Concrete Damage 101: Spalling

Concrete spalling is the breaking away of concrete, often exposing reinforcing steel. It commonly results from corrosion, moisture, freeze-thaw cycles, chloride exposure or failed waterproofing.

Concrete spalling is one of the most common forms of concrete deterioration found in commercial, institutional, residential, and infrastructure structures. It occurs when pieces of concrete break away from the surface, exposing deeper layers and, in many cases, the reinforcing steel beneath. 

While small areas of spalling may appear isolated, they are often a sign of underlying deterioration that should be evaluated before more extensive repairs become necessary. 

What Is Concrete Spalling? 

Spalling is the breaking, chipping, or flaking away of concrete from a structural element. Unlike scaling, which primarily affects the surface, spalling usually extends deeper into the concrete and may expose reinforcing steel. 

Spalling can occur on: 

• Parkade slabs and beams 

• Balconies and balcony edges 

• Building façades 

• Columns and walls 

• Bridge decks 

• Loading docks 

• Exterior stairs and walkways 

The severity can range from small localized patches to widespread deterioration across an entire structure. 

What Causes Concrete Spalling? 

Concrete spalling is typically caused by conditions that allow moisture to penetrate the concrete over time. 

Common causes include: 

• Corrosion of reinforcing steel 

• Freeze-thaw cycles 

• Water infiltration 

• De-icing salts and chloride exposure 

• Carbonation of concrete 

• Inadequate concrete cover over reinforcing steel 

• Poor drainage or failed waterproofing systems 

• Impact damage or structural movement 

As reinforcing steel corrodes, it expands. This expansion creates internal pressure that causes the surrounding concrete to crack, separate, and eventually break away. 

Why Does Spalling Matter? 

Spalling is more than a cosmetic issue. 

As concrete separates from the structure, it reduces the protective cover around reinforcing steel, allowing additional moisture and chlorides to accelerate corrosion. Left untreated, this cycle can lead to progressively larger repairs and reduced service life. 

Potential consequences include: 

• Accelerated reinforcement corrosion 

• Loss of concrete cover 

• Water infiltration 

• Falling concrete hazards 

• Increased maintenance costs 

• More extensive structural repairs if deterioration continues 

Addressing spalling early can help preserve structural integrity and reduce long-term repair costs. 

How Is Concrete Spalling Repaired? 

The appropriate repair strategy depends on the extent of deterioration and the condition of the reinforcing steel. 

Typical repair methods may include: 

• Removing all loose and deteriorated concrete 

• Cleaning and preparing exposed reinforcing steel 

• Replacing or supplementing reinforcing steel where required 

• Installing high-performance repair mortars or concrete 

• Applying corrosion protection systems 

• Restoring waterproofing membranes or protective coatings 

• Repairing drainage issues contributing to moisture intrusion 

In some cases, structural strengthening may also be recommended where deterioration has significantly affected load-carrying elements. 

When Should You Arrange an Assessment? 

A professional assessment is recommended if you notice: 

• Pieces of concrete breaking away 

• Exposed reinforcing steel 

• Rust staining on concrete surfaces 

• Cracks surrounding damaged areas 

• Hollow-sounding concrete 

• Water leaks through concrete slabs 

• Recurring deterioration after previous repairs 

These conditions often indicate that deterioration extends beyond the visible surface and should be investigated to determine the appropriate repair approach. 

Retro Insight 

Spalling rarely develops overnight. It is usually the visible result of years of moisture intrusion and reinforcing steel corrosion occurring beneath the surface. 

A successful repair involves more than replacing damaged concrete. Identifying and addressing the source of deterioration—whether it’s water infiltration, chloride exposure, failed waterproofing, or corrosion—is essential to achieving long-term performance. 

Early condition assessments can help identify deterioration before it affects larger areas of the structure, allowing repairs to be planned more efficiently and helping extend the service life of the asset.