IS 2185:2005 Part 1 is the Indian Standard (BIS) for concrete masonry units - specifications: part 1 hollow and solid concrete blocks. This standard (Part 1) specifies the requirements for solid and hollow concrete masonry units used in load-bearing and non-load-bearing walls. It outlines standard dimensions, materials, physical criteria such as compressive strength, drying shrinkage, and water absorption, as well as sampling and testing procedures.
Specifies requirements for hollow and solid concrete blocks used in masonry construction.
Key values for concrete block classification, dimensions, strength grades, durability limits, and sampling criteria.
| Reference | Value | Clause |
|---|---|---|
| Block Density Classification (Grade A)— Based on oven-dry density. | > 1500 kg/m³ | Cl. 4.2 |
| Block Density Classification (Grade B)— Based on oven-dry density. | ≤ 1500 kg/m³ | Cl. 4.2 |
| Dimensional Tolerance (Length/Width) | ± 5 mm | Cl. 5.2 (Table 1) |
| Dimensional Tolerance (Height) | ± 5 mm | Cl. 5.2 (Table 1) |
| Min. Face Shell Thickness (Hollow)— For blocks with width > 75 mm. | 25 mm | Cl. 5.3.1 |
| Min. Web Thickness (Hollow) | 20 mm | Cl. 5.3.2 |
| Min. Avg. Compressive Strength (Grade 3.5)— Average of 3 units on net area. | 3.5 MPa | Cl. 6.2 (Table 2) |
| Min. Avg. Compressive Strength (Grade 4.5)— Average of 3 units on net area. | 4.5 MPa | Cl. 6.2 (Table 2) |
| Min. Avg. Compressive Strength (Grade 5.5)— Average of 3 units on net area. | 5.5 MPa | Cl. 6.2 (Table 2) |
| Min. Avg. Compressive Strength (Grade 7.0)— Average of 3 units on net area. | 7.0 MPa | Cl. 6.2 (Table 2) |
| Min. Avg. Compressive Strength (Grade 8.5)— Average of 3 units on net area. | 8.5 MPa | Cl. 6.2 (Table 2) |
| Min. Avg. Compressive Strength (Grade 10.0)— Average of 3 units on net area. | 10.0 MPa | Cl. 6.2 (Table 2) |
| Min. Avg. Compressive Strength (Grade 12.5)— Average of 3 units on net area. | 12.5 MPa | Cl. 6.2 (Table 2) |
| Min. Avg. Compressive Strength (Grade 15.0)— Average of 3 units on net area. | 15.0 MPa | Cl. 6.2 (Table 2) |
| Min. Individual Block Strength— Acceptance criteria for any single block from the sample. | ≥ 80% of specified avg. strength | Cl. 6.2 |
| Max. Water Absorption (Avg. of 3) | 10 % by mass | Cl. 6.3 |
| Max. Drying Shrinkage | 0.06 % | Cl. 6.4 |
| Max. Moisture Movement | 0.09 % | Cl. 6.5 |
| Sampling Scale (Visual & Dims)— Sample size for visual and dimensional inspection. | 8 blocks / 10,000 | Cl. 8.2.1 (Table 3) |
| Sampling Scale (Strength Test)— Sample size for compressive strength test. | 3 blocks / 10,000 | Cl. 8.2.1 (Table 3) |
| Sampling Scale (Density Test)— Sample size for block density test. | 3 blocks / 10,000 | Cl. 8.2.1 (Table 3) |
BIM-relevant code. See the BIM Hub for ISO 19650, IFC, and LOD/LOIN frameworks used alongside it.
IS 2185 (Part 1):2005 is the Indian Standard for Hollow and Solid Concrete Blocks for Use in Masonry — Specification. It covers the regular (non-autoclaved) concrete masonry units that have replaced fired bricks across most Indian urban construction since the 2010s.
