ACQ Information Sheet
In 2003, manufacturers of treated wood products made a voluntary decision to discontinue production of consumer-use pressure-treated lumber products by December 31, 2003, in favor of recently developed arsenic free wood preservatives. Unfortunately, these new preservatives (primarily Alkaline Copper Quaternary (ACQ) and Copper Boron Azole (CBA) have proven to corrode fasteners and hardware more readily than Chromated Copper Arsenate (CCA), which was the prevalent treatment process for wood prior to 2004.
The 2003 International Building Code (which supercedes the Building Officials Code Administrators (BOCA) code due to the merger of BOCA, International Conference of Building Officials (ICBO) and Southern Building Code Conference International (SBCCI) into the new International Code Council (ICC) in 1994), specifies the use of hot-dipped zinc-coated galvanized steel, stainless steel, silicon bronze or copper fasteners for use with preservative treated and fire-retardant-treated wood. In 2004 the ICC will be considering a proposal which modifies this language to recognize the equivalency of mechanical galvanization to hot-dipping. |
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Our No-Co-Rode plating uses the same basic plating material used in hot dip galvanizing but applies it using the mechanical galvanizing process. Hot-dip galvanizing works well with nails but tends to clog the driving recess and threads of a screw. Our No-Co-Rode mechanically galvanized screws have historically out-performed hot-dipped galvanized fasteners when used in CCA treated wood in most common exterior uses. In addition, we expect 100% of our No-Co-Rode plated screws to have functional recesses - unplugged by the plating process. McFeely's Square Drive Screws performs its own plating thickness measurements in-house on every fastener production lot to insure compliance with our coating thickness requirements - a critical factor affecting corrosion resistance.
In a recent test, screws with our No-Co-Rode plating showed no appreciable difference in corrosion rates between their use in CCA treated lumber or the new ACQ treated lumber. In this test, fasteners driven into these pressure treated materials were subjected to 1104 hours exposure in a neutral salt spray chamber. Unlike some mechanically galvanized fasteners, our No-Co-Rode plating includes the addition of a clear, proprietary sealer coat, which provides a barrier coat over the sacrificial zinc plating.
As an alternative to steel with some type of protective covering or plating, fasteners made from Stainless Steel are inherently corrosion resistant. When properly sized and installed, Stainless Steel fasteners are generally expected to outlast the material they are securing in all but the most demanding environments. For many projects and applications, their maintenance-free service life makes it relatively easy to justify their higher cost compared to plated products.
At this point, no one knows whether the bar of expectation for galvanized fastener life will need to be lowered or not. There is no question that the new pressure treated materials can accelerate galvanized fastener corrosion. You can be sure, however, that McFeely's Square Drive Screws is committed to making sure that our NoCoRode galvanized fasteners are as corrosion resistant in the new materials as possible. Nevertheless, woodworkers should carefully balance the extra cost of stainless steel fasteners against the probable service life of their project when deciding which fastener type to use.
Various Wood Treatment Manufacturers' statements concerning fasteners:
www.chemspec.com (ACQ)
"As a minimum requirement for use with Preserve® and Preserve Plus® treated wood, hot-dipped galvanized coated fasteners should conform to ASTM Standard A-153. For optimum performance and longevity in treated wood, stainless steel fasteners should be considered."
CSI One Woodlawn Green
200 East Woodlawn Rd, Suite 250
Charlotte, NC 28217
Tel: 1-800-421-8661
www.naturalselect.com (Copper Azole CBA)
"The effect of Wolmanized Natural SelectTM wood on fasteners is similar to that of CCA treated wood. Hot-dipped fasteners meeting ASTM A-153 are recommended for protection against the moisture often present where treated wood is usually used. For Permanent Wood Foundations, use 304 or 316 stainless steel. Aluminum should not be used in direct contact with this wood."
Arch Wood Protection, Inc.,
1955 Lake Park Drive, Suite 250
Smyrna, Georgia 30080
Tel: 1-770-801-6600
www.osmose.com (Borate Treated Lumber and ACQ)
"Fasteners for use with NatureWood® preserved wood products include hot-dip galvanized fasteners conforming to the ASTM Standard A-153. Stainless steel fasteners are required for Permanent Wood Foundations below grade and are recommended for use with treated wood in other severe exterior applications such as swimming pools, salt water exposure, etc. Type 304 and 316 are the recommend grades to use."
Osmose, Inc.,
1016 Everee Inn Road
Griffin, Georgia 30224
Tel: 1-800-241-0240
Building Code Requirements
2003 International Residential Code - Fastener Statement - Section R319.3
"Fasteners for pressure-preservative treated wood shall be of hot-dipped galvanized steel*, stainless steel, silicon bronze or copper. Exception: One-half inch (12.7 mm) diameter or greater steel bolts."
