Cob: bonding layers

[Bob]

I am glad the whole question of bonding layers has come up because I would
like to ask your opinion on a system I imagine but have not tried.

It seems to me the building of a cob wall could be made easier, less work,
a little faster, by using a crude derrick, something easily built with
local materials, no costly machinery.

A tall tripod made of poles could be on wheels so it would easily move
alongside the growing wall. The three legs would be connected to each other
at the base so it moved as one unit.

Hanging down from the peek of the tripod is a strong rope that holds the
lever becomes the fulcrum.

On one end is a box or bucket that holds the cob material.  On the other
end is a rope the bucket controller can pull down until he can reach the
end of the lever.  

The bucket end is dropped to the ground where the cob material mixers fill
it.  It is then hoisted up over the wall.  From 4 to 6 feet above the wall
it is dumped onto the wall, the force increasing its bonding.  
(When  one stuccos a wall the mixture is slung vigorously against the wall
and bonds to it partly from the force of the  impact.)  Cavities like those
made with a cob finger could be first made in the top of the wetted
previous day's wall if necessary.  Using a little wetter mix might also
improve the bonding.

The slammed down mix does not slide off both sides of the wall because
there is a moveable form.  This form is flexible because it is a kind of
mat made of woven sticks 3/4 to 1" thick and allows any kind of curved in
the wall.  The form is held in place with cord running from one side of the
top of the wall to the other which  becomes embedded in the layer being
built but can be easily pulled out of the "mud" at the end of the work on
that particular part of the wall so  the form can  be moved to another part
of the wall.
The lower end of the form is held in place by the finished wall.  How tight
the cord is will determine the taper in the wall, tighter a greater taper.

With this system there would probably be no need for anyone to  be on top
of the wall except  for moving the forms along as it grew and this might
better be accomplished by persons on ladders on both sides when it was out
of reach from the ground.  

The surface, when the form was moved would  be corrugate, and interesting
texture.  It could  be trimmed, plastered over or just left with its
interesting design.

THE ROUTINE

The mud mixers fork the material into a wheelbarrow, probably 30 to 40
pounds.  That is dumped into the bucket sitting on the ground.  The derrick
operator pulls down on the rope on the other end until he can reach the
lever end and swings it around to reach the place over the wall to be built
on.  Because the derrick pole is slung from the tripod there is some lea
way to allow the bucket to be maneuvered without moving the tripod for each
wall addition.  High over the wall the charge is released -- whump, it
slams down on the wall. The  bucket either has a bottom that can be opened
from the ground or the whole lever, pole can be twisted so as to invert it.
 The cross handle on the other end makes twisting the lever pole easy.

After 5 or 6 feet of wall are built up the cord holding the forms is untied
and pulled out and the forms are mounted further down the wall.  No bracing
is needed for the forms, as in concrete pouring, since the existing wall
provides all the support needed.  The cord between the forms on both sides
rests on the previously finished wall and remains connected while the forms
are there.   The form reaches down the finished wall 8" or so the bottom
pressing against the wall as the top part is filled.

It is possible with this system a work crew with half as many people could
put us as much wall.  There would be no noisy machinery, no machinery cost
and the enjoyment of working together would not be spoiled.  The derrick
wheels could be old bicycle wheels.

This is offered as a suggestion.  Let me know what you think, especially if
you try it.  

Bob Luitweiler <owl at steadi.org>