Wood preservatives affect fastener selection

New pressure-treated wood can cause premature fastener corrosion.

The EPA banned the use of chromated copper arsenate (CCA) in pressure-treated wood January 1, 2004. While wood suppliers were allowed to sell remaining stocks, any pressure-treated wood produced after that time must be preserved with a non-arsenic-based chemical, according to a report from the USDA Forest Products Laboratory.

The new pressure-treated wood uses alkaline copper quant (ACQ), copper azole or copper HDO as a preservative. “These formulations can cause fasteners to corrode twice as fast as when compared with the old CCA formulations,” says Jeff Matthews, Senco fastener product manager.

The new pressure-treated wood reacts readily with the zinc coating on galvanized nails, resulting in rapid rusting and, in some cases, concern about structural failure.

Confusion clearing up
The switch caused confusion in the marketplace in the first quarter of the year, report fastener representatives. Conflicting reports as well as insufficient testing concerned contractors as building inspectors interpreted the new regulations. Some building inspectors even went so far as to require suspect fasteners to be replaced.

“There is no doubt that the copper-based preservatives cause fasteners to corrode at least twice as fast as the arsenic-based preservatives,” says Thomas Mardo, global fastening product manager at Stanley-Bostitch

“From the beginning of the year, there was some market confusion. Frankly, it was a communication issue. Fastener manufacturers had little time to react to the new formulations. However, wood treaters continue to adjust their formulations so they are less corrosive. That will also help reduce the problem,” he says.

The resulting corrosion will likely be only aesthetic, but no manufacturer is willing to make that claim. “There is no universal standard or governing body that has established a testing protocol to test fasteners. ISANTA is developing a standard, but they are up to 12 months away from agreement. At Stanley-Bostitch, we set our old fasteners’ performance in the arsenic-treated wood as a baseline, then tested the new fasteners with a salt-spray test in a humidity chamber that accelerates the fastener corrosion. We also tested them to the AWPA-E12 standard,” he says.

In the AWPA-E12 test, the fastener is weighed, then sandwiched between wood in an accelerated corrosive environment. At the end of the test, the fastener is weighed again and it is calculated how much of the galvanized coating has oxidized.

“Unfortunately, these tests only indicate corrosion resistance and have varying correlation to the real world,” says Mardo. “In the end, it is up to the fastener manufacturer to warrant the product and identify where it should be used.”

Look on the label
The second quarter of 2004 brought a bit more clarity to the issue. Fastener manufacturers came out with clearly marked fastener packaging that identified which fasteners to use with the new pressure-treated wood. Still, there is no set standard, so buyers must still beware.

“Conventional electro-galvanized fasteners should never be used with the new pressure-treated lumber. It has about one-tenth of the zinc coating of hot-dipped fasteners, and will quickly corrode,” says Matthews.

However, Stanley Bostitch offers an electroplated fastener that can meet the demands of the new pressure-treated lumber. “We put the claim right on the box that our Thickcoat brand galvanized nails can be used with the new pressure-treated wood,” says Mardo. “They have two and one-half times more galvanization than a conventional electroplated fastener plus a chromate coating for additional corrosion resistance, plus a polymer coating that increases withdrawal performance.”

Senco experts advise contractors to use hot-dipped galvanized or stainless steel fasteners with the new pressure-treated wood. “It’s best to talk with your building inspector to see what the local codes require. The majority of municipalities allow hot-dipped galvanized, stainless steel or proprietary fastener products designed for use with ACQ-type pressure treated lumber,” Matthews says.

However, the fastener manufacturers warn that claims such as “hot galvanized product,” “4X zinc-coated,” or “nickel coating” cannot be construed as claims of usability with the new ACQ-type lumber.

“There is no standard wording that must be used. For example, Paslode uses the phrase, ‘Good for use in ACQ’ on its fastener boxes,” says Mardo.

Both experts agree it’s best to ask your building inspector and building supplier for recommendations on which fastener to use.

“I recommend that builders tack up a part of the fastener box in an inconspicuous location so building inspectors can see what fastener was used. Inspectors can’t tell whether they are electroplated, hot-dipped or even a stainless steel fastener once they are driven into the wood. This clears up any concerns,” says Matthews.

When aesthetics are important,
use stainless steel
Because of the effects of salt air on conventional fasteners, municipalities within 10 miles of the seashore generally require the use of stainless steel fasteners. “If red-heading, streaking or staining is a concern on any job, spend the extra money on stainless steel fasteners,” recommends Matthews. “Stainless steel fasteners of grade 304 or greater are the best to use if corrosion is an issue.”

Stainless steel fasteners are more expensive, which often takes them out of consideration on jobs. “I would recommend the use of stainless steel fasteners wherever corrosion and aesthetics are an issue. Even with the best galvanized fasteners, it is only a matter of time before corrosion reaches the base material of the fastener and causes red-heading,” says Mardo.

Stainless steel fasteners are typically two to three times as expensive as other fasteners, but in the total cost of the project, it won’t increase costs that much. “We suggest offering it to customers as an option, especially if they are spending the extra money to use some of the new composite products. Over the life of the project, the slightly higher cost is worth it,” says Matthews.

Published in the November/December 2004 issue of Contractor Tools and Supplies magazine.

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