Which of the following defects is caused by vaporization of entrapped moisture or solvents in a painted surface?

🔬 Understanding the Mechanism of Blistering

The question describes a specific failure mechanism in paint. Let's break it down:

• Entrapped Moisture/Solvents: This means liquid (either water from a damp surface or solvent from the paint itself) gets trapped under the paint film. This usually happens if the top layer of paint dries too quickly, forming a skin.
• Vaporization: When the surface is heated (e.g., by sunlight), the trapped liquid turns into a gas (vapor).
• The Result: This gas exerts pressure on the underside of the paint film, pushing it outwards and forming a bubble or blister. This process is the direct cause of the defect known as blistering.

⚖️ A Detailed Guide to Common Paint Defects

Understanding the different types of paint failures is crucial for proper diagnosis and repair.

Saponification

Appearance: Formation of soapy, sticky patches on the paint film.
Cause: A chemical reaction between the binder (especially oil-based ones) and alkaline substances in the underlying surface (like new plaster or cement). The alkali essentially turns the oil in the paint into soap.

Blooming

Appearance: Formation of dull, cloudy patches on a glossy or polished surface.
Cause: This is often caused by moisture condensing on the paint film during drying, especially in humid or poorly ventilated conditions. It can also be due to defects in the varnish or paint itself.

Cissing

Appearance: The wet paint film crawls or pulls back from the surface, leaving small craters or bare spots.
Cause: Surface contamination. The paint is unable to wet the surface properly due to the presence of grease, oil, wax, or silicone.

Flaking

Appearance: The paint lifts and peels away from the surface in flakes.
Cause: Poor adhesion, often because the surface was not properly cleaned or primed, or due to moisture getting behind the paint film.

Fading

Appearance: The gradual loss or lightening of the paint's original color.
Cause: The effect of ultraviolet (UV) radiation from sunlight breaking down the chemical bonds in the pigment.

Grinning

Appearance: The underlying surface or previous coat of paint is visible through the final coat.
Cause: Insufficient opacity (hiding power) of the topcoat, or it was applied too thinly.

Sagging & Running

Appearance: Sagging appears as droopy, curtain-like drips on vertical surfaces. Running is when paint flows back, leaving uncovered spots.
Cause: Applying the paint too thickly on a vertical surface (sagging) or painting on a surface that is too smooth or glossy for the paint to adhere to (running).

💡 Study Tips for Paint Defects

• Blistering = Bubbles: The most direct visual association. Think of water boiling under a lid—the pressure builds up.
• Saponification = Soap: The name itself sounds like "soap." This defect is a chemical reaction that literally creates soapy patches.
• Grinning = Grinning Through: Imagine the old surface is "grinning" or peeking through the new, thin coat of paint.
• Cissing = Contamination: Remember that Cissing is caused by a contaminated surface that repels the paint.