Light fixtures sometimes need to be fastened to concrete in both
outdoor and indoor applications. Installation may be needed in a home or
commercial building. The weight of the light fixture will determine the
diameter of concrete anchor that should be used. The
configuration of the mounting plate and space provided by the cover will
also help determine the type of anchor that will be required. The
following article describes the various types of concrete fasteners
commonly used for fastening a light fixture to concrete as well as the
considerations that need to be addressed.
Considerations
A concrete fastener's holding value is a factor of the diameter
of the anchor being used. As the weight of the lighting fixture
increases, so will the size/diameter of the concrete anchor that should
be used. The heavier the light fixture, the deeper the embedment will
need to be as well. Each diameter of anchor has a minimum embedment to
meet minimum holding values in the concrete. As diameter increases, so
does the minimum embedment. For example, a 3/8" diameter wedge anchor
has a minimum embedment of 1-1/2" while a 1/2" wedge anchor has a
minimum embedment of 2-1/4". The deeper the embedment, the better the
holding values. The deeper the penetration into the concrete, the more
likely it will be to hit rebar. Rebar can be drilled through for anchor
placement, but this makes the job much more costly and involved.
The mounting fixture that comes with the light fixture will have
holes in it for mounting it to the base material. Depending on the size
of the fixture, the holes can range from 1/4" to 5/8" or larger. The
concrete fasteners must fit through the fixture holes. The diameters of
the anchors will not match up with the diameters of the holes in the
fixture. A 3/8" wedge anchor will not fit through a 3/8" hole in a
mounting fixture. The threaded part of the anchor matches up but the
part that goes into the concrete will be slightly larger than the
nominal diameter of the anchor. It is important to check that the anchor
will fit through the mounting hole. A good rule of thumb is to use an
anchor one diameter smaller than the holes in the fixture. For example, a
3/8" hole would require the use of a 5/16" diameter anchor.
If the light fixture is to be placed outdoors or in an area where
there is constant moisture or other chemicals, it is best to use
stainless steel concrete anchors. Fasteners that are zinc plated will
rust over time. Zinc plated fasteners will work fine for indoor use but
not outdoors.
Concrete fasteners
are set into concrete with different and sometimes inconsistent results
in terms of how far the anchor protrudes from the concrete. The type of
fastener chosen may be determined by the amount of space allowable for
the anchor to protrude into the cover of the light fixture. Some smaller
diameter fasteners have been designed so that they don't protrude while
others are designed in such a way that it allows the anchors to be
countersunk in the mounting plate. In heavier and larger light fixtures,
the fixture is designed to accept larger concrete anchors with space
for the anchor to protrude into.
Concrete Fasteners Used for Attaching Light Fixtures to Concrete
Wedge Anchors
The wedge anchor is a stud type concrete anchor that is designed to be used in concrete only. Wedge anchors
have the best and most consistent holding values of any type of
mechanical concrete anchor and come in a wide variety of diameters and
lengths. Wedge anchors are available in zinc plated, hot dipped
galvanized and stainless steel. The hole that needs to be drilled for a
wedge anchor is the same as the diameter of the anchor. Wedge anchors
may protrude from the base material at different lengths and may not be
suitable for use with certain light fixture covers.
Tapcons
Tapcon® is a registered brand name for a concrete screw.
Concrete screws tap threads into a predrilled hole in concrete, brick or
block. The standard Tapcon® comes in two diameters- 3/16" and 1/4".
They are available in two head styles- slotted hex washer and flat
phillips countersunk. Tapcons
have excellent holding values in most base materials and are very
versatile. Concrete screws are available with a Climaseal® coating that
provides excellent rust resistance as well as a 410 stainless steel
screws. Hole size for Tapcons needs to be smaller than the designated
diameter of the screw. Large diameter Tapcons are also available in a
variety of diameters and finishes (zinc plated and stainless steel).
Tapcons have a finished head and will not protrude into the light
fixture cover.
Hammer Drive Anchors
Hammer drive anchors
are excellent light duty fasteners that can be used for light fixtures.
For this application, they are available in 1/4" diameter with a zinc
plated or stainless steel nail. The low profile head is perfect for most
light fixture plates and covers. Anchor diameter equals hole size and
the wide mushroom head provides excellent bearing surface for pullout
strength.
All of these concrete anchors and fasteners
would work when fastening light fixtures to concrete. The type of
anchor chosen will depend on the unique application and the type of
light fixture being installed.
As with any anchoring project, it is important to keep safety in mind and follow instructions carefully. Always remember to wear safety goggles, handle all tools with extra care and follow all technical specifications. This article is meant to serve only as a basic explanation of concrete fasteners. Always refer to manufacturer's instructions or consult a contracting expert during any anchoring project.
Article Written By:
Bob Carlisle, President of Concrete Fasteners
Concrete Fasteners, Inc. has over 40 years of experience selling concrete fasteners. We can ship out one box or a whole pallet of concrete anchors. Our products are of the highest quality... "your satisfaction is guaranteed". We ship all orders the same day the order is received.