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 corrosive.
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