wetter than another. Saturation near footings can reduce soil strength, so you should repair the source of the moisture before fixing the wall surface.
Building materials expand and contract as temperature and moisture conditions change. These small movements can place stress on plasterboard joints, framing connections and wall-to-ceiling junctions over time. Sydney experiences clear seasonal temperature differences, with stronger variations in western areas such as Penrith.
Plasterboard itself remains relatively stable, but movement in the framing behind it can still produce cracks. Correctly positioned control joints can help accommodate building movement and reduce stress on plasterboard surfaces.
Not every wall crack comes from structural movement. Poor plastering, incorrect Gyprock fixing, weak joint preparation or missing movement joints can cause cracking along joins, corners and wall-to-ceiling connections. Plasterboard installation and jointing should follow the relevant Australian standards and the manufacturer's installation requirements.
Poor joint positioning and insufficient control joints can also increase the chance of plasterboard damage. Plaster and Gyprock require different repair methods, and a professional service for plastering in Sydney provides both traditional plaster finishes and plasterboard systems.
Walls can crack when structural loads aren't properly supported or transferred through the building. This can occur after renovations, the removal of a load-bearing wall or the creation of an opening without adequate structural support. A load-bearing wall carries weight from parts of the building above and transfers it into the structure below.
If wall cracking begins after structural renovation work, don't simply fill and repaint it. Have the altered area checked by a suitably qualified professional first, then repair the plaster once you've confirmed the structure is stable.
Trees can affect foundations by changing moisture levels in the surrounding soil or, in some situations, through direct root growth near footings. Trees and shrubs can dry nearby soil, causing shrinkage that may reduce support under parts of a building. Root growth can also sometimes exert pressure near foundations.
That doesn't mean every tree near a home causes cracks in wall surfaces. Soil type, tree species, distance from the building, drainage and foundation design all influence the risk, so don't remove a mature tree without first identifying the actual cause of the movement.
Reactive clay soils shrink when they dry and swell when they absorb moisture. If these moisture changes occur unevenly around a home's foundations, parts of the building can move differently and produce cracks in masonry, plaster or Gyprock. Many areas of Western Sydney contain clay soils formed from underlying shale.
Seasonal moisture changes in clay soils can affect perimeter footings before gradually extending further beneath a building. Good drainage and consistent moisture conditions around the home can help reduce extreme differences between wet and dry areas.
A plumbing leak behind a wall can damage plaster or Gyprock and may also contribute to movement if water reaches the soil around your foundations. Common warning signs include bubbling paint, staining, damp smells, softened plasterboard and a crack wall area that keeps returning after repair. Fixing the visible damage without stopping the leak means the damage is likely to continue.
Concentrated water near footings can also saturate clay soil and reduce its ability to support the structure. Repair the plumbing or waterproofing problem first, allow the area to dry and then complete the appropriate wall repair.
Older Sydney homes can contain wall systems ranging from traditional lath-and-plaster and solid plaster over masonry to later plasterboard construction. Decades of building movement, renovations, moisture exposure and material deterioration can make cracks more common, although age alone doesn't mean a wall is unsafe. Older homes across Sydney and NSW may still contain traditional lath-and-plaster and plastered masonry systems.
Sydney also has a large number of later brick-veneer homes, including housing built throughout the 1970s to 1990s. Because old plaster and modern Gyprock behave differently, the correct repair method depends on the wall system rather than simply applying filler to every crack.
Most cracks in walls don't automatically mean your home has a serious structural problem. Fine cracks can result from normal material movement, settlement or minor finishing issues, while more persistent cracks may relate to moisture, reactive clay soils, foundation movement, poor installation or ageing building materials. The most important things to check are the crack's direction, width, location and whether it's changing over time. If you're uncertain, monitor the crack and have it assessed before covering it.
If the underlying structure is sound and your wall needs professional repair, Sydney Wide Plastering provides plastering service in Sydney both plaster and Gyprock work. Call us now at 0405 847 224 or visit our contact page for emergency plastering works and repair across Sydney and surrounding suburbs!
