Quick guide to fasteners for treated wood

By Sharon Thatcher, Rural Builder Magazine –

A surprising amount of science goes in to the making of those small but mighty screws, bolts and connectors used in preservative-treated woods. The science has been standardized by ASTM, with box labeling used to help builders simplify the user process.

Joe Stager, vice president for product development and marketing at Triangle Fastener Corporation, said the standards for proper use are fairly simple to follow. Unfortunately, assuming that all fasteners and connectors are created equally is an all-too common fallacy.

“The way the code is written, it’s pretty precise,” Stager said. “What they say is: with any treated lumber you need to use a fastener that is coated correctly. The coating at the minimum has to be hot-dip galvanized, or stainless steel is preferred. So right away if it’s treated lumber, don’t even think about using anything else but something that meets or exceeds the hot-dip galvanized finish on the fastener.”

Stager said the biggest problem is when a builder runs to the local big box store and just grabs a box off the shelf assuming it’s going to perform as well as any other. “There have been situations where a building official comes in and says ‘hey, those lag bolts aren’t hot-dip galvanized’ and you’ve got to pull them out and put in hot-dip galvanized.”

The ultimate goal of the standards are simple: performance longevity. “The reason you use pressure-treated lumber is so it doesn’t rot and decay, so why would you want to use a screw that will rot and decay easily,” Stager asked.

He continues, “There’s are times where [a builder] will install this nice looking metal wall panel and they’ll use a real inexpensive screw. They come back a year later and the screws are all rusty. They have this beautiful panel with these little dots of rusty screws everywhere. Although it’s not the treated wood that’s corroding the screws, it highlights how screws that are plated too thin will corrode quickly even in normal environments.”

Stager notes that some screws with proprietary coatings are not specifically mentioned in the standards but are recognized as approved for use in treated lumber by the manufacturer. In fact, some products, such as wood screws, are not available in hot-dipped galvanized so proprietary coatings fill that need. “Ours [Triangle Fastener] happens to be Tri-Seal, [Buildex] has Climaseal, and there are many others. But the best option is to use wood screws made of stainless steel,” he noted.

To assure the quality of the fastener or connectors you use, your supplier should be able to provide technical information that supports the science behind the product. RB

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