Water absorption limit — after immersing a brick for 16 hours, the wet weight should not exceed the dry weight by more than: Choose the correct percentage.

Introduction / Context:
Water absorption is a key indicator of brick quality and durability. Excessive absorption can lead to frost susceptibility, efflorescence, and reduced strength. Standards specify maximum permissible absorption by weight after immersion for a defined period.

Given Data / Assumptions:

• Immersion period: 16 hours (commonly used test duration).
• We are considering ordinary good-quality burnt clay bricks.
• Percentage increase is measured relative to dry weight.

Concept / Approach:
For general-purpose common bricks, traditional specifications allow up to about one-fifth increase in mass after 16–24 hours immersion. Higher-grade facing bricks may have tighter limits (often 15% or lower), but the typical textbook answer for “good quality” common bricks is 20%.

Step-by-Step Solution:

Verification / Alternative check:
Legacy building codes and materials handbooks frequently cite 20% as the typical limit for ordinary bricks, noting stricter values for higher grades.

Why Other Options Are Wrong:

• 15%: Tighter than typical common-brick limits; applicable to selected grades.
• 10%: Too stringent for ordinary bricks.
• None of these: Incorrect because 20% is acceptable for common good-quality bricks.

Common Pitfalls:
Using limits for special bricks (e.g., engineering bricks) when the question context implies ordinary “good quality” bricks.

Final Answer:
20%