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
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.
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.
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.
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
concrete anchors require the same basic installation steps. Each anchor
is set in different ways and the manufacturer's instructions should
always be followed.
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
2. Clean out all debris from the hole before inserting the anchor into the hole.
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.
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 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