[Cob] Local Responses, long rant

[Barbara Roemer]

Warning: long rant, and perspective is North Murrican!

I must have missed a couple of digests because I found there were several
contributions recently to which I wanted to respond.  After Steve asked for
R values for cob and John F pointed out the need for funding research on
quantifiable measures, other folks posted several values for components
(clay as in adobe blocks, and light straw clay).  Then Alan (Earthed)
responded to Jill about how best to prepare clay for cobbing.  Both topics
point to the logic of applying local solutions to local materials and
conditions, while still maintaining a focus on quantification to spread the
(low-) technology.

Earthed Alan has cobbed in our neighborhood in the Sierra Foothills, among
many other places in the world, and dealt as he described (dry) with our
clay soil, pure and sticky enough to pot with right out of the ground.
While Karen in Alberta found that this sort of clay was best managed by
leaving it out to weather, that method is appropriate in her latitude and
climate and may not work as well in other locations.  We live near the 37th
parallel, in Zone 8, with very little cold weather, avg. min. winter lows
about 10 degrees F, and have 65 inches of precipitation.  It's plenty of
rainfall to erode a pile of clay left unprotected, but inadequate for
freezing/thawing cycles to result in expanded, broken up clay, so dry
screening works best for us, as Alan pointed out.

I concur with Alan about how the best cob is made.  That's with the approach
that is most appropriate for YOUR LOCAL project.  Cob for our oven was
hand-mixed since only a small batch was needed. We used a cement mixer for
our floors since there was a greater volume of material.  And for the light
straw clay building to which Charmaine referred, my son designed and built
an 8 foot long machine to tumble clay, water, and straw together. Most of
the light straw clay in that home went up in one day with a crew of more
than 50 people! The large mixer seemed an appropriate technological response
since it will be used in several large buildings and has already been
employed by folks all over the state.

Similarly, the best construction method for you may be a either cob, bale or
light straw clay.  Or, it might be a hybrid house, with bales on the north
and perhaps the west for insulation, light straw clay on the south for ease
of working around large expanses of glass, and as much cob as you can
incorporate to best use its mass, depending on your heating and cooling
degree days.  Again, where we live, where the number of heating degree days
much exceeds the cooling degree days, we need some insulation to keep heat
in the structure in winter and out of it in summer to begin with.  Then we
need the mass of cob and stone to capture heat for diurnal swings.  The mass
will also temper the heat in our couple of months of hot summer.  On our
northern flank, the winter wind would suck the heat out of uninsulated
northern mass, so bales make sense for us on that wall.  We want the
flexibility of light straw clay for framing the southern exposure; for some
curves that bales don't make as well; and for some interior partitions where
we want more sound control. Our barn will be LSC because it goes up quickly
when adequate preparations are made, and since it will be mostly unheated,
we just want it comfortable for critters and our active working. But our
solutions suit our climate, materials, time, energy, and the available
technology and expertise.  They wouldn't be the same ones in different local
circumstances.  

Of light straw clay, Charmaine is correct: it's not as great an insulator as
is claimed for it.  If a typical LSC wall is 12" thick (usually that's
max.), and typically LSC is lightly stuffed with a 2 x 4" into the forms to
fill all the corners, rather than rammed as in rammed earth, then with the
value of much denser cob being somewhere between R- .5 and -.7 /inch, and
the R-value of straw being somewhere between 1.5 and 2 R/inch, there is no
way the wall value of LSC could be nearly R-2/inch.  There is little cob OR
straw in a LIGHT straw clay wall: the mix results in a lot of trapped air.
On the other hand, at least in our climate and latitude, I can attest to the
fact that almost no heating and no cooling is necessary in the passive
solar, LSC house our friends built. It's much warmer in winter than an R-12
house "ought" to be, even considering the great construction, orientation,
and passive solar technology. One very positive aspect of LSC is that,
well-built, there is virtually no thermal bridging. But any building is a
system of components, each of which must be assessed for its contribution to
maintaining comfort.  In our friends' house, there is a lot of concrete in
foundations and flooring, and further mass in the stone that covers the
concrete, all of which will moderate the temperature swings.

