Every new house, bungalow and apartment block in India reaches the same question once the RCC frame is up: what should the walls be made of? The contractor may push red bricks because his masons know them; the AAC dealer promises lighter, cooler walls; the fly ash brick supplier offers a lower price and a greener story. Owners often decide on the price per piece, which is the least useful number of all, because a brick, a fly ash brick and an AAC block are different sizes, need different amounts of mortar and labour, and change the weight the structure has to carry.
The wrong choice, or the right choice built badly, shows up for years. Walls crack along beams and columns; plaster sounds hollow; external walls soak up monsoon rain and stain; west walls radiate heat into bedrooms late into the night. In Surat and much of Gujarat, where summers are long and much of the state lies in moderate to high seismic zones, both heat and weight deserve attention. This article compares the three main walling materials used in Indian buildings today on the points that decide performance and cost, and explains how to build each one properly.
A short history of the three materials
Fired clay brick is one of the oldest manufactured building materials in the world, and India has one of its longest histories. The cities of the Indus Valley civilisation, in their mature phase roughly between 2600 and 1900 BCE, were built of standardised fired and sun-dried bricks, famously proportioned close to a ratio of 1:2:4 for thickness, width and length. Later builders used bricks of many sizes; the thin lakhori bricks of Mughal and later North Indian buildings, laid in lime mortar, are a well-known example. Under British rule the larger brick of about 9 × 4½ × 3 inches — roughly 230 × 115 × 75 mm — became the common standard, and it is still the size most Indian masons picture when they say "brick".
Autoclaved aerated concrete is a twentieth-century European invention, developed in Sweden in the 1920s: a mix of fine sand or fly ash, cement, lime, gypsum and a small amount of aluminium powder that reacts to make the mix rise like bread, after which it is cut into blocks and cured under steam pressure in an autoclave. It spread across Europe after the Second World War and grew rapidly in India in the 2000s and 2010s as high-rise RCC construction boomed and plants opened near major cities. Fly ash bricks grew from a different pressure: India's coal-fired power stations produce very large quantities of fly ash, and government policy since the 1990s has promoted bricks and blocks made from it, both to use the ash and to reduce the topsoil dug for clay bricks. Machine-pressed fly ash–lime and fly ash–cement bricks are now produced across the country, usually in the same size as clay bricks.
| Material | Made from | How it is made | Governing IS standard |
|---|---|---|---|
| Burnt clay brick | Clay or alluvial soil, sometimes with additives | Moulded by hand or extruded and wire-cut, dried, fired in kilns | IS 1077 (common burnt clay building bricks) |
| Fly ash brick | Fly ash, lime or cement, sand or stone dust, gypsum | Machine-pressed, cured with water or steam — not fired | IS 12894 (pulverised fuel ash–lime bricks) |
| AAC block | Fly ash or fine sand, cement, lime, gypsum, aluminium powder | Aerated, cut, then cured under steam pressure in an autoclave | IS 2185 Part 3 (autoclaved cellular concrete blocks) |
| Masonry practice | — | — | IS 2212 (brickwork), IS 6041 (AAC block masonry), IS 1905 (structural masonry) |
Sizes, densities and quantities
The first practical difference is size. Clay and fly ash bricks are small units laid in 10–12 mm cement mortar joints; an AAC block is roughly eight to nine times the volume of a brick and is normally laid with a thin-bed polymer adhesive about 2–4 mm thick, or with conventional mortar if the mason is not trained in adhesive. Fewer, bigger units and thinner joints mean faster walls and less mortar, but also mean that the block must be cut accurately and laid level from the first course.
| Property | Clay brick | Fly ash brick | AAC block |
|---|---|---|---|
| Common size (mm) | ≈ 230 × 110 × 75 (modular 190 × 90 × 90) | ≈ 230 × 110 × 75 | 600 × 200 × 75 / 100 / 150 / 200 / 230 / 250 / 300 |
| Dry density (typical) | ≈ 1,600–1,900 kg/m³ | ≈ 1,600–1,900 kg/m³ | ≈ 550–800 kg/m³ (commonly 550–650) |
| Units per m³ of masonry | ≈ 400–500 | ≈ 400–500 | ≈ 40–42 (600 × 200 × 200) |
| Units per m² of 230 / 200 mm wall | ≈ 95–115 | ≈ 95–115 | ≈ 8.3 |
| Joint | 10–12 mm cement mortar (commonly 1:6) | 10–12 mm cement mortar | 2–4 mm thin-bed adhesive, or 10–12 mm mortar |
| Dimensional accuracy | Variable; hand-moulded bricks vary most | Good; machine-pressed | Very good; wire-cut |
Strength, weight, heat, sound, fire and water
In a typical Indian RCC-framed building, walls are infill: the columns, beams and slabs carry the load, and the walls carry only themselves, plaster, fixtures and wind. For infill, compressive strength well above about 3.5 N/mm² rarely matters; weight, heat, moisture behaviour and workmanship matter far more. Load-bearing construction — one- and two-storey houses without a frame, compound walls, older-style buildings — is different, and there the strength class, the masonry design to IS 1905 and the structural engineer's specification decide.
