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Why bricks crack and what causes them to crack
In short: Bricks crack when the foundation moves (reactive clay soils, leaking pipes, poor drainage, tree roots) or from movement in the wall itself (thermal expansion, brick growth from moisture, salt attack) and from poor workmanship. Hairline cracks that do not grow are usually cosmetic. Cracks wider than a few millimetres, stepped cracks through mortar joints, cracks that keep growing, or doors and windows that start to jam need a structural assessment.
Cracked bricks are a common issue in residential construction, and understanding why they happen is essential for builders and architects. By recognising the factors that cause bricks to crack, preventative measures can be taken to ensure the longevity and safety of the structure.
Foundation-related causes of cracking
Uneven foundations: changes in soil moisture can cause the house foundations to move unevenly. This often happens because of:
- Leaking pipes: excess water from leaking pipes alters the soil moisture around the foundation, causing movement and brick cracks.
- Inadequate site drainage: poor drainage around the building lets water pool near the foundation, causing soil movement and instability.
- Tree removal or root damage: removing a nearby tree changes the moisture in the soil and affects the stability of the foundation.
Above-ground causes of cracking and damage
Thermal expansion: temperature changes cause bricks, and the walls they form, to expand and contract. That movement stresses the brickwork and can crack it.
Moisture movement and brick growth: bricks absorb moisture from the air and surrounding materials and expand. It is particularly common in new buildings, and over time the growth can crack the brickwork.
Chemical reactions in brickwork: salt attack occurs when soluble salts inside the brick form crystals as they react with moisture; as the crystals grow they disrupt the brick and cause cracking and decay. Efflorescence, the white powdery deposit often seen on bricks, is mostly cosmetic but can indicate moisture movement and chemical reactions inside the brick.
Workmanship: poor construction practice leaves weaknesses in the brickwork and increases the likelihood of cracks.
Preventative measures
- Proper site planning: prepare the site well, including soil stabilisation and drainage planning.
- Moisture control: monitor and control moisture around the foundation and brickwork.
- Quality materials: use good bricks and mortar to reduce chemical reactions and water damage.
- Expansion joints: design walls with joints that accommodate movement from temperature and moisture.
- Regular maintenance: inspect regularly and address issues early.
By understanding these causes and taking preventative measures, builders and architects can create durable, long-lasting brick structures. If you are seeing cracks that are growing, stepping through mortar joints or affecting doors and windows, a structural assessment will tell you what is moving and what to do about it.
Need an assessment or a design? Request a quote or call 02 9756 1211.