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Michael Smith, natural building pioneer

Ashan-File #216
Interview - Michael Smith (2/4)

What follows is part two of a four-part edited transcript of an
interview that
I conducted in November 2005 with Michael Smith, natural building
pioneer, instructor, and author, in the intentional community of Emerald
Earth, in Northern California, where he resides.  In part two of the
interview, Michael spoke about the inherent advantages of earthen
architecture, and the special qualities and characteristics of cob.


The biggest advantage, I'd say, of earth building is that earth is such
a ubiquitous material.  Most places that people are building, there's
 And that's huge!  That's a huge, huge factor.  I think it's hard for
people who are raised in an industrial society, where energy is very,
very cheap, to understand the significance of that fact.  Because we're
used to thinking nothing of moving, you know, huge amounts of material,
including very heavy material, very long distances.

But traditionally, throughout the history of humanity, that has not been
an option, and it's very possible that will come to be less of an option
in the near to middle future, even in wealthy places like the United
States.  So just learning to build with the stuff that is there on the
site is an incredibly valuable thing for us, I'd say, at this stage in
our history, to re-learn that.

There's a technical aspect to building with earth that makes it very
accessible to lots of people.  Even natural materials that are commonly
used, one that springs readily to mind is wood, require a little bit
more training and technique to get good at.  Carpentry is actually, as
it's practiced currently in the western world, is a very technical
skill, it's a craft.  And people take years to learn how to become good
carpenters.  Most of the earthen building techniques are so simple that
people can learn how to do them in a matter of hours to days.

And then we have lots of experience with Cob Cottage Company in workshop
teaching of people who took, say, a week-long workshop, with very little
to no previous building experience, and went from that directly into
building their own homes.  Usually people require some help with the
more technical aspects of the building, especially the carpentry, things
like wiring and plumbing, if those are included into the home.  Those
are things that people can't learn as quickly.  But the actual
earth-building technique is so simple that most people can pick it up
very quickly.

* * *

One of the other big advantages that earth has as a building material is
its weight.  Because earth is a massive, heavy material, it has the
ability to store heat, or conversely, to store coolness, over a long
period of time.  A heavy earthen wall, and this also goes for other
heavy materials like brick and stone, takes a long time to heat up, and
a long time to cool down.  And it turns out that that's critical for
efficient passive solar construction.  If you want to build a house that
is going to be heated mainly with the sun, you need a way to store the
heat that's coming in from the sun during the daytime, and keep it in
the building to release during the nighttime, which is when you really
need it.

In the daytime, the sun's out, temperatures are high, everything's good.
 But at night, temperatures are going to drop, you're a lot more likely
to be inside your house at night, and that's really when you need that
heat!  So the thermal mass of earth, either in your walls, or in your
floor, can hold and store that heat until you need it.  And that's true
not only on a daily cycle, where you have daily temperature swings, hot
in the middle of the day, cool at night, but also over longer periods of

Another way to do that, or another way to take advantage of that thermal
mass, is by having the mass of the cob or other earthen material in
close proximity to a wood-burning heat source.  The wood stove right
here is built right up against this surrounding cob hearth.  So when the
wood stove is going, it's releasing a lot of heat through radiation,
some of which is projecting out into the room to warm us directly.  I
can feel a lot of heat coming off that stove right now to me.  But in
addition, a lot of that heat is going back and being absorbed into this
cob wall, and the cob is heating up.  So what that means is, in an hour,
we can stop feeing the wood stove, the fire will go out, but then the
cob will be continuing to heat the space.

And that principle's been used for millennia, probably, particularly in
really cold climates like Scandinavia, where there's something called a
Finnish stove.  Germans had a similar technique called a kakalofen.
Chinese had something called a kang.  All of them are basically very,
very heavy massive wood burners in which you can make a very hot fire
for a short period of time, heat up all that mass, and then have the
heat from that mass continue to radiate and heat your space for a period
of time afterwards.  It's a much more efficient way of using the energy
that's released by the combustion of the wood than relying entirely on
the heat that's released at the time of combustion.

So, again, it's using the thermal mass of the earth as a battery to hold
the heat for when you actually need it.

