Most rot-resistant pressure-treated lumber sold for homeowner use relies on two copper-based wood preservatives -- alkaline copper quaternary and copper azole -- in place of the arsenic-based compounds formerly used. Unfortunately, the copper-based preservatives cause rapid corrosion of ordinary steel screws, nails or bolts, resulting in early structural failure. But there are corrosion-resistant fasteners intended for wood preserved with copper compounds.
Galvanized With Zinc
Galvanized steel screws, nails and bolts used with copper-treated wood must be hot-dipped in molten zinc at 850 degrees Fahrenheit. These dull-gray fasteners must meet the ASTM A153 standard for zinc coating quality and the G-185 standard for coating amount. The G-185 coating is equivalent to 1.85 ounces of zinc per square foot of steel.
Corrosion-resistant stainless steel screws, nails and bolts in grades 304 and 305 can be used for copper-treated wood in most areas, while grade 316 should be used in coastal areas. But stainless steel fasteners can cost five to 10 times more than similar galvanized fasteners. And unlike other fasteners, stainless steel screws, nails or bolts cannot be used safely with galvanized structural connectors because of adverse chemical reactions.
Polymer-coated steel screws, nails and bolts rely on a thin zinc plating covered with a non-reactive organic polymer coating to fight corrosion in copper-treated wood. The polymer coating acts like a plastic wrapper to keep water and dissolved copper from reaching and reacting with the zinc and steel.