Cob: caution

[Bob]

Dear good experimental people,

It is great to know innovative people.  Your are the salt of the earth
until you, like the Pied Piper, lead others, like children off the deep end.

There are many ways of making thin walled houses but be careful.  Thousands
of people are killed almost every year by having their houses fall on them.
 Many parts of the world are subject to earth quakes.  Sometimes quakes
come in new ways and new places because we life on a fluid planet.
Building codes, though frequently misused, are intended to make buildings
safe, to over reach the limits of the materials and designs so people won't
be killed.  When there are corrupt governments like in Mexico City
officials turn a blind eye to the quality of buildings until an earthquake
kills thousands.

In Managua, Nicaragua thousands were killed in their small capital city by
a severe earth quake.  I never would have guessed the cause.  They  told me
it as not due to the caving in of the adobe buildings, however, but from
the dust that was so thick from the falling houses people suffocated. Now
adobe is illegal there. 

None of  you would think of storing many boxes of dynamite in your basement
even thought it would likely not go off.  Why build a house that can be
equally dangerous.  Every building material has its limits.  Brick
buildings that aren't reenforced come down in earthquakes.  Clay, the
adhesive of cob buildings also has its limits and there is no point in
going to the edge, endangering all the people under the falling building.

Let us consider the ways cob could fail.  Earth quaker is one of the most
likely ones.  I like Ianto Even's curved buildings because a curved wall
will stand where a straight one of the same thickness is more likely to
topple over.  So those of you who want to build thinner walls be sure they
are curved, not straight.  

Organic fibers are valuable reenforcement so long as they don't rot or get
eaten by termites. It is good if the fibers run in many directions.  Why
doesn't someone in this discussion build a thin walled tool shed with lots
of straw and then measure its stability?  You could play a water sprinkler
on it for a few days.  You could tie a cable onto the roof and tug at it
with the tractor. You could even put a strong spring scale in the cable
line to see just how much force it took to budge it.  Then you would get
answers far more useful than speculation, answers that would not cost as
much as fancy vibrations tables and lab tests, but useful all the same.
If anyone does that i hope they will report the results to all of us.

Another thing to consider is that there are many different kinds clay,
perhaps hundreds.  There are different shapes of sand, some is round, some
is sharp, some is from one kind of mineral, some another.  Therefore a cob
wall made with clay and sand from one place may be quite different from a
wall make with clay and sand from another.  MARGIN OF SAFETY  means not
walking the narrow edge but having plenty of extra space. So why play with
dynamite on your roof.

If you did succeed in building a 3" or 4" wall cob house and it stood up a
few years until the hurricane blew a tree down on it or hurled at 100 miles
an hour a 2 x 4 through the wall ( that is the way the hurricane testing
lab checks houses) and it killed most of the occupants the damage would be
more than you at first imagined.  Even though unreasonable, it would give
cob bad press nationwide.  It would make it more difficult for everyone in
the country to get permission to build a cob house.  So please, friends,
don't walk the edge and endanger not only your family but all of us who
want to see cob succeed.  

 Try some innovate methods that have been proven for stabilizing adobe
bricks and earthen roads.  The addition of a little Portland cement does
wonders to resist soaking water.  The addition of some crank case oil may
also work, though I don't care for black walls. 

One thing I would like to try to make my walls less subject to damage by
blowing rain is a stucco of clay and large gravel or small sharp stones.
The idea is the rain will wash down the wall over the parts of the stones
sticking out and not get into the clay that is holding the stones in place.
Use no mortar that creates a vapor barrier that holds the moisture in and
softens the wall.  If anyone has information or experience with this
technique please let me know.

Bob Luitweiler <owl at gentil.org>