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This custom-designed exterior accent for a Boulder, Colo., prAna store is combed gypsum
plaster applied over a textural base coat. It was fi nished by sanding, sealing and glazing with
a light stain to create a slightly aged appearance.
Photo courtesy of Stonelace Designs
surfaces to be breathable.” Lime plasters
and earth plasters are naturally moldresistant,
she adds.
Besides avoiding chemical off -
gassing and preventing mold, earth
plaster can actually improve indoor air
quality. “Our product helps to moderate
humidity,” says Carol Baumgartel
of American Clay in Albuquerque,
N.M. By absorbing moisture when it is
available and releasing it back into the
room when the air is drier, clay plaster
maintains a more constant humidity
level. “People notice that their homes
don’t have as much fl uctuation in
temperature,” Baumgartel says. “People
report that their energy costs go down.
Right now, we’re documenting whether
it’s actually the plaster or whether it’s the
feeling of comfort that you get by being
in these environments.”
Th e thought of earth plasters may
bring to mind images of dusty walls
with mud being smeared on them by
aging fl ower children. Baumgartel’s
explanations of their benefi ts hint at the
stereotype, but also have some scientifi c
legitimacy. Clay releases negative ions
into the air when it hydrates, and some
medical experts say negative ions may
produce positive biochemical reactions
in people. “When you’re taking a hike,
you’re probably being aff ected by around
100,000 negative ions,” Baumgartel says.
“When you’re sitting in your offi ce with
computers and other equipment, you
probably have between 600 and 1,200
negative ions in your environment.
Th at’s not a lot, which is probably why a
lot of us are pretty grumpy.”
Th e clay plaster’s negative charge
generates other benefi ts, too. “You
don’t have to scrub your walls because
they naturally repel dust and grime,”
Baumgartel says. “You don’t have the
constant presence of that dust and
pollen and grime in your environment.
We believe, and we have in process
some documentation to say, that it
actually helps to reduce asthma issues in
children’s rooms.”
Embodied energy
Th e amount of embodied energy
in a product also aff ects its greenness.
Because of the high heat required
to manufacture synthetic plasters
and portland cement-based plasters,
they contain more embodied energy
than gypsum, lime or clay plasters.
Comparisons are complicated, however.
Gypsum requires less manufacturing
energy than lime, but some plasterers
consider lime-based products to
be greener because of the chemical
additives that are often added to gypsum
plasters. Furthermore, transportation
contributes to a product’s embodied
energy. “We use many diff erent lines
of products, some of which come from
Italy,” Hudak says, “and while that is
quite a distance, we use them because
the material composition is pure in the
sense that it’s relying on traditional
slaked lime rather than acrylic-fortifi ed
fi ller. It’s always a balance between all of
those factors.”
Ingredients
While some ingredients, such as
biocides and petrochemicals, may be
considered nongreen, others can boost
a product’s environmental qualities.
For instance, the U.S. Green Building
Council’s LEED rating system awards
points for using recycled or reclaimed
products. Baumgartel says that
American Clay plasters contain more
than 60 percent reclaimed material.
Th e aggregate in two of the company’s
plasters consists of marble dust from
Arizona mines. “Our third product,
Marittimo, consists primarily of crushed
shells, which come from the Gulf
Coast,” she says. “Millions and millions
of mollusks were destroyed in Hurricane
Katrina, so there are mountains of shells
that need to be reclaimed.”
Hudak reports blending pulverized
plastic and glass into his plasters and
using plant-based binders such as soy
resin. “We’re using a plant-based binder
with a recycled material,” he says. “Th at’s
about as green as it gets.”
“Plant fi bers can have a structural
element to them,” says Christine
Wallner, also of Stonelace Designs.
“For instance, eucalyptus or bamboo
fi bers have a very high content of silica,
so over time, they would mineralize
Spring 2008 ◆ www.Hawk-n-Trowel.com ◆ 19