[Cob] Handicap Accessible Cob Cold Frame

[Henry Raduazo]

	For people living in zones 6, 7 and 8 it is not to late to build a cob cold frame. I am on my fifth cold frame some of them have lasted as long as 4 years. My last one only lasted two years. This year I am building a handicap accessible cold frame. Since the cob list does not post pictures you will have to send me a personal request if you want the pictures that go with this article.


THE HANDICAP ACCESSIBLE COLD FRAME

	 Cobbing as taught with The Hand-Sculpted House book is the equivalent of a three credit college course. In fact most of the three credit courses that I took in college covered less material and were less demanding than the ten day Basics of Cob class that I first took in Sooke, British Columbia. Because of the way cob is taught and because of its major use as a home construction material, people tend to treat cob as a big deal. It is not a big deal. Cob is a structural building material, a plaster and a refractory material, and anyone can learn to make any one of these materials in about one hour. It should be an every-day material for use in simple things such as this handicap accessible cold frame. 
	The basic material for making this structure came into my hands when I found a dumpster full of cinder blocks. Someone tore down a block wall with a front-end-loader and dropped the blocks into a dumpster. I jumped into the dumpster with my masonry hammer and salvaged a truckload of the used blocks.
	I have used these blocks over and over again, connected together with a cob mortar. When the resulting structure was finished serving its purpose, I tore it down and reused the blocks for subsequent projects including this current experimental structure.  Four times I have used and reused recycled blocks and bricks to make cold frames. One of those cold frames lasted four years. The one below I used only two years. Unfortunately the multiple panes of glass leaked too much cold air. Lettuce will grow and thrive as long as the temperature inside the cold frame remains above 20℉. Lettuce gets frost burn or turns to mush at temperatures below 20℉. 
	Another disadvantage to the previous cold frames was that I had to get on my hands and knees and reach over a block or brick wall to weed and harvest my lettuce. Not easy for a 75-year-old guy with a bad ankle and bad knees. The two photos below show previous designs. In the first design you can see some of the frost burned lettuce. The second photo shows an alternative design where the panes of glass are mounted on an A-frame perpendicular to the angle of the sun at winter solstice.

(Fig. 1)


(Fig.2)

	Below is my current cob cold frame project. It consists of a 48 inch by 79 inch block frame, 4 courses of blocks, with 14 blocks per course. The area inside the lower four courses of blocks is filled with wood chips. The blocks in the lower 2 and 1/2 courses are  also filled with wood chips, and the upper 1 and 1/2 courses of blocks will be jammed full of cob. Note the "cobber’s thumb" sticking in the rear-right corner block, used to compact the cob in the upper courses of block to unify them. You can see below that I am half way through ramming the cob into the upper blocks. After unifying the upper blocks my next step will be to create a cob A-frame to support a fixed, south-facing, sliding glass door panel 48” x 80". Three removable, high quality, double pane glass panels will cover the north side of my cold frame, giving me easy access at waist height to weed, water and harvest my lettuce. As usual all glass is free recycled glazing panels.
	The upper 8 inches of the cold frame will be filled with some homemade potting soil which I am getting from a water harvesting trench. That is a trench positioned to intercept water flowing down hill from my yard. The trench was initially filled with wood chips 6 years ago. The trench, now 6 years old and filled with clay-rich potting soil. This cold frame will be very well drained so I will need the clay in the mix to hold lots of water.

(Fig. 3)

IN SEARCH OF THE THIRD HORIZON

	I started making the cob by rototilling an area of ground at a convenient location. The blades of the tiller quickly cut through the first horizon of rich black compost. I raked this to the side, exposing the second horizon. The second horizon consisted of dark soil that was hard and dry. I could probably use this soil to make good cob but since it is good top soil…

(Fig. 4)


	I broke it up with a dirt fork and tilled it to form granular topsoil which I removed to expose the top of the third horizon.