Work with your local climate, elevation, sun angles, latitude, materials,
and appropriate technology.  They're at least as important as the crew, the
working conditions, the permits, or any other aspect of your planning.

Barbara

  

> 
> Message: 9
> Date: Tue, 5 Jul 2005 11:35:45 -0000
> From: Earthed <earthed at macunlimited.net>
> Subject: [Cob] Making good cob
> To: <coblist at deatech.com>
> Message-ID: <E1Dpkq8-000216-00 at vogon.deatech.com>
> Content-Type: text/plain; charset="iso-8859-1";
> 
> Dear cob fanatics,
> 
> I have just read what Jill Hogan wrote On Mar 4, 2005,and need to reply as
> what she says is very misleading. Jill stated:
> 
> "the secret of a good cob mixture is to get the platlets lying parallel.
> When you use a mixer it tears the platlets apart as opposed to the
> stamping with feet like wedging clay for pottery you get the platlets
> lying flat together. Hence buildings built this way have stood for
> hundreds of years. There are no short cuts
> 
> Secondly solving the clay issue simply put you clay in a tub cover it
> with water and it will dissolve. When you need to add it simply take
> it out of the tub with a spade and add it to your mixture."
> 
> 1. Good and bad cob can be made with feet, a tractor, a cement mixer, horses
> and probably by many other methods. Many of the buildings on our website
> www.earthedworld.co.uk were built using cement mixer cob. Kevin Mcabes
> houses are all built using tractor cob. Clay is the glue which holds the
> sand and straw together, see what Ocean Liff-Anderson says.
> 
> 2. Lumps of subsoil with very high clay content do not usualy 'dissolve'
> when soaked. Which is a shame, because it means if your soil has a lot of
> what looks like potters clay in it you are going to have more work to do!
> Clay will quite happily sit in water without doing anything for a long time,
> hence it is used to line ponds and pits in landfill sites. To make good cob
> from this type of subsoil you will need to break it down, usually better
> done when it is dry, because clay becomes plastic and sticky when wet,
> making it harder to break up.
> We know this becuase we have built cob structures using many types of
> subsoil. You need to keep in mind that many of the older cob buildings here
> in Devon and Cornwall have only around 15% clay in the cob mix, the rest is
> silt, sand, rock and straw.
> If your soil dissolves in water then it probably has a lot of silt and sand
> in it and you may be in for an easier ride!
> 
> Happy cobbing,
> Alan Cameron-Duff
> ______________________________________________
> This email was sent online by
> macunlimited.net
> The UK's mac dedicated service provider
> 
> 
> 
> 
> ------------------------------
> 
> Message: 10
> Date: Tue, 05 Jul 2005 08:16:24 -0600
> From: Dognyard <dognyard at stockroom.ca>
> Subject: Re: [Cob] Making good cob
> To: coblist at deatech.com
> Message-ID: <42CA9638.9FF40D84 at stockroom.ca>
> Content-Type: text/plain; charset=us-ascii
> 
> 
> 
> Earthed wrote:
> 
>> 2. Lumps of subsoil with very high clay content do not usualy 'dissolve'
>> when soaked. Which is a shame, because it means if your soil has a lot of
>> what looks like potters clay in it you are going to have more work to do!
> 
> We have this kind of soil! I can literally make sculpture with it with
> very little amendment. Since we live with this soil every day, we
> learned a few things about it. One is how to break it down easier. Let
> nature do it. We have bitterly cold winters, which I believe helps the
> breaking-down process.
> 
> If you can plan ahead, you dig it out and simply pile it...then let it
> sit over the winter. By next spring - ta-da! - it becomes very granular
> and easy to use. Near as I can tell, it's simply the action of freezing
> and thawing working on the water content in the clay.
> 
> Karen in Alberta
> 
> 
> 
> ------------------------------
