Ted Cushman is right on when he notes that the
corrosion of metal hardware in contact with treated wood can be
worse in the field than what lab results show ("Fasteners for
Treated Wood," Soundings, January/February 2008). Within months of
building my first coastal deck after CCA was phased out, there was
red rust on the G-185 hangers and hot-dipped nails and bolts I
used. That's when I began using isolation membranes.
While Grace does make a butyl-based peel-and-stick, Vycor Deck
Protector is an asphalt-based material, not butyl-based, as we
reported in the last issue.
I've used Grace Vycor Deck Protector and other similar
peel-and-stick membranes as isolation membranes, and all are
asphalt-based (not butyl as noted in the article).
The working temperature range for asphaltic membranes is pretty
good but not as wide as butyl adhesives used in window flashing
tapes. I find membrane adhesion is weak below 40°F, especially
on damp treated lumber. Still, even with isolation membranes, G-185
galvanized hardware, and other proprietary coatings, I'm becoming
more of a fan of stainless steel hardware for exterior connections
in coastal areas regardless of how aggressive or inert the lumber
treatments are. Galvanized coatings — no matter how thick
— are still going to give way to the steel beneath. It's only
a matter of time before rust sets in, be it two years, five years,
or 20 years.
Stainless steel hardware is not very costly when you look at other
expenses on a job. And I've found that the labor cost saved by not
applying isolation membranes and trimming off the excess when
"upgrading" to stainless almost covers the extra cost.
East Greenwich, R.I.