Effective December 31, 2003, the pressure treated wood industry has voluntarily discontinued the use of CCA-C to preserve wood intended for most residential and general consumer applications. Since that time, there has been some upheaval about the accelerated corrosion of fasteners and connectors that come in contact with these next-generation types of preserved wood. People inside and outside the industry have begun to express concern about the potential risks and expenses involved should a connector or fastener fail. While this is understandable, it’s important to note that the corrosion issue as a whole can be avoided through education on what has caused fastener/connector deterioration in the past and ascertaining the products used in your project are suitable for their intended application.

The Facts:

The new preservatives aren’t new. In fact, they’ve been around and in use for over ten years. The treatments are commonly known as copper azole (Type A and Type B, used in Natural Select™) and ACQ. The only difference now is that these types of preservatives will be the only ones available, instead of as an option to traditional CCA-C.

The preservatives used today are more environmentally friendly. One of the major contributing factors to changing from CCA-C preservatives to alternative systems is the positive environmental impact. While CCA-C treated wood has low corrosivity, there was a perception that its preservative presented health and environmental hazards.  

So, while the new treatments have the potential to corrode certain fasteners, when the new preserved wood is used correctly it is just as long-lasting as CCA-C treated wood and generates greater confidence regarding the health and well being of the people, animals, plant life, and eco-systems that come in contact with it.

Testing shows the new preservative-treated wood will perform as intended if used properly. According to Arch Chemicals’ Tech Notes Series 1.0 from February 2004, they have completed extensive testing and research both in and out of the lab in accordance to the American Wood-Preservers’ Association regarding the new wood treatments. Their Tech Notes Series 1.0 states they have “submitted AWPA E12 Corrosion Tests on both copper azole Type A and B for committee consideration. These tests showed that corrosion rates of Natural Select™ (CBA-A and CA-B) treated wood as well as CCA treated wood, in contact with hot dipped galvanized steel, were less than 2 mils per year (mpy) and in the ‘excellent range’ of 1-5 mpy according to the ‘Corrosion Engineering Handbook’.  The makers of ACQ have also provided data to the AWPA on 3 of the 4 types of ACQ, Types B, C, and D. Their recent results for the amine formulations in the range of 6-7 mpy are categorized as ‘good’ in the ‘Corrosion Engineering Handbook’.”

Additionally, Arch has performed ten years of research into the real life service of copper azole treated wood throughout the world. According to their statement, they found that Wolmanized® Natural Select™ treated wood (copper azole treated wood) “can be expected to perform as intended.”

Corrosion is avoidable. While few things last forever, corrosion in fasteners and connectors can be at least minimized. What’s important is that specifiers are knowledgeable about the products they are working with and select connectors and fasteners made of the correct metal or made with coatings suitable for their intended purpose.

For years, the treated wood industry has recommended the use of stainless steel or hot-dip galvanized fasteners and connectors. Even with the new preservative treatments, this recommendation holds although thickness levels must now be taken into consideration as well.  As Tommy Kyzer, vice president of Arch Chemicals stated in a Technical Note issued on February 25, 2004, “If builders and DIYers follow our hardware recommendations, they can expect no corrosion problems in structures built in typical environments.”

Connector and fastener corrosion has always occurred. Corrosive environments and materials that may cause deterioration in metal connectors and fasteners are everywhere and always have been. Some of the more common examples are: dissimilar metals, fire-retardants, fertilizers, fumes, and ocean salt air. Unfortunately, there are just too many variables in any single situation to predict when, or even if, corrosion will compromise the stability of a structure.

Recommended Practices and Uses:

Arch Chemicals states that when using treated wood for permanent wood foundations, use 304 or 316 stainless steel. For most other applications, “hot-dipped galvanized fasteners (meeting ASTM A 153) and connectors (ASTM A 653 Class G185 sheet), or better, are recommended.” They further assert that aluminum should not be used in direct contact with treated wood.

Simpson Strong-Tie states, “thicker galvanizing generally extends service life of a product. The treated wood industry recommends use of Stainless Steel and hot-dip galvanized connectors and fasteners with treated wood. G60 galvanized products should not be used with treated woods. G90 galvanized connectors can be used with Sodium Borate (DOT - Disodium Octaborate Tetrahydrate) treated woods. Sodium Borate treated woods are not suitable for applications where moisture exposure is likely. They are suitable for mudsill applications when transported, stored, and installed appropriately.  When using Stainless Steel or hot-dip galvanized connectors, the connectors and fasteners should be made of the same material. We suggest that all users and specifiers obtain recommendations for Batch/Post HDG, G185 HDG, mechanically galvanized, or other coatings from their treated wood supplier.” Adhering to their own philosophy, Simpson has upgraded their ‘normal’ fasteners from a G60 coating (.60 ounces per sq. foot of zinc.) to a G-90 coating. Z-Max, their high-end fastener, is rated a G-185 coating (1.85 ounces per sq. foot of zinc) for superior protection.

At Truitt and White, we have made a number of inventory adjustments in our connector and fastener department to meet the requirements of hardware and treated wood compatibility. Dave Yungert, in our hardware sales department comments, “We now stock more stainless steel fasteners to meet the growing demand, and have also added Simpson’s heavier zinc coated products to our regular stock (instead of keeping them special order). Additionally, we’re stocking a wider selection of Simpson’s hot-dip galvanized products. And as always, any fastener we don’t have in stock, we can special order.”

Overall, the new preservative treated wood systems are not drastically different from traditional CCA-C wood, they just require a little more thought regarding your choice of fasteners and connectors. Should you require more information on the preservative treated wood changes, our store carries literature that addresses the changes and the effects it will have on construction projects. And of course, our staff is well prepared with extensive on-site knowledge, training, and education to help you choose the right fasteners and connectors. For technical information about specific projects and installations, we always recommend checking with your local building department, engineer or architect.

Happy Building!