“Concrete Delamination: Why the Surface Separates and Where Forming Fits In” non è ancora disponibile in Italiano

Delamination is a thin troweled crust separating from sound concrete a few millimetres below it, caused by finishing the surface before bleed water and air had finished rising. It sounds hollow or drummy when tapped. Spalling is broader flaking and chipping of the surface, often deeper, driven by reinforcement corrosion, freeze-thaw, impact, or fire. Delamination is a near-surface finishing problem; spalling is usually a deeper durability or damage problem.

The core cause is finishing (floating or troweling) before bleeding has finished, which traps bleed water and air under a sealed crust and forms a weak separation plane. It is made worse by rapid surface drying from wind, sun, and heat; by hard-troweling air-entrained concrete indoors, which drives entrained air to the surface; and by a cool or slow-setting subgrade that keeps the lower concrete bleeding longer. All of these sit on the placement and finishing side, not the formwork.

First map the full extent by sounding, since the drummy area is usually larger than the visible damage. Chip or grind the delaminated crust back to sound concrete, profile the exposed surface, then restore it with a polymer-modified cementitious resurfacer or a bonded topping for broad areas, or low-viscosity epoxy or polyurethane injection to re-bond tighter partial separations. Match the repair to the floor's loading and exposure, and cure it properly.

The clearest sign is a hollow, drummy sound when you tap the surface or drag a chain across it, compared with the sharp ring of sound concrete. Visually, look for blistering on hard-troweled floors, flaking or peeling crusts, and isolated raised domes that later crack open. A surface that looks intact can still be delaminated underneath, which is why the sounding test is the reliable way to find the full extent.