* * *

The biggest disadvantage of adobe is because it's made of a lot of
little separate units that are kind of stuck together with mud, but
there's no real continuity, there's no tensile connection between all
those different units.  If you get a big shake, or the ground moves, in
an earthquake, or something like that, there's a tendency for those
units to shift and come apart.  And, in the worst-case circumstance, for
the building to collapse.
 So, adobe, of the 3 major load-bearing techniques is probably the least
strong in earthquake conditions.

And the actual ingredients and mixture in a cob building can be very,
very similar to what goes into an adobe structure.  It's once again a
mixture of clay and sand and straw.  And there's some huge advantages to
[cob], relative to the other techniques.

One is we don't need any forms.  We're just building and sculpting our
walls in place as we go.  You can do sculptural stuff with concrete,
etc. etc.  But to do a curved sculptural concrete building, you first
need to build a curved form, which is fairly technically difficult.  To
achieve the same result out of cob, you don't need any special tools,
and you don't need any special training.  So, it's very, very easy for
people without much training and without much technical background to
achieve really spectacular results.  In fact, it's practically
inevitable.  [Laughs].  I've almost never seen anybody build anything
out of cob that wasn't beautiful.  So that's pretty remarkable, in and
of itself.

The other significant advantage besides the sculptural qualities of cob
is that if you build carefully, you needn't have any seams, any weak
joints in your entire structure.  So the ideal is, you're always adding
the new cob onto the wall before the cob underneath it is completely
dry.  And you're able to "sew" using either your fingers, or using a
tool that we call a "cobber's thumb," which is a worked piece of wood.
You're able to sew the new cob into the layer of web, sticky cob
underneath it, and you're able to get very, very good connection, good
adhesion between those layers.

I haven't been myself to Africa, but I've seen photographs, where one of
the solutions is to build each course of cob sort of triangular in
section, actually kind of like a upside-down heart shape in section.
And then the next upside-down heart shape locks itself in place on top
of the previous course.  So there are certainly ways around the poor
connection that you tend to get with coursing.  But, just as a general
statement, I'd say cob has the potential to be much stronger in
earthquake conditions than especially adobe.  Because you don't have all
those inherent weak points in the seams between the different courses.

* * *

You know, any of these techniques, you can build with very, very few
tools.  So, with adobe, really all you need is a form, and you can do
the rest, you know, a shovel's helpful, a wheelbarrow's helpful, and a
hose is helpful.  With rammed earth, it's pretty much the same, you need
a form and a tamper.  With cob, the tools that you actually need to do
it are even fewer.  You could pretty much just do cob with a stick or a
shovel or something.  A tarp, a few buckets, a wheelbarrow, a hose, a
machete, those things are really, really helpful, and I wouldn't
encourage anybody to try to build a cob house with nothing but a stick.
But it is a very, very low-tech technique at its root, as are all these
other traditional building techniques.

Now what that doesn't necessarily mean is that cob has to be a low-tech
technique.  And in fact, there's some limitations, there are some pretty
severe limitations on treating it as exclusively a low-tech technique.
The majority of the work that goes into a cob building is in mixing the
cob.  That can take up to three-quarters, two-thirds to three-quarters,
of the labour in the building of the actual cob walls themselves.

There are ways, pretty good ways, to mechanize that.  So, either using a
tractor, a technique called tractor cob; using a mortar mixer; in
Britain, they're using just a heavy truck, and driving back and forth
over the mix, and mixing it that way.  So, it's certainly feasible, and
reasonable, I would say, to throw some kind of industrial equipment at
the cob process, and speed up the mixing part of the equation a lot.

And I think what that enables, is it enables projects to happen more
quickly, it enables people who are working with a budget and a tight
timeline, which most professional builders, most contractors are working
under those circumstances; it enables them to consider cob as something
that they could use in their professional work.  So I'd say that's a
positive development that's happening lately in cob.

Still haven't seen it really turn into a mainstream technique that's
being used for mass marketing, mass housing developments, and maybe it
never will.  But in the meantime, I think the biggest impact that cob is
having is allowing people who want to be building for themselves, and
who don't have a lot of resources, or a lot of training, to learn a
technique quite quickly that enables them to build a really beautiful
and really special home for themselves.
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