A.John Wagner
responds: In addition to copper, conventional
CCA preservative contains chromium and arsenate,
which the Environmental Protection Agency (EPA) has
labeled "hazardous." Though these two toxins bind
almost entirely with the wood, CCA’s
manufacturing process creates several hazards.
First, it’s dangerous to touch CCA residue
(chemicals that have not become "fixed" in the wood
during the treating process). It’s also
dangerous to touch or breathe the sawdust. Many
homeowners rightly wonder if CCA is safe for decks,
playgrounds, and picnic tables, especially where
children will have direct contact with the
wood.
These fears and dangers inspired Chemical
Specialties Inc. (CSI, One Woodlawn Green, Suite
250, Charlotte, NC 28217; 704/522-0825) to develop
ACQ Preserve, a new product that has several
preservative qualities identical to CCA, but that
has a much lower toxicity, both during its
manufacture and with its subsequent handling. ACQ
uses a water-borne preservative that contains
ammonia, copper, and "quat" — quaternary
ammonia, a disinfecting detergent — as an
insecticide and fungicide treatment. It
doesn’t use any chemical compounds listed
by the EPA as hazardous, and it comes with a
"green" label from Scientific Certification Systems
(a commercial environmental labeling group).
Performance. Wood
performance isn’t affected by preservative
chemicals, whether you are using ACQ or CCA,
except when the water used in the
preservative-impregnating process dries unevenly
during storage or shipping. This causes or
accelerates splitting and checking. However, wood
performance and finishing characteristics
are greatly affected by the wood species,
or — more specifically — the
wood’s grain patterns. The species
typically used in pressure-treating with CCA and
ACQ — southern yellow pine, fir, and
hemlock — are fast-growing flat-grained
woods with wide grain bands that readily soak up
the water-borne preservative. On the downside, the
grain patterns in these species are unstable, so
weathered decks built with pressure-treated woods
commonly suffer from cupping, splintering,
splitting, cracking, warping, twisting, and nail
pull-out.
There are two ways to help ensure a more stable
wood, whether it’s treated with ACQ or
CCA. First, use pressure-treated wood
that’s factory-treated with a water
repellent. The alternative is to immediately apply
a penetrating finish, such as a water repellent
(often listed as WR on the label), water repellent
preservatives (WRP) with a mildewcide additive, or
a semi-transparent stain (an oil-based, pigmented
WRP). None of these penetrating finishes flake,
crack, or peel. (Film-forming finishes, such as
paint and solid-color stains, are not
recommended.)
Regardless of whether you choose CCA or ACQ, and
whether you use factory-sealed material or apply a
sealant soon after installation, make sure you
inform your clients that the wood must be
refinished every year with a penetrating stain or
water repellent — not every other
year as some manufacturers claim.
John Wagner is a freelance writer in
Montpelier, Vt., who often writes about building
technology.