A small portion of the painted surface is sometimes seen lose, it is known as the

Understanding Paint Adhesion Failure

The question describes a situation where paint is physically detaching from the surface. This is a classic sign of adhesion failure, where the bond between the paint film and the underlying surface (or between paint layers) has broken.

Flaking: This is the paint defect characterized by the lifting and detaching of small, loose pieces (flakes) of paint from the substrate. It is a direct result of a loss of adhesion.

Common Causes of Flaking:

Improper Surface Preparation: Painting over a dirty, greasy, or glossy surface without proper cleaning and sanding.
Moisture Intrusion: Water getting behind the paint film from inside the wall or through cracks, breaking the adhesive bond.
Paint Incompatibility: Applying an oil-based paint over a latex-based paint (or vice versa) without the correct primer.
Age: The paint film becomes brittle over time and loses its flexibility and adhesion.

Detailed Guide to Other Paint Defects

It's important to distinguish flaking from other defects that relate to the paint's appearance or application.

(b) Flaking

Appearance: Small, loose pieces of paint breaking away from the surface.
Core Issue: Loss of adhesion. This is a physical failure of the paint to stick.

(a) Flashing

Appearance: Uneven, glossy patches on what should be a uniform, matte, or satin surface.
Core Issue: Uneven application or absorption. The paint has not dried to a consistent sheen. This is a visual defect, not a physical detachment.

(c) Grinning

Appearance: The underlying surface or previous coat of paint is faintly visible through the topcoat.
Core Issue: Lack of opacity. The topcoat is not thick enough or does not have enough hiding power. This is also a visual defect.

(d) Running

Appearance: The paint sags and flows downwards after application, leaving drips or uncovered areas.
Core Issue: Application error. The paint was applied too thickly or to a surface that was too smooth for it to grip properly.

Study Tips for Paint Defects

Flaking Falls Off: The easiest association. Flakes are pieces of paint that are literally falling off.
Flashing is about Finish: Think of a camera "flash" creating a shiny spot. Flashing is a defect related to inconsistent gloss or finish.
Grinning is See-Through: The old surface is "grinning" or peeking through the new coat.
Running Runs Down: This defect describes the action of gravity on wet paint that has been applied too heavily.