LIMESTONE: Limestone is a sedimentary rock, formed from shells and other “limy” material in the oceans that in past ages covered the “limestone regions” of now dry land. Shells and coral owe their stiffness to calcium carbonate (CaCO3), often called “carbonate of lime”. Limestone too is mainly calcium carbonate and a microscope reveals the remains of the sea animals that formed it. An important building material, it wears better than sandstone, is more easily shaped than granite, and weathers from nearly white to a beautiful gray. Marble is a crystallized form of limestone transformed by pressure and heat.
Used as a durable facing material on large buildings and as trim and accent detail elsewhere, limestone is quarried, cured and cut to the desired dimensions and shaped. Common applications include archways, encasements, keystones, lintels, pier caps, coping, quoins, sills, banding, balusters, columns, and corner stones.
CAST STONE or PRECAST: Architectural precast concrete building stone is a man made alternative to limestone. It is a portland cement based product that is produced in specially shaped molds to the desired design specifications. Color, shape, texture and to some extent weight can be controlled during the manufacturing process.
The applications of precast trim includes all those listed above for limestone.