Crazing is the formation of very fine, shallow hairline cracks on the surface of concrete, typically creating a random, closely spaced pattern.
Explanation
Crazing develops due to differential shrinkage between the surface layer and the underlying concrete. It is often associated with rapid surface drying, over-finishing, or the use of high cement content mixes.
Unlike deeper cracking, crazing is limited to the surface and does not usually follow structural stress patterns. It commonly appears shortly after curing and is more visible when the surface becomes wet.
Contributing factors include premature finishing while bleed water is still present, inadequate curing, and environmental conditions such as wind or heat that accelerate moisture loss.
Although similar in appearance to map cracking, crazing is typically finer and more uniform, affecting only the top surface layer.
Why It Matters
Crazing is generally non-structural, but it can affect the surface integrity and permeability of concrete. Fine cracks may allow the ingress of moisture and contaminants, particularly in exposed or trafficked areas.
In concrete repair and finishing, preventing crazing is important to maintain durability, ensure proper bonding of coatings, and achieve a high-quality surface finish.