[Cob] Wall thickness

[Ed Raduazo]

            Below is a series of three letters responsive to Gene's request for information. To get the full letters with pictures send a request to me, not to the entire entire cob list, as I understand that pictures are not permitted on the cob list.
                Thank you,

                    Ed DC Cobbers


Gene: What temperature zone are you in and what do you intend to do with your greenhouse?  You are planning to build a relatively small greenhouse and putting a lot of work into it.  I live in zone 7, and I too wanted to build a greenhouse. I even built the foundation for it, but then I started experimenting with other alternatives. My reason for building a greenhouse was lettuce I want lettuce in the winter. Lettuce turns to mush when the temperature gets below 20℉.       I started with lettuce (bottom) and then switched to tomatoes in March. the Top picture is the tomatoes ready to be transplanted out in May. To be continued…(pictures n and o deleted)
       Here in zone 7 the residual heat from the earth will generally keep the night time temperatures above the critical 20℉ needed to prevent freeze damage to lettuce. The day time temperatures will rise above freezing thus promoting growth. You need to crack the glass on warm sunny days to keep the cold frame from getting too hot.
       I later did another version of this cold frame (below) with a salt box roof. The roof was formed from woven bamboo strips and plastered with a mix of shredded paper and clay then painted with boiled linseed oil to make it water proof. This also worked, but we had a really mild winter that year.  I never tested it on a really cold DC winter.        The walls for this salt-box were made of ordinary cob built on a foundation of recycled cinderblocks and the window sections had a neat inter fitting seam This was really tight so it did a good job of holding in the heat at night. It would have been perfect if I had double pain glass.
       It should be noted that here in zone 7 bunching onions, spinach, kale, Swiss chard and beets usually grow all winter. Today is February 5 I have plenty of green onions growing in my unprotected garden along with a little bok choi, beet greens and spinach. I cut the tops off the green onions to make omelets and other onion dishes and the roots, which remain in the ground, will grow new tops. I highly recommend doing a little research before committing to build a full out greenhouse, read Four-Season Harvest by Eliot Coleman. it is probably available free in the library if you don't feel like buying it.(pictures p, q and r deleted) To be Continued...


         A few years ago I had a very serious ankle injury. The Doctor said he could fuze one or both ankle joints to stop the pain, but ankle replacements are experimental, and he did not recommend them so we settled on a brace. I decided to build a handicap accessible cold frame from cob.            Here in the Washington DC area people throw away everything if you wait long enough. This design is based on recycled cinderblocks out of a dumpster and a double pane sliding glass door which was being thrown away by Goodwill. You know that if sliding glass doors are not pre-mounted in a frame which is in perfect condition Goodwill does not want them, and will throw them away. Thank you very much Goodwill.            I started with 3 double pain glass panels on the north side. In this picture you can see the wire brackets cobbed into the cinderblocks used to retain a sliding glass door panel which is not yet installed. The overhead bar is used to hold my lighting (and heating) system.(picture u deleted)

               This is a picture of the cold frame filled with lettuce:(picture v deleted)
           This was a cold winter for zone 7 and unlike my previous designs you can not count on the residual heat from the earth when you rain up the cold frame 3 feet above the ground. To keep my plants from freezing at night,  I provided grow-lights. This picture shows a 4 foot florescent fixture on one end and a 1' X 1' LED grow light at the other end.(picture w deleted)
       This was a cold winter, but my lettuce did rather well. I later replaced the double pain glass windows on the north side with foil backed foam panels held in place against the wind with a brick. It is amazing what people throw away here.(picture x deleted)
P.S. The hole going through the cob wall in this picture is a solar powered fan that is supposed to cool the cold frame on hot days. I had to buy this, and I am not sure if it was worth the cost.


-----Original Message-----
From: Gene Forster <gene.forster at hotmail.com>
To: coblist at deatech.com <coblist at deatech.com>
Sent: Mon, Feb 3, 2020 6:56 pm
Subject: [Cob] Wall thickness

Hello all
My project this summer is building a roughly 6foot x 8 foot greenhouse using cob for the walls.
It would be around 7 feet tall at its highest point. The shape can be described as a rectangle with curved
walls and corners, but not quite oval.

My questions are 1)How thick should I make the walls at the base?
 and 2) Could a person build two thinner cob walls and stuff straw in between for insulation?
Gene
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