| Criterion | Clay brick (230 mm) | Fly ash brick (230 mm) | AAC block (200 mm) |
|---|---|---|---|
| Compressive strength | IS 1077 classes from 3.5 N/mm² upward; common site bricks often 3.5–7.5 | Machine-pressed bricks commonly 7.5–10 N/mm² declared | Commonly about 3–4.5 N/mm² declared |
| Wall weight, unplastered | ≈ 400–440 kg/m² | ≈ 380–430 kg/m² | ≈ 120–160 kg/m² |
| Thermal transmittance, plastered (U) | ≈ 2.0 W/m²·K | ≈ 1.8–2.1 W/m²·K (similar to brick) | ≈ 0.75–0.8 W/m²·K |
| Thermal mass (heat storage) | High | High | Low to moderate |
| Airborne sound | Good — heavy wall | Good — heavy wall | Fair for its thickness; lighter wall |
| Fire resistance | Excellent, non-combustible | Excellent, non-combustible | Excellent, non-combustible |
| Water absorption | Up to about 20 % by weight for common classes | Up to about 20 % for common classes | High porosity but slow capillary uptake; must be plastered or coated outside |
| Efflorescence risk | Moderate; depends on clay and firing | Low to moderate | Low |
| Fixing heavy items | Easy with ordinary anchors | Easy with ordinary anchors | Needs AAC-specific anchors or through-bolts |
| Embodied impact | Fired in kilns; uses topsoil | Uses power-plant ash; no firing | Uses ash or sand; autoclave energy, low weight |
The thermal numbers explain why AAC has become the default for external walls of air-conditioned buildings. A plastered 230 mm brick wall lets roughly two and a half times as much heat through as a 200 mm AAC wall. In a Gujarat summer, an east or west bedroom wall of AAC stays noticeably cooler on its inside face in the evening, and the air-conditioner works less. The trade-off is thermal mass: a heavy brick wall stores heat and releases it slowly, which can help in naturally ventilated rooms with night cooling but hurts when the stored heat reaches bedrooms at night. This site's guides on thermal insulation and keeping homes cool without AC explain how shading and roof insulation work alongside the wall.
What lighter walls do to the structure
A storey of 230 mm brick infill weighs roughly three times as much as the same walls in 200 mm AAC. That weight sits on beams, columns and foundations, and in an earthquake it increases the inertial forces the frame must resist. Lighter infill can therefore allow a more economical structure, which is one reason AAC is common in high-rise construction. The saving is not automatic: the structural engineer must design for the walls actually specified, and changing from AAC to brick during construction — or adding heavy brick walls later, for example on a terrace — needs the engineer's approval.
How each one should be built
All three materials can give good walls, and all three give poor walls when rushed. The common rules: soak clay bricks before laying so they do not suck water from the mortar, but lay fly ash bricks and AAC blocks only lightly damped or as the manufacturer directs; keep courses level and plumb; stagger vertical joints by at least a quarter of a unit; cure mortar joints; and do not build more than about 1–1.5 m height of wall in a day so that the lower courses can set.
Clay and fly ash bricks
Lay in cement mortar, commonly 1:6 cement–sand for 230 mm walls and 1:4 for 115 mm half-brick partitions, with joints of about 10 mm, fully filled. Half-brick partitions longer or taller than about 3 m need reinforcement — commonly a pair of steel bars or bed-joint mesh every few courses, or an intermediate RCC band — as specified by the engineer. Rake joints about 10 mm deep for a good plaster key. Fly ash bricks are more uniform than most clay bricks, so joints stay thinner and plaster uses less material.
