Plastering exposed brickwork — recommended cement:sand proportion For plastering exposed brick walls (external plaster), which cement–sand mortar proportion is generally recommended among the following choices?

Introduction / Context:
External plaster must provide a durable, weather-resistant skin capable of resisting rain, moderate abrasion, and thermal cycling. The cement:sand ratio governs strength, permeability, workability, and crack propensity. Selecting an appropriate proportion is a balance between durability and constructability.

Given Data / Assumptions:

• Exposed exterior brick masonry requiring plaster.
• Conventional hand application with proper curing.
• No special polymer modifiers considered.

Concept / Approach:
For exterior plaster, a moderately rich mix such as 1:4 is commonly adopted, often in two coats (base and finish), delivering adequate strength and resistance to rain ingress while remaining workable. Richer mixes (1:2 or 1:3) can be strong but may be less workable, more shrinkage-prone, and uneconomical. Lean mixes (1:6 or 1:8) may be too weak and porous for severe exposure if used without additives or protective finishes.

Step-by-Step Solution:

Verification / Alternative check:
Many specifications list 1:4 to 1:6 for exterior plaster; among options, 1:4 best fits “exposed brick walls” for robust performance.

Why Other Options Are Wrong:

• 1:2, 1:3: stronger but often unnecessary and more crack-prone.
• 1:6, 1:8: may lack durability and water tightness for exposed conditions.

Common Pitfalls:
Poor curing and inadequate surface preparation; applying a very rich mix without controlling shrinkage; ignoring movement joints leading to map cracking.

Final Answer:
1:4