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How Does a Concrete Wedge Anchor Work?

By Shane Grey ; Updated September 21, 2017
Wedge anchors attach building materials to solid concrete walls.
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Builders often use concrete wedge anchors to attach structural load-bearing components to walls and floors, such as joist-supporting ledgers or sill plates. Additionally, concrete wedge anchors can secure all types of building hardware to masonry surfaces, including shelf brackets, picture hangers and door hardware. Wedge anchors, also called expansion anchors, have a hollow, wedge-shaped butt that grabs and holds the interior of a pre-drilled hole. With an understanding of how wedge anchors work you can determine if wedge anchors are the right choice for your building project.

Parts of a Wedge Anchor

The largest component of a concrete wedge anchor is a headless, threaded rod. One side of the rod accepts washers and nuts, like the open end of a bolt. Opposite its open end, the rod tapers outward into a hollow, conical tip, called a wedge. A thin, ribbed sleeve of metal, called a collar, encircles the base of the conical tip.

How a Wedge Anchor Works

Builders sometimes call concrete wedge anchors "expansion anchors" because the anchor literally expands during installation. Builders place the wedge end of the anchor into a pre-bored hole and pound the open end with a hammer or mallet. The pounding force smashes the anchor's hollow tip against the bottom of the hole and causes the tip to "explode" or expand. The tip's expansion forces the collar's ribs to grip the sides of the hole and become permanently lodged in place.

Wedge Anchor Installation Tools

Builders use either a combination hammer and driver power drill equipped with a masonry drill bit to bore holes for concrete wedge anchors. Although both hammers and mallets pound anchors into place, soft-headed mallets are less likely to deform the anchor's tip. To tighten the anchor's nuts, builders use standard wrenches, such as box wrenches, adjustable wrenches or socket wrenches.

Wedge Anchor Installation Tips

Forgetting to attach washers and nuts before pounding and improperly preparing the anchor hole are the most common mistakes made by builders unfamiliar with wedge anchor installation. If pounding an anchor deforms the shank's external threads, the anchor nut's internal threads will no longer match and bind with the shank's threads. Avoid this mistake by placing washers and nuts onto the anchor's shank prior to pounding the anchor into its hole. Additionally, dust residue from drilling can prevent the anchor's collar from properly gripping the sides of the hole. To remove concrete dust prior to anchor installation, blow into the hole with an air compressor or clean the hole with a cylindrical tubing brush.


About the Author


Based in Hawaii, Shane Grey began writing professionally in 2004. He draws on his construction experience to write instructional home and garden articles. In addition to freelance work, Grey has held a position as an in-house copywriter for an online retailer. He holds a Bachelor of Arts in theater arts from Humboldt State University.