Damp-proof course (horizontal D.P.C.) in masonry: what is the typical thickness of cement concrete (1:2:4) provided as a horizontal D.P.C. layer?

Introduction / Context:
A horizontal damp-proof course (D.P.C.) prevents capillary rise of moisture from foundations into walls and floors. Correct thickness and mix ensure durability and continuity under walls.

Given Data / Assumptions:

• D.P.C. material: cement concrete of proportion 1:2:4 (cement:sand:coarse aggregate) with waterproofing admixture where specified.
• We seek typical thickness adopted in practice.

Concept / Approach:
For load-bearing walls, a 4 cm thick cement concrete D.P.C. is commonly provided at plinth level, finished smooth to receive the first course of masonry. Thicker layers may be used for special cases or alternative materials (e.g., mastic asphalt), but the standard teaching value remains 4 cm.

Step-by-Step Solution:
Identify standard practice: 1:2:4 CC D.P.C. at plinth.Select typical thickness from options: 4 cm.

Verification / Alternative check:
Building specifications and measurement handbooks frequently state 'CC 1:2:4, 40 mm thick, with waterproofing compound' for horizontal D.P.C. under walls.

Why Other Options Are Wrong:

• 2 cm: too thin and prone to cracking/voids.
• 6–10 cm: unnecessarily thick for a D.P.C. layer; increases cost without added benefit.

Common Pitfalls:

• Omitting continuity across wall thickness or not lapping D.P.C. with floor membranes, leading to moisture bridges.

Final Answer:
4 cm