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Guidelines for Selecting the Proper Materials and Coatings

updated 12/28/16

Simpson Strong-Tie connectors, anchors and fasteners 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. For more information on selecting connectors, anchors and fasteners based upon corrosion resistance, please see General Corrosion Risks, Guidelines for Selecting the Proper Materials and Coatings, Materials and Coatings Available – Connectors, and Materials and Coatings Available – Fasteners for more information on selecting products based on corrosion resistance.

Evaluate the Application

Consider the importance of the connection.

Evaluate the Exposure

Consider these moisture and treatment chemical exposure conditions:

  • Dry service: Generally INTERIOR applications and includes wall and ceiling cavities, raised floor applications in enclosed buildings that have been designed to prevent condensation and exposure to other sources of moisture.
  • 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 the AWPA UC4A.
  • Elevated Service: Includes fumes, fertilizers, soil, some preservative-treated wood (AWPA UC4B and UC4C), industrial zones, acid rain and other corrosive elements.
  • Uncertain: Unknown exposure, materials, or treatment chemicals.
  • Ocean/Water Front: Marine environments that include airborne chlorides and some splash. Environments with de-icing salts are included.
  • Treatment Chemicals: See AWPA Use Category Designations. The preservative-treated wood supplier should provide all of the pertinent information about the wood being used. The information should include Use Category Designation, wood species group, wood treatment chemical, and chemical retention. See appropriate evaluation reports for corrosion effects of treatment chemicals and fastener corrosion resistance recommendations.
  • Fire-Retardant-Treated (FRT) Wood: Metal connectors in contact with FRT wood in dry service applications may generally be uncoated, painted or galvanized G90 zinc-coated steel. Refer to the FRT wood manufacturer’s recommendations for fastener and connector protection requirements. The 2015 IBC Section 2304.10.5.4 and 2015 IRC Section R317.3.4 refer to the manufacturer’s recommendations for fastener corrosion requirements. In the absence of recommendations from the manufacturer, the code requires fasteners to be hot-dip galvanized, stainless steel, silicon bronze or copper. Fastener shear and withdrawal allowable loads may be reduced in FRT lumber. Refer to the FRT manufacturer’s evaluation report for reduction factors.

Use the Simpson Strong-Tie Corrosion Classification Table

If the treatment chemical information is incomplete, Simpson Strong-Tie recommends the use of a 300 series stainless steel product. Also if the treatment chemical is not shown in the Corrosion Classification Table, then Simpson Strong-Tie has not evaluated it and cannot make any recommendations other than the use of coatings and materials in the Severe category. Manufacturers may independently provide test results of other product information; Simpson Strong-Tie expresses no opinion regarding such information.

Corrosion Resistance Recommendations
Low Medium High Severe
FASTENERS & ANCHORS
Phosphate (gray, black),
Clear (bright) zinc (ASTM F1941),
Heavy electro-galvanized (ASTM A641-Class 1),
Yellow zinc (ASTM F1941),
Electrocoat (E-coat),
Type 410 stainless steel
Mechanically galvanized (AS 3566.2-C3, N2000, ASTM B695-Class 55),
Quik Guard® coating,
Hot-dip galvanized (ASTM A153-Class D),
Double-barrier coating,
Type 410 stainless steel with protective top coat
Type 304 stainless steel,
Type 305 stainless steel
Type 316 stainless steel,
Hot-dip galvanized (ASTM A153-Class C),
Silicon bronze, Copper
CONNECTORS
Simpson Strong-Tie gray paint Powder coating Standard G90 zinc coating ZMAX® (G185) Hot-dip galvanized (ASTM A123) Type 316L stainless steel Type 316L stainless steel
Corrosion Resistance Classifications
Environment Material to be Fastened
Untreated Wood or Other Material Preservative-treated Wood FRT Wood
SBX-DOT Zinc Borate Chemical Retention ≤ AWPA, UC4A Chemical Retention > AWPA, UC4A ACZA Other or Uncertain
  1. These are general guidelines that may not consider all application criteria. Refer to product specific information for additional guidance.
  2. Type 316/305/304 stainless steel products are recommended where preservative treated wood used in ground contact has a chemical retention level greater than those for AWPA UC4A; CA-C, 0.15 pcf; CA-B, 0.21 pcf; micronized CA-C, 0.14 pcf; micronized CA-B, 0.15 pcf; ACQ-Type D (or C), 0.40 pcf.
  3. Testing by Simpson Strong‑Tie following ICC-ES AC257 showed that mechanical galvanization (ASTM B695, Class 55), Quik Guard coating, and Double Barrier coating will provide corrosion resistance equivalent to hot-dip galvanization (ASTM A153, Class D) in contact with chemically treated wood in dry service and wet service exposures (AWPA UC1-UC4A, ICC-ES AC257 Exposure Conditions 1 and 3) and will perform adequately subject to regular maintenance and periodic inspection.
  4. Mechanical galvanizations C3 and N2000 should not be used in conditions that would be more corrosive than AWPA UC3A (exterior, above ground, rapid water run off).
  5. If uncertain about Use Category, treatment chemical, or environment, use Types 316/305/304 stainless steel, silicon bronze or copper.
  6. Some treated wood may have excess surface chemicals making it potentially more corrosive than lower retentions. If this condition is suspected, use Type 316/305/304 stainless steel, silicon bronze, or copper fasteners.
  7. Type 316 stainless steel, silicon bronze, and copper fasteners are the best recommendation for ocean salt-air and other chloride-containing environments. Hot-dip galvanized fasteners with at least ASTM A153, Class C protection can also be an alternate for some applications in environments with ocean air and/or elevated wood moisture content.
  8. Some woods, such as cedars, redwood and oak, contain water-soluble tannins and are more susceptible to staining when in contact with metal connectors and fasteners. According to the California Redwood Association (calredwood.org), applying a quality finish to all surfaces of the wood prior to installation can help reduce the amount of staining, which in redwood, for example, is caused by surface tannins leaching out during rains.
  9. Fasteners in contact with FRT lumber shall be hot-dip galvanized, stainless steel, silicon bronze or copper unless recommended otherwise by the FRT manufacturer. Some FRT manufacturers permit low-resistant finishes for interior dry conditions. Fastener shear and withdrawal capacities may be reduced in FRT lumber. Refer to the FRT manufacturer’s code report for reduction factors.
Dry Service Low Low Low High Med High Med
Wet Service Med N/A Med High High High High
Elevated Service High N/A Severe Severe High Severe N/A
Uncertain High High High Severe High Severe Severe
Ocean/Water Front Severe N/A Severe Severe Severe Severe N/A

Dry Service

dry-service

Wet Service

wet-service

Severe

severe