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Plaster

On the last day of the workshop, Becky showed us how to make plasters, and we sampled them on small sections of the walls, just as a learning exercise. The real plastering of the hermitage will be done during spring workshops. Plaster will protect the earth building and can also add beauty. Cement-based plaster or stucco does not allow natural buildings to breathe and can actually cause it to deteriorate faster. Becky recommends a basic earth plaster. To make it, we took the same ingredients in the same ratios as if we were making cob and we sifted it all through window screens until it had a fine texture. Straw takes a little effort to sift if it is long and coarse. There are many alternatives to straw to add fibrous strength to plaster if straw isn't your favorite texture. One of Becky's favorites is the fuzz from cattails. Africans and Central and South Americans often add various plants and or manure to earth plaster. Once you've got your plaster mixed, you can also add natural pigments or make whitewash out of builder's lime to go over the plaster once it dries. Interior whitewashed plaster walls are particularly beautiful. (Interior plaster usually goes on after the roof and ceiling are done, but before the floor.) We used our hands and plastic yogurt container lids to apply the plaster, but you can also use a trowel or paintbrush. This is a good time to embed tiles and your shell collection in the mantel or along a doorway, sill, or countertop.

Floors

The Cob Builder's Handbook gives some good basic directions for putting in earthen floors. For more detailed descriptions of methods for making earthen floors, see Earthen Floors by Athena and Bill Steen (The Canelo Project, HCI, Box 324, Elgin, AZ 85611). (Bill and Athena wrote about building strawbale homes in MEN #153) You can surface your floor with any surface you want, including wood or tile, but an earthen, stone, or brick floor can increase your thermal mass greatly.

You can make a one-piece earthen floor from cob mix. Becky says make your cob mix for your floor as dry as possible while still being wet enough to trowel, so it will dry quickly and crack less. Using a little more sand in the mix helps avoid cracks. A few additives can be helpful—Elmer's glue or flour to harden the floor, psyllium seed husks to give the floor a rubbery quality that might be easier on your feet. Becky recommends making two-foot round test samples of your floor mix. If your sample cracks, you have too much clay, but compensating for cracks with too much sand will result in crumbling floors.

To make a floor, level your ground, figure out your desired floor height, and mark it. Then pound your floor with a tamper for as long as you can stand it. Next put in a gravel base to raise it up off of the ground. This will keep your floor drier, and the base provides stability and a little insulation. This is another common place for a moisture barrier in a conventional house, but natural builders tend to avoid them altogether. Finally, dampen the base, and trowel—on the floor. Let it harden for a few weeks and trowel-on your next layer. Your level should play a role, but there's no real reason a floor has to be 100% perfectly level. After a cob floor has dried a few weeks, you can put on a sealant like linseed oil.

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