How bricks are made
A brick's color records its recipe: iron turns it pink or red, and lime turns it pale yellow or white.
- stations
- 7
- things upstream
- 2
- raw sources
- 2
- step from the ground
- 1
The short version
Clay bricks are made from clay and shale ground to a paste with water, squeezed through a die as a long slab, and cut into bricks by a wall of wires. The raw bricks ride through a tunnel kiln on conveyors or kiln cars, where firing makes them hard and durable.
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Dig the clay and shale
Clay and shale are the raw ingredients. They are the product of thousands of years of erosion of rocks such as granite, and they are chemically stable. Silica makes up 50% to 60% of the mix by weight and alumina 20% to 30%.
Goes in -
Grind it with water
The clay is ground and blended with water in a pugmill. For extruded bricks the mix is 10–15% water if stiff, or 20–25% if soft.
10–15% water for stiff extrusion
Goes in -
Squeeze out a column
The mix is forced through a steel die to make a long cable of clay with the width and depth of a brick. Most structural bricks are made this way because it produces hard, dense bricks.
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Slice with wires
A wall of tensioned wires cuts the column into brick lengths. The wires can leave faint drag marks, which is how you can recognize a wire-cut brick.
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Dry the green bricks
Cut bricks still carry the water they were mixed with. They are dried before firing so that water does not flash to steam and crack them inside the kiln.
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Fire in a tunnel kiln
Bricks ride slowly through the kiln on conveyors, rails or kiln cars, so every one sees the same heat. Soft-mud bricks are fired at 900–1,000 °C. The finished color depends on the clay chemistry, the temperature and the kiln atmosphere.
900–1,000 °C for molded bricks
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Test the strength
Samples are crushed to check compressive strength. In the United States, brick strength ranges from about 7 to 103 MPa depending on use, while a common English house brick shows 20–40 MPa.
Worth repeating
- The oldest known bricks, made of shaped mud, date to before 7500 BC and were found at Tell Aswad.
- The floors of the three pits of the Terracotta Army were paved with an estimated 230,000 bricks.
- At the end of the 19th century, 130 brickyards along the Hudson River produced about 1 billion bricks a year at their peak.
Back to the ground
Follow every input upstream and brick starts as these 2 raw sources.
Keep walking
Sources
Cite this page: "How bricks are made." Assembly Line, 2026-11-03. https://assemblyline.org/make/brick