Since new treated wood formulas entered the market in 2004,
contractors have had to adapt to a new ball game, one for which the
rules continue to change. Within a few years of the phase-out of
CCA (chromated copper arsenate) and the introduction of ACQ
(ammonium copper quaternary), newer entries, such as MCQ
(micronized copper quaternary) and µCA (dispersed copper
azole), have begun to replace ACQ on lumberyard racks. In fact,
according to industry expert Mike
Freeman, micronized and dispersed formulas now account for as
much as 90% of the treated wood on the residential market.
The new formulas bring new complications to lumber labeling, and
to lumber use and performance. Recently, controversy has bubbled up
over whether Osmose's MCQ lumber, in particular, can perform as
well in service as the original ACQ it has replaced. And there's
now a related dispute over whether products like Osmose's
MCQ-treated "NatureWood" should use the name of the American Wood Protection Association
(AWPA) in their marketing literature or in labeling their products
— even though they have not been through the full process of
AWPA standardization.
In early March, Osmose, the manufacturers of MCQ, sued Viance,
makers of ACQ, in federal court in Georgia over what Osmose calls a
"false and malicious" media campaign to discredit MCQ. In a court
filing, Osmose said, "It appears Viance is attempting to disrupt
and confuse the marketplace in an effort to slow or stop the
success of micronized copper wood preservative products until
Viance can develop a viable replacement for its older wood
preservative system, Alkaline Copper Quaternary ('ACQ')." (Download
a PDF of Osmose's
complaint.)
The complaint stems from an advertising campaign by Viance,
based on a claim that Osmose MCQ-treated posts, tested for Viance
by an independent testing firm called Timber Products, Inc. (TPI),
had rotted in service and created a risk of structural failure.
According to the Viance publicity, widespread risk of premature rot
in MCQ-treated structural wood is exposing sellers and users of
Osmose's MCQ lumber to legal liability. But according to Osmose,
the wood that was tested was being used as signposts, not as
structural lumber. And Osmose says some of the wood Viance tested
may not have been treated at all, much less with MCQ. In any case,
says Osmose, standardized testing as well as field experience bears
out the durability of Osmose's treated lumber. (Osmose claims that
more than 10 million MCQ-treated 4x4 posts are currently in
service, and that the wood has a good track record.)
Soon after the Viance ad campaign began, TPI released its own
statement disavowing the use of its test results to disparage
Osmose's treated wood. TPI pointed out that the tested wood was
pre-selected by Viance and did not represent a random sample of
wood in service. Also, TPI noted that the visual inspection methods
it used are subjective.
AWPA Standards
One criticism of Viance's testing of Osmose's products has been
that the methods used have not always conformed with official test
protocols of the AWPA. Osmose says that based on accepted AWPA
methods, its wood has demonstrated equivalent performance to other
types of treated wood. But now, AWPA itself has entered the fray,
pointing out that while Osmose may have followed the AWPA test
protocols, it did not pursue a full listing of its product in the
AWPA standardization process — opting instead to pursue a
different pathway to code acceptance -- an Evaluation Service
Report from the International Code Council Evaluation Service.
Osmose and Michigan Tech’s “Wood Protection
Group” included these graphs in a joint presentation to a
2008 meeting of the International Research Group on Wood Protection
(slides published with permission).
It's true that Osmose has publicized test results for its
product that are based on AWPA standard testing. For example, these
charts (above) are from a presentation by Osmose wood scientists,
along with professors from the Michigan Tech's "
Wood
Protection Group," at a 2008 meeting of the International
Research Group on Wood
Protection, a global association of more than 300 wood scientists
from 51 countries.
The upper chart compares the performance of MCQ-treated wood
with ACQ wood in AWPA standard "soil block" tests, where small
chunks of wood are placed in jars of wet soil inoculated with
different fungi. In that example, MCQ performed as well as or
better than ACQ.
The lower chart compares the performance of MCQ lumber treated
to different preservative concentrations, or "retentions." It's
clear that the higher treatment levels provide the best protection
— test stakes treated to the highest levels suffer
essentially no decay for 52 months in ground exposures in Hawaii.
(Download a PDF of the
complete
presentation.)
Match the Exposure
For end users, the most significant issue is not which type of
lumber to use — any brand on the market will have passed some
form of code-sanctioned testing to demonstrate its durability. More
important is that the lumber be rated for the exposure it faces.
For posts in the ground, that means either the AWPA "UC 4" ("Use
Category 4") label, or the ICC "Ground Contact" rating. These days,
not all wood in the market is treated to those levels, so it's
important to check the labels carefully.
Beyond that, however, the word on the street is that for rough
exposures, it's still possible to special-order lumber that is
treated with the old, arsenic-based pre-ACQ and pre-MCQ treatment.
CCA lumber, which has stood up to decades of outdoor,
ground-contact exposure on continuously monitored test plots, is
still available through some supply chains. In recent months, I've
spoken to deck builders in Oregon, Massachusetts, and Oklahoma who
all told me that for ground contact exposures, they still use CCA
wood when they feel that it's appropriate.
And for marine exposures or for pile foundations, CCA wood is
still in the playbook. For extensive detailed information on using
treated wood for docks and other marine construction, you can
download the manuals, "Treated Wood in Aquatic Environments" and
"Aquatic and Wetland Structures" from the website of the
Southern Pine
Council