The heat exchangers were vented through brick or masonry chimneys. The sills are bolted to the masonry or concrete foundation. Rocket is effective against bunkers, masonry and concrete walls and light armor. It was built with walls of sandstone pillars and smaller blocks of Ashlar masonry. The wealthy had houses of stone masonry with flat roofs. Most of the remaining masonry is made from concrete. It is easy to work with and less expensive than steel, masonry, or concrete. Terra cotta is lighter and easier to work with than stone masonry. It was well known for its stone masonry that includes rustication and ashlar. Designers typically enclosed the riser pipes in decorative masonry or wooden structures. There are two main types of sedimentary stone used in masonry work, limestones and sandstones. A traditional unit of volume for stone and other masonry. Built of rubble masonry and ashlar, they are mostly still extant. The gates are in grey ashlar masonry. Installer bits are available in various materials and styles for drilling wood, masonry and metal.