A concrete screw
is one designed and manufactured so the threads of the screw will tap
threads into concrete, brick or block. The threads are hardened without
making the body of the screw so brittle that the screw would shear off.
ITW/Buildex developed the first concrete screw in the late 1970s and in
the early 1980s began to market their Tapcon® brand concrete screw. It
revolutionized the installation of these screws into concrete. Prior to
the Tapcon®, installation was done using powder actuated and plastic
type female anchors.
Brands of Concrete Screws
Since the development of concrete screws,
many companies have produced their brand of concrete screw. Hilti has
the Kwik-Con®, Powers sells the Tapper®, Simpson Strong-Tie has the
Titen® and others have a generic, imported screw. Most of the concrete
screws sold today are a blue color in order to resemble the original
Tapcon®. Tapcons are American made and the blue coating is Climaseal®, a coating designed to resist rust.
Types of Concrete Screws
Concrete screws come in two different basic
head styles- the hex head and flat head. The hex head full description
is a hex head washer slotted and the flat head is a countersunk flat
head phillips drive. These screws come in different lengths of 1-1/4" up
to 6" in length in order to accomodate different material thicknesses.
Concrete Screws Embedment
Unlike most concrete fasteners, the concrete
screw has a maximum embedment that is should be placed into the base
material. A concrete screw should not be embedded into the base material
any deeper than 1-3/4" because the threads' ability to tape the base
material may cease and the lead thread will wear to the point of being
non-effective. Concrete screws have a minimum embedment of 1", which
means that the screw must penetrate the base material at least 1" for
effective holding values.
Length of Concrete Screws
To determine the minimum length of concrete
screw to use, add the thickness of the material being fastened to the
minimum embedment of 1". To determine the maximum length of screw to
use, add the thickness of the material to be fastened to the maximum
embedment of 1-3/4". Hex head concrete screws are measured from under
the head, while the flat head screws are measured as overall length.
Drill Bits for Concrete Screws
Concrete screws require that a hole be
drilled into the base material before the screw can tap threads. The
hole size is critical and the proper drill bit should be used to ensure
that proper tolerances are met. A 3/16" screw requires a 5/32" hole and
the 1/4" requires a 3/16" hole. A carbide bit meeting ANSI standards
should also be used in the hammer drill so the hole is the proper size
Depth of Hole for a Concrete Screw
The hole drilled in the base material must be
a minimum of 1/2" deeper than the screw will penetrate. This will allow
space for any debris created during the tapping process and will help
ensure that the screw will not bottom out in the hole.
Concrete Screw Installation
1. Drill hole using a hammer drill with the
correct ANSI standard carbide drill bit to a depth at least 1/2" deeper
than the screw will penetrate.
2. Using a wire brush, compressed air or a vacuum, clean the hole of all dust and debris.
3. Insert the concrete screw through the
fixture or directly into the hole. Turning clockwise by hand or with a
rotation drill, allow the threads to tap the base material.
4. The concrete screw is properly set once
the head of the concrete screw is securely against the fixture. Make
sure that the screw is not allowed to strip the threads in the base
material by avoiding over-torqueing.
There are many brands of concrete screws to
choose from. Tapcons are the American made concrete screw and is treated
with a rust resistance blue coating. It is important to choose the
correct size, type and lenth of screw before completing installation.
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