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Guidelines for Selecting the Proper Materials and Coatings
for Connectors For Wood Construction
and Anchoring and Fastening Systems for Concrete and Masonry
updated 3/21/12

Simpson Strong-Tie® products feature a wide range of materials and coatings designed to meet specific performance criteria. It is important to select a material and/or coating that is suitable for the intended application and environment based upon factors such as corrosion resistance and mechanical properties of the material. Please see General Corrosion Risks and Simpson Strong-Tie Materials and Coatings Available for more information on selecting connectors and anchors for concrete and masonry based upon corrosion resistance.

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 product will be used is an important factor in selecting the most appropriate material and coating for use. To help in your decision making, consider the following general exposure information:

Interior Dry: 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 Dry: Includes outdoor installations in low rainfall environments and no regular exposure to moisture.

Exterior Wet: Includes outdoor installations in higher moisture and rainfall environments.

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 used

When metal is in contact with most untreated wood and other common building materials, additional corrosion risk caused by the material is not a significant factor. When fastening dissimilar metals carefully consider the correct combination of fastener and material necessary to avoid galvanic corrosion.  For preservative-treated wood applications proceed to step four, otherwise proceed to step five.

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.  It is also advisable to obtain a recommendation from the treated-wood supplier for a 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 the Environment/Treatment Classification Chart below to match the proper classification to the environment and base material application.  Then use the appropriate Materials and Coatings Available listing to select the proper coating or material..

If a preservative-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 coatings/materials shown in the "high" category below. Manufacturers may independently provide test results or other product use information; Simpson Strong-Tie expresses no opinion regarding any such information.

Environment/Treatment Classification Chart
Environment Untreated Wood SBX/DOT & Zinc Borate MCA/MCQ ACQ-C, ACQ-D (Carbonate),
CA-B, CA-C & μCA-C 7		 ACZA Other
or
Uncertain
No Ammonia With Ammonia Higher Chemical Content 1
Interior Dry Low Low Low Med 3 Med High High High
Exterior Dry 8 Low N/A 2 Med Med High High High High
Exterior Wet 9 Med N/A 2 Med 4, 5 Med 4, 5 High High High High
Higher Exposure or Uncertain High N/A 2 High High High High High High
  1. Higher chemical content refers to wood for ground contact with actual retention levels greater than 0.40 pcf for ACQ, 0.34 pcf for MCQ, 0.21 pcf for CA-B, 0.15 pcf for CA-C and MCA, or 0.14 pcf for μCA-C.  In these cases, stainless-steel products are recommended. Verify actual retention levels with the wood treater.
  2. Borate treated woods are not appropriate for outdoor use.
  3. Where noted in the table, applications where the wood is dry (moisture content less than 19%) when installed and will remain dry in-service may use a minimum classification coating recommendation of "Low" for connectors.
  4. Some treated wood may have excess surface chemicals making it potentially more corrosive.  If uncertain, use types 304/305/316 stainless steel products.
  5. Test results indicate that ZMAX, hot-dip galvanized, and mechanically galvanized (class 55 and 65) will perform adequately, subject to regular maintenance and periodic inspection. However, the test protocol followed was a modified version of the nationally recognized test method AWPA E12-94. This test method is an accelerated test, so data over an extended period of time is not available. Also noteworthy is that tests run in a laboratory may not correlate to service conditions. If uncertain, use stainless steel.
  6. Type 316 stainless-steel products are the minimum recommendation for ocean-salt air and other chloride environments.
  7. Ammonia is typically used as a chemical carrier for difficult to treat wood species, such as, but not exclusive to, Douglas Fir and Hem Fir, which are usually found in the western United States. Amine carriers are used in some of the eastern species, such as Southern Yellow Pine. If uncertain, verify chemical with wood treater.
  8. Exterior Dry applications only apply to connectors. For anchors, use Exterior Wet for any exterior application.
  9. Mechanically galvanized Titen HD® anchors (medium classification) are only recommended for temporary exterior applications.

 

Additional information

For additional critical information please see the Preservative Treated Wood Technical Bulletin (PDF), Preservative Treated Wood Frequently Asked Questions, and General Corrosion Risks.

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