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 CCA-C. (See technical bulletin T-PTWOOD for details).

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).

top General Simpson Strong-Tie 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.

top Guidelines for Selecting the Proper Fastener Coating

1. Evaluate the Application.
   Consider the type of structure and how it will be used. These recommendations may not apply to non-structural applications such as fences.
2. Evaluate the Environment.
   Testing and experience indicate that indoor dry environments are less corrosive than outdoor environments. Determining the type of environment where a fastener will be used is an important factor in selecting the most appropriate material and coating for fastener use. To help in your decision making, consider the following general exposure information:
   
   Interior Dry Use: Includes wall and ceiling cavities, and raised floor applications in enclosed buildings that have been designed to ensure that condensation and other sources of moisture do not develop.
   
   Exterior: Includes outdoor construction in conditions other than Higher Exposure Use.
   
   Higher Exposure Use: Includes exposure to ocean salt air, de-icing salts, fire retardants, large bodies of water (e.g. dock boards), fumes, fertilizers, soil, some preservative-treated woods, industrial zones, acid rain, and other corrosive elements.
3. Evaluate the material to be fastened.
   When fastening most untreated wood and other common building materials, additional corrosion risk caused by the fastened material is not a significant factor. For preservative-treated wood applications, proceed to step four otherwise proceed to step five.
   
   When fastening dissimilar metals carefully consider the correct combination of fastener and material necessary to avoid galvanic corrosion.
4. Familiarize yourself with the preservative-treated wood to be fastened.
   The preservative-treated-wood supplier should provide all of the pertinent information about the wood being used. This information should include the specific type of wood treatment used, if ammonia was used in the treatment and the chemical retention level. If this information is not available, then Simpson Strong-Tie Company Inc. recommends the use of types 304, 305 or 316 stainless steel, copper or silicone-bronze fasteners. It is also advisable to obtain a recommendation from the treated-wood supplier for a fastener coating or material that is suitable for use with their formulation in the intended environment. If this recommendation differs from those shown in the table below, Simpson Strong-Tie Company Inc. recommends that the most conservative recommendation be followed.
5. Use this chart, which is based on Simpson Strong-tie testing and experience, to select the fastener coating or material.
   If the material or preservative-treated wood product to be used is not show on the chart, Simpson Strong-Tie has not evaluated it and cannot make any other recommendation than the use of coatings/materials shown in the "high" category shown below. Manufacturers may independently provide test results or other product use information; Simpson Strong-Tie Company Inc. expresses no opinion regarding such information.