Types of Bricks and Their Uses in Construction

"Brick" gets used as if it's one material, but a load-bearing wall, a garden edging, and a gas-fired kiln lining might all technically be built from something called a brick, at wildly different quality, cost, and purpose. Knowing the actual classification — and what it's really measuring — is the difference between picking a brick because it was cheapest that week, and picking the right brick for what the wall is actually going to do.

The classification that matters most: class by crushing strength and quality

For ordinary burnt clay bricks, IS 1077 sorts them into classes based primarily on compressive strength and finish quality:

• First class bricks — table-moulded, with sharp, well-defined edges and a smooth surface, minimum crushing strength of 10.5 N/mm² (105 kg/cm²), low water absorption. These are used for exposed, load-bearing, and important structural brickwork where both strength and appearance matter.
• Second class bricks — ground-moulded rather than table-moulded, so edges are less perfectly sharp and the surface is somewhat rougher, with a lower minimum strength requirement than first class. Used for general brickwork that will be plastered over, where the slightly rougher finish won't show.
• Third class bricks — irregular shape, noticeably rougher texture, the lowest strength and durability of the three, and generally not recommended for permanent or load-bearing work. Historically used for temporary structures or non-critical, low-load applications.

The practical takeaway: the class isn't just a quality label — it's a direct proxy for how much load the brick can actually carry and how well it will hold up to weathering, so using a lower class where a higher one is warranted is a real, measurable risk, not just an aesthetic compromise.

Fly ash bricks — a different manufacturing process entirely

Fly ash bricks are made from fly ash (a by-product of coal-based thermal power generation) combined with sand, lime, and gypsum, then either autoclaved or air-cured — no firing/kiln process at all, unlike conventional clay bricks. They're generally lighter, more uniform in size and shape than clay bricks, and offer a way to use an industrial by-product that would otherwise need disposal. Their compressive strength can be competitive with or better than ordinary clay bricks, and their more precise, uniform dimensions often mean less mortar consumption and thinner joints. Their main limitation compared to clay brick is generally lower resistance in continuously wet or wave-battered conditions, so they're less favoured for below-grade or heavily water-exposed masonry.

Engineering bricks — built for strength and low absorption, not appearance

Engineering bricks are burnt at higher temperatures for longer, giving them very high compressive strength and notably low water absorption compared to ordinary bricks — properties valued in applications where structural load-bearing capacity or resistance to water ingress matters more than finish or appearance. They show up in retaining walls, manholes, drainage structures, and foundations in contact with damp or aggressive ground conditions, precisely because their density and low porosity resist water penetration and chemical attack better than a standard first-class brick would.

Reading a brick before you commit to it

A few quick, genuinely useful field checks, none requiring a lab:

• Sound test: two bricks struck together should give a clear metallic ring; a dull thud suggests under-burning or internal cracks.
• Water absorption: a well-burnt brick shouldn't absorb more than about 20% of its own weight in water after a defined soaking period (the exact limit varies by class and standard) — excessive absorption is a durability red flag.
• Scratch test: a fingernail shouldn't leave a visible scratch on a properly burnt, good-quality brick.
• Break test: a good brick should break into fairly sharp, uniform fragments, not crumble.

Matching the brick to the job

As a rule of thumb: first class for load-bearing and exposed work, second class for plastered general brickwork, engineering bricks where water resistance or high strength genuinely matters (foundations, drains, retaining structures), and fly ash bricks as a strong, more uniform, and often more sustainable general-purpose alternative where continuous wet exposure isn't the primary concern. The mistake worth avoiding isn't using a lower grade — plenty of genuinely non-critical work doesn't need first class brick — it's using a lower grade in a place where the load or exposure conditions actually demanded better.