Oil paints – identifying the most important constituent for film formation In a conventional oil paint system used on building works, which constituent is considered the most important?

Introduction / Context:
Oil paints protect and decorate substrates by forming a continuous film after application. Understanding the role of each ingredient helps in selecting, specifying, and troubleshooting coatings in civil projects. This question asks which component is fundamentally the most important to the final film’s integrity and performance.

Given Data / Assumptions:

• Typical constituents: vehicle (drying oil/binder), pigment, thinner, drier/extenders.
• Focus is on the factor that dominates film formation and durability.
• Context is building finishes (woodwork, metals, plaster).

Concept / Approach:

The vehicle (binder) is the film-forming component. In oil paints, the drying oil (e.g., linseed or tung) polymerizes by oxidation to create a coherent film that encapsulates pigments and adheres to the surface. Pigments provide color/opacity; thinners aid application and evaporate; extenders adjust cost and rheology. Without a sound vehicle, no durable film remains after drying.

Step-by-Step Solution:

Verification / Alternative check:

Coatings technology emphasizes binder chemistry (alkyd, oil-modified, polyurethane) as the prime determinant of adhesion, hardness, and resistance, confirming the vehicle’s primacy.

Why Other Options Are Wrong:

Thinner: Evaporates; primarily influences application and flow.

Pigment: Gives color/hiding but does not create the film by itself.

Base/extenders: Modify properties and cost; secondary to binder.

All of the above: Not correct because their roles are not equal; the vehicle is fundamental.

Common Pitfalls:

Overvaluing pigment load for durability; assuming more solvent improves performance; ignoring the binder’s curing mechanism and film continuity.

Final Answer:

Vehicle (drying oil/binder)