All of these materials were found locally in Arcata, California. The clay was found on campus and the sand was found by a river. The paper for the pulp came form the recycle center here in Arcata and the cow manure came form the local farms. All of the materials were free. The importance of each material goes as follows;

Clay- is an adhesive or natural glue, it is needed to bind the materials together.

Sand- is a geometric structural component; it gives strength to the mixture. River sand works best because of the rough edges ability to hold different particles together.

Paper pulp- was used as a cohesive fiber and allows the plaster to remain strong because of the "lignified vessel elements that hold water are rigid". This helps with cracking.

Cow Manure- an additional fiber that helps with water resistance while allowing the plaster to breath.

The testing took place at a Campus Center for Appropriate Technology workshop with Peggy Frith. The three most important ingredients to test are clay, sand and a fiber. These components are what earthen plaster is made with. For the testing the fibers used were straw, cow manure, horse manure, and paper pulp. The ratios for testing plaster are always the same six (6):

1 part* sand with 1 part clay

2 parts sand with 1 part clay

3 parts sand with 1 part clay

4 parts sand with 1 part clay

1 part sand with 2 parts clay

1 part sand with 3 parts clay

Each proportion is then mixed together with two fibers. In order to receive optimal results it is recommended by Jeff at CCAT to make as many as 15-20 different mixtures. The recipe that was chosen for the final plaster was chosen based on a few very important tests.

First, you want the plaster with the least amount of cracking.

Second, you want to scratch the surface of the plaster (after it dries) in order to determine whether it has to much sand content.

Thirdly, you might want to tug at the edges of the plaster in order to see how well it bonded to clay slip covered wall.

The last step is to spray the test plaster down to see if there is any run off. Another important aspect of this last testing method is to determine whether or not this particular mixture can hold up through a wet and dry cycle.

After the test were complete the final plaster was chosen and the work of plastering a wall could commence.

* "part" is whatever size you choose