I have found the most tiresome aspect of creating an earth plaster to be clay preparation. I have seen it screened, mixed in cement mixers, trampled in all sorts of pits, and rototilled into submission. These techniques require time-consuming set-ups, motorized equipment, or a tremendous amount of physical labor. Since I often work alone, usually after work or on weekends, these factors all decrease the likelihood that I will get any plastering done.
However, over the past three years, I have worked out a system that makes small or large batches of earth plaster faster, easier, and less…well…muddy. What I do is dig clay from whatever mound or hole is handy and dump the damp clay into a 5-gallon bucket. If there are big clots, I break them down a bit with the shovel. I then fill the bucket with water up to about the level of the top of the clay clods. If I have my act together, I do this the day before, but it will work quite well without waiting too.
The next step is to take a hoe and place the flat side on top of the water and start a very gentle up and down motion. It is important in this process to not mash the hoe into the bottom of the bucket or you will end up with water on the top and a block of clay at the bottom. As you suck the water up and down, the clay will start to go into suspension. After doing this for a little while, you will want to take the corner of the hoe (if it is a small hoe) or something like a large crowbar and pull up some of the bigger chunks from the bottom. With a small amount of work, most of the clay will go into suspension, creating a nice pudding- like batch with chunks of rock, root, and obstinate clay balls floating around within.
In a nearby wheelbarrow, I have the sand and other ingredients ready with a 1/4-in. mesh screen box sitting on top. I then dump the crème de mud into the screen and run the hoe over it until most of the mud has gone through and the junk is left on top. Clays vary in its consistency and I have found that some of the easiest to mix have a fairly high sand content and have been either sitting around for several years or come straight from the upper soil layers where the critters have loosened it up. The worst clay comes mauled by a large machine from the subsoil and has a low sand content. These clays can weather through the winter into easy-to-use material, but often there can be a fair amount of clay at the bottom of the bucket that refuses to go into suspension. If possible, it is best to use dry sand in your plaster mixes, using this technique as extremely wet sand combined with mud soup can yield a too wet mix to use right away.

Sam Droege lives with his family in Upper Marlboro, Maryland. He has organized and participated in natural building colloquia and workshops sharing his expertise in harvesting trees and in timber framing and other areas. He can be reached at <beeguild@aol.com> 301.497.5840 (office), 102 Queen Anne Bridge Rd., Upper Marlboro, MD 20774