A road surface built from loose stone
Before smooth, sealed roads became routine, macadam offered a practical way to make a durable surface: workers spread crushed stone in layers and compacted it so the pieces locked together. But the gaps between stones could let water in, and traffic could kick up dust or loosen the surface.
Tar-bound macadam addressed those problems by coating and binding the stones with tar. The sticky material helped hold the aggregate—the crushed rock—together and kept water from penetrating as easily. The result was a firmer, less dusty road than loose macadam, though it still depended on carefully prepared stone and a binding material.
From product name to everyday word
The tar-bound method was marketed under the name Tarmac, which gave the material a memorable label. As the product became familiar, people began using the brand name for road surfacing more generally, even when the surface in front of them was made by another method.
That distinction still matters: modern roads commonly use asphalt or concrete, not the original tar-bound macadam. And “tarmac” is often used informally for an airport apron or runway, but those paved areas are not necessarily made of tar. A product name outlasted the precise recipe—and became a word for the paved surface itself.
