What AAC Blocks Are
Autoclaved Aerated Concrete (AAC) blocks are made from a mixture of cement, lime, fly ash, aluminium powder, and water. The aluminium reacts with lime to produce hydrogen gas, creating millions of tiny air pockets throughout the mix before it is autoclaved (steam-cured under pressure). The result is a block that is 80% air by volume — very light, thermally insulating, and dimensionally precise to within 1–2mm.
Indian producers include Ultratech, Siporex, JK, and a growing number of regional manufacturers. Sizes are standardised: the most common is 600×200mm with thicknesses of 100mm, 150mm, 200mm, and 230mm. A standard 200mm AAC block weighs around 18 kg — compared to 3.0–3.5 kg for a standard red brick, but one AAC block replaces approximately 8–10 bricks in a wall, so the productivity per block laid is dramatically higher.
The Cost Comparison Done Honestly
An AAC block in the ₹48–65 range (ex-factory) costs more per unit than a red brick at ₹7–9. However, the cost comparison should be done at wall cost, not unit cost. A 1 sqm of 200mm AAC block wall (including mortar, plastering, and labour) in most Indian cities comes to ₹580–₹720 per sqm. The equivalent red brick 230mm wall costs ₹620–₹780 per sqm — more, not less, because of the additional material and significantly higher labour.
The labour comparison is the key number. An experienced mason can lay 250–300 AAC blocks per day versus 1,000–1,200 red bricks. Since one AAC block equals roughly 9 bricks, 300 blocks = 2,700 equivalent bricks. AAC construction is faster per square metre of wall, which reduces both the total mason days required and the project programme. On a 30,000 sqft housing block, switching from brick to AAC typically saves 18–25 days of masonry cycle time.
Structural and Code Advantages
The Energy Conservation Building Code (ECBC) mandates minimum thermal performance for walls in buildings above a certain size in most climate zones. A 200mm AAC block wall achieves a U-value of approximately 0.55 W/m²K, comfortably within ECBC requirements for composite and warm-humid zones without any additional insulation. A 230mm red brick wall achieves approximately 2.0 W/m²K and fails ECBC requirements without significant additional treatment.
The structural advantage of lower dead load is significant. AAC walls reduce the overall building weight, which reduces column and beam sizes, reduces foundation loads, and therefore reduces steel and concrete quantities. Structural engineers working in steel optimisation estimate 8–12% savings in structural steel when switching an equivalent building from brick to AAC. In seismic zones, the reduced inertial mass also means lower seismic forces — smaller structural elements.
Common Contractor Concerns Addressed
The first concern is cutting and chasing for MEP. AAC cuts cleanly with a hand saw or standard circular saw — no hammer and chisel required. Electrical chases are cleaner than in brick. The material does not shatter or spall. The second concern is nail and screw holding. Standard nails do not hold in AAC — you need nylon plugs or proprietary AAC screws. This is not a structural concern but requires a different site practice. Suppliers provide fixing guides. The third concern is weathering at the external face. AAC should not be left unplastered for extended periods in high-rainfall areas — it absorbs moisture, which can cause surface deterioration. Keep plastering within 2–3 months of block-laying and use an alkali-resistant primer before finishing.