AAC blocks
Lay the first course in ordinary cement mortar on a clean, level base to correct any unevenness in the slab, then lay the remaining courses in thin-bed adhesive spread with a notched trowel, following IS 6041 and the manufacturer's instructions. Cut blocks with a hand saw or band saw rather than breaking them with a trowel. Tie the wall to RCC columns with bed-joint ties or mesh at intervals — commonly every second or third course — and leave a small gap below the beam to be packed later. Use lintels or a lintel band over openings with adequate bearing, and AAC-compatible primers and plasters, or a bonding coat, before plastering.
| Defect | Most likely cause | Prevention |
|---|---|---|
| Vertical crack at wall–column line | Different movement of masonry and concrete; no ties or mesh | Ties to columns, mesh strip over the junction before plaster |
| Horizontal crack under beam | Wall built tight to beam; beam deflects or wall shrinks | Leave a top gap, pack it after the wall has settled |
| Map cracking in plaster | Plaster too rich or thick; poor curing; AAC not primed | Correct mix, two thin coats, curing, bonding coat on AAC |
| Hollow-sounding plaster | Dusty or dry substrate; no key | Clean, dampen or prime; rake brick joints |
| Diagonal cracks at window corners | Stress concentration; no lintel band or short bearing | Lintel with ≥ 150 mm bearing; mesh at corners |
| Damp patches and efflorescence | Rain penetration, rising damp, salts in bricks or sand | Good external plaster and paint, DPC, drip edges, clean sand |
| Anchors pulling out of AAC | Ordinary plastic plugs in a soft block | AAC-specific anchors, chemical anchors or through-bolts |
Cost per unit and per square foot of wall
Comparing the price of one brick with the price of one block says almost nothing. The fair comparison is the cost of a finished square metre or square foot of wall, including mortar or adhesive and labour, and then the knock-on effects — plaster thickness, structural savings, construction speed and energy over the building's life. The ranges below are indicative October 2026 figures for Gujarat and comparable Indian markets, excluding GST and transport over long distances; prices vary widely by region and season, and should always be confirmed locally.
| Item | Indicative October 2026 price | Per sq ft of built wall (material + mortar/adhesive + labour, before plaster) |
|---|---|---|
| Red clay brick (common, ≈ 230 × 110 × 75) | ≈ ₹7–12 per brick | 230 mm wall ≈ ₹130–220; 115 mm partition ≈ ₹70–115 |
| Fly ash brick (≈ 230 × 110 × 75) | ≈ ₹5–8 per brick | 230 mm wall ≈ ₹110–180; 115 mm partition ≈ ₹60–95 |
| AAC block (600 × 200 × 200) | ≈ ₹3,500–5,000 per m³ (≈ ₹85–120 per block) | 200 mm wall ≈ ₹95–145; 100 mm partition ≈ ₹55–85 |
| Thin-bed AAC adhesive | Per bag, by brand | Included above; uses far less material than 1:6 mortar |
| Wire-cut facing brick for exposed work | Higher than common brick | Exposed brick wall incl. pointing ≈ ₹180–400 (this site's exposed brick guide) |
For a typical house, the wall itself is a modest share of construction cost — this site's planning guides use about ₹2,200–2,800 per sq ft of built-up area for a standard specification — so the choice should be made on performance first and price second. Two hidden savings favour AAC in framed buildings: thinner plaster on accurate blocks, and fewer days of masonry work. Two hidden costs can cancel them: untrained masons who lay AAC in thick mortar and break blocks instead of cutting them, and the extra care needed at junctions to avoid cracks. Fly ash bricks often give the lowest built cost where a good plant is nearby.
Which material where
No single material is best everywhere. The table below reflects common Indian practice; the structural engineer's specification takes precedence, especially for load-bearing walls and in higher seismic zones.
