Cob: Cob/light clay hybrid

[ben graham]

  It is essential to understand the strength performance and appropriateness 
of what we are doing.
  But we are also inventors and experimentors.  I think this is the spirit 
that makes us ask, "well, no one's tried this, why not try it?" this is how 
breakthrough's happen.  Most of the time because one crazy person ignored 
the advice of all their peers.
  So let us experiment, with all the respect in the world for time-honored 
tradition.

Ben Graham


>From: John Fordice <otherfish at home.com>
>Reply-To: John Fordice <otherfish at home.com>
>To: Roxboro Yurt <theyurt at yahoo.com>
>CC: "K. Clouston" <dognyard at worldgate.com>, coblist at deatech.com
>Subject: Re: Cob: Cob/light clay hybrid
>Date: Thu, 19 Apr 2001 08:05:28 -0700
>
>Karen & all,
>It is important to bear in mind a couple of things when thinking about
>cob and insulation:
>
>Cob is essentially a low strength material, and it gets its structural
>capacity by being built as THICK and INTEGRAL walls.  The splitting of a
>cob wall into two separated or honeycombed vertical wall layers will
>compromise the structural capacity unless both layers are of sufficient
>thickness.  I surmise that traditional builders didn't make their walls
>thick just because they liked to work.  Always remember that traditional
>earth wall construction evolved as thick walls for a reason - because
>the buildings with thick walls were the successful ones.
>
>Making cob walls the requisite thickness is a bloody LOT OF WORK.  Why
>build two thick and thus stable walls of cob when you only need one ?
>If you want / need to insulate your walls, do so in a manner that makes
>it easy for you ( 1.e. less work ) and that works with the materials you
>are using.  Put your cob on the inside where it will do the most good as
>a thermal mass to store the precious interior heat you need, and put
>your insulation on the outside where it will serve to keep the heat from
>being lost by both radiation and convection.
>
>A simple method to do this is make a wide enough foundation to allow you
>to wrap the exterior heat loosing walls (East, North & West in the
>Northern hemisphere) with stacked up straw bales (relatively inexpensive
>& ready / easy to use) and if you want / need to protect the bales,
>simply plaster with an inch or so of mud.   Simple, easy to do, easy to
>repair, low cost, & structurally sound if correctly done.
>
>Don't make things more complicated than the need to be.
>
>john fordice
>maker of cobbers thumbs
>TCCP
>
>
>Roxboro Yurt wrote:
>
> > This isn't a very scientific answer, but I don't think
> > this is a very good idea.  Seems like thin hollow
> > walls would be  more prone to cracking (and cob is so
> > heavy it needs a thick base to hold up the top) and
> > any water damage would have much more severe
> > consequences (if your thin wall washed away anywhere
> > the whole thing might crumble)
> >
> > The only way I think this might work is if the cob was
> > honeycombed so that the two sides were connected in
> > many places but the straw or light clay could  fill in
> > the holes.  Also - I don't know if you would actually
> > want to tamp the straw - air is a good insulator and
> > the more air between the straw pieces the better
> >
> > --- "K. Clouston" <dognyard at worldgate.com> wrote:
> > > Has anyone tried building a cob house building
> > > essentially hollow walls
> > > (with cob inside outside, letting them dry/cure,
> > > then tamping the hollow
> > > middle with light clay or slip straw? If so, how
> > > thick would the cob
> > > walls need to be in order to withstand the tamping
> > > of the slip straw?
> > >
> > > I'm wondering if this could, in essence speed up the
> > > drying/curing time
> > > of the walls. I live in a cold climate with
> > > potentially severe winters
> > > and would like to find a workable solution to the
> > > problems of
> > > freezing/thawing of uncured cob.
> > >
> > > Likewise, has anyone considered building large
> > > bricks of slip straw (not
> > > as large as straw bales, storing them until cured,
> > > then using those as
> > > infill within cob walls...perhaps in a honeycomb
> > > pattern or implementing
> > > a light wood frame construction with slip straw /
> > > cob walls?
> > >
> > > Karen Clouston,
> > > Alberta
> > >
> >
> > __________________________________________________
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>

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