Do you remember the joy of playing with mud as a child? The feel of that cool substance slipping between your fingers… the slap slap of bare feet on the semi-solid ground… the gleeful satisfaction of presenting an unsuspecting parent or older sibling with a mud pie or mountain teeming with worms?
Working with earthen plaster gives grownups a chance to relive that childhood pleasure. It’s a great way for green builders to lower their carbon footprint, and an easy way for DIY home builders to get their hands dirty while creating their own dwellings.
Joseph Beck with ION Ecobuilding, an Olympia, WA-based company that serves western Washington, says he got interested in the material because it was a way to create a meaningful experience between people, their dwellings and the earth. “You can have work parties to install earthen plaster,” he says. “You can do the application with your hands and make it in the traditional way of mixing it in a pit with your bare feet. It’s so healthy that kids can be involved.”
Becker defines earthen plaster as a clay- or earth-based plaster that can be used in a variety of ways over a variety of surfaces. “It’s typically made up of simple, minimally-processed materials like aggregates, sand, sometimes fibers and other additives to make it thicker or stronger,” he says. Those materials are mixed with clay, which acts as a binder to hold the plaster together.
Once earthen plaster is made, it can be applied to interior walls just like conventional plaster. It can also be thinned out to create a veneer coat. “Typically in conventional settings in America it’s done mostly on the interior, but with good overhangs and good detailing it can be used outside,” Becker reports.
Like lime or gypsum plaster, earthen plaster can be applied over the top of just about anything, including wallboard, straw bale, light straw clay, adobe, lath and plaster, waddle and dab and insulated concrete forms.
There are many benefits to using earthen plaster. “It’s a vapor-permeable and environmentally-friendly finish that can be repaired and reused for a long time,” Becker says. “It’s minimally processed and has about the lowest embodied energy that you can have. It’s also very healthy, as it regulates interior temperatures, balances interior humidity, creates a negative creates an ionic charge, cleans the air and has no chemicals in it.”
Although it’s possible to purchase pre-mixed earthen plaster, many green home builders and DIY home builders choose to make it with local or even site-sourced materials. This allows the eco-conscious builder to lower their carbon footprint, and anyone to express the beauty and special characteristics of the place they live.
“I just did a project for a biodynamic dairy farm on Whidbey Island, and I used cow manure from their own animals,” Becker says. “A lot of joy came in because of the site-sourced materials.”
If earthen plaster sounds like the right fit for your home, Becker offers a few things to think about before you get started.
Hire a project facilitator
While you can make and apply earthen plaster on your own, there are nuances to really getting it right. Because of that, Becker recommends hiring a project facilitator. They can help you mix and test different recipes, explain how to apply it, and provide instruction on the best way to make transitions between the plaster and other materials such as flooring and windowsills.
Find earthen plaster experts through an online search, then check references. You can also ask your local green building council for recommendations.
Have a plan for protecting high impact areas
One of the drawbacks of earthen plaster is that it’s more easily damaged than conventional plasters. Homeowners should take steps to protect the material, especially in high traffic areas. “You might want to consider corner trims, door transitions and baseboard trim to keep things from banging into the plaster,” Becker says. These items can also add a nice decorative element to homes.
Given the greater likelihood of damage, families with small children or lots of pets might give more careful consideration to whether earthen plaster is the right choice for them.
The good news is that earthen plaster is easier to repair than traditional plasters. That’s another reason homeowners should strongly consider participating in the plastering process, Becker points out. If you know how to mix and use the material, you can repair any areas that are damaged over the home’s lifetime.
Consider the artistic possibilities
“There’s a huge variety of textures and colors and shapes and sculptural potential that’s available with earthen plaster,” Becker says. “That’s a really exciting thing for some people. You can leave the finish polished or coarser. You can include cattails, cork, oyster shells, hemp or chopped straw in the mixture. You can create all kinds of colors using pigments, but you can also use the color of the clay and sand and what the ingredients have to offer. It can be incredibly fun to use it as a form of expression.”
For visual inspiration, Becker recommends visiting the website of Clayworks, a British earthen plaster manufacturer. People interested in learning to mix and use earthen plaster themselves can check out the books The Natural Plaster Book: Earth, Lime, and Gypsum Plasters for Natural Homes by Cedar Rose Guelberth and Dan Chiras, and Using Natural Finishes: Lime and Earth Based Plaster, Renders and Paints by Adam Weismann and Katy Bryce.
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