Concrete spalling

Spalling is a deterioration of the concrete surface: the top film flakes, peels or crumbles, exposing the aggregate it covered. It is seen mostly on exterior and horizontal surfaces, slabs, balconies, steps, garages, sidewalks.

Common causes

freeze-thaw cycles combined with water and de-icing salts are the primary culprits. Add to that poorly proportioned or overly wet concrete, a finish that drew water to the surface (bleeding), a lack of entrained air, or inadequate curing at the time of the pour. New surfaces poorly protected against their first winter are particularly vulnerable.

Signs to watch for

a surface that flakes in patches or scales, exposed aggregate, small craters, concrete dust on the ground, rough areas that spread from one winter to the next, debris accumulating at the foot of the element.

Why you should not ignore it

spalling does not stop on its own, it progresses with every freeze cycle. As it worsens, it reduces the thickness of concrete protecting the reinforcement; once the steel is exposed to water, it rusts, swells and bursts the concrete from within. What was only a surface defect can then become an issue of durability, even capacity, on a load-bearing element such as a balcony.

What a professional assessment reveals

Surface spalling and concrete whose integrity is compromised do not have the same consequences. An assessment gauges the real depth of the damage, tells a cosmetic defect apart from ongoing degradation and documents the conditions (drainage, de-icing salts) that sustain it, a useful read during a pre-purchase inspection.