The second weekend of our straw bale construction workshop (led by Mark Morgan of Bearpaw Design and Construction ), we got a chance to try earthen clay plastering on the interior walls of the building.
The first weekend, we troweled concrete stucco on the outside of the straw bale walls. I found it an intimidating process. The Portland cement, once mixed with water is on a one-way trip to the solid state. A chemical process is initiated, and you have a limited time to apply your mix. It is also a toxic substance that you are trying (in my case very unsuccessfully) to keep off your skin.
Also, concrete that slips (oh, so easily) off your trowel if you don’t have precisely the right trajectory and propulsion as you approach the wall hits the ground and is not reusable. An amateur can be very wasteful in applying concrete.
The inside walls of earthen clay were a different story!
I love working with this material. The clay is nonthreatening and very forgiving.
I gradually mastered how to hold my hawk of clay in my left hand and scoop up trowelfulls with my right hand and move the trowel surely enough to make contact between my dollop of clay and the straw bale of choice.
But I’m a long way from a master plasterer at this point, and I had plenty of trowelfulls of clay dropping to the concrete floor just before meeting with the wall. No problem! Just scoop it up and try again. That’s what I call an agreeable material!
The clay needs to be worked deeply into the ends of the straw and cover it completely. Eventually three layers of clay will be about 2” deep, but each individual layer is very workable.
Mark does not build his straw bale houses with vapor barriers. It is perfectly alright for the walls to absorb moisture from the air. In fact, it’s preferable. In humid weather your walls act as a dehumidifier, drawing the moisture out of the air and into the wall. When the conditions become dry, the walls release their moisture load back into the air, making it more comfortable in both conditions. Mark assured us this does not damage the wall in the least. I’m sold.
It’s easy to see how the creation story in Genesis depicted man being formed from clay. When you have your hands in clay, you feel like anything is possible.
There is a very good book out by Cedar Rose Guelberth and Dan Chiras called The Natural Plaster Book: Earth, Lime and Gypsum Plasters for Natural Homes.
Some of the benefits that they list for earthen plasters include:
Add Unrivaled Beauty to a Home
I can attest to that. Just the first coat that we applied made the room incredibly inviting. Clays come in many colors creating endless options. Some people add mica flakes to give a wall a bit of sparkle. Others rub oil and beeswax on earthen finished interiors walls for added luster. I’m really looking forward to exploring this possibilities.
Create a Soft and Quiet Surface
Even after just the first layer, I could sense this quality in our clay-plastered room. Clay has a sensuous feel. It is so elemental and timeless and just interacts with its surroundings in a gracious and welcoming way. And the rounded corners!
Fun to Work With
I’m here to tell you that they are. That is not to say that they are easy to work with. I expect I will have to build up my upper body strength to tackle plastering and I expect to come out the other end with very buff arms indeed.
Safe to Work With
Allows Work to Proceed at a More Relaxed Pace
I found this to be true. The clock was not ticking and the whole process became timeless. It was almost like meditation. And if you have clay left at the end of the day – no problem. Just cover it and continue tomorrow.
Easy to Clean up After
I was amazed how easily my hands rinsed off in the tub of increasingly brown water sitting outside. Wet clay just melts away in water from both hands and tools.
The nice thing about plastering over straw bale is that the whole process is a bit to begin with and meant to have irregularities. They add interest. And they put the process within the power of an ordinary person who wants to make their own walls.
Categories: Eco architecture