Most often caused by freeze-thaw cycles with deicing salt on concrete that has too little entrained air, too high a w/cm, or a top weakened by finishing in bleed water and poor curing. It starts as small patches and spreads until the coarse aggregate stands proud. Driveways and sidewalks scale most, especially in their first winter or where ammonium-based fertilizers and deicers are used.
Homeowner put rock salt on it the first winter and now the whole apron is scaling down to the stone.
The standard advice to homeowners is no salt the first winter; sand gives traction without the scaling risk.
Also heard as
- scale
- surface scaling
- flaking
Do not mix it up with
- Spalling: Spalling breaks out larger, deeper chunks, often from corroding steel; scaling is a thin surface loss.
Related terms
Air entrainment
Deliberately building billions of microscopic air bubbles into concrete so it survives freezing and thawing.
Bleed water
Water that rises to the surface of fresh concrete as the heavier solids settle.
Curing
Keeping fresh concrete moist and warm enough, for long enough, that the cement keeps hydrating.
w/cm
Water-to-cementitious-materials ratio: the weight of mix water divided by the weight of cement plus SCMs.
Spalling
Chunks or flakes breaking away from a concrete surface or edge, often from corroding rebar beneath.