Both are lightweight, light grey and sold as alternatives to brick, and they are often confused on site. The difference lies in how they are made — and that decides how they behave in your walls.
How Is Each Made?
| AAC | CLC | |
|---|---|---|
| Full name | Autoclaved Aerated Concrete | Cellular Lightweight Concrete (foam concrete) |
| Ingredients | Fly ash or sand, cement, lime, gypsum, aluminium powder | Cement, fly ash or sand, water, foaming agent |
| How cells form | Chemical reaction releases gas that expands the mix | Pre-formed foam is mixed into the slurry |
| Curing | High-pressure steam in an autoclave | Air or water curing |
| Production | Large, automated factories | Often small plants, sometimes on site |
| Standard | IS 2185 (Part 3) | IS 2185 (Part 4) |
Why Does Autoclaving Matter?
Steam curing at high pressure and temperature changes the chemistry of AAC, forming a stable crystalline structure. The result is a block that is:
- Dimensionally stable, with low drying shrinkage.
- Consistent, because the process is controlled in a factory.
- Precise in size, which allows thin-bed adhesive joints.
CLC, cured in air, continues to dry and shrink for weeks. If blocks are laid before they have dried, they shrink in the wall, and that movement shows up as cracks at joints and in the plaster.
How Do They Compare in Use?
| AAC | CLC | |
|---|---|---|
| Consistency between batches | High | Varies by producer |
| Drying shrinkage | Low | Higher |
| Strength at similar density | Generally higher | Generally lower, more variable |
| Size accuracy | High; suits thin-bed adhesive | Lower; often laid in mortar |
| Price | Moderate | Often lower locally |
| Availability in Hyderabad | Widely available from established brands | Varies |
When Might CLC Be Acceptable?
CLC from a reliable producer, with test results and blocks properly cured before dispatch, can perform adequately for internal partitions. Ask for compressive strength and density test results, check the age of the blocks, and avoid laying freshly made blocks.
The Short Version
For house walls, choose AAC from an established manufacturer: autoclaving gives it the stability and consistency that keep walls crack-free. CLC is a possible saving only where the producer is reliable and the blocks are properly cured.
