[Cob] Dorothy's Obelisk: A Habitat for Bees, and Rainwater Harvesting Trench One-Person Cobbing: The Ultimate Small Crew

[Henry Raduazo]

Dorothy's Obelisk: A Habitat for Bees, and Rainwater Harvesting Trench
	One-Person Cobbing: The Ultimate Small Crew

	I love cobbing with friends, but all my friends are gainfully employed earning a living, so I am happy to help them with projects but reluctant to ask them to help me. I will be 74 in September and due to ankle tendonitis I can't walk very well. That makes cobbing on a tarp not easy, but I do have a cheap 5HP tiller. Dorothy wanted me to build an obelisk, but standing in a pit and throwing cobs up to me on a ladder is not her favorite thing to do these days, so I was wondering what sort of project I could do all by myself.
	The cob obelisk seems like a good demonstration and just what my garden needs, providing both water and a bee habitat on the upper edge of the garden. I think the size is manageable but challenging. Wet cob weighs about the same as wet cement the way I mix it. That means I will have to mix and move around 6500 pounds of material to build a 7 foot obelisk with a 30" x 30" base. This is by far the lightest and easiest project I have ever done but still big enough to make it interesting. I began this project in October of 2014, quit for the winter, and the bees started moving in the next spring. 
	Fig. 1 cliff dwelling bee and turret 

	Fig 2 multiple turrets in lower obelisk:

	When designing and building a rainwater harvesting project, the first thing you need to do is know your land. Here in Virginia we tend to have much of our rain in the winter and early spring, followed by intensely hot and dry summers. Also some of the summer rains tend to be scattered showers. The second week in August, for example, we had a 10-minute "gully washer," a short cloud burst that dumped 1 inch of rain, followed by a light drizzle, and then nothing for weeks before or after the brief rainstorm. Obviously my landscaping should be designed to harvest 100% of that and it did. If you recall the $100 wood shed (Haiti demonstration project), I turned my water easement into a large water harvesting trench followed by a 25 square foot pond followed by a berm made of yard waste and wood chips. The pond was totally dry after the rain, meaning that we successfully harvested all of the water from my house and yard and that of my neighbor. That was easy, but what about 4 or 5 inches of rain?
	Obviously when it does rain we want to catch and hold as much of it as possible where it is most needed. For this reason I built my trench at the top of my garden transverse to the natural slope of the yard. Rain that overflows my rain barrels is directed to the center of the slope and flows straight downhill to the center of the trench. 
	 I don't want the captured water sitting around on the surface where it will attract mosquitos and evaporate, so the trench will be filled with biodegradable yard waste and wood chips. At first a trench dug into heavy clay soil will hold water for a very long time, but as earthworms and insects go to work on the wood chips it becomes a very leaky hole in the ground which will catch and hold much more rainwater than a barrel or other container of equal size. Note: I have been able to get wood chips free from tree companies who must pay $70 per ton to dump their chips at the Lorton waste management site.
	Tools of the Trade
	If you have a friend who will throw balls of mud to you while you stand up on a ladder that may be all you need to do this project, but if you plan to work alone you need a good scaffold. I have two of them. The first is a pair of 24" sawhorses with a 2" x 8" board, and the second is a pair of ladders which can support a board up to 5 feet above the ground. I also have a 24" square board which I can attach to my scaffold board with decking screws to form a pallet that can hold almost a wheelbarrow full of cob.
	Fig. 3 Scaffold with cobbing pallet:


	DC Cobbers have two rototillers available to them; I prefer the larger 5HP tiller. Many years ago I had a 5 HP tiller with reverse. That would sure be useful when pit mixing. The 5 HP one-direction tiller that we now have tends to run itself into deep wet cob and get stuck in the bottom of the pit. The only way to get it unstuck is to stop tilling and drag the tiller back across the soft mud, sand and straw mixture in order run forward again. Reversible tines to help in moving the tiller backwards sure would be nice. Alternatively. the pit should be open at both ends so you can run the tiller in on one side and out on the other to reverse directions on level ground. Note: Tillers with power driven wheels do not work for cobbing. Our smaller tiller is a Hoffco or "Hoffie" which I will try out on my next solo project.
	Fig. 4 The big tiller


