Cast stone is concrete that has been poured into individual molds to simulate natural stone. It usually has a smooth or tooled texture, or it may be more coarsely textured to imitate weathered stone.
Like poured-in-place concrete, cast stone is made of a binder (cement), fine aggregate (sand) and coarse aggregate (gravel), mixed with water. The binder is usually Portland cement, though other binding materials may be combined with the cement. Finely-ground pigments or variously-colored aggregates may alter the color of the cast stone. Admixtures added to the concrete mixture may also alter the strength of the concrete, the rate at which it hardens, or the temperature at which it hardens, amongst other things. Like poured-in-place concrete, cast stone usually contains steel reinforcing bar (rebar) to improve the concrete’s tensile strength.
Although technically not cast stone, concrete masonry units (also known as ‘cinder blocks’ or ‘concrete blocks’) are also made of a mixture of cement and aggregate that is cast into individual units. They have paired hollow cells and are manufactured in modular sizes.