Fastener Corrosion

Fasteners consist of nails, screws, bolts, staples, etc and are widely used in the construction industry to connect lumber, sheathing, shingles, and other wood-based products.  Nail guns allow for nails to inserted at a rapid fire pace.  Chromated copper arsenate (CCA) was the primary preservative used for residential uses. 

CCA has been used for timber treatment since the mid-1930s. It is a mix of chromiumcopper and arsenic (as Copper(II) arsenate) formulated as oxides or salts, and is recognizable for the greenish tint it imparts to timber.

In February 2002, the U.S. Environmental Protection Agency (EPA) announced a voluntary phase-out by industry of most residential uses of this arsenic-based wood preservative. The agreement states that beginning in January 2004, CCA-treated wood can no longer be manufactured for decks and patios, picnic tables, playground equipment, walkways/boardwalks, landscaping timbers, or fencing.

Some of the water-borne alternatives to CCA for residential use include  alkaline copper quaternary (ACQ) compounds, copper azole (CuAz), copper citrate, inorganic boron (SBX), copper HDO (CuHDO) and others.  You will note that many of these biocides contain copper, which is an excellent fungicide and also a good conductor.  After the voluntary phase-out of CCA lumber for residential use a significant amount of treated lumber was produced that led to rapid corrosion of the fasteners.  A galvanic cell can occur and promote corrosion “rust” on the fastener.  Over time the integrity of the fastener can be compromised and the effective diameter of the fastener is decreased.  The solution is to always use galvanized fasteners and perform regular inspections of your fasteners for corrosion and your wood for early stages of decay.   Preservative treated lumber has been modified in recent years and the risk of fastener corrosion is now very minimal.  It is still advisable to use galvanized or stainless steel fasteners for any project that will be subject to moisture.  This is true for projects with untreated wood as well as treated wood.

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