Corrosion Information for Connectors and Fasteners with Wood
In the discussion and charts of this section, Simpson Strong-Tie presents a system to determine which product coatings and base metals to use in a range of corrosion conditions. These are general guidelines that may not consider all relevant application criteria. Refer to product-specific information for additional guidance.
Simpson Strong-Tie evaluated the AWPA Use Categories (See AWPA U1-16) and ICC-ES AC257 Exposure Conditions and developed a set of corrosion resistance recommendations. These recommendations address the coating systems and materials used by Simpson Strong-Tie for fastener, connector, and anchor products. Although the AWPA Use Categories and ICC-ES AC257 Exposure Conditions specifically address treated-wood applications and some common corrosion agents, Simpson Strong-Tie believes that its recommendations may be applied more generally to other application conditions, insofar as the service environments discussed are similar. You should consult with acorrosion engineer concerning the application where advisable.
Guidelines for Selecting Corrosion-Resistant Connectors and Fasteners
Step 1 — Evaluate The Corrosion Conditions
- Dry Service: Generally INTERIOR applications including wall and ceiling cavities, raised floor applications in enclosed buildings that have been designed to prevent condensation and exposure to other sources of moisture. Prolonged periods of wetness during construction should also be considered, as this may constitute a Wet Service or Elevated Service condition. Dry Service is typical of AWPA UC 1 and UC 2 for wood treatment and AC257 Exposure Condition 1. Keep in mind that dry-service environment may contain airborne salts. AC257 Exposure Condition 2 reflects the presence of airborne salt in a dry-service environment and corrosion hazard to exposed metal surfaces. It does not include effects of treatment chemicals. This condition is generally considered in Elevated and Uncertain assessments.
- Wet Service: Generally EXTERIOR construction in conditions other than elevated service. These include Exterior Protected and Exposed and General Use Ground Contact as described by AWPA UC4A. The AWPA U1 standard classifies exterior above-ground treatments as Use Categories UC 3 (A and B) depending on moisture run-off; and for exterior ground-contact levels of protection, it has Use Categories UC 4 (A-C). ICC-ES AC257 considers the exterior exposure to be limited by the presence of treatment chemicals, and corrosion accelerators. In general, the AC257 Exposure Condition 1 includes AWPA Use Categories UC 1 (interior/dry) and UC 2 (interior/ damp), while Exposure Condition 3 is a surrogate to UC3A, 3B, and 4A (exterior, above-ground and ground-contact, general use). The ICC-ES AC257 Exposure Conditions 2 and 4 are exposures that are salt environments.
- Elevated Service: Includes fumes, fertilizers, soil, some preservative-treated wood (AWPA UC4B and UC4C), industrial-zone atmospheres, acid rain, salt air, and other corrosive elements.
- Uncertain: Unknown exposure, materials, or treatment chemicals.
- Ocean/Water Front Service: Marine environments that include airborne chlorides, salt air, and some salt splash. Environments with de-icing salts are included.
Step 2 — Determine Your Corrosion Resistance Classification
To determine the appropriate classification, please refer to the Corrosion Resistance Classification table on the General Corrosion Information page.
Step 3 — Match Your Corrosion Resistance Classification to the Coatings and Materials Available
To match your classification to the available coatings and materials, please refer to Materials and Coatings for Connectors or Materials and Coatings for Fasteners.
Preservative Treated Wood Information
Simpson Strong-Tie Concrete Embedded Products in Hawaii
Simpson Strong-Tie is aware of problems regarding concrete spalling and corrosion around the perimeter of some homes in the State of Hawaii, related to certain concrete embedded products made by multiple manufacturers, including Simpson Strong-Tie. The specific Simpson Strong-Tie products include STHD/LSTHD strap-tie holdowns and MAS/MASA mudsill anchors. We have investigated these products extensively and do not believe any defect in their design or manufacture is the cause of the problems. Information gathered to date indicates it is a minority of strap-tie holdowns and mudsill anchors that are experiencing the corrosion problem. Nonetheless, Simpson Strong-Tie takes these instances seriously and is investigating the cause of corrosion with these embedded products.
At this time, we have not yet been able to determine a definitive underlying cause for the corrosion on these homes. In general, we have identified a number of factors that may cause corrosion in the embedded products, including: mis-installation, the local environment, and construction practices and materials. In some instances, non-Simpson Strong-Tie metal products in contact with the foundation, such as bottom tracks and reinforcing bar, are also experiencing corrosion. For additional information on corrosion and corrosion resistance of Simpson Strong-Tie products, please go to strongtie.com/corrosioninformation.
Until better guidance can be provided to the Hawaii construction industry about how to avoid corrosion of strap-tie holdowns and mudsill anchors, Simpson Strong-Tie recommends builders work closely with their specifiers and corrosion experts to make sure they understand the corrosion issues that may present themselves on any given project. Our company, along with other manufacturers, offers alternative interior products which have not experienced spalling or corrosion issues. It may be more appropriate to use those products until a more definitive answer is available for the corrosion issues with the STHD/LSTHD strap-tie holdowns, and MAS/MASA mudsill anchors in Hawaii.
If you have additional questions or need further assistance regarding this matter, please contact our Hawaii representative at (808) 479-1216 or the Simpson Strong-Tie Engineering department at (800) 999-5099.