| Situation | First choice | Also suitable | Notes |
|---|---|---|---|
| External walls of an RCC-framed house or flat | 200 mm AAC | 230 mm fly ash brick | AAC for heat; protect with good plaster and exterior paint |
| Internal partitions in flats | 100–150 mm AAC | 115 mm fly ash or clay brick | Light, fast; use proper anchors for wall-hung units |
| Load-bearing one- or two-storey building | 230 mm clay or fly ash brick | Engineered AAC systems only where designed | Design to IS 1905; RCC bands as per seismic zone |
| Compound and boundary walls | 230 mm clay or fly ash brick | 200 mm AAC, plastered | This site's compound wall guide gives costs per running metre |
| Bathrooms and wet walls | Clay or fly ash brick, or AAC with waterproofing | — | Waterproof to at least shower height; avoid soft blocks at floor level |
| Below plinth, foundations, retaining | Clay brick, stone or concrete | — | Not AAC; it is not meant for continuous wet ground contact |
| Exposed brick feature walls | Wire-cut facing clay bricks | Brick slips over any wall | See this site's exposed brick guide |
| Terrace rooms and additions on old buildings | AAC (lightest) | — | Only after a structural check of the existing building |
Where walling is going
Three directions are clear in Indian construction. First, lighter walls: AAC, AAC panels and lightweight concrete blocks keep growing in framed buildings because they reduce load, speed up work and help meet energy codes such as the residential Eco-Niwas Samhita, which sets targets for the heat gain through the building envelope. Second, lower-carbon units: fly ash and other industrial by-products, compressed stabilised earth blocks and cleaner kiln technologies for clay bricks are all being promoted to reduce topsoil use and emissions. Third, drier and faster methods: thin-bed adhesives, ready-mix plasters, gypsum plaster on internal walls and precast or dry-wall partitions reduce the water and time that traditional masonry needs. Clay brick will not disappear — it remains the material of load-bearing houses, heritage repair and exposed brick architecture — but the default infill wall of a new Indian building is increasingly a block, not a brick.
Rules for choosing and building walls
- Compare materials per finished square foot of wall, not per piece.
- Use 200 mm AAC for external walls of air-conditioned framed buildings, especially facing east and west.
- Use clay or fly ash brick for load-bearing walls, below plinth and where heavy fixings or mass are needed — as the engineer specifies.
- Do not change the wall material during construction without the structural engineer's approval.
- Buy from plants that supply test certificates against IS 1077, IS 12894 or IS 2185 Part 3.
- Lay AAC with thin-bed adhesive and saw-cut blocks; use trained masons.
- Tie walls to columns, leave and later pack the gap below beams, and fix mesh over every frame junction before plastering.
- Cure masonry and plaster properly, and plaster or coat AAC on the outside to keep rain out.
Frequently asked questions
Which is better for house construction: red brick or AAC block?
For the walls of an RCC-framed house, AAC is usually better: lighter, faster and much better at keeping heat out. Red brick is better for load-bearing construction, foundations and exposed brickwork, and where heavy items must be fixed with ordinary anchors. Either works well only if built carefully.
Do AAC block walls crack more?
Cracks in AAC walls are usually junction or shrinkage cracks caused by poor detailing — no ties to columns, walls built tight under beams, no mesh over junctions, plaster applied without a bonding coat. Brick infill cracks in the same places for the same reasons. With correct practice, AAC walls perform well.
Are fly ash bricks stronger than red bricks?
Good machine-pressed fly ash bricks commonly have a higher and more consistent compressive strength than ordinary site clay bricks, and they are more uniform in size. Quality varies between plants, so ask for test certificates and check a sample for edges, uniformity and soundness.
Can wall-mounted TVs and kitchen cabinets be fixed to AAC?
Yes, with the right anchors. Use AAC-specific mechanical anchors, chemical anchors or through-bolts with plates, and for heavy kitchen overheads consider fixing into RCC members or adding a timber or metal backing rail. Ordinary plastic plugs can pull out of a soft block.
Is AAC good for Surat's climate?
Yes, especially on east and west walls and in air-conditioned rooms. Its low U-value cuts heat gain through the wall. Because it is porous, external AAC walls must be well plastered and painted, with drip edges at sills, to keep monsoon rain out.
Sources & standards
- Bureau of Indian Standards — IS 1077 (Common burnt clay building bricks — specification) and IS 2212 (Code of practice for brickwork)
- Bureau of Indian Standards — IS 12894 (Pulverised fuel ash–lime bricks — specification)
- Bureau of Indian Standards — IS 2185 Part 3 (Autoclaved cellular (aerated) concrete blocks) and IS 6041 (Construction of autoclaved cellular concrete block masonry)
- Bureau of Indian Standards — IS 1905 (Structural use of unreinforced masonry) and IS 1893 (Criteria for earthquake resistant design of structures)
- National Building Code of India 2016 — Part 6 (Structural design, Section 4 masonry) and Part 11 (Approach to sustainability)
- Bureau of Energy Efficiency — Eco-Niwas Samhita (Energy Conservation Building Code for residential buildings)
- This site's guides on thermal insulation, exposed brick and compound walls — for consistent U-values and wall costs
- Price ranges: indicative October 2026 estimates — confirm locally before budgeting
