Much ado about fasteners

Fasteners are to the building package as referees are to a typical athletic event — you know they are doing a good job when you don’t notice them. Recently, when a Rural Builder editor asked a builder what type of fasteners he used on a project, the builder responded “Don’t remember, irrelevant.”
But if you happen to be a builder who doesn’t give fasteners a second thought, listen up. Because of the ever-changing world of wood treatments, choosing the right fastener for your post-frame building is more important than ever.
“Fasteners have never been more critical than they are now,” says Maze Nails marketing director Kim Pohl. “Before, builders may have been able to get away with using a typical post-frame fastener, but now, what worked with CCA is probably not going to work and last with the new treated lumber. People have to step up and use a good, top-performing fastener.”
It looks more and more as if CCA, the lumber treatment of choice for years, will become less and less available for use with post-frame buildings. The Environmental Protection Agency has seemingly approved the use of CCA with nail-laminated columns, and 4x6s may get an official EPA blessing. But even if lumber suppliers continue to treat products with CCA, it appears that at least one product will need to be treated with one of the alternatives: skirtboards.
The top two candidates to replace CCA, copper azole and alkaline copper quat, both contain higher levels of copper than CCA. Copper, as a more noble, cathodic metal, can be expected to corrode a less noble, anodic metal like zinc, the coating for conventional G-60 electro-galvanized fasteners.
Fastener manufacturers have reported rapid corrosion when standard fasteners are placed in wood treated with copper-heavy chemicals — some tests have shown the alternative treatments to be twice as corrosive as CCA. But safer, albeit more expensive, fastener alternatives exist, and are being promoted by both fastener companies and chemical manufacturers.
“The key to corrosion protection is understanding the alternative pressure-treated woods on the market, and which fastener products are suitable for each type of wood treatment,” says Mark Crawford of Simpson Strong-Tie.
Stainless steel and bronze are closer to copper on the galvanic scale, and therefore less corrosive in contact with the alternative treatments. But bronze (and copper) fasteners are not readily available in the construction industry, and stainless products cost considerably more than galvanized. Stainless steel fasteners and connectors are required for permanent wood foundations below grade, with type 304 and 316 the recommended grades to use.
Hot-dipped galvanized fasteners, which come with a considerably heavier coat of protective zinc, will likely prove to be the most popular choice for builders. There are two main processes used to hot-dip galvanize parts, continuous hot-dip galvanizing and batch or post hot-dip galvanizing. Continuous hot-dip galvanizing is generally used to galvanize steel coils at various speeds on lighter gauge steel. Batch hot-dip galvanizing is generally used to galvanize heavier individual parts not capable of being fabricated from galvanized steel coils, and can be used to galvanize fasteners and anchors as well. The parts are dipped into molten zinc for a longer period than with the continuous method, usually resulting in a thicker coating and more protection against corrosion.
Hot-dip galvanizing provides fasteners with between 40 and 80 microns of coating, according to Tom Langill, technical director of the American Galvanizers Association, compared to about 5 microns of coating with the electro-galvanizing process (25 microns is equal to 1 mil).
“It’s a fairly thick coating in terms of corrosion protection, that’s what gives hot-dipped galvanized parts longevity,” says Langill. “When you look long term, the amount of zinc determines the life of the coating. Obviously, you shouldn’t put too much zinc on a part, it still has to be able to work as a fastener.”
Hot-dipped galvanized fasteners should meet ASTM-A153 specifications. A153 requires fasteners to be coated with a minimum of 1 ounce of zinc per square foot of surface area (about 1.7 mils). By comparison, a G-60 coating would have 0.60 ounces per square foot of surface area. The result is a more consistent and thicker coating applied to the carbon steel metal from which fasteners are manufactured.
Hot-dipped galvanized fasteners should not be confused with hot-galvanized fasteners. Hot-galvanized fasteners are coated by sprinkling zinc chips on cold steel fasteners in a barrel, then rotating the hot barrel in a furnace to melt and distribute the zinc. The melting zinc washes off on the nails, but the zinc is not uniformly distributed.
Langill, who is chairman of the subcommittee that makes changes to A153, says the committee has been asked to include other processes, like hot galvanizing, in A153. The committee has discussed it, and will likely discuss it again in May. “In terms of corrosion protection, (hot-dipped and hot galvanizing) may be pretty similar,” says Langill. “I don’t know what the uniformity and repeatability is with hot galvanizing.”
Other methods for applying zinc coatings to fasteners include mechanical plating, where fasteners are rolled with zinc dust, glass, and water in a barrel, and electro-galvanizing, where an electric current deposits zinc anodes onto the surface of the fasteners.
Huck DeVenzio of Arch Wood Protection, which manufactures both CCA and copper azole, says the technical committee of the International Code Council, unprompted by the three chemical companies, has approved an amendment to the model codes that will require fasteners used with treated wood to meet A153. The amendment will be voted on by full membership at ICC’s spring meeting, and is expected to pass.
Jay Levy of Ideal Building Fasteners stresses A153 is only a specification for a galvanizing process and zinc thickness, and is not the same as actual testing of fasteners’ performance in an ACQ or copper azole atmosphere. Levy also says that when taking the total building package into account, fasteners with advanced levels of corrosion resistance may account for only a small percentage of the total fasteners used.
“The builders I’ve talked to, these guys said to me that most of the lumber they use above ground is untreated, unless it’s a high moisture environment,” he says. “Most of the fasteners are going into untreated lumber. ACQ may only come into play on the skirtboard.”
In that case, Levy advises builders to use 300 series stainless steel fasteners around the skirtboard, even though it would require pre-drilling holes. “It makes more sense to spend a small fraction of his time and money to ensure there are no problems,” he says.
Whether using hot-dipped galvanized or stainless steel products, both fasteners and connectors must be of the same metal type and have the same coating and finish. Also, aluminum should never be used in direct contact with the new copper-heavy treatments.
Chemical manufacturer Osmose maintains a list of hardware manufacturers with products recommended for use with ACQ treated wood (available at www.osmose.com/acrobat/NaturewoodFastenerInfoSheet.pdf).
Builders are advised to contact fastener suppliers for their recommendations regarding proper fasteners for use with ACQ and copper azole.

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