All photos link to larger images.

One of the most exciting discoveries during our project has been American Clay's earth plaster. This small Albuquerque-based company manufactures a line of natural plasters that are earth friendly and extraordinarily beautiful. The clay plaster comes in many colors made from natural pigments that can be mixed to create even more variations. They ship their product across the United States. Click on their logo above to visit their web site.
Below we will be describing the interior wall finish process from beginning to end and will be adding photos as our walls are completed. Bookmark this page if you'd like to watch the process over the next couple weeks.
In a passive solar home, thermal mass inside collects and stores the solar heat. Since we are using in-floor radiant heat for our conventional system, we can't use the (concrete) mass in the floor for this purpose. Instead, we are distributing the mass inside with cement plaster walls (instead of gypsum plaster). Spreading a 1/2" layer of cement across many square feet of interior walls will give us the mass we need for the home to heat and cool itself passively. The crew from Joe Saenz Stucco applied expanded metal lath over black, 15# roofing felt on the walls to prepare for the cement plaster. Interior sound insulation is visible in the interior walls and ceiling.
Here, Carol Baumgartel from American Clay (manufacturers of Clayote natural clay plaster), is helping us select our clay colors. The final coat of plaster will be their natural clay which will be applied to the brown coat of the cement plaster. Here Carol is working with actual samples of their product. It is helpful to see the colors in the rooms where they will eventually be with the natural light in each room.
We lined up the clay samples alongside flooring materials to see how their colors interacted. Clayote can be textured with bits of straw, mica or shell to vary the texture and look. We will be using some of these in our home.
Croft Elsasser, CEO and inventor of Clayote will be instructing our plaster crew on the application. Fortunately, clay is similar to conventional plaster in its application but much easier to work with and more forgiving. Clayote sets up more slowly than conventional plaster and can be reworked until it's sealed. Since it doesn't dust off, many people choose to leave it unsealed, which allows for easy repair.
Cement plaster will be on all the walls, but we are using drywall in the closets and behind shelving. In areas where the drywall will show, as in these bookshelves, we will be using clay as the final coat over the drywall, instead of texture and paint. The clay will also be applied directly to the ceiling panels. Since clay adheres very well to a primed OSB surface, we won't have to drywall the ceilings first, which saves time and money.
Croft came down to apply some clay before the GreenBuilt tour. He began with the ceiling, and since our ceilings were OSB, primed them with El Rey Gypsum Bond, then taped the seams. The clay is applied with the same tools and technique that conventional plaster is applied. The main difference is that the clay sets up much more slowly and allows the plasterer more time to work the clay. Also, unlike gypsum plaster, clay can be rewetted and reworked any time until it's sealed. Sealing is optional and unsealed clay will be easier to repair in the future.
After the ceiling, the walls are done. As with conventional plaster, the clay can be applied with a texture or smooth. Textures can be heavy or light and the style of the texture is as varied as the people applying it. Because of the forgiving nature of Clayote clay plaster, it's much more suitable for inexperienced, owner/builders or do-it-yourselfers.
Case in point, here Croft is instructing Evan on the fine points of applying clay plaster to the ceiling. He caught on very quickly and enjoyed the process (and the upper body work!)
Once the clay was applied around the doors and windows, Croft came back and sprayed the rough areas with water so he could smooth them out. Jon asked for a smooth finish in the office and ordered bits of straw in the clay. Rewetting and working the walls after they've dried will bring out the clay and smooth the surface.
Croft told us that the color of the clay when wet is 3 times darker than the dry color, but it wasn't until it began to dry that I could see what 3 times really looked like. It's significantly lighter when dry, and matched the samples.
Here's the office ceiling almost dry. The cracks between the sheets of OSB have a bit more clay and took a bit longer to dry. Once totally dry, we'll be able to see if the ceiling will need another thin coat of clay to cover any remaining sins below the clay. Because of the forgiving nature of this material, we can continue to work on problem areas caused by the nature of the materials below until all is concealed and looks the way we want it.
Here Joe Saenz, owner of the stucco + plaster company we've hired, is trying out the clay for himself. He said it's important for the plasterer to work with any new material to see how it behaves. He said the clay went on very easily and is excited about using it. He was able to give his workers a few pointers and they've taken over to continue the other rooms in the house. Go to Entry 24 for more clay photos. WOW!