Everyone agrees that "green" means environmentally friendly. But when it comes to deciding which plasters can be considered green, it depends on whom you ask.
Green means different things to different people. Manufacturers of all types of plasters can point out characteristics that make their version environmentally sound. The difficulty comes in comparing degrees of "greenness" and in deciding whether being green means sacrificing quality.
It is generally accepted that a material's off-gassing of volatile organic compounds (VOCs) plays a critical role in the definition of "green." Some people insist on zero-VOC content, while others are satisfied with "low-VOC" products, which have VOC concentrations of 25 grams per liter or less. "It's important that the binders in the plaster are not high-VOC content," says Rye Hudak of Stonelace Designs in Berkeley, Calif. "For example, it's not uncommon for Venetian plasters to contain a high acrylic content. In that arena, we would use a plaster that does not rely on an acrylic binder and is more traditional in composition."
Despite general agreement that lower VOC content corresponds to greater greenness, there is room for disagreement about the way standards are written by organizations such as Green Seal. "I think Green Seal should rewrite the GS-11 certification standards in terms of grams per room, as opposed to grams per liter," says Doyle Self of the School of Italian Plasters, which holds classes in Dallas, San Diego and Verona, Italy. He points out that one liter of his company's acrylic resin and mineral-based Stucco Veneziano will cover 200 square feet. On the other hand, several other Venetian plaster manufacturers list coverage rates of 40 square feet to 80 square feet per liter. "When you look at how thick you have to put the other stuff on, ours has actually less VOC per room," Self says. He also notes some of his competitors' VOC-free products have to be waxed. "So you're introducing something that generally has high VOCs on top."
Another factor that affects indoor air quality is mold prevention. Some plaster manufacturers add chemical biocides to their products, while others use basic ingredients that naturally resist the growth of fungi and prevent the accumulation of moisture in walls. "The reason why (synthetic paints and plasters) were developed in the last hundred years is because the general thought in the United States was that buildings must be waterproofed very thoroughly," says Orit Yanai of Orit Yanai Inc. in San Francisco. "If you don't allow breathability in your walls, then eventually moisture will gather up on the inside of your walls and create dry rot and mold issues. Most synthetic materials do not allow the surfaces to be breathable." Lime plasters and earth plasters are naturally mold-resistant, 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 fluctuation 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."
The thought of earth plasters may bring to mind images of dusty walls with mud being smeared on them by aging flower children. Baumgartel's explanations of their benefits hint at the stereotype, but also have some scientific 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 affected by around 100,000 negative ions," Baumgartel says. "When you're sitting in your office with computers and other equipment, you probably have between 600 and 1,200 negative ions in your environment. That's not a lot, which is probably why a lot of us are pretty grumpy."
The clay plaster's negative charge generates other benefits, 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."
The amount of embodied energy in a product also affects 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 different 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-fortified filler. It's always a balance between all of those factors."
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. The 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. "That's about as green as it gets."
"Plant fibers can have a structural element to them," says Christine Wallner, also of Stonelace Designs. "For instance, eucalyptus or bamboo fibers have a very high content of silica, so over time, they would mineralize and act almost like stone rebar." Other materials she and Hudak use in their plasters include sawdust, rice chaff, and coconut fibers.
"One of the main issues with plasters is what happens when there is a ding in the wall," says Yanai. "You normally see the repair in all other plasters, but when you work with earth plasters there are techniques to do a touch-up flawlessly." She dismisses the concern that earth plasters are too easily marred. "Even though earth plaster is softer than gypsum, it's not softer than joint compound," she says. "If your child throws a toy against a sheetrock-and-joint-compound wall, it will injure exactly the same as the earth plaster, if not more. It may need a bit more force if you have gypsum-based plaster, but once the wall is dinged there's no way you can repair it successfully."
"Another thing to consider would be the life cycle, or how long it's going to stay up and how often you're going to redo them over the life of the building," says Nurit Regev of TexSton Industries in Canoga Park, Calif. "The lime-putty plasters last the longest. They have quite a long lifespan - much longer than most buildings are up in this country, unfortunately."
Yanai places the lifespan of earth plasters on par with lime plasters, saying that both kinds "will last forever."
Last but not least, is there a cost penalty for using the most environmentally friendly plasters? Again, it depends on how you look at it. First, there is no need for special tools. Second, ease of application may reduce labor costs. "Technique-wise, I would say earth plasters are the easiest," says Yanai. "When I teach contractors, they can't believe it's so easy. It's a lighter material, so you don't have to carry as much on your hawk. It's much more pliable, and it doesn't have the crazy setup time."
As for product costs, Baumgartel says lime-based plasters are the same price or maybe cost a little more than her clay plasters. Natural gypsum plasters cost somewhat less, but additives increase costs. Yanai says synthetic plaster costs less than earth or lime, but won't last as long. "The whole idea of a green building is to think of the big picture," she notes.
Dealing with waste, or the lack of it, is part of that picture. "Contractors know that when they work with gypsum plaster, some of it is going to dry too fast, and they're going to have to throw it away, so they calculate that into the bid," says Yanai. "When you use earth-based plaster, there is no waste. If it falls off your hawk, you either pick it up and reuse it, or you can let it dry on the floor and crumble it back into your bucket the next day."