Yesterday we finished off the plastering of Jerry's cob oven. The only thing left is to coat it with boiled linseed oil to help protect it from inclement weather.
On Memorial Day Jerry and I began screening all the components. We put the sand through window screen to get out the little pieces of gravel which will mar the surface of the plaster when you're troweling it smooth. We screened the soil and straw too, and I picked lumps of horse manure out of the mess I'd scooped up in Annadel State Park. We ended us screening those with the wider mesh screen the next day when Krista joined us.
We mixed it all up in a plastic tub, using a shovel and a drill with a paddle bit. In hindsight I would've skipped the straw entirely and used more horse manure. It has the perfect kind of fiber for plaster, and to my surprise it didn't smell at all. The straw, even though we'd screened it three times, ended up showing up on the surface of the plaster, just a bit. Cattail fluff would have been better, but it was out of season.
Because the surface of the cob oven was already sculpted into snail shell ridges, we applied the plaster by hand. I think we could've gone back over the sides with a trowel though. They ended up just a bit lumpier than I'd have liked. Even if we had used trowels though, I think putting on with our hands was essential to really work it in. We had made a gazillion little thumb sized divots so that this coat would adhere, and there was a lot of straw sticking out that had to be worked around.
After the plaster had set for an hour or so, we took smooth plastic lids from yogurt tubs and smoothed it down. This was challenging around all the ridges, but incredibly satisfying to me. The oven ended up looking smooth and almost shiny.
It would have been interesting to have added pigment to the plaster. Perhaps a dark orange color? It ended up looking pale tan, but that will change with the linseed oil, which has a tendency to darken the clay.
All in all a wonderful project. I think the pizzas will taste even better now, if that's possible!
To see photos of the entire project, you can visit my Flickr set by clicking here. Most of the photos have notes.