> 
> Message: 11
> Date: Tue, 5 Jul 2005 21:49:36 -0700
> From: ocean <ocean at woodfiredeatery.com>
> Subject: [Cob] Natural building apprentice opportunities at Ahimsa
> Sanctuary!
> To: canbuild at deatech.com, coblist at deatech.com
> Message-ID: <5AA0DCDA-EDD9-11D9-A68B-003065CEB998 at woodfiredeatery.com>
> Content-Type: text/plain; charset=US-ASCII; format=flowed
> 
> Hello Everyone!
> 
> We are resuming our natural building projects at Ahimsa Sanctuary this
> summer during July, August and September.
> 
> We have two existing cob buildings nearing completion, and will be
> building a smaller kiosk shelter from the ground up (foundations,
> drainage, etc.)  We are completing finish plaster on the cob kiva, and
> it is looking very beautiful!  This is an excellent opportunity to
> learn all aspects of cob building - an ancient technique for
> constructing very low cost, ecological and beautiful structures out of
> natural materials - earth, sand and straw.
> 
> The location is Ahimsa Sanctuary, just outside of Philomath on the edge
> of the Mary's Peak Watershed.  We offer volunteer apprentices great
> food (from our organic restaurant - yum!), camping on 25 acres of
> forested land, friendly company of other builders and two fun dogs,
> even a sauna when the work is done.  For those interested in organic
> farming, we are also involved with several market garden and seed
> growing projects.
> 
> You can come to learn and help out for a weekend, a week, a
> month...please email me if you are interested and I'll get you
> directions.  Check out our websites below for more info on our retreat
> and restaurant.
> 
> Blessings,
> Ocean Liff-Anderson
> Steward, Ahimsa Sanctuary  http://www.peacemaking.org
> Proprietor, Intaba's Wood Fired Eatery  http://www.intabas.com
> 
> 
> ------------------------------
> 
> Message: 12
> Date: Wed, 06 Jul 2005 09:33:05 +0100
> From: Kathryn Marsh <kmarsh at iol.ie>
> Subject: Fwd: Re: [Cob] posts/pillars
> To: coblist at deatech.com
> Message-ID: <6.0.1.1.0.20050706093300.046f21b0 at pop.iol.ie>
> Content-Type: text/plain; charset="iso-8859-1"; format=flowed
> 
> 
>> Date: Wed, 06 Jul 2005 07:05:08 +0100
>> To: Copper Harding <copperharding at yahoo.com>
>> From: Kathryn Marsh <kmarsh at iol.ie>
>> Subject: Re: [Cob] posts/pillars
>> Bcc: ƒ\cob list
>> 
>> At 22:03 20/06/2005, you wrote:
>>> Jfrost wrote:
>>> 
>>> I've always wondered how the connection is made at the
>>> base of the
>>>    "post" or Pillar"  when I see photos of large tree
>>> trunks that have
>>> been
>>> used  as the post on  porches etc.   they don't sink
>>> them in the
>>> ground,
>>>   but what do they do?  anyone know?
>>> 
>>> ----
>> Just got back from visiting a 17th century farmhouse in the Netherlands
>> which has four corner posts. Two have recently had to be renewed. They are
>> tree trunks standing on large cowhides - stone would just sink into the
>> peat in that area unless it had pilings underneath.
>> My grandparents' house in the English fens had its king post simply
>> standing on end on the ground and that had rotted through at ground level
>> at some time during its 700 years of existence leaving the king post
>> supported by the rest of the cob structure and simply swinging free with
>> the stairs to the second floor pegged into it - very un-nerving for a
>> small child to climb on the way up to bed. Now gone alas. I've seen others
>> of the same date with a stone underneath and they are still fine.
>> 
>> And on the subject of floors my grandparents added another coat of beeswax
>> every winter to their ancient mud floor. Don't know how long this had been
>> happening but the shine seemed to go on down forever.
>> 
>> kathryn
> 
> 
> 
> 
> 
> ------------------------------
> 
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> 
> End of Coblist Digest, Vol 3, Issue 49
> **************************************