According to IS: 654-1962, the maximum water absorption percentage of Class AA Type Mangalore pattern tiles is:
🏠 Understanding Clay Roofing Tiles (IS 654)
Mangalore tiles are a type of clay roofing tile known for their distinctive shape, which allows them to interlock. They are widely used in India for pitched roofs. The quality of these tiles is crucial for ensuring a waterproof and durable roof. IS 654: 1962 specifies the requirements for these tiles, classifying them into two categories based on quality: Class AA and Class A. Water absorption is a key parameter, as high absorption can lead to leakage and faster degradation of the tile.
🔬 Detailed Analysis of the Options
C. 18%
This is the correct answer. According to IS 654: 1962, Class AA tiles are the higher grade and are required to have a maximum average water absorption of 18%. This lower absorption rate indicates a denser, better-fired tile that will provide superior performance and longevity.
A. 29%, B. 35%, and D. 25%
These options are incorrect.
- A water absorption of 25% or higher would be indicative of a very porous, low-quality tile, unsuitable for roofing purposes as it would not be watertight.
- The standard specifies a maximum of 20% for the lower grade (Class A) tiles, so any value above that is non-compliant for either class.
📊 Summary: IS 654 Requirements for Mangalore Tiles
| Characteristic | Class AA (Higher Grade) | Class A (Standard Grade) |
|---|---|---|
| Max. Water Absorption (%) | 18% | 20% |
| Minimum Breaking Load (kN) | ||
| Average (for 410×235 mm) | 1.0 | 0.80 |
| Average (for 420×250 & 425×260 mm) | 1.10 | 0.90 |
| Individual (for 410×235 mm) | 0.90 | 0.68 |
| Individual (for 420×250 & 425×260 mm) | 1.00 | 0.78 |
💡 Study Tips
- AA is Superior: Remember that Class AA is the better quality tile, so it will have the stricter requirements (lower water absorption, higher strength).
- The 18/20 Rule: Associate Class AA with 18% and Class A with 20% for water absorption. It's a small, easy-to-remember difference.
- Know the Code: IS 654 is the specific standard for clay roofing tiles. Don't confuse it with codes for bricks (like IS 1077 or IS 3495).
- Think Function: Roofing tiles must keep water out. Therefore, a lower water absorption value always means better quality.