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Fly ash bricks vs red clay bricks: an honest comparison
How fly ash bricks and fired clay bricks differ in raw material, manufacture, size accuracy, curing and environmental impact.
Possible Machines Private Limited ·
Red clay bricks have been the default walling material in India for generations. Fly ash bricks are now common on building sites too, especially near thermal power plants. Here is how the two compare, for builders choosing a brick and for entrepreneurs deciding what to make.
What each brick is made of
Red clay bricks are moulded from clay, usually dug from fields, then dried and fired in a kiln.
Fly ash bricks are pressed from fly ash, the fine ash left when coal is burned in thermal power plants, mixed with sand or stone dust and a binder such as lime or cement, often with a little gypsum. They are not fired. They gain strength as the binder reacts with the fly ash and water while they cure.
Side by side
| Fly ash brick | Red clay brick | |
|---|---|---|
| Main raw material | Fly ash, an industrial by-product | Clay, often topsoil |
| How it is made | Pressed in a machine, then water-cured | Moulded, dried and fired in a kiln |
| Firing fuel | None | Coal, wood or other fuel |
| Size and shape | Uniform, with sharp edges from a steel mould | Varies with moulding and firing |
| Colour | Grey | Red to brown |
| Quality depends on | Mix design, compaction and curing | Clay quality and firing temperature |
Where fly ash bricks have the edge
- Uniform size. Every brick comes from the same mould under the same pressure, so walls go up straighter, joints are thinner and plaster can be thinner too.
- No kiln. There is no firing fuel and no kiln smoke. Curing needs only water and time.
- Uses a waste product. Fly ash would otherwise sit in ash ponds, and using it saves the fertile topsoil that clay bricks consume.
- Policy support. Government notifications on fly ash use, first issued in 1999 and revised several times since, push construction near coal and lignite power plants towards fly ash-based products.
Where clay bricks still make sense
- Far from any power plant, the cost of hauling fly ash can outweigh its advantages.
- Where brickwork is left exposed and a red finish is wanted, clay or facing bricks may be preferred.
- Some buyers simply know clay. Fly ash makers often need to show test reports and finished walls to win them over.
Strength and water absorption
Both kinds of brick can be good or bad. A fly ash brick with the right mix, full compaction and proper curing is consistent from one to the next. A badly cured one is weak, however good the press, just as an under-fired clay brick is. For fly ash-lime bricks the Indian Standard is IS 12894. Ask your supplier, or your own lab, for test results on compressive strength and water absorption rather than relying on claims.
For brick makers
If you are thinking of making fly ash bricks, check two things first: a steady fly ash source within reasonable hauling distance, and buyers who will take your output. Our guide to starting a fly ash brick business covers the rest, and our fly ash brick machines are built for exactly this work.