What is Spalling? (Concrete Cancer Explained)

What is Spalling? (Concrete Cancer Explained)

Spalling is surface flaking—pieces of concrete break off, exposing aggregate underneath. It's called "concrete cancer" because it progressively worsens. Understanding what causes spalling and how to prevent it protects your concrete investment.

What is Spalling?

Spalling is the flaking or chipping of the concrete surface:

• Surface flaking: Pieces of concrete surface break off
• Exposes aggregate: Rocks become visible where surface flakes away
• Progressive: Gets worse over time if not addressed
• Cosmetic and structural: Affects appearance and can weaken concrete

What Causes Spalling?

Spalling happens when water freezes inside concrete pores.

The Freeze-Thaw Cycle

1. Water enters pores: Water gets into tiny pores in concrete
2. Freezes: Water freezes and expands (water expands 9% when frozen)
3. Expansion pressure: Expansion creates pressure inside concrete
4. Pops surface off: Pressure forces surface layer to break away
5. Repeats: Process repeats with each freeze-thaw cycle, making it worse

Why It's Called "Concrete Cancer"

• Progressive: Gets worse over time
• Spreads: Affects larger areas as it progresses
• Destructive: Damages concrete structure
• Difficult to stop: Hard to prevent once it starts

Where Spalling Occurs

• Cold climates: Where freeze-thaw cycles happen
• Horizontal surfaces: Driveways, patios, sidewalks (water collects)
• Unsealed concrete: Concrete without proper sealing
• Poor drainage: Where water accumulates

How to Prevent Spalling

• Proper sealing: Seal concrete to prevent water entry
• Good drainage: Ensure water drains away from concrete
• Air entrainment: Additives that create tiny air bubbles to absorb expansion
• Proper mix: Use appropriate mix for your climate

How to Repair Spalling

• Remove loose material: Clean out all loose concrete
• Patch with appropriate material: Use concrete patch or resurfacer
• Seal after repair: Seal to prevent recurrence

The Bottom Line

Spalling is surface flaking caused when water freezes inside concrete pores and expands, popping the top off. It's called "concrete cancer" because it progressively worsens with each freeze-thaw cycle. Prevent spalling by sealing concrete, ensuring good drainage, and using proper mix design. Once spalling starts, repair it promptly and reseal to prevent it from spreading.

Have spalling concrete? Contact Local Concrete Contractor. We can assess the damage and repair it properly to prevent further deterioration.