This book is dedicated to our two greatest teachers, tradition and innovation.
To the indigenous first peoples of the world who are in danger now, as never before, for their lives, their land, their languages and cultures. We must join their struggle since our future depends as much as theirs on the preservation of the practical wisdom of their ancestors. If there is hope for a healthy future, we can't build it without them.
And to the new pioneers of sustainability, the women and men of the natural building and permaculture movements. Learn, laugh, plant, sing, grow!
-- Page 2
The Cobber's Companion is not a theoretical textbook. It's a practical guide based on the experience of The Cob Cottage and our associates. The ideas and techniques in this book have been developed and tested during the construction of at least 40 cob buildings in Oregon, Washington, British Columbia, California, New Mexico, Colorado, Ohio, Texas, Mexico, Denmark, Australia, and New Zealand. We hope you will use this guide for practical purposes. Build something, experiment, ask questions, push the known limits of the materials, systems, and techniques described herein. This book is intended as a companion to, rather than a substitute for, workshops and other hands-on learning.
-- Page 4
It's no secret that the global ecosystem is ill. The housing industry is a major contributor to the problem. Here in the Northwest we see the evidence all around us; the trail from clear-cut to sawmill to building site is easy to follow. Other major modern building components depend on destructive mining: gypsum for sheet rock; iron for hardware, rebar and roofing; lime and other minerals for cement. Every material used in a typical modern building is the product of energy-intensive processing. The mills which saw our lumber, the factories which make plywood and chipboard, the foundries which make steel, the plants which turn natural minerals into cement by subjecting them to enormous heat, all consume vast quantities of power, supplied either by the combustion of coal and oil, the damming of rivers, or the splitting of atoms. These manufacturing processes also release toxic effluent into the water and hazardous chemicals into the air. The manufacture of Portland cement, for example, is responsible for an estimated 4% of greenhouse gasses. And even after our building materials are made, modern construction depends on an endless stream of polluting trucks to deliver them to us, usually from hundreds of miles away.
-- Page 11
Of course, it's impossible to build a house with no environmental impact, but it's our responsibility to minimize and localize the damage. Digging a hole in your yard for clay to make a cob house may look ugly at first, but it's a lot less ugly than strip mines, giant factories and superhighways. Nature has enormous capacity to heal small wounds; that hole in your yard would make an excellent frog pond. Many of us religiously protect the trees on our property, then go to the lumber yard to purchase the products of wholesale clear cutting. If we choose to build with wood, it seems a lot less hypocritical to take down a few select trees near our homesites and run them through a small portable mill, or thin overcrowded woodlands of small-diameter poles and build with those. Keeping our environmental footprint under our noses insures that we will minimize our impact and to protect the health of our local ecosystems, which we see from our windows and walk through every day. Building with natural, local materials reduces our dependence on the polluting and energy-intensive manufacturing and transport industries.
-- Page 12
One of the simplest ways to determine
roughly what a soil is made of is the shake test, which uses gravity to separate soil
particles according to weight. You will need a clear glass jar with straight sides and a
tight lid (quart or pint sized Mason jars work well). Take a sample of your soil and
remove any twigs or large stones. If the soil is clumpy, grind it to break the lumps. If
you sieve it through a screen, make sure to save the pebbles and large sand grains that
don't pass through, and add them back into the sample. Otherwise, you will alter the
composition of the soil.
Fill the jar about one third full with prepared
soil and add clean water to the top of the jar. Add a teaspoon of salt to help the clay
settle. Then shake very thoroughly so that any lumps of soil break apart. Sometimes you
may need to let the contents of the jar soak for a few hours to hydrate and break down
completely. When the lumps are all dissolved, shake up the jar again, then place it on a
level surface where you can leave it undisturbed for a few days. Watch the jar closely for
a couple of minutes after setting it down.
Within the first three seconds, you will see
first pebbles and then large sand grains settle to the bottom of the jar. This is the
coarse sand which is most useful in building stable cob. Mark the level of deposition on
the side of the jar after three seconds. After the coarse sand, fine sand and silt will
begin to settle out. (The line between fine sand and silt is somewhat arbitrary, but for
our purposes we will divide them at the point where you can no longer see individual
grains.) Both will settle out within ten minutes or less, and you will be left with a
sediment of graded rock particles on the bottom of the jar, with liquid above. Any humus
or vegetable matter present be floating on top.
