Synthetic material comprising an aggregate (small pieces of stone or other hard materials, such as broken brick or clinker, usually graded with sand) and a binding agent (usually a mortar made of cement and/or lime), mixed with water. This gives a semi-fluid workable mass that sets to form a material as hard as brick or stone and of great compressive strength, although weak in tension. Its ultimate appearance is determined by the detailed design of the shuttering or formwork in which it is cast, and by the use after the removal of the shuttering of such surface treatments as bush-hammering, spraying and rendering; alternatively, it can be left in its raw state, showing the marks of the shuttering, as in board-marked concrete (béton brut). Chemical set-retardants can also be used to leave decorative aggregates exposed.