2003 International Building Code - Fastener Statement Section 2304.9.5
"Fasteners for preservative-treated and fire-retardant-treated wood shall be hot-dipped zinc-coated galvanized steel*, stainless steel, silicon bronze or copper."
Note: Electroplated galvanized fastener and metal products are typically not accepted by the building codes for use in exterior applications, regardless of the type of wood used.
* International Code Council pending code changes
Agenda for the 2004 Code Development Final Action Hearings (FAH) to be considered May 17-20, 2004, in Overland Park, Kansas
INTERNATIONAL BUILDING CODE - STRUCTURAL
Committee action is to amend and modify proposal as follows:
1. 2304.9.5 Fasteners in preservative-treated and fire-retardant-treated wood. Fasteners for preservative- treated and fire-retardant-treated wood shall be of hot-dipped (remove word hot dipped) zinc-coated galvanized steel, stainless steel, silicon bronze or copper. The coating weights for zinc-coated fasteners shall be in accordance with ASTM A 153, (add following statement) or an equivalent coating thickness in accordance with ASTM B 695. Fastenings for wood foundations shall be as required in AF&PA Technical Report No. 7.
Committee Recommendation: Amend
Comments: Exception is taken to the use of the word hot-dipped. The use of the word hot-dipped in this code implies and limits the use of galvanized fasteners to only those produced from the hot-dipped process. The coating thickness weights as published in ASTM A 153 can be achieved by other galvanizing methods, specifically mechanical galvanizing. Mechanical galvanizing has been published and widely accepted as an alternative to hot-dip galvanizing for over thirty years.
By limiting the language to hot-dip many manufactures, galvanizers, and end users will be at a disadvantage. Although the two processes are applied differently they both offer equivalent coating thicknesses and corrosion protection. However, in some cases each process offers its special advantages. One example being recessed fasteners. The hot-dip process will fill the recess making the fastener unusable, where as the mechanical galvanizing process because of its application will coat all surfaces of the fastener without head fill. In summary, by changing the language to allow for both forms of galvanizing you offer the industry a choice to best fit their specific need while maintaining a standard for coating thickness and corrosion resistance.
Why Galvanize?
Any type metal can corrode. Corrosion is the reaction between a metal or alloy and its environment. This chemical reaction, generally oxidation, results in a deterioration of the material and alters its mechanical properties. Any steel nail or screw left unprotected the presence of oxygen and an electrolyte will eventually deteriorate.
Zinc is used as a protective coating when applied to steel - It is sacrificial - meaning it will corrode before the steel, until the zinc is gone. The Zinc coating protects the base steel by sacrificing itself slowly by galvanic action to a making use of it's self-healing properties. This continues as long as any zinc remains in the area.
Mechanical Galvanizing
Hot Dip Galvanizing is a good choice for corrosion protection of larger pieces of steel but presents problems for some small parts which may be difficult to hot dip effectively, or may have recesses prone to plugging. Connectors, bolts, and fasteners such as square drive screws require clean threads and recesses that can require extensive clean up after hot-dip galvanizing. Mechanical Galvanizing delivers the sacrificial protection of zinc and the smooth finish required for this type application. Our NoCoRode plating results when mechanically galvanized fasteners are top-coated with a clear sealant coat that offers another layer of protection.
Pressure Treated Wood Options
CCA- chromated copper arsenate has been the historical standard for pressure treated wood. The wood is immersed in a solution of preservative and the vat is pressurized, forcing the chemical into the cells of the wood. CCA leaches arsenic throughout its life, which can threaten groundwater has the potential to be hazardous to anyone in contact with it. It is an unregulated hazardous waste that should not be disposed of in landfills. This potential toxicity is one of the reasons manufacturers voluntarily removed this product for use in residential applications and playground equipment as of Dec. 31, 2003
Alternatives to CCA
CBA- copper boron azole
Copper is the principal active ingredient, protecting against termites and fungal decay. Protection against copper-tolerant fungi is provided by an organic azole compound. The formulation renders the wood useless as a food source for termites and fungi.
ACQ- Alkaline Copper Quaternary
Alkaline Copper Quaternary (ACQ) is one of several wood preservatives developed in recent years because of environmental or safety concerns with CCA. The fungicides and insecticides in ACQ are primarily copper oxide and an ammonium compound. Multiple variations of ACQ have been standardized or are in the process of standardization. ACQ formulations are available for a range of different applications.