top Understanding the Issues

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, 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.

In the last several years, pressure-treated wood formulations have changed significantly. Many 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), CBA-A 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 pressure treatment formulations, fluctuating retention levels, moisture content, and because the formulations may vary regionally, or change without warning, understanding which connectors and 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.

305/316 stainless steel is the most effective solution to corrosion risk. However, it is also more expensive and sometimes more difficult to obtain. To best serve our customers, Simpson Strong-Tie 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® and Quik Guard® coated fasteners (see coating recommendations).

Because increased corrosion from some newer pressure-treated wood is a new issue with little historical data, we have to base our recommendations on the testing and experience we have to date. It is possible that as we learn more, our recommendations may change, but these recommendations are based on the best information we have at this time.

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 of enclosed buildings that have been designed to ensure that condensation and other sources of moisture do not develop.
   
   Exterior (Deck Boards): For outdoor deck board installation in conditions other than Higher Exposure Use.
   
   Higher Exposure Use: Includes exposure to ocean salt air, 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 and select a suitable pressure-treated wood for the intended application and environment.
   The treated wood supplier should provide all the information needed regarding 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 the needed information is not provided then Simpson would recommend the use of 305/316 stainless steel fasteners. You should also ask the treated wood supplier for a coating or material recommendation.
4. Use this chart, which was created based on Simpson Strong-Tie testing and experience to select the fastener coating or material.
   If a pressure-treated wood product is not identified on the chart, Simpson Strong-Tie has not evaluated test results regarding such product and therefore cannot make any recommendation other than the use of 305/316 stainless steel with that product. Manufacturers may independently provide test results or other product use information; Simpson Strong-Tie expresses no opinion regarding any such information.
5. Compare the treated wood supplier's recommendation with the Simpson Strong-Tie recommendation.
   If these recommendations are different, Simpson Strong-Tie recommends that the most conservative recommendation be followed.