The five types of wedge anchors
are categorized based on the steel of which they are made or the
coating that protects them. Zinc plated wedge anchors are not
recommended for outdoor use because the zinc plating has low rust
resistance. Galvanized wedge anchors (both hot dipped and mechanically
galvanized) can be used in unpolluted, exterior environments because
they provide a medium level of rust resistance. These anchors are also
suitable for humid environments. The stainless steel wedge anchor is
available in three different types of stainless steel including: 303,
304 and 316 stainless steel. Type 303 and 304 perform equally well in
certain corrosive environments. For the greatest degree of corrosion
resistance, use the Type 316 stainless steel wedge anchor. Find more technical information about wedge anchors.
Wedge anchors will corrode and may lose some
load carrying capacity if they are installed in corrosiveareas or
exposed to different types of corrosive materials.The areas and
materials which may create a corrosive environment range from pressure
treated wood (ACQ), salt water, ocean salt air, fertilizers and the
exposure to two dissimilar metals or to other elements that are
There are numerous variables that make it
impossible to predict if or when corrosion may occur in the environment
in which the wedge anchor is placed. Therefore, it is essential that
periodic inspections and regular maintenance be scheduled on wedge
anchors used outdoors.
When using wedge anchors in an outdoor
application, it is not uncommon for some corrosion to occur. Stainless
steel wedge anchors may even corrode in some specific types of
applications, although small amounts of corrosion may not affect the
anchors' holding values. If a large amount of corrosion is suspected, it
is imperative that the wedge anchors be inspected and replaced by a
professional if needed.
Hot dipped galvanized wedge anchors are anchors that have been coated
with Zinc through a method of galvanizing iron or steel by passing it
through a bath of molten zinc. This process is done in order to prevent
galvanic corrosion. Hot dipping steel is a procedure that has been done
for more than 150 years in order to create a physical barrier for the
exposed steel. Hot dipped galvanized wedge anchors are favored over
stainless steel because of their lower cost.
Wedge anchors are also available in stainless
steel. Stainless steel is a steel alloy with a minimum of 11% chromium
content by mass. It is important to remember that stainless steel is stain-less not stain-proof.
The difference between stainless steel wedge anchors and carbon steel
(i.e. zinc plated and hot dipped galvanized wedge anchors) is the amount
of chromium present. Carbon steel will rust when exposed to moisture
and air. The rust, or iron oxide film, is very active and will
accelerate corrosion by forming even more iron oxide. Sufficient amounts
of chromium present on stainless steel provides a film of chromium
oxide which prevents corrosion from spreading.
The cost of wedge anchors increases with the
more rust resistance it offers. Below is an outline of the different
types of wedge anchors:
Zinc plated wedge anchors
provide the least rust resistance and are the least costly but are not
recommended for outdoor use. These anchors are excellent for indoor
usage or in a location where moisture is not present.
Hot dipped galvanized wedge anchors
provide a medium level of corrosion resistance and are suitable for use
outdoors or in humid environments. These anchors cost about twice as
much as the zinc plated anchors.
Stainless steel wedge anchors in
the 303 and 304 designations provide excellent corrosion resistance and
work well in most corrosive environments. It is estimated that they
cost about 2x as much as the hot dipped anchors. The 316 stainless steel
provides the greatest corrosion resistance in the most environments.
These stainless steel anchors cost about twice as much as the 303 or
304 stainless steel.
If wedge anchors are the correct concrete
fasteners for your application, make sure that you purchase the correct
one for outdoor use. Also, inspect these wedge anchors regularly after
installation to be certain that corrosion has not affected the holding
values of these anchors.
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