Kumar IronWhat each material is
Red bricks are clay moulded and fired in a kiln. Common burnt clay bricks are covered by IS 1077. AAC stands for autoclaved aerated concrete: a mix of cement, lime, fly ash or sand and aluminium powder that foams, is cut into blocks and cured in a steam autoclave. AAC blocks are covered by IS 2185 (Part 3).
Comparison table
| Point | AAC block | Red brick |
|---|---|---|
| Typical size | 600 x 200 x 100 to 300 mm | 230 x 110 x 70 mm (about 9 x 4.5 x 3 in) |
| Density | About 550 to 650 kg/m³ | About 1600 to 1900 kg/m³ |
| Compressive strength | 3 to 4.5 N/mm² typical | 3.5 N/mm² and higher, by class |
| Heat insulation | Very good, much lower conductivity | Average |
| Dead load on structure | Much lower | Higher |
| Wall building speed | Fast, large blocks | Slower |
| Mortar and plaster | Thin bed jointing mortar, thin plaster | Thick joints, thicker plaster |
| Water absorption | High, needs good plaster and waterproof finish | Moderate |
| Wastage and breakage | Low if handled right | Moderate |
Values vary by manufacturer and brick quality. Ask for the test report of the batch.
Why AAC suits upper floors and framed buildings
In an RCC framed house the walls only fill the gaps between columns and beams. They do not carry the building. A lighter wall means lighter dead load, smaller footings and column loads, and better earthquake behaviour because a lighter building attracts less seismic force. AAC also keeps rooms cooler in summer. One block 200 mm x 600 mm x 200 mm replaces roughly 20 or more bricks of wall volume, so walls go up much faster.
Where red bricks still win
- Load bearing walls in single storey houses and boundary walls.
- Below plinth level, in damp ground and where water splashes: bricks tolerate moisture better.
- Places where you need to fix heavy things into the wall without special fasteners.
- Small repairs and extensions where matching existing brickwork matters.
Using AAC the right way
- Use only thin bed AAC jointing mortar or a polymer modified adhesive, not thick sand cement mortar, or you lose the insulation and strength advantage.
- Keep blocks dry on site. Do not soak them like bricks. A light spray before plaster is enough.
- Plaster with a recommended AAC plaster or a lean cement sand mix of about 1:5 to 1:6, with a mesh strip at junctions of block and RCC to stop cracks.
- Fix heavy fittings with proper AAC anchors, not plain nails or plugs.
- Add a bond beam or lintel band as your engineer specifies, and protect external walls with a waterproof coat and paint.
A fair way to compare cost
Per piece, AAC looks costlier than a brick. Compare per cubic metre of finished wall instead. Add the block or brick cost, mortar, plaster, labour and the saving in structure load. Rates change often, so ask us for today's price of AAC blocks and of bricks and we will help you work out the wall cost.
Frequently asked questions
- Are AAC blocks strong enough for a house?
- Yes for non-load-bearing infill walls in a framed building, which is how they are normally used. Do not use thin AAC for load bearing walls unless the design allows it.
- Do AAC blocks keep the house cooler?
- Yes. Their thermal conductivity is much lower than clay brick, so walls transfer less heat in summer.
- Can I use AAC blocks below the plinth?
- It is not advised. Use bricks or solid concrete blocks below plinth level, and start AAC above a proper damp proof course.
- Why do AAC walls crack?
- Usual causes are thick cement mortar, no mesh at junctions, wet blocks and poor curing. Use thin bed mortar, mesh strips and a waterproof finish.