Classic Walls

…make their revival, as natural materials become more builder-friendly


If attendance at pro training sessions and do-it-yourself workshops is any indicator, plaster is well on its way to a serious revival. It's never truly gone away, of course. Traditional gypsum and cement plasters have been a popular decorative choice for many years. But elegant versions of the classic clay plasters and lime plasters from an earlier age are drawing a wide assortment of new fans.

In earlier generations, these materials were in common use for both residential and commercial use. Artisans would cook up plasters using a recipe of locally available minerals and colorants, with little standardization from one craftsman to the next. When manufacturers of gypsum and concrete plasters came along with standardized products that behaved consistently from one batch to the next, those materials opened up the industry to a greater number of tradesmen. But many traditionalists continue to prefer the look and performance of natural clay and lime plasters.

These plasters began drawing fresh attention when some architects began experimenting with alternative building practices such as straw bale, cob, and rammed earth construction. It seemed that ‘natural' plasters might be the preferred option for a structure that was built with walls that could flex and breathe. In addition, the clay or lime based materials were the product of a much less energy-intensive manufacturing process. So when standardized plasters began appearing in the U.S. market that offered the same batch consistency as other modern building materials, designers began looking for new ways to use them.

They liked what they saw. When American Clay introduced its first clay plasters, a major part of their appeal was the product's increased set time, which allowed people to work the surface a bit longer. Its initial offering, Loma Plaster, could be skip troweled or sponged to an attractive array of textures – creamy matte, a subtle suede, or a soft polished look.

Properly applied, that can lead to a very touchable surface that exhibits enough warmth and depth that it seems to increase the size of a room. American Clay is available in a palette of 43 hues. The color is impregnated throughout the plaster, and can easily be repaired if necessary.

The product line also earned points for its affect on indoor air quality. All of the clay plasters are VOC- and formaldehyde-free and virtually dust-free. But Carol Baumgartel, American Clay's VP/Marketing, says that their products truly add to indoor air quality. “We create walls of comfort,” she asserted. “When our plaster is in a room it actually increases the comfort level of people in that space.” As Baumgartel explains it, a clay plaster surface, unlike painted drywall, interacts with a room's climate whenever humidity is re-introduced into the air. “It actually introduces negative ions into the space,” she told us. That, in turn, balances the positive ions released by electronic equipment (such as computers and televisions) to increase the comfort level of people in the space. Clay plaster also helps to moderate sound levels.

Until recently, American Clay featured 3 varieties of clay plaster: Loma, which lends itself well to texturing; Porcelina, which produces an ultra-smooth finish without sanding; Marittimo, which contains crushed shell aggregate to produce greater patina.

American Clay's newest finish, Enjarre, was specifically designed for spray application, making it a nice choice for builders and contractors accustomed to working at a faster pace. “We just completed one of our 3-day professional classes,” said Baumgartel, “and we sprayed Enjarre on a 160 square foot sample wall. It was sprayed and back-trowled in 8 minutes. And it was beautiful.” Baumgartel compares Enjarre's impact resistance and abrasion resistance to Structo-Lite. It can be applied directly to most surfaces, although OSB may require pre-priming.

The plasters are shipped in 50 pound sacks, and can be mixed up with a paddle mixer at the jobsite. Depending on the desired texture, a product like Enjarre costs between 17 and 25 cents per square foot.

American Clay has always encouraged its dealers to offer regular workshops and hands-on demonstrations for their customers. “The core of our growth has been the dealers and their relationship with our applicators,” said Baumgartel. “At the same time, we're willing to help them introduce the material and their business to designers and architects, to their local USGBC chapters, and to their local AIA chapters. We are more than happy to go in with them.”

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Lime Plaster – A ‘Real' Material

One of the strongest markets for lime plaster is in restoration. “The reason for that,” says Michel Couvreux of TransMineral USA, “is that we have a real material.”

Couvreux was recently involved in restoring the exterior of the San Carlos Cathedral in Monterey – the oldest stone building in California – under the supervision of the Getty Foundation. “When they became involved with the Cathedral, they looked at it and recognized there was no choice; they had to use lime plaster,” Couvreux related.

And not just for appearance sake.The ‘technology' behind lime plaster goes back thousands of years, and can still be seen in the temples of ancient Greece and the cathedrals of medieval Europe. Once a hydraulic lime surface cures back to limestone, it's finished making chemical changes. It won't shrink and it's not affected by abrasive chemicals such as sea salt. As a result, Couvreux favors his company's LimeStone and LimePlaster as protective cladding for structural concrete.

The strength of the finished surface is a little more complicated. “A lot of people, even architects, believe that the ‘stronger' the material the better. That's a big, big mistake,” Couvreux contends. “Why should you use something that is 2,000 psi when 200 psi will give you greater elasticity. You cannot have strength and elasticity at the same time.” A lack of elasticity will makes a rigid material such as concrete stucco more likely to crack than a limestone surface.

A lime plaster used indoors offers another set of advantages. Mold has become a major health concern, and it's often caused by trapped vapor adhering to interior surfaces. Rather than trapping the humidity, lime plaster promotes a high level of vapor exchange. While that's important in conventional construction, it can be vital when working with alternative materials such as straw bale.

Lime plaster also adds an elegant dimension to interior walls. “A lot of people today are talking about how much they love faux finishes from Tuscany,” said Couvreux. “So we ask them, ‘Why would you choose a faux finish when you can have the real thing with lime plaster?'”

Hydraulic lime earns LEED credits as a low-emitting material with a long cradle-to-cradle life cycle.

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The Casein Connection: Milk Paint Goes Pro-Friendly

Milk paint was widely used on walls and ceilings, dating back to colonial times. Although there was no single recipe, the basic formula utilized lime as a solvent to dissolve milk proteins to form the coating's binder. Native clays and other natural fillers would give the paint additional body, and the pigment came from other nearby sources – earth pigments such as iron oxides, raw umber, and ochre. That may sound primitive, but many of those home-brewed finishes at work have withstood the test of time in Williamsburg and Mount Vernon. In fact, they're notoriously hard to remove. MIlk paint was rendered obsolete when pre-mixed coatings started appearing in cans.

The concept was revived in the 1970s when the Old Fashioned Milk Paint Co started supplying its powered, pigmented mixes by the bag. But that product was seen as a craft paint suitable for small projects, not architectural use. Now a new formulation aims to restore casein-based coatings to their historic place on walls and ceilings.

Safe Paint™ is a completely non-toxic milk paint that can be applied by brush, roller, or spray gun. It's a water resistant coating that can be applied effectively to conventional or alternative building substrates. According to Anne Thibeau, president of Old Fashioned Milk Paint Co., Safe Paint is practical for residential or commercial use. “We've had people use it in restaurants and large retail stores,” she said. “We've gone into a lot of L.L. Bean stores, and other locations like that. They'll buy hundreds of pounds at a time, mix it up, and apply it with either roller or sprayer.”

The product earns the ‘safe' part of its name because it is free of ingredients that might be troublesome for chemically sensitive individuals, and also because it's a breathable coating. It's available to dealers in 20 pre-mixed colors, or in a tint-base that accepts universal colorants.

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