Coastal builders and remodelers rely on preservative-treated
wood for a range of uses, including decks, boardwalks,
landscaping, and accessory structures. So when wood treaters
made an agreement with the Environmental Protection Agency in
2003 to change their wood-treating formulas, coastal
contractors were directly affected.
The old CCA formula, based on chromium, copper, and arsenic,
was pulled off the market as of 2004. In its place came ACQ
(Ammonium Copper Quaternary) and CA (Copper Azole). Chemical
suppliers kept the copper, which is considered relatively safe,
but added a few new "co-biocides." Alongside the copper, ACQ
uses quaternary (or "quat"), a compound based on ammonia with
some added elements, including chlorine. Copper azole uses
tebuconazole and propiconazole, two EPA-registered pesticides
already well-established in agriculture for control of fungi
and insects (grape growers in California are the biggest users
Early copper-based formulations used to replace CCA in
pressure-treated wood came with their own set of problems
related to the corrosion of metal connectors and fasteners.
Despite claims that new "micronized" copper formulas have
solved that problem, many coastal contractors still prefer
stainless steel fasteners.
But ACQ and CA created a new problem: metal corrosion. They're
not compatible at all with aluminum flashing or aluminum nails,
and they also may attack galvanized nails and screws,
galvanized flashing, or galvanized connectors and joist
hangers. The corrosion issue prompted Simpson Strong-Tie to
come out with new, more heavily galvanized hardware, and to
recommend exclusive use of stainless steel hangers for coastal
areas. Simpson posts
and recommendations about the corrosion issue.
But technology is still changing fast in the world of treated
wood, most notably in the way copper is applied to the wood.
ACQ and CA use copper dissolved in an ammonia or amine carrier.
By 2007, new "micronized" formulas, which use finely-ground
solid copper particles in a mostly water-based carrier, were
pushing ACQ and Copper Azole out of the picture. Already,
"micronized copper quat," "micronized copper azole,", and
"dispersed copper azole" account for about 80% of the market
for residential treated wood, according to industry expert Mike
Common brand names for the micronized systems include "Micro
Pro" from Osmose, "SUSTAIN" from PhibroWood, and
"µCA-C" from Arch Treatment Technologies.
The vendors claim that these new micronized formulas are less
aggressive and corrosive toward fasteners, hangers, and
flashings. Micro Pro, according to Osmose, is even okay in
contact with aluminum flashing. But outside of the vendors
themselves, it's hard to find third-party confirmation for
these assurances. Simpson Strong-Tie's experts, for example,
recommend the same level of galvanizing for connectors used in
contact with the new micronized formulas as they recommended
for ACQ. Of course, use conditions make a difference, and
coastal environments carry a higher risk of corrosion because
of salt spray and salt vapor in the air. Within a few miles of
the coast, or even near a swimming pool where chlorine is a
factor, Simpson still calls for stainless steel — no
exception for micronized treatments.
If you want to keep up with the changes, you have to study. One
excellent general resource for contractors is this free PDF
download from the Southern Pine Council,
Pressure-Treated Southern Pine."
Even better for coastal builders (and also free) is
Treated Wood in Aquatic Environments," a long, detailed
handbook about dock and pier construction for marine
environments, where CCA lumber, ACZA (ammonium copper zinc
arsenate) wood, or even creosote and penta formulations may
still be permitted because of the tougher conditions.
The changes keep coming. Next year, insiders say, some existing
brands that are currently only permitted for above-ground use
will get approval for ground-contact applications —
including, says Mike Freeman, one formula that uses no copper
at all. And the industry is still busy developing new chemical
formulas: Richard Vlosky, director of the Louisiana Forest
Products Development Center at LSU, says researchers at the
school are currently testing and evaluating several innovative
preservative systems for industry clients. The Journal of Light
be taking a closer look at all these developments in spring of
2009. (Hanley Wood, which publishes this newsletter, also
Meantime, the International Code Council has been working on
new or revised standardized test methods for preservative
treatment performance (Acceptance Criteria AC-326), and for
assessing fastener corrosion in treated wood (Acceptance
Criteria AC-257). Strictly speaking, the 2006 International
Building Code (IBC) and International Residential Code (IRC)
currently only allow four fastener materials with treated
lumber: stainless steel, hot-dipped galvanized steel, copper,
or silicon bronze. But hundreds of alternative fasteners are on
the market, using various other metals and polymer, ceramic, or
metallic coatings, and advertised as suitable for use with ACQ
treated wood. None of those alternative screws or nails have
building code recognition yet — because the new
criteria for acceptance, AC-257, has only just taken effect as
of January 1, 2009. However, by year's end many coated screws
are likely to have gone through AC-257 testing, and received
formal Evaluation Reports from the International Code Council
Evaluation Service (ICC-S).
We'll keep you posted as the situation develops.