Spalling is the gradual flaking, chipping or breaking away of material from the surface of concrete, masonry or natural stone. It is a form of material damage caused by frost, moisture, chemical attack or mechanical loading.
What causes spalling?
Spalling has several causes:
- Freeze-thaw cycles — water enters the material, freezes and expands, forcing fragments off the surface
- Reinforcement corrosion — in concrete, the steel reinforcement rusts, expands and pushes the concrete cover off
- Salts — de-icing salts or ground salts crystallise within the material and exert pressure
- Alkali-silica reaction (ASR) — a chemical reaction in concrete that causes internal swelling
- Poor quality — overly porous material or insufficient concrete cover
Application
Understanding spalling is important for:
- Maintenance inspections — spalling concrete or brickwork signals an underlying moisture issue
- Concrete repair — damaged concrete is cut back to sound material and repaired with repair mortar
- Facade renovation — spalling bricks or pointing are replaced
- Bridges and overpasses — spalling concrete often indicates reinforcement corrosion requiring structural repair
Prevention
- Adequate concrete cover — sufficient concrete over the reinforcement (at least 25–50 mm)
- Water-repellent treatment — hydrophobic coating on concrete or masonry
- Frost-resistant materials — use of bricks and concrete rated for freeze-thaw exposure
- Good drainage — prevent water from ponding on or against the material
Related terms
- Concrete
- Masonry
- Weathering
- Reinforcement
- Frost line
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