CAROLYN'S BLOG ABOUT THE HOUSE CONSTRUCTION
AND THE YEARS BEYOND
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Sun, Jan 16
7:45 am

Life with Earthen Plasters: My house has earthen plasters (clay, straw, and water, covered with white glue) inside and outside. For 9 of the 10 years I have lived here, the plasters have had no other covering, but just last year, I coated the exterior plasters with a lime finish. It is these thick earthen plasters on both sides of the straw, that make the house very stable and solid - well along with other things. I'll discuss what all that is and how it holds up.

The earthen plasters on the outside of the house with made with high-clay soil that I bought from the Pasqua Yaqui tribe and is generally used for adobe houses. These plasters are made of soil, chopped straw, and water. We chopped the straw in a leaf mulcher. I have a 7-foot porch around the house to protect them from the rain, which they do need. I think there is some illusion that using prickly pear gel in the water will make them waterproof, but this is not true. If you are wondering if your plasters will hold up in a rainstorm, turn the hose on them full-blast and see what happens. Adobe houses add asphalt emulsion to this mixture to make it more waterproof. I have never done that, so I can't comment on that. I did see some tests and it looked like it really works, though. I did get some pitting on my plasters after our summer thunderstorms for the first few years and then the storms subsided and I had no issues for the last six or seven years. Coating the lower part of my walls with stucco waterproofing (it's clear) helped them resist the thunderstorms. I coated them with lime because the birds were pecking holes in them. I'll discuss the lime coat further down this blog.

The reasons to use earthen plasters instead of stucco are: earth will let the straw breathe, so if it gets damp, it can dry out. To apply these plasters, you don't need to coat the house with wire - you can just damped the straw with clay/water and then apply the plasters with your hands. So, it is less expensive than stucco because you aren't using expensive concrete and you are doing it by hand. The problem is that you will most likely have to do this by hand - no general contractors that I have met understand earthen plasters. I think you might be able to hire an expert and fly them out, but I have no idea what this would cost - a lot, I think. I think earthen plasters should be done by hand and become an expression of art by the owner. You can scult them, color them, embed shells, glass pieces, glass bottles, or anything else you feel like embedding. If you don't like what you did, you can scrape it off and start again. It becomes a wonderful, fun hobby and is very inexpensive.

My interior plasters are the same as the exterior, with a finish coat. This finish coat is comprised of white powdered clay from a pottery store (costs about $10 for 50 lbs), a little gold oxide powder to remove the gray color - you can use any color you want, powdered clay comes in many colors - or once I used some clay that I found in the ground in New Mexico - this is mixed with only water and when it is dried, I coat it with white glue/water. Lowes carries gallons of white glue. This is far less expensive than paint and much more beautiful. Once you have applied the clay, before it dries, you can embed whatever you want, or shape it into window and door frames. I also made a headboard for my bed from earthen plasters.

Benefits of the interior plasters: They also let the walls breathe and dry out if they get damp, they allow fresh air to filter through the walls, as long as the exterior is earthen also. They are a little uneven, so they are acoustically very soft - a good thing in a small house. They are chemical-free. They make the house feel like a home with their handmade unevenness and natural, earthy tones. It is not the straw in the wall that stands out in my home, but the plasters.

Recently, I began coating the interior plasters with lime paint, also and that is because I found that the clay darkens over the year. I think it's a natural oxidizing process. Lime does not and is again a little more durable than clay. But I like the clay better, actually, I'm beginning to think of retiring some day (I'm 60 now) and thinking of renting out the house when I do, so I want to make things a little more general-public friendly. Clay plasters are softer and you can't scrub them if someone throws ketchup on them. When they are coated with white glue, however, you can wipe them down. The lime paint is brighter, but it does not have the color inflections of clay. Here is a photo of the difference in the walls:
http://www.ahouseofstraw.com/limepaint.htm

Lime plasters: On the outside, I roughed up the surface of the clay plasters with a wire brush, then troweled on a mixture of powdered S lime (from home improvement stores), #60 silica sand (from sand-blasting supply co), water and ferrous sulfate fertilizer for color. The ferrous-sulfate fertilizer is from a wholesale garden supply center. All the ingredients are inexpensive. The result looks like peach suede and I'm very happy with it. Here is a link to a photo with the new exterior plasters: http://www.ahouseofstraw.com/westhouselime.htm
Lime is more durable than earthen plasters, but it also lets the walls breathe. On the inside, I just made a lime paint - lime, ferrous sulfate, water - no sand - and painted it on with a paint brush. It doesn't have all the nuances of the exterior plaster - it's much more like regular paint - but it's bright and durable. It still has more of a natural color and highlight than paint, I think. I also coat this with white glue and water when I'm finished to make it more scrubbable, if needed. I guess I could mix the glue into the paint, too. I might try that.

Hope that answers some questions.

Have a great day and be kind!
Carolyn