ASTM Committee C-18 on Dimension Stone has developed a new document called ASTM C 1242 "Standard Guide for Design, Selection, and Installation of Exterior Dimension Stone Anchors and Anchoring Systems," published in September 1993. It sets forth basic requirements for the design of anchorage systems and provides a practical checklist to make sure each requirement has been considered. DESIGN CONSIDERATIONS Before you can select a suitable anchoring system, you need to establish a number of factors: 1. The physical characteristics of the stone. 2. Design loads and safety factors for the cladding. 3. Wind and seismic loads on the building. 4. Anticipated dimensional changes in the building. ERECTION STANDARDS Construction documents set standards for materials and workmanship and identify the scope of the work. In addition to the usual architectural drawings and specifications, dimension stone projects need shop drawings that detail all parts of the work required. The construction documents also specify erection tolerances that contractors are bound by contract to work within. In some instances, the services of professional stone cladding designers can be helpful. ANCHOR TYPES Strap anchors are flat metal bars designed to fit into a slot or kerf cut into the edge of the stone. Rod or dowel anchors are round metal bars designed to fit into holes drilled into the stone. Tooled rod anchors are round bars with a tooled shape at one or both ends that fits into a matching hole in the stone. Adhesive embedded anchors are rods or bars that are bonded into angled holes in the stone. BACKUP STRUCTURES ASTM C 1242 provides guidelines for the backup systems commonly used. Masonry and concrete backup walls are seldom used behind stone cladding. Dimension stone cladding can be anchored to metal struts attached to the building frame. Prefabricated metal truss backup systems offer several significant benefits, especially for complex facade configurations.