These pages document the design and construction of a double-vault composting toilet at the Malu 'Aina Center for Nonviolent Education and Action organic farm in Hawai'i. Please contact me if you are interested in my teaching and/or consulting services for similar or related projects.

	In constructing the composting chambers for this double-vault system, rocks carried onto Malu 'Aina's land in a massive flood several years prior to construction were one primary material. Another primary material was ferrocement, used for reasons which will become clear as this story unfolds. My ferrocement garage project provides more details on this material. For additional online information on ferrocement from other sources I suggest starting with a visit to ferrocement.net.
The first step was to find an appropriate site. The location needed to be convenient to the common house, and also to several smaller shelters used by interns and visitors, as one purpose of this facility was to reduce the load on the existing removable drum compost toilet and indoor flush toilet when larger groups were visiting. It also needed to have a secluded setting for privacy. This picture shows rock walls in progress, built starting from an existing drop-off in the terrain to reduce overall labor and materials needs.
	Building curved walls provides various advantages. A curved wall encloses more space per unit of material used than a straight wall - which means less materials and labor for a given volume. Also, all else being equal, curved walls are stronger than straight walls and square corners. In addition, it will be easier to remove the finished compost from the rounded inside of these chambers than from chambers with square corners. This picture shows the front, or entrance, side of the structure, facing the high side of the natural depression in which the chambers are being constructed.
This rock wall is made of rough stone gathered from Malu 'Aina's land. Rocks of various sizes and shapes are dry-laid by hand in ascending layers so as to rest solidly in place, overlap previous layers, and support each other. Relatively small amounts of cement mortar mix (cement, mortar sand and/or #4 rock, gravel in some batches, and water) are packed and/or poured in to fill inner gaps between stones and further stabilize them within the wall. The mortar does not hold the wall together - it simply stabilizes the stones in place once they are laid. This view of the partially completed wall shows mortar fill in the near end of the wall and dry-laid rock waiting for mortal fill continuing towards the far end.
	The top of the lava rock portion of the wall was finished off with a bond beam consisting of a piece of 3/8" rebar embedded in the concrete mortar fill between the topmost layer of rocks. At this point I had decided to add additional height to the composting chambers using ferrocement. Vertical rebar to attach the metal mesh ferrocement armature to can be seen sticking up from the top of the wall.