Practical knowledge for better construction.

Concrete can crack or spall for several reasons, and understanding the cause is essential before selecting a repair method.

Cracking occurs when stresses or movements exceed the concrete's ability to resist them. Common causes include drying shrinkage, thermal movement, settlement, excessive loading, inadequate curing and structural movement.

Spalling occurs when portions of the concrete surface break away or detach. One common cause is reinforcement corrosion. When embedded steel corrodes, the resulting expansion can generate internal pressure, leading to cracking, delamination and loss of concrete cover.

Other contributing factors include poor compaction, inadequate concrete cover, impact damage, chemical exposure and repeated environmental deterioration.

Not every crack indicates structural failure, but cracks should be assessed for their width, depth, location, movement and possible cause.

Before repairing damaged concrete, it is important to determine whether the deterioration is superficial or affects the structural integrity of the element.

A proper repair may involve removing unsound concrete, assessing and treating exposed reinforcement, preparing the substrate and reinstating the damaged area with a suitable repair system.

Where cracking, significant corrosion or structural distress is suspected, assessment by a qualified structural engineer may be necessary.

Simply covering damaged concrete with mortar without addressing the underlying cause can result in further deterioration.

Not every concrete crack or damaged area can be repaired simply by filling it with mortar.

The appropriate repair method depends on the type of damage, its underlying cause and whether the affected concrete is structural or non-structural.

For example, surface defects and localized areas of deteriorated concrete may be suitable for reinstatement using an appropriate cementitious repair mortar, provided the substrate is properly prepared and the cause of deterioration has been addressed.

Cracks require particular attention. A stable, non-structural crack may require a different treatment from an active crack that continues to move. Structural cracks may require specialist assessment and an engineered repair solution rather than ordinary mortar filling.

Where reinforcement is exposed or corroded, simply covering it with repair mortar may not prevent further deterioration. Unsound concrete must be addressed, and the reinforcement and surrounding substrate should be assessed and treated as required by the selected repair system.

Successful concrete repair therefore begins with identifying the cause of damage, removing unsuitable material where necessary, preparing the substrate and selecting a compatible repair system.

If the damage affects structural performance or involves significant cracking or reinforcement corrosion, a qualified structural engineer should assess the element before repairs proceed.