How to Anchor to Concrete

Anchoring into concrete is accomplished with the use of concrete fasteners. Concrete fasteners are designed specifically for attaching an item to concrete. The item can be anything from a light fixture, sign or steel plate to a 2x4 piece of wood. Concrete fasteners are used in applications that are different from the applications for other types of fasteners. For example, one of the pieces of a concrete anchor is a solid, thick and hard piece of material and the other side is non-accessible. A hole must be drilled into the concrete first. A hammer drill must be used for this operation in order to provide the best tolerance hole. The quality of the hole is critical when installing concrete fasteners.

There are two different types of concrete fasteners- female type and male type. Female anchors are set into the concrete and then a bolt or screw is inserted through the fixture and into the concrete anchor. Male anchors are placed through the fixture and into the concrete with part of the anchor protruding above the surface of the concrete. The diameter of anchor to be used for any specific application is determined by both the hole in the object being fastened and the weight of the object. Usually, the heavier the object then the larger the diameter of the concrete anchor. Concrete anchors derive their holding values from the concrete. Anchor failure is usually failure of the concrete. The deeper into the concrete a fastener is placed, the better the holding values that can be obtained. If a concrete anchor is to be placed outdoors, it is advisable to use stainless steel since it offers better rust resistance than regular, zinc plated fasteners. The number of fasteners and the placement of these fasteners depend on the specific requirements of the application. When setting any concrete fastener, they should be placed no closer than 10x the diameter of the anchor from eachother and a minimum of 5x the diameter from any unsupported edge of concrete.

There are many different types of concrete anchors. Each has features and benefits that meet specific application requirements. For example, lag shields come in a short and long version for each diameter. The short lag shield anchor is used in applications where the base material is very hard while the long lag shield is most commonly used in softer base materials. Wedge anchors, strike anchors and drop-in anchors can be used in solid concrete only and can't be used in brick or block. The sleeve anchor is very versatile and can be used in brick, block or concrete but the shear values are lower because the bolt size is smaller than the anchor diameter. Some anchors may be chosen based on the type of bolt that needs to be used for a specific application. A machine screw anchor uses a bolt with machine threads that are national coarse threads 1/4"-20. Lag shield anchors use a bolt with lag screw threads. Some applications require removability. An example of this type of application would be a bench that is placed outdoors in the summer and is brought inside during the fall. If the base material is concrete, a drop in anchor may be used. Drop-in anchors are female type anchors that do not stick up above the surface of the concrete and allows for bolting and unbolting.

A number of concrete anchors are designed for light duty anchoring to concrete, brick or block base material. They are called different names by different manufacturers but the generic names for each are the split drive anchor, hammer drive anchor and nylon nail-it anchor. Most of these anchors come in only one diameter (usually 1/4") with different lengths that can be used for different applications. Hole size is anchor size and the depth of the hole in the base material should be drilled a minimum of 1/2" deeper than the anchor will penetrate. All of these anchors are installed using a hammer to insert them into the hole in the concrete.

There are a large number of concrete anchors available for your specific application. A list of these concrete fasteners follows.

Male Concrete Anchors: wedge anchor, sleeve anchor, strike anchor, hammer drive anchor

Female Concrete Anchors: drop-in anchor, lag shield, machine screw anchor, single expansion anchor, double expansion anchor

Concrete Anchor Installation Instructions

All concrete anchors require the same basic installation steps. Each anchor is set in different ways and the manufacturer's instructions should always be followed.

1. Drill a hole in the base material using a hammer drill and carbide tipped drill bit that matches the correct diameter needed for the anchor being installed.

2. Clean out all debris from the hole before inserting the anchor into the hole.

3. Female anchor: Insert the anchor into the hole and move the object to be fastened over the anchor until the hole in the object lines up with the concrete anchor.
Male anchor: Insert the anchor through the hole in the object being fastened and into the hole drilled in the concrete.

4. Turn the bolt or nut until finger tight and then turn another 3-4 times with a wrench. If the anchor has a setting nail, use a hammer to drive the anchor until the head of the nail is flush with the head of the concrete fastener.

Concrete anchors and fasteners can be used in various concrete applications and projects. Before installing any concrete anchors, it is important to use the correct type of anchor in the right diameter embedded into the concrete correctly to achieve maximum holding values.





 

Please remember with all fastening jobs to keep safety in mind. Always follow safety instructions on all tools, and refer to manufacturer's installation instructions when available and always remember to wear safety goggles!

Article written by: Bob Carlisle, President Concrete Fastening Systems, Inc

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