If the water is already clear, there is no clay
present. Find different soil to build with. If the water is cloudy or opaque, leave the
jar undisturbed while the clay settles out. This will take from a few hours up to
several days, depending on the type and quantity of clay. The water on the top of the jar
will begin to clear as the clay settles. Eventually the settling will stop, and you can
make some observation about relative quantities of sand, silt and clay in your soil.
-- Pages 20-21
Arches, niches, vaults, and domes are
constructed in the same manner. To make an arch, for example, build up both sides with
regular cob until they are flat and level, then begin corbelling out from both sides at
the same rate. Don't be concerned about finish; it's much easier to trim later than to aim
for perfection during the building process. Build up the surrounding area with regular cob
as you go, to support the arch. Be extra careful as you near the top. Allow the arch to
dry substantially before placing the "key cob" across the top.
The other way to make an arch is by cobbling
over a rigid form. Make the form out of plywood or boards, and prop it firmly in place so
that it will not shift under the weight of the cob. Use great care to marry adjacent cobs
to one another, which is more difficult because of the form. Leave the form in place for
at least a few days, until the cob begins to get firm. In this manner we have built
archways as much as 6' across all at one time. It is faster that corbelling (if you don't
factor in the time to make the form) but is probably not quite as strong.
-- Page 72
by Ianto Evans
We've noticed a few serious mistakes first-time builders are likely to make. You'll note that all of them have to do with preparation and planning. Most construction errors can be rectified; these can't. Roughly in order of importance:
1) Poor siting. Frost hollows; north or west slopes; flood plain; no long views. All are impossible to rectify.
2) Insufficient solar access. Make sure your building gets as much sun as possible in cool times.
3) Inadequate design exploration. Make a model. Invest in modeling clay or use cob, sticks, etc. Make sure of circulation, levels, doors and major openings before you begin digging.
4) Poor drainage. Realistically project yourself into the worst possible, longest, hardest rainstorm. Make sure water can flow away fast enough.
5) Heavy machinery wrecks the site, compacts soils, damages ecology. Keep mechanized equipment under constant supervision. Better yet, keep it off the site altogether.
6) Too big. Start your first building tiny to make sure you can finish the first season. You can add on later.
7) "Clay" turns out to be something else. Make sure in advance you have a clay source. Don't take anyone's word. Test it, make cob bricks, dry them, load-test them, scratch for hardness.
8) Inadequate foundation. Foundation too low, discontinuous or lacking reinforcement. Footing trench not compacted. Foundations are critical and nearly impossible to replace.
9) Floor levels not worked out. Install permanent datum stakes! They should be numerous and well-marked, at each interior floor level, thresholds, and outside against the building.
10) Foundation not finished in time for the construction program or for a workshop. Foundations take longer than you think, especially rock walls.
11) Beginning too late in the season. Cob needs time and dry weather to dry. Wet walls can be damaged by frost. Wet straw in them may putrefy during the winter. Working in the cold and dark is no fun! Wet earthen floors dry extra slowly.
12) Thin walls too straight. Cob needs lateral buttressing, either by building thick, building curved, adjoining walls or structural buttresses.
13) Roof spans too long. If you don't want to truss your roof structure, keep spans short. 10'-12' is plenty, unsupported. Remember the stress on the beam is proportional to the square of its length.
14) Eaves too short. You don't want rain running down your cob walls. Observe rain direction on your site. Make eaves long on that side, and/or stucco the wall.
15) Insufficient protection from weather. If you build a roof first, either temporary or permanent, then you can work unhindered by rain and sun. Make sure it is large enough to keep the whole site and materials dry, and high enough to be out of the way of building.
16) Running out of materials. Stockpile in advance (months, years) all the glass, lumber, beams, etc. you'll need. Particularly in workshops, building happens fast. Have windows, door frames, etc. ready in advance. Know where you will go for more soil, sand and straw should you run out.
17) Running out of water can set your building schedule back unexpectedly. Store extra in barrels or tanks in case your well runs dry or your electricity fails.
-- Page 127
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