(Fig. 5)

	You can tell that I have reached top of the third horizon because lighter colored soil has been reveled and it shows signs of “shovel shine” in areas grazed by the shovel removing the second horizon. The lighter color in the center of the photograph below does not show up too well in the photo, but it is very obvious when you see it live.

(Fig. 6)

	I then broke up this third layer with a dirt fork and then rototilled it…

(Fig.7)

	Next I wet the soil and tilled it again, added straw, wet the straw and rototilled it a third time.
	Note that the straw in this picture is “thrice mown straw”…

(Fig.8)

	To make thrice mown straw I sharpen the blades of my friend's lawn mower and gently lower it onto flakes of straw laid out on the ground. Since this is a side discharge mower it throws the chopped straw against the wall of the house.

(Fig. 9)

	I then rake up the straw and do it again two or three more times. [Note: Lawn mowers are not designed for this purpose so for your safety and lung health wear eye protectors and an N-95 dust mask.] A key factor in chopping straw is to make it short enough so that it cannot wrap itself around the tines of your tiller.

(Fig. 10)

	Having tilled the wet straw and clay together, I picked it up out of the trench with my dirt fork and rolled the “cob" to my structure. The word cob means ball or loaf in old English. Here I am making cob without making it into cobs. 
	When I get to the cold frame I pick the cob out of the wheelbarrow and jam it into the blocks. This is the first time that I have touched the cob with my hands. 

(Fig. 11)

	It rained all night and into the morning but the rain stopped around 1:00 and this gave me a four hour window to do some more work on the cold frame.
	My first task was to make some retaining brackets for the glass door panel. I made them from sign holding brackets left in my neighborhood by some political candidate, . (The real political signs, by the way, make great shingles. The exposed tab should be 1/3h - 1 inch and the first three courses should start with widths of w, 2/3w and 1/3w. Where h= the height of the signs and w = the width of the signs. I don’t know how long the signs will stand up to UV light.)

(Fig. 12)

	I placed the brackets into the cavities of the blocks and cobbed them in place. When cobbed in place, the 48” glass panel will fit between the cob and the wire (see the second photo below).

(Fig. 13)

	After 4 hours of work you can see the slope of the end wall start to take shape. I guess that the best slope for this panel would be half way between lines perpendicular to the sun at winter solstice and spring equinox, but I haven’t got the luxury of picking and choosing because the triangle is determined by the 48” sliding glass door panel and the 24” removable glass panels. Since the removable panels are on the north side of the cold frame I suppose that they could be made of styrofoam. I saw some at Lowe’s that was foil backed and would have increased the light intensity inside the cold frame, but I have decided to do everything at no cost.
	You can see the first ventilator tube. On really hot days I will be able to either open ventilator tubes on each end or remove one of the glass panels. There will also be a rod at the peak of the cold frame to mount red and blue LED grow lights on nights when I want to add a little heat to the cold frame.

(Fig. 14)

	It rained all night again and into the morning. I don't have to worry about the rain barrel running out of water everything is filled to overflowing including the pit where I was mixing cob, but by noon there was just a slight mist so I decided to finish. I found a new way to mix cob. Just throw some straw out on the ground wet it with the hose and till.
	I finished what I wanted to do in just another two hours.The cob is so wet though I do not dare put the big glass panel on top. For that I will need to wait another week, Then I will add cob to seal and match everything up. 

(Fig. 15)

	One more change I decided to move the support bar up near the top so as not to block me from reaching across the bed to the other side.  I need to add 8 inches of potting soil, Then plant lettuce, water and I am done. I need to get a couple of high low thermometers to track the temperature. If there is any danger of dropping below the magic 20℉ I can put a couple of lights in the enclosure. I think it should be very tight thus avoiding the frost burn that I had with the last cold frame. I will also put milk jugs of water to store up daytime heat and to provide irrigation water that is at the same temperature as the inside of the cold frame.

(Fig.16)

For a copy of this article including the pictures send a letter to me Ed Raduazo 

raduazo at verizon.net <mailto:raduazo at verizon.net>