How Masonry Anchors Work

• There are three basic types of masonry anchors: 1) mechanical, 2) powder-actuated and 3)chemical. It's unlikely that you'll need a chemical anchor unless you're building a bridge, and in many states, certification is required to use powder-actuated fasteners. This document describes how to use mechanical anchors.
• Products do vary from one manufacturer to the next; if the manufacturer's installation instructions are different than the information in this document, always follow the manufacturer's instructions. One caution when installing masonry anchors-always wear eye protection and follow the manufacturer's safety instructions.
• Most masonry anchors work in one of two ways-either by expanding against the sides of the hole and gripping the concrete (see image above) or by friction against the sides of the hole (see image). The holding power of any anchor depends on the quality of the concrete and on where the anchor is placed. If the concrete is old and crumbly, the holding power of the fastener will be reduced.
• Likewise, if the anchor is placed near the edge of the concrete-or two anchors are placed too close together-the force generated by the anchor may break the concrete. The general recommendation is that any anchor should be placed no closer than five diameters from the edge of the concrete. In other words, a 1/2" diameter anchor should be no closer than 2-1/2" (1/2" x 5) from the edge of the concrete.
• Two anchors should never be placed closer than 10 diameters from each other. In other words, two 1/2" anchors should be at least 5" (1/2" x 10) apart.