Cast stone, a type of architectural precast concrete, is manufactured to simulate natural stone. Manufacturers use special formulations of portland cement, lightweight aggregates, and iron oxide colors to cast the veneer from hundreds of individual molds, essentially eliminating any look-alike pieces. Installed as an adhered veneer, cast stone usually is stronger than natural stone. Cast stone also resists weather better, has more color consistency, and often costs less than natural stone. Also, the veneer is lighter (weighing 8 to 10 psf) than natural stone (30 to 50 psf). LAYING THE STONE It doesn't matter where you start laying stone on a wall: work from the bottom up or the top down. Regardless of where you start, you must follow certain steps: Prepare the backup wall. Use Type S premixed mortar or mix your own in accordance with ASTM C 270, Specification for Mortar for Unit Masonry. Press each cast stone into the mortar bed firmly. Install L-shaped corner pieces first. Install flat pieces working from the corners toward the center of the wall. Cut and trim cast stone using widemouthed nippers or a hatchet. Grout the joints with a grout bag if full-depth joints are desired. Tool joints with a wooden stick or metal jointing tool when they have become dry to the touch. Clean the wall when the mortar has sufficiently set.