Use it whenever you specify or procure: - Hollow concrete blocks (HCB) for load-bearing or non-load-bearing internal/external walls - Solid concrete blocks for partitions, retaining walls, foundations below DPC - Standard sizes: 400 × 200 × 200 mm (the dominant block), 400 × 200 × 150 mm, 400 × 200 × 100 mm - Density categories: Type A (densest, 1500-2000 kg/m³), Type B, Type C (lightest, 1000-1300 kg/m³)
Sister codes: - IS 2185 Part 2 — Hollow and solid lightweight concrete blocks (LWA-based, density 800-1200 kg/m³) - IS 2185 Part 3 — Autoclaved Aerated Concrete (AAC) blocks — a separate market, governed by IS 6041 for construction - IS 12440:1988 — Precast concrete stone-masonry blocks (decorative cladding)
Do not confuse with IS 1077 (common burnt clay building bricks) or IS 12894 (fly-ash–lime bricks) — those are different products entirely.
Grade classification (Clause 4.2 of Part 1) — based on minimum compressive strength tested on the gross area (full footprint, not net area):
| Grade | Min compressive strength (N/mm²) | Typical use | |---|---|---| | A (3.5) | 3.5 | Non-load-bearing partition walls | | A (4.5) | 4.5 | Load-bearing internal walls (G+1, G+2) | | A (5.5) | 5.5 | Load-bearing external walls (mid-rise) | | A (7.0) | 7.0 | Load-bearing external (taller) + retaining | | A (8.5), A (10), A (12.5), A (15) | 8.5-15.0 | High-rise load-bearing, structural use | | B (3.5) | 3.5 | Same strength categories, but Type B uses lighter aggregate | | C (3.5), C (4.5), C (5.5) | Same | Type C — lightweight insulating blocks |
Other acceptance limits: - Water absorption (Clause 5.6.4): ≤ 10% for Type A; ≤ 15% for Type B; ≤ 20% for Type C (24-hour soak test per Annex C) - Drying shrinkage (Clause 5.6.5): ≤ 0.10% from saturated to oven-dry (typical limit; excessive shrinkage cracks plaster) - Moisture movement: ≤ 0.09% - Dimensional tolerances (Clause 5.4): length ± 5 mm, height ± 3 mm, width ± 3 mm — visibly excessive variation rejects the lot - Block density (Clause 5.6.2): Type A 1500-2000 kg/m³; Type B 1300-1500; Type C 1000-1300
Sampling and frequency: per Clause 6, 3 blocks per 5,000 produced (or per consignment, whichever smaller). For site QC, every truckload should be inspected dimensionally; full lab testing once per project or per 50,000 blocks.
Problem: G+3 residential building, brick-equivalent external wall thickness. Design floor span 5 m, DL+LL per floor 12 kN/m². Choose block grade.
Step 1 — Tributary load at base of external wall (per metre run, supporting 5 m span × 4 floors): - Floor self-weight + finish + LL per metre: 12 × 5 / 2 = 30 kN/m per floor - Wall self-weight per metre per floor (assume 200 mm hollow block, density 1700 kg/m³ × 0.2 × 3.0 m height): 1700 × 9.81 / 1000 × 0.2 × 3.0 = 10 kN/m per floor - Total per metre run at base: 4 × (30 + 10) = 160 kN/m
Step 2 — Required block strength per IS 1905:1987 (masonry code — load-bearing design): For 200 mm thick HCB wall on 5 m span, slenderness ratio = 3.0/0.2 = 15 (acceptable, < 27 limit). Basic compressive stress fb depends on block strength and mortar grade.
For 'H2' mortar (1:6 cement-sand) and 200 mm wall, IS 1905 Table 8 gives basic stress ≈ 0.50 N/mm² for 5.5 grade block, 0.65 N/mm² for 7.0 grade.
Step 3 — Stress check: Applied stress = 160 × 1000 / (1000 × 200) = 0.80 N/mm² (per metre run)
Using IS 1905 reduction factors (slenderness, eccentricity, area), permissible stress ≈ 0.65 N/mm² for 7.0-grade block with H2 mortar.
0.80 > 0.65 — undersized. Increase to 8.5-grade block: permissible stress ≈ 0.80 N/mm² ✓
Specification: 'Hollow concrete blocks per IS 2185 (Part 1):2005, Type A (8.5), 400 × 200 × 200 mm, with H2 grade mortar per IS 2250'.
Alternative: keep 7.0-grade block but increase wall thickness to 250 mm (where 250 mm available) or transition to RCC frame above 3rd floor. In practice for G+3 most designers go RCC framed structure with infill blocks; pure load-bearing masonry typically stops at G+2 in Indian seismic zones.
