Experts in Concrete Patio installation
Seeing cracks in your concrete patio can be alarming, but not all cracks are created equal. While some are minor cosmetic issues that won’t affect safety or structure, others could signal deeper problems that need attention.
In this guide, we explain the key differences between hairline and structural cracks, how to identify each, and what action you should take depending on the type of damage.
Concrete can crack for many reasons, and not every crack is a major concern. Here’s how to identify whether the damage you see is superficial or a sign of something more serious beneath the surface.
These are extremely thin cracks, typically less than 1mm wide, and often appear shortly after installation as the concrete cures and shrinks. Hairline cracks are usually surface-level and don’t affect the strength or safety of the patio. They can be sealed for appearance and moisture resistance, but they’re rarely a structural risk.
Structural cracks are wider, deeper, or accompanied by movement. They may run through the full thickness of the slab, and can indicate a failed sub-base, ground movement, or weight-related stress. If your crack is wider than 3mm, shows uneven edges, or spans across multiple slabs, it’s likely a structural issue that needs professional assessment.
Hairline cracks tend to appear randomly and are often short or spiderweb-like. Structural cracks are more directional and can follow stress lines, such as near corners, joints, or where loads are applied. Long, straight cracks or those that intersect at corners are more concerning and suggest tension points within the slab.
If you notice a height difference across the crack, even a few millimetres, it’s a clear sign of slab movement. This is often due to poor sub-base preparation or water erosion beneath the patio. Any visible sinking or lifting indicates more than just surface cracking and should be investigated before worsening.
Cracks that allow water to enter and freeze in cold weather can widen and become structural over time. If you’re seeing moisture seepage, algae growth, or frost-related spalling around cracks, sealing is no longer enough, repair or reinforcement may be necessary to restore safety.
Not necessarily. Hairline cracks are common as concrete cures and shrinkage occurs. As long as the patio was properly laid, these small cracks are typically harmless and easy to seal.
If the crack is wider than 3mm, shows depth or movement, or continues to grow, it may be structural. Uneven surfaces or water pooling near the crack are also warning signs to investigate further.
Yes, depending on the cause and extent of the damage, options like resin injection, slab lifting, or partial replacement can restore structural integrity without a full rebuild.
Proper sub-base compaction, well-placed control joints, and using a sealer are key to preventing cracks. Avoid placing heavy loads on unsupported areas, and ensure water drains away from the patio.
Sealing is a great preventative measure for hairline cracks, but it won’t stop structural movement. If the crack is deep or recurring, further repair work will be needed to address the underlying issue.
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