Tuesday, February 3, 2009

Use special nails, screws, staples in treated lumber

By David Burton
University Extension

There was a change in chemical preservatives used for pressure-treated lumber available for residential use in the United States starting in 2004. As a result different fasteners need to be used when working with ACQ treated lumber according to Bob Schultheis, natural resource engineering specialist with University of Missouri Extension.
“Pressure-treated Southern pine lumber that was preserved with Chromated Copper Arsenate (CCA) was phased out due to public health concerns about the arsenic it contained,” said Schultheis. “The new preservatives replacing CCA are Alkaline Copper Quaternary (ACQ) or, less commonly, Copper Azole.”
Both of these chemical treatments are perceived to have less environmental or health risks than the old CCA chemicals. However, these new chemical treatments are more corrosive to nails, screws, and any other metal fasteners or parts that come in contact with the lumber.
“The days of being able to use just any fastener with your pressure treated lumber are over,” said Schultheis. “Using the wrong fasteners could have an adverse effect on the structural performance and service life of buildings built with ACQ lumber.”
The corrosiveness of the new chemicals also means that much of the commonly-used metal siding or other parts or equipment, whether aluminum or steel, are likely to be damaged if they are allowed to come in direct contact with the ACQ treated lumber.
No carbon steel or aluminum siding or other metal should be used directly against ACQ treated lumber.
Treatment manufacturers now recommend fasteners that are Type 304 or Type 316 stainless steel, or hot-dipped galvanized that meet ASTM A153 standards. Connectors and sheet steel should meet or exceed the ASTM A653 Class G185 standard.
Never mix galvanized and stainless steel in the same connection.
“These requirements apply across the board, whether for ground contact or not, wet or dry conditions. No fasteners should be used unless they are clearly labeled as ‘Approved for use with ACQ’,” said Schultheis.
The bright-colored electroplated galvanized screws commonly available in home improvement centers are examples of fasteners that are non-approved for use with ACQ according to Schultheis.
How do you know if you have ACQ lumber? Look for either an inked stamp on the broad side of the lumber stating the lumber grade and preservative, or a plastic tag on one end of the lumber member that states the lumber grade and preservative used.
Although CCA treated lumber is still manufactured and sold for certain industrial and marine applications, including agricultural posts and poles, most lumber yards may now just carry the ACQ treated lumber.
“If you’re getting bids on a building, be aware that ACQ-approved fasteners are much more costly than fasteners used for common lumber, so the low bid may not necessarily be the best bid, if you’re concerned about the service life of the building,” said Schultheis.
More information about these fastener corrosion issues can be found on-line at www.awc.org/HelpOutreach/faq/CorrosionFactSheet.pdf and www.southernpine.com/ptfasteners.shtml.
Details about CCA lumber and its alternatives can be found on-line at www.epa.gov/oppad001/reregistration/cca/
For more information on farm and home building topics, check out the University of Missouri Extension website at extension.missouri.edu/explore or contact Schultheis at the Webster County Extension Center in Marshfield at (417) 859-2044.

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