The water absorption for good brick should not be more than
💧 Understanding Water Absorption in Bricks
Water absorption is a critical property that indicates the quality and durability of a brick. It measures the amount of water a brick can soak up relative to its own weight. This property is directly related to the brick's porosity (the volume of empty pores). A good brick should be well-burnt and dense, which results in low porosity and, consequently, low water absorption.
The standard test (as per IS 3495 Part 2) involves immersing a dry brick in water for 24 hours. The percentage of water absorption is always calculated based on the brick's dry weight using the formula:
Water Absorption (%) = [ (Wwet - Wdry) / Wdry ] × 100
🔬 Detailed Analysis of the Options
B. 15% of its dry weight
This is the correct answer. For a brick to be considered "good quality" (equivalent to a First Class brick), its water absorption should not exceed this threshold. While Indian Standards allow up to 20% for first-class bricks, a value of 15% is widely accepted as the limit for higher-grade bricks and is a reliable benchmark for durable masonry. Low water absorption ensures higher strength, better resistance to weathering and frost action, and prevents dampness in walls.
A. 10% of its dry weight
This is incorrect. While a water absorption of 10% indicates a very high-quality, dense brick (often classified as an engineering brick), it is a stricter standard than what is generally required for a "good" common building brick. Therefore, 15% is a more appropriate and standard upper limit.
C. 10% of its saturated weight & D. 15% of its saturated weight
These options are fundamentally incorrect. The standard calculation for water absorption is always expressed as a percentage of the brick's dry weight, not its saturated weight. Using saturated weight as the base would be conceptually wrong and would not align with any building code or standard testing procedure.
📊 Summary: Water Absorption Limits by Brick Class (IS 1077)
| Brick Class | Max. Water Absorption (% of Dry Weight) | Key Characteristics |
|---|---|---|
| First Class Brick | < 20% (ideally < 15%) | Well-burnt, uniform shape, sharp edges. Used for exposed work. |
| Second Class Brick | < 22% | Slight irregularities in shape. Used for plastered masonry. |
| Third Class Brick | < 25% | Under-burnt, soft. Used for temporary, non-structural work. |
💡 Study Tips
- Dry Weight is the Denominator: Always remember that water absorption is calculated with respect to the brick's oven-dry weight. This will help you eliminate incorrect options immediately.
- Lower is Better: A lower water absorption percentage signifies a denser, stronger, and more durable brick.
- Know the "Why": Understand the consequences of high water absorption. It leads to reduced strength, makes the brick susceptible to frost damage (spalling), and can cause efflorescence (white salty deposits on the brick face).
- The 15/20 Rule: For exams, remember that the limit for a good/first-class brick is generally cited as 15% to 20%. The 15% value represents a higher quality standard within that class.