Earth plaster & clay slip for straw bale homes

The material used on the outside of straw bale homes is made of clay, sand, and organic matter. These days it’s called earthen plaster, but this mud mix has been used for about centuries in the form of wattle and daub, rammed earth and adobe. Until mud bricks were first fired and construction methods evolved, clay was an essential ingredient for home building. JSCW previously reported on sustainable building methods which have made a comeback and even here in the temperate rain forest of southwest British Columbia. (Click here to see our article on cob homes or here to begin reading our series on the history of bricks.) Today, I am concentrating on earth plaster and clay slip, the substance troweled and painted on the finished surface of a home built with these methods. This form of building is eco-friendly, inexpensive and easy to fix. The surface plaster differs from stucco which is made of lime and sand or Portland cement, sand, and water. When I was looking for a source of earth plasters and more information, I turned to a company that makes one of the clays I use, Plainsman Clay, in Medicine Hat, Alberta. Plainsman appears to have a good selection of earth plasters and it certainly knows its clay. After clicking on the link above, scroll to the bottom of the page to see natural colorants. Another writer enlightened me about the final coating on traditional strawbale home and was I ever surprised! And, naturally, once I learned about it, I found it very appealing. “A clay slip, known to some as an aliz, is used on an earth-plastered wall almost like paint is used on other surfaces,” says Carol Crews on the Last Straw site. “The purpose is to seal and beautify the surface.” She uses kaolin and ground mica as the basis of her clay slip, to which she adds flour paste. The kaolin would certainly make a smooth finish. She cautions people to use a mask to prevent inhalation of particulates, a familiar warning. (Over the weekend, I made sure I was wearing a mask when I used the Dremel to grind down the edges on a clay mold I’d made.) If you are interested in seeing actual straw bale homes in use, take a look at this International Straw Bale Registry Project for homes in your area and to learn whether you can drop in to visit the owners or whether you have to make an appointment. In my area, there is a straw bale house on Denman Island. You can read about it on the owner’s blog, Stuff from Denman Island. It is a straw bale house that has mixed lime plaster on its outer walls. Yet, from what I’ve been able to tell, if your eaves are deep enough and your foundation good enough, you won’t have trouble with earth plaster if your house is built correctly. A most interesting touch with  straw bale homes is the truth window, through which viewers can see the building material. I love the very idea of it and whatever metaphors can be divined. As my husband said, it would make a good name for a book.

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About Jan

I have a background in ceramics, graphic design and journalism.
This entry was posted in Articles and Interviews, Featured Artists, Fun, Home and Garden, How-to-do-it, Video/Photos/Slide Show and tagged , , , , , , , , , . Bookmark the permalink.

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