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RE: Rusty Nails

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A light amount of rust probably is not a concern; however, rust that
result in a surface powder feel will reduce the coefficient of friction
that the nail relies upon for strength (withdrawal and to some extent
lateral shear).  

Worse is continued rusting where I have inspected diameter loss due to
rust and cellulose deterioration.  There are some material experts who
claim the water and rust mix create an acidic solution that breaks down
the cellulose thus enlarging the plywood or wood member hole size around
the nail. (Not good).

Galvanized gun nails are available here in California quite easily.  In
fact, most of our large panelized roofs are nailed with Galvanized
Screw-shank gun nails.  The most prolific nailing subcontractor in
California (now there's a specialty!) uses the screw-shank nail on all
his jobs regardless of the plan's specifications.  This nail is less
subject to backing out during the roofing operation.

As an industry panelist, I will discussing more at the Wood Solutions
Fair in Long Beach!

John Lawson SE
Kramer & Associates Structural Engineers, Inc.