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Fastener Corrosion Information
Metal fasteners will corrode and may lose load-carrying capacity when installed in corrosive environments or exposed to corrosive materials. There are many environments and materials which may cause corrosion including ocean salt air, fire-retardants, fumes, fertilizers, preservative-treated wood, de-icing salts, dissimilar metals, and other corrosive elements.
The many variables present in a single building environment make it impossible to accurately predict if, or when, significant corrosion will begin or reach a critical level. This relative uncertainty makes it crucial that specifiers and users be knowledgeable of the potential risks and select a product coating or metal suitable for the intended use. It is also important that regular maintenance and periodic inspections are performed, especially for outdoor applications.
It is common to see some corrosion especially in outdoor applications. Even stainless steel can corrode. The presence of some corrosion does not mean that load capacity has necessarily been affected or that a failure will occur. If significant corrosion is apparent or suspected, then the wood, fasteners and connectors should be inspected by a qualified professional engineer or qualified general contractor and may need to be replaced.
Preservative-treated wood formulations have changed significantly, and some
of the new formulations are more corrosive to steel connectors and fasteners
than the traditionally used formulation of CCA-C. Simpson Strong-Tie testing
has shown that ACQ-C, ACQ-D (Carbonate) and CA-B treated woods are
approximately 2 times more corrosive than CCA-C, while SBX-DOT
(Sodium Borate) treated woods were shown to be less corrosive than
Due to the many different preservative-treatment formulations, fluctuating retention levels, moisture content, and because the formulations may vary regionally, or change without warning, understanding which fasteners to use with these materials has become a complex task. We have attempted to provide basic knowledge on the subject here, but it is important to fully educate yourself by reviewing our technical bulletins on the topic, and also by viewing information and literature provided by others. Additionally, because the issue is evolving it is important to get the very latest information on the topic by visiting our website at www.strongtie.com/info.
Types 304/305/316 stainless-steel, copper and silicone-bronze fasteners are the most effective solution to corrosion risk. However, they are more expensive and sometimes more difficult to obtain. To best serve our customers, Simpson Strong-Tie Company Inc. is evaluating the options to identify the safest and most cost-effective solutions. Based on our testing and experience there are some specific applications that are appropriate for N2000®, mechanically galvanized (C3, N2000®, Class 55), double barrier and Quik Guard® coated fasteners (see coating recommendations).
Outdoor environments are generally more corrosive to steel. If you choose to use N2000®, mechanically galvanized (C3, N2000, Class 55), double barrier and Quik Guard® coated fasteners on an outdoor project (i.e. deck), you should periodically inspect your fasteners or have a professional inspection performed. Regular maintenance including water-proofing of the wood used in your outdoor project is also a good practice.
For preservative-treated lumber used above ground, with actual retention levels higher than 0.05 pcf for μCA-C, 0.06 pcf for MCA and CA-C, 0.08 for CA-B, 0.15 pcf for MCQ and 0.2 pcf for ACQ, types 304/305/316 stainlesssteel, copper or silicone bronze fasteners are recommended.
Testing indicates wood installed dry reduces potential corrosion. If dry wood is used, see this website for additional information.
Due to the many variables involved, Simpson Strong-Tie Company Inc. cannot provide estimates on service life of connectors, anchors or fasteners. We suggest that all users and specifiers also obtain recommendations for N2000, mechanically galvanized (C3, N2000, Class 55), double barrier and Quik Guard coated fasteners, or other coatings from the treated-wood supplier for the type of wood used. However, as long as Simpson Strong-Tie Company Inc. recommendations are followed, Simpson Strong-Tie Company Inc. stands behind its product performance and our standard warranty applies.