Delamination

Delamination describes the loss of bond between adjacent layers of a material or between a surface coating and its substrate. In building surveying and structural inspection, the term is most commonly applied to concrete (separation of a surface layer from the body of the element), render and plaster (loss of adhesion between render coats, or between render and masonry), and cladding systems (separation of panels, tiles, or facing materials from the backing structure).

Delamination differs from spalling in that the delaminated layer may not yet have broken away — it is detached or partially detached but still in place. This distinction matters for risk assessment: delaminated concrete on a soffit above a public walkway presents an immediate falling hazard even before any material has actually fallen. Surveyors use hammer sounding (tapping the surface with a hammer or coin and listening for a hollow tone) to identify delaminated areas not yet visible to the eye.

In concrete, delamination is often an early stage of the same deterioration process that eventually produces spalling. Corrosion-induced delamination typically produces a characteristic horizontal plane of separation at or just above the level of the uppermost reinforcement layer. Freeze-thaw delamination tends to affect surface layers uniformly. Thermal movement in thin cladding systems can cause progressive delamination of adhesive-fixed tiles or panels, particularly at edges and corners where movement is greatest.

Render delamination is extremely common in older masonry buildings, particularly where Portland cement render has been applied over lime-based masonry substrates. The differential movement characteristics and moisture behaviour of the two materials create shear stresses at the interface that accumulate over time.

Documenting delamination requires careful description of the affected area (extent), the nature of the separation (full or partial), and the substrate condition beneath the delaminated layer. Where access permits, probing the delaminated layer to assess its stability is standard practice. 360° photographic surveys are effective for capturing the extent of delamination across large surfaces — a panorama taken from the centre of a floor slab can capture the full soffit condition in a single image, with all delaminated regions visible and spatially referenced to the structural grid.