What is concrete spalling and what causes it?

Concrete spalling refers to the deterioration, flaking, or separation of the surface or outer layers of concrete. Recognizable by patches of crumbling, cracked, or missing concrete, spalling can appear on sidewalks, parking garages, balconies, facades, structural columns, and more. In commercial, municipal, or multi-unit properties, spalling not only affects aesthetics but, more importantly, can compromise safety and the long-term structural integrity of the building.

The primary causes of concrete spalling often involve the interaction of moisture and reinforcement. When water infiltrates through cracks, joints, or porous surfaces, it can reach embedded steel reinforcement (rebar). In cold climates like New England, this moisture is further subjected to repeated freeze-thaw cycles. As water freezes, it expands, putting internal pressure on the concrete and causing it to fracture or delaminate. Chloride-laden de-icing salts, commonly used in parking garages and walkways throughout Massachusetts and the Northeast, can accelerate steel corrosion by breaking down the passive layer protecting the reinforcement. When steel corrodes, it expands, exerting internal forces that crack and spall the surrounding concrete.

Other contributing factors may include poor initial installation, inadequate concrete cover over reinforcement, use of low-quality materials, and insufficient drainage that allows water to pond or migrate into structural slabs. Older concrete in historic properties or under-maintained facilities is especially susceptible as protective coatings degrade and joint sealants fail over time.

Spalling is more than a cosmetic issue. It can expose structural reinforcement, reducing overall durability and stability, allowing for more rapid deterioration and costly future repairs. For commercial and public buildings, ongoing inspections are essential to detect early signs of spalling and to identify underlying causes before they compound. Regular maintenance planning, timely patching, professional waterproofing, joint repairs, and protective coatings can help reduce the risk and extend the lifespan of concrete elements exposed to New England’s harsh conditions.

A professional evaluation is recommended to determine the appropriate repair strategy, as improper patching or surface treatments may only provide short-term relief. Effective spall repair often requires removal of damaged material, assessment of reinforcement, remediation of corrosion, and implementation of preventative waterproofing details designed for the structure’s exposure and use.