Painting Practice – Typical Composition of an Oil-Based Priming Coat for New Work Which of the following compositions correctly represents a traditional priming coat formulation used on absorbent building surfaces before finishing coats?

Introduction:
Priming prepares porous surfaces (e.g., new plaster or timber) to receive finishing coats by reducing suction, improving adhesion, and providing a uniform base. Traditional primers often used white lead and chalk bound with linseed oil to seal and consolidate the substrate.

Given Data / Assumptions:

• New, absorbent surfaces require a sealer/primer before paints.
• Components: pigment (white lead historically), extender (chalk/whiting), and binder (boiled linseed oil).
• Ratios control viscosity, penetration, and sealing capacity.

Concept / Approach:

A workable primer balances body (from chalk and white lead) with penetration and film formation (from boiled linseed oil). Excessive oil or pigment skews penetration and drying. The classical proportion listed in option (a) reflects long-used site practice for priming before oil-bound paints (noting modern lead-free formulations now prevail).

Step-by-Step Solution:

Verification / Alternative check:

Older painting specifications and manuals list similar proportions for priming coats on new work, prior to modern lead-free alkyd/latex primers.

Why Other Options Are Wrong:

(b) Overloads white lead relative to chalk and may not be standard; (c) uses insufficient oil and raw oil, affecting penetration and drying; (e) lacks binder—cannot form a durable priming film; (d) is invalid since a correct composition is provided.

Common Pitfalls:

Using raw linseed oil leading to slow drying; skipping primer on highly absorbent plaster causing patchy finish.

Final Answer:

One part white lead, eight parts chalk (whiting), and four parts twice-boiled linseed oil