Use of forms in superadobe

[Shannon C. Dealy]

On Mon, 28 Apr 1997 goshawk at gnat.net wrote:

[SNIP]
> While I am waiting I hope to start on some forms. I'm not sure 
> if they do much in the way of forms with standard cob but 
> using the sandbags filled with earth, cob, stabilized earth or 
> clay coated staw you can build arches. The arches are then 
> used to put windows and doors in the dome structure. This 
> eliminates the need for headers or lentals (sp?).
> 
> You can build a standard sized form and use it for all you windows.
> I'll just stick a frame in the arc and put cob infill where ever it is
> needed.  
[SNIP]

With cob you don't need forms, you can build your arches directly by
corbelling.  Basically what you do is to take your standard cob mix
and form it into the shape of a small loaf of french bread (perhaps 1' to
1-1/2' long), then take some long straws that are about the same length as
the cob 'loaf' (perhaps two dozen?) and place them on your cob so
they are all oriented parallel to the loaf, then work them into the cob,
keeping them oriented the same direction and retaining the same
approximate size and shape for the cob loaf.  To apply the cob loaf, you
wrap it lengthwise around the edge that you are trying to build into an
arch. By wrapping successive layers you can slowly build up the arch.
Start the arch from each side, and then build them up until they meet in
the middle at the top.

Really cruddy line drawing of layers.  Each continuous line represents a
separate layer of cob applied and wrapped around the previous edge.  Note
that it starts with just a square wall corner, and gradually works its way
up and over.
     ______ 
____/____ |
__/ ___ | |
___/  | |/
----- |/
    |/
    |
    |

Orienting the straws all in the same direction provides tremendous
strength and anchors the arch directly into the wall that is supporting
it.  Done correctly, you can build shelves as a part of your cob
walls which are capable of supporting hundreds of pounds (they also make
convenient places to stand while working on the top of the wall :-)

___
  |
  |  
  |__
    /   <- Cob wall with shelf created by corbelling
   /
  |
  |
  |
__|

In addition to arches and shelves, you can add windows that don't open
by embedding a piece of glass directly into the cob.  Basically what you
do is start by building up the cob on either side of where the window
will go, then insert the glass and place cob on either side of the pane
around the edges to hold it in place.  Once you are ready to start arching
over the top, start using the corbelling cobs described above to arch the
cob to either side of the window over the top.  It is a good idea to do
this while the surrounding wall is lower than the window, you want to give
the cob around the window time to harden somewhat so that it doesn't give
under the weight of the surrounding cob and crack the glass, for this
reason, it is particularly important to build up the cob above the window 
slowly. Your next question, is what the heck do I do when the window gets
broken?  Simple, knock the broken pieces of glass out and then dig out the
broken glass using a hatchet or machette (or whatever you used for
trimming the walls when you built them).  Next trim back the inside or
outside cob wall around where the window goes, insert the new piece of
glass, and use fresh cob to fill back in the area that you trimmed.

Using the above technique, you can get the appearance of custom cut window
panes (hearts, circles, stars, etc) using any old piece of glass, and you
don't even have to cut it.  You simply build the cob around the glass to
form the shape you desire, the excess glass that would normally have to be
cut is hidden in the wall.

Safety note:  We wrapped the edges of the glass in duct tape to help
prevent anyone from getting cut while working on the cob around the glass.



Shannon Dealy
dealy at deatech.com