1. Wetting blocks excessively before laying — unlike fired clay bricks (which need 24-hour soaking per IS 1077), HCBs should be sprinkled with water just before laying, NOT soaked. Over-saturation causes the block to bleed water into the mortar, weakening the bond and causing shrinkage cracks 4-8 weeks later. The IS 2185 commentary explicitly warns against soaking.
2. Drying shrinkage cracks at junctions — HCBs continue to dry-shrink for 60-90 days after laying. Plastering immediately seals moisture in and causes shrinkage-vs-restraint cracks at corners and around openings. Best practice: allow walls to dry for 28 days minimum before plastering; provide control joints at 8-10 m spacing.
3. Specifying gross area strength but checking net area — IS 2185 is gross-area strength. ASTM C90 (US) is net-area strength (excluding hollows). They are NOT comparable — net-area strength is typically 2-2.5× higher. Don't accept ASTM-tested blocks against IS specification limits.
4. Mortar mismatch — using rich 1:3 cement-sand mortar with low-strength (3.5-grade) blocks causes 'differential shrinkage' — strong mortar cracks weak block at bed joints. Match mortar grade to block grade: H2 (1:6) for 3.5-5.5 grade blocks; H1 (1:4) for 7.0+ grades.
5. Treating Type C (lightweight) blocks as load-bearing — Type C is intended for non-load-bearing partitions and insulating walls. Some contractors substitute Type C for Type A to save cost — the block looks identical but density is 30% lower. Mandate density testing on site receipts (simple weighing of representative blocks at known volume).
6. Inadequate keying for plaster — HCB faces are smoother than fired brick; plaster bonds poorly. Either (a) brush-apply cement slurry coat first, (b) use chicken-wire mesh at large unbroken surfaces, or (c) score the block face before plastering.
IS 2185 Part 1:2005 is the current revision (it superseded IS 2185:1979). The 2005 revision added the higher strength grades (10, 12.5, 15 N/mm²) for high-rise load-bearing applications and clarified the dimensional tolerances. There's no public sign of another revision underway as of 2026.
Market reality: Indian construction is dominated by two types of HCB: 400 × 200 × 200 (5.5 to 7.0 grade) for external load-bearing, and 400 × 200 × 100 (3.5 grade) for internal partitions. Type C lightweight blocks are rare in mainstream practice; AAC (IS 2185 Part 3 / IS 6041) has won the lightweight wall market for both thermal insulation and reduced dead load.
Quality control reality: Indian HCB manufacturing varies enormously. Premium brands (e.g., Ultratech, Holcim, JK) consistently meet IS 2185 strength + dimensional tolerances. Tier-2 local producers often miss strength (90% compliance, 10% sub-grade in random samples), and rarely test for shrinkage at all. For load-bearing masonry, always procure from BIS-licensed manufacturers and test 3 blocks per 50,000 minimum. For non-load-bearing partitions, dimensional inspection on site is the practical QC measure.
Sustainability angle: HCB has 40-60% lower embodied carbon than fired clay brick (no kiln firing). For green-building rated projects (GRIHA, LEED, IGBC), specifying HCB earns 1-3 points in the materials category. Worth noting in the specification justification.
| Parameter | IS Value | International | Source |
|---|---|---|---|
| Minimum Compressive Strength (Net Area) | 3.5 N/mm² (for lowest loadbearing grade) | 2000 psi (~13.8 N/mm²) (average of 3 units) | ASTM C90-23 |
| Maximum Water Absorption | 10% (by mass) | Varies by density, e.g., 13 lb/ft³ (~208 kg/m³) for Normal Weight concrete | ASTM C90-23 |
| Maximum Drying Shrinkage | 0.06% | 0.065% | ASTM C90-23 |
| Dimensional Tolerance (Length/Width) | ±5 mm | ±1/8 in. (±3.2 mm) | ASTM C90-23 |
| Dimensional Tolerance (Height) | ±3 mm | ±1/8 in. (±3.2 mm) | ASTM C90-23 |
| Density Classification (Normal/Heavy) | Grade A: > 1500 kg/m³ | Normal Weight: ≥ 125 pcf (≥ 2000 kg/m³) | ASTM C90-23 |
| Minimum Face Shell Thickness (150-200mm block) | 25 mm | 1.25 in (31.8 mm) | ASTM C90-23 |