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Re: Rusty Nails

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In response to the inquiry on rusting nails, if the rusting is initial
exposure only (resulting from green wood, rain during construction, etc.)
and then the wood remains at less than 20 percent m.c. (dry) afterward,
there is no cause for concern and nail lateral and withdrawal loads should
not be affected.  If the wood is subjected to regular wetting after driving
the nails, then corrosion will continue and the nail shank will reduce in
diameter, often at the interface of adjoining members where the oxygen
supply is greater.  The problem is, it's difficult to tell how much
corrosion has taken place without pulling out a few nails to spot check;
they can be replaced with new nails.  If the wood has deteriorated (decay),
then it's almost certain the nails will be badly corroded too.
The vinyl coating does two things: 1) protects the nails from corrosion
until driven, and 2) heats and melts during driving from friction, allowing
the nail to drive more easily.  It then may recure/harden to form a bond
with the nail shank and wood to increase withdrawal resistance, but
subsequent heating (as in roof or south/west wall exposure) may cause loss
of initial added withdrawal resistance, or might even reduce withdrawal
resistance.
For more info on vinyl or other polymer coatings on fasteners, contact
ISANTA in LaGrange, IL (NER-272).
John Rose/APA, Tacoma, WA

TRYAN(--nospam--at)ci.tacoma.wa.us wrote:

> I recently had a 'discussion' in the office about using vinyl sinkers in
> framing.  The statement was made that the vinyl sinker sheds the vinyl
> (which we all know) then the nail rusts.  The statement was also made
> that this rust is a benefit to the connection.  I do know that the main
> reason we use vinyl sinkers is for ease of driving - and because there
> are no galvanized nails for nail guns.  I am mainly concerned about
> indoor framing (ie. Small, enclosed buildings).
>
> My questions are these:  Does the nail rust to a point then stop?  Does
> the rust add a benefit to the connection over galvanized nails?
>