Brick Mould Dimensions – Allowance for Drying and Burning Shrinkage In order that the finished, burnt bricks meet the specified nominal size after drying and firing, the size of the green brick mould is generally kept how, relative to the specified size?

Introduction:
Bricks shrink during drying and burning. If the mould matched the final size exactly, the fired brick would end up undersized. Hence, moulds are made slightly oversize to compensate. This question checks that you understand that practical allowance.

Given Data / Assumptions:

• Green (freshly moulded) bricks lose moisture and undergo sintering.
• Both stages produce dimensional shrinkage.
• Specifications demand finished bricks within tight tolerances.

Concept / Approach:

The mould must be dimensioned to offset expected shrinkage so that the final product meets the nominal standard upon completion of burning and cooling. The exact percentage varies with clay composition and process, but the qualitative rule is that the mould is slightly larger than the finished size.

Step-by-Step Solution:

Verification / Alternative check:

Brickmaking manuals specify typical shrinkage allowances (often a few millimetres depending on mix and process), confirming oversize mould practice.

Why Other Options Are Wrong:

Smaller or equal moulds would yield undersized bricks; fixed 10% or 20% oversize is unrealistic and excessive for most clays.

Common Pitfalls:

Assuming a single percentage suits all clays; ignoring quality control adjustments based on measured shrinkage.

Final Answer:

A little larger than the specified size to allow for shrinkage