Earthen Plaster


I had always been curious about working with natural building and earthen materials. Then as fate would have it I was given the opportunity at Humboldt State University, located in Arcata, CA, in an Engineering course called Appropriate Technology: 305. For Engineering 305 I had to choose a semester project. The co-directors of the Campus Center for Appropriate Technology were just finishing the completion of a straw bale wall and needed someone to plaster the wall. Thus began my sojourn into the use of earthen plaster.

What is earthen plaster? Earthen plaster, also known as natural plaster, is a plaster made from materials found in your own backyard, or in your neighbors yard or locally. It can consist of clay, sand, and a fiber, for example, straw, manure, paper pulp, etc... For my project I used a recipe of clay, paper pulp, sand and cow manure.

So how do you make and use earthen plaster? First, a number of tests were conducted to find the best mixture of plaster for this project. After the right mixture for the plaster was chosen, it was time to begin preparing for the plastering. Myself and a few others began mixing and applying a clay slip, also known as an aliz, to the straw bale wall.




A clay slip is used because it acts as a bond to the straw bale wall and to the plaster. After the clay slip is applied and allowed to dry, plaster can be mixed and applied to the wall. A trick to smooth out corners and fill in caps between the wood beams and the wall, was to use burlap sacks. The sacks were covered in the clay slip, nailed into the wood post, folded over and then smoothed onto the wall. Next, the plaster was put onto the wall by simply taking a hand full, throwing it onto the wall and smoothing it out using a trough. After many return visits to the wall and more help from friends, the wall was completed; at least the plastering was completed. Thus, began my experimenting and use of natural paint.

What is natural paint? Natural paint is mixed without the use of harsh chemicals and does not act as a vapor barrier. Natural paint can consist of milk curds, lime, sand, clay, flour paste, etc... Once again a group was gathered and a number of tests were done to find different mixtures. For this project I used a recipe mixture that was a combination of flour paste, clay, sand, and water. Add a natural pigment, such as Yellow Oxide or in my case I used Spanish Red Iron.

There were a few cracks in my wall, which I have been told is to be expected. In order to fill in the gaps, I could have applied another coat of plaster or simply apply the paint. Since the caps were rather large in some spots, I made an additional batch of paint that had extra sand mixed into it. I used this batch of paint with the extra sand to fill in the gaps in the plaster, the sand goes into the cracks, hardens in the gaps, acting as filler. Since it is the same color as the paint it was rather easy to then paint over with another layer.

After a semester of working on this project, I was (finally) finished with painting on December 4th. This experience was rewarding, educational, and fun! I was able to tap into the culture of Appropriate Technology through the medium of earthen plaster and natural paint. My curiosity has been more than peaked, and it has certainly not been satisfied. Not only was this a rewarding experience for me, additionally it offered an opportunity for many. From Engineering 305 to the CCAT Co-directors to my friend Dania, all of us (I hope) were able to acquire some kind of knowledge and practical experience. I am thankful for the help from my classmates and friends. I would encourage any and all whom are interested in working with natural materials to pursuer that interest. Pursue that interest, if for no other reason than, its fun to get dirty!!!