Updated 7/1/2008
Metal connectors, anchors, and fasteners will corrode and lose load carrying capacity if installed in corrosive environments or exposed to corrosive materials. Ocean salt air, fire-retardants, pressure-treated wood, fertilizers, fumes, dissimilar metals, and other elements are potentially corrosive materials that may adversely affect the load carrying capacity of these products. Connectors, anchors, and fasteners should not be installed in potentially corrosive conditions unless the product coating or metal is suitable for the intended use. Some Simpson products are available in stainless steel or with coating options that are more corrosion resistant. The most appropriate products should be carefully selected for the intended use. To further increase product durability and safety, Simpson recommends that compatible metals always be used together, including fasteners, and that the products receive frequent post-installation inspection, especially for outdoor applications. There are many variables affecting corrosion: environmental variables, including heat, moisture, humidity, rain, salt, cleaning products, proximity to bodies of water, pools, animal facilities or other corrosive environments; fire retardants, fertilizers, fumes, chemicals, and other corrosive materials and factors; wood-based variables, including wood species, moisture content, type of wood preservative, chemical carriers and additives, chemical quantities and retention levels, curing, storage, and installation.
Pressure Treated Wood
The pressure-treated wood industry has transitioned away from the use of Chromated Copper Arsenate (CCA-C) to alternative preservative systems for residential use, effective 12/31/03. Some of the replacement alternatives are generally more corrosive than CCA-C. The corrosive content of treated wood may be variable. Over time, the durability and load-carrying capacity of Simpson products used with treated woods can vary widely depending on the many variables. This makes it impossible to predict accurately if, or when, significant corrosion of connectors, anchors, and fasteners will begin or reach a critical level. The treated wood industry specifies or recommends stainless steel and hotdip galvanized products for use with pressure treated wood. To select the appropriate connector for use with various pressure treated woods, see the Pressure Treated Wood Technical Bulletin.
Warning
While galvanized steel provides some protection, testing has shown that it is still likely to corrode if in contact with treated wood. The service life of galvanized parts depends on many variables including the location, installation, exposure, and the thickness of the galvanized coating.
Guidelines for Selecting the Proper Connector
Consider the type of structure and how it will be used. These recommendations may not apply to non-structural applications such as fences.
Testing and experience indicate that indoor dry environments are less corrosive than outdoor environments. Determining the type of environment where a connector or fastener will be used is an important factor in selecting the most appropriate material and finish for use on the connectors and fasteners. 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 - 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, large bodies of water, fumes, fertilizers, soil, some preservative treated woods, industrial zones, acid rain, and other corrosive elements.
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 Stainless Steel connectors and fasteners. You should also ask the treated wood supplier for a connector coating or material recommendation.
If a pressure treated wood product is not identified on the chart, Simpson has not evaluated test results regarding such product and therefore cannot make any recommendation other than the use of Stainless Steel with that product. Manufacturers may independently provide test results or other product use information; Simpson expresses no opinion regarding any such information.
| Environment |
Untreated Wood |
SBX/DOT & Zinc Borate |
MCQ |
ACQ-C, ACQ-D (Carbonate), CA-B & CBA-A |
ACZA |
Other or Uncertain |
||
|
No Ammonia |
With Ammonia Higher |
Chemical Content1 |
||||||
| Interior Dry | Low | Low | Low | Med5 | Med | High | High | High |
| Exterior - Dry | Low | N/A2 | Med | Med | High | High | High | High |
| Exterior - Wet | Med | N/A2 | Med3, 4 | Med3, 4 | High | High | High | High |
| Higher Exposure | High | N/A2 | High | High | High | High | High | High |
| Uncertain | High | N/A2 | High | High | High | High | High | High |
Low = Use Simpson standard painted and G90 galvanized connectors as a minimum.
Med = Use ZMAX®/HDG galvanized connectors as a minimum. Use fasteners which meet the specifications of ASTM A153 or SDS screws with double-barrier coating.
High = Use Type 303, 304, 305 or 316 Stainless Steel connectors and fasteners.
- Woods with actual retention levels greater than 0.40 pcf for ACQ and MCQ, 0.41 pcf for CBA-A, or 0.21 pcf for CA-B (Ground Contact level).
- Borate treated woods are not appropriate for outdoor use.
- Test results indicate that ZMAX/HDG and the SDS double-barrier coating will perform adequately, subject to regular maintenance and periodic inspection. However, the nationally-approved test method used, AWPA E12-94, is an accelerated test, so data over an extended period of time is not available. If uncertain, use Stainless Steel.
- Some treated wood may have excess surface chemicals making it potentially more corrosive. If you suspect this or are uncertain, use Stainless Steel.
- 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 coating recommendation of "Low".
If these recommendations are different, Simpson recommends that the most conservative recommendation be followed.