	I began this obelisk by burying a cedar post as deep as possible with a post hole digger. My thought is that since this is a habitat for bees it will be allowed to deteriorate and fall apart naturally like the Always Becoming exhibit at The Museum of the American Indian in Washington, DC. When it falls apart I want it to fall away from the center post in small pieces and not fall to one side in one big heavy piece that could hurt someone.
	The second step was to dig around the post to the first horizon. That is the point at which the earth changes color indicating that you are below all or most of the top soil. I placed a ring of cinder blocks around the cedar post, placed a 2" x 8" x 24" scrap of wood on top of the cinderblocks and pounded them down into the subsoil with an Ugly Stick, an ugly piece of wood with knots and irregular grain with a chain-saw-made handle just above waist height. The ring of cinderblocks were not quite high enough so I also supported a ring of used bricks on top of the blocks to get my desired height above the ground. My goal, as always, is to get an air space between the earth which may be wet and my lowermost layer of cob which must remain dry.
	I filled the space around the cedar post and inside the cinderblocks with urbanite scraps and was now ready to begin cobbing.
	Fig. 5 The foundation hole:

	I intended to do pit mixing for this structure so the next step was to select a location where water flows down across my land during rain events. I ran the tiller in a line perpendicular to that flow and shoveled out the topsoil and mulch, then did it again until I reached the first soil horizon. Below this line the predominant material is clay. I dumped a wheelbarrow of sand into the pit and mixed it into the subsoil with a dirt fork and tilled them together, added water and did it again. I then added straw and more water if needed and ran the tiller over this one or two times, just enough to incorporate the straw. This produced around 400-500 pounds of cob which I then moved onto the structure or onto the scaffold with a dirt fork and/or a pull fork. 
       Note 1: Pit mixing is often uneven so I sometimes need to add more water and do additional hand mixing after removing the cob from the pit. I do this either inside a wheelbarrow or on the scaffold pallet.
	Note 2: The tiller will only reach 2-3 inches into the soil, and since the sand is on top I use a dirt fork to mix sand with the subsoil before tilling. Here I found that a dead end trench was a big problem in that, at 74 years of age I do not have the body strength to keep dragging the tiller back across and through the mud. Despite that difficulty I was easily able to build 6"-12" per day while working only a few hours per day.
	In Fig. 4 above the dark area from the surface of the scaffold up is 4 day's worth of work but they were not consecutive days.

	Fig. 5 a trulli roof: 

	Fig. 6 my living roof:

	Originally I planned to build a trulli roof in honor of my Italian heritage, but someone gave me a big chunk of living roof fabric so I decided to use that instead and try to create a living roof. I found that loose dirt could not be stacked up with the proper angle of repose to create a good point on the obelisk, so I mixed two parts clay-rich topsoil with one part compost and one part sand and made this into a cob mix to encase the topsoil to form a pyramid. I then took the most invasive and hardy plants from my living roof and poked them into holes in the compost-rich cob. For awhile I will water the plants to see if they can take hold, but if this does not work I may go back to the trulli idea with the slope of the slate tiles reversed to draw water into the core to support plant life.
	
	For For a copy of this article including pictures showing the tiller, tools and finished project, send a separate letter to me. Ed:    raduazo at cox.net  .
	The next project is to finish the water harvesting trench while building a sun goddess seated upon a column. Anyone who would like to learn cob mixing with a rototiller and who lives  in the Washington, DC area can contact me. I plant to use both the larger tiller and the little Huffie on the column project.


For more information on rainwater harvesting see:
Rainwater Harvesting for Drylands and Beyond, by Brad Lancaster et al.