Indian brick types classified by compressive strength as per IS 1077, fly ash bricks per IS 12894, and AAC blocks per IS 2185 Part 3. Compressive strength tested per IS 3495 Part 1 on flat (frog up, filled with mortar). Water absorption tested per IS 3495 Part 2 by 24-hour cold immersion. All values are minimum averages for a sample of 5 bricks.
Common Burnt Clay Bricks (IS 1077)
Standard modular size 190×90×90 mm; non-modular 230×115×75 mm. Tested as per IS 3495.
| Type | Class | Strength | Absorption | Density | Use |
|---|
| First Class — Heavy Duty | Class 35 | 35 MPa | ≤20% | 1800–2000 kg/m³ | Heavy-loaded walls, piers, abutments, retaining walls |
| First Class — Heavy Duty | Class 30 | 30 MPa | ≤20% | 1800–2000 kg/m³ | Multi-storey load-bearing, bridge parapets |
| First Class — Heavy Duty | Class 25 | 25 MPa | ≤20% | 1800–2000 kg/m³ | Load-bearing walls (3+ storeys), manholes, exposed brickwork |
| First Class | Class 20 | 20 MPa | ≤20% | 1700–1900 kg/m³ | Load-bearing walls (up to 3 storeys), compound walls, drains |
| First Class | Class 17.5 | 17.5 MPa | ≤20% | 1700–1900 kg/m³ | Load-bearing walls (low-rise), plinth, boundary walls |
| Second Class | Class 15 | 15 MPa | ≤22% | 1600–1800 kg/m³ | Non-load-bearing partitions, one-storey buildings, garden walls |
| Second Class | Class 12.5 | 12.5 MPa | ≤22% | 1600–1800 kg/m³ | Partition walls, one-storey construction in dry areas |
| Second Class | Class 10 | 10 MPa | ≤22% | 1500–1700 kg/m³ | Non-structural walls, temporary works, filling |
| Third Class | Class 7.5 | 7.5 MPa | ≤25% | 1400–1600 kg/m³ | Temporary structures, lime mortar work, rural construction |
| Third Class | Class 5 | 5 MPa | ≤25% | 1300–1500 kg/m³ | Soling, sub-base filling, temporary boundary walls |
| Sun-dried / Unburnt | Class 3.5 | 3.5 MPa | Not tested | 1200–1400 kg/m³ | Temporary rural walls, kacha construction, filling |
Fly Ash Bricks (IS 12894)
Made from fly ash, lime/cement, sand/stone dust. Modular size 230×110×75 mm or 190×90×90 mm.
| Type | Class | Strength | Absorption | Density | Use |
|---|
| Fly Ash Lime Brick — Grade I | Class 12.5+ | 12.5 MPa | ≤20% | 1700–1850 kg/m³ | Load-bearing walls, external walls, multistorey flats |
| Fly Ash Lime Brick — Grade II | Class 10+ | 10 MPa | ≤22% | 1600–1750 kg/m³ | Internal partitions, non-load-bearing walls |
| Fly Ash Cement Brick — High Strength | Class 15+ | 15 MPa | ≤18% | 1800–1950 kg/m³ | Load-bearing in multi-storey, external facade, exposed work |
| Fly Ash Cement Brick — Standard | Class 7.5+ | 7.5 MPa | ≤22% | 1500–1700 kg/m³ | Partition walls, infill in framed structures |
AAC Blocks (IS 2185 Part 3)
Autoclaved Aerated Concrete. Typical sizes 600×200×100 to 600×200×300 mm. Lightweight; needs thin-bed mortar or polymer-modified mortar.
| Type | Class | Strength | Absorption | Density | Use |
|---|
| AAC Block — Density Grade 1 | Density 451–550 kg/m³ | 2.0 MPa | ≤15% (by volume) | 451–550 kg/m³ | Partition walls, non-load-bearing infill in high-rise |
| AAC Block — Density Grade 2 | Density 551–650 kg/m³ | 3.0 MPa | ≤15% (by volume) | 551–650 kg/m³ | Internal & external non-load-bearing walls, infill panels |
| AAC Block — Density Grade 3 | Density 651–750 kg/m³ | 4.0 MPa | ≤15% (by volume) | 651–750 kg/m³ | Load-bearing low-rise (up to 2 storeys), external walls |
| AAC Block — Density Grade 4 | Density 751–850 kg/m³ | 5.0 MPa | ≤15% (by volume) | 751–850 kg/m³ | Load-bearing walls, boundary walls, plinth masonry |
Notes
• Field test — Drop Test: A first-class brick dropped from 1 m onto hard ground should not break
• Field test — Ring Test: Two bricks struck together should produce a clear metallic ringing sound, not a dull thud
• Field test — Nail Scratch: A fingernail should not leave an impression on a first-class brick surface
• Efflorescence: Tested per IS 3495 Part 3 — rated as Nil, Slight, Moderate, Heavy, or Serious. First-class bricks must be Nil or Slight
• Dimensional tolerance per IS 1077: Length ±3%, Width ±3%, Height ±3% of standard size for Class 20 and above
• For AAC blocks, water absorption is measured by volume (not weight) since the blocks are very light — 15% by volume ≈ 40–50% by weight
• Fly ash bricks should be cured for 14–21 days and aged at least 28 days before use in construction
• IS 3495 Part 1 specifies testing 5 bricks per lot of 50,000 — individual brick strength can be 20% below class minimum
• Always soak clay bricks in water for 1–2 hours before use to prevent suction of moisture from mortar
• AAC blocks must NOT be soaked — only lightly wetted on the face before applying thin-bed adhesive mortar