Subject: [Homestead] Stumbled across new term---Cobwood
Date: Fri, 04 Feb 2005 17:17:41 -0500
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Taylor Publishing, Cutten, California
Cobwood
*Alternative and Free Materials:
Papercrete Ideas continued....*
In Earthworks (July/August 1999) I described the new Papercrete material
made of newspaper and cement, and mentioned a more earth-friendly recipe
I prefer called "Cobwood,"which is made without cement. Cobwood is
basically sawdust added to clay, lime and sand, with dry grass clippings
or straw for tensile strength. I use it as a soft, sculptable building
material, much like Cob- the ancient Welsh earthen recipe. Cob is a mix
of sand, clay and chopped straw hand applied in loaves the "cobs" to
build a wall. Cob is also similar to Adobe mixes in which a ratio of 30%
clay:70% sand is considered ideal. These natural materials have been
used, in various proportions, for many enduring structures the world
over. *Visit this Papercrete information page for basic instruction
<http://www.northcoast.com/%7Etms/papercrete.html> *
*Many materials can be used.*
People who are looking to use unprocessed and indigenous materials, are
experimenting with harvested clay, sawdust, woodchips, hemp, weeds,
straw, dry grass, and lime, forgoing the high embodied energy Portland
cement altogether.
Agstone
/Hillside steps made of Agstone/
The mixes I experiment with have ranged widely, with satisfactory
results. I am not attempting to use Cobwood for load bearing walls, or
for critical structural areas, and I am not a construction engineer or
architect. However, these natural materials have been used since the
beginning of man's (and woman's) shelter building attempts, and are easy
to play with for anyone interested in exploring alternative ideas.
*And that is the beauty of using nature's gifts...free and readily
available, unwanted and uncommercialized, with no profit in restricting
your access to grass, weeds, river or beach sand, clay or rubble. In
fact, clearing away scrap shrub and weeds is seen as an improvement to
most property!*
Most of what you need can be found in your own back yard, down the road,
or in a local field or stream. The only item which must be purchased is
hydrated lime, sold in 50 pound sacks, available at most builder's
supply and home improvement retailers, or feed & grain stores, and
costing about $6-$12 .
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You may have a perfect 30:70 subsoil on your property. This is great for
making traditional cob, or for adding sawdust and lime to make Cobwood.
Experiment with what you have, make test bricks, and handle the material
to see how you like using it. As with papercrete, there is no one right
way to make it, and your available, indigenous materials may dictate
your final results.
/Compost bin walls are made of a three layer pour of Agstone, using
board formworks./
------------------------------------------------------------------------
Agstone maker, John Stahl, uses dry chopped weeds, shrubs, branches and
donated hemp stalks as his filler material. Industrial hemp stalks,
available in Canada and France, and weeds (available everywhere) make a
great free filler. Dry brush, shrubs, teasel, yellow dock, even pine
needles can be finely chopped and used. John Stahl has tossed newspapers
and magazines into a wood chipper/shredder and used it along with weeds
to make Agstone.
shredding
/A professional wood chipper is used to chop and shred materials./ What
is amazing is how simple it is to use these dry unwanted materials and
create something practically for free. Clearing a weedy, overgrown, and
hilly property could provide the filler material, and back-hoeing to
make a level building spot can provide the clay solving two problems,
and recycling two ingredients at one time.
The three primary ingredients of Cobwood are mixed while wet, and all
are measured by volume. I use a basic recipe of 9-3-2-1 and work the mix
into a 5 gallon pail. Nine wetted, aged sawdust (soaked overnight, then
drained for a few hours), three clay slurry, (thick as sour cream), two
lime putty (also like sour cream), and one sand, usually dry. I¹ve made
mixes with sand and without, and prefer the smoother texture when sand
is used, as it fills in the voids between sawdust grains; more sand can
also be used. Dry chopped grasses are added last before building. This
pliant material can sit overnight, or for a day or so; is like a wet
cob, and can be poured, hand applied, or thrown, "harled" as the Scots
do with exterior renders, (wear protected gloves).
My Cobwood mix is high on sawdust because it is both freely available,
and comes ready-to-use, with no chopping necessary. Redwood sawdust
mixed with gray clay produces a soft gold or honey color. When
completely dry the surface is dun colored, very hard, and only slightly
friable. A nail or stick can scrape marks in the surface only with
strong pressure. Mixing is done by hand with a garden hoe, and clay is
often slurried first with a paint stem mixer attached to a 1/4 HP hand
drill. For larger construction projects a cement or mortar mixer can be
used.
DRILL
The outdoor garden bench I built is made entirely of various
experimental Cobwood mixes poured over a rubblestone base of broken
concrete chunks. Mixes were added one pail at a time, and left to dry.
Hand shaping of the back, arms and seat was not difficult, and a form
could have been used to build the base quickly. The design for a bench
or seat can vary widely, and could take any shape. Curved driftwood can
be used for the arms, river stones can stud the base and seashells or
other elements can be embedded into the bench for more personal,
creative expression.
*Endurance*
A brick, or wall, or garden bench left completely exposed to driving
rains will begin to return to the earth. If lime was used in the mix any
rainwater will cause less damage, but building under a tree for shelter
(as with my bench), or plastering a wall for protection is best. I have
no experience with freeze/thaw cycles on my Cobwood, however cob houses
in England and Wales have endured for hundreds of years through
extremely harsh winters. These houses were rendered with pure lime
plasters and have stood the test of time. John Stahl does get below
freezing temperatures in the mountains of Leggett CA, and both of us
endure long, very wet winters, and these natural materials have stood up
well.
Traditional cob will also perform well, and saves adding lime or sawdust
to the mix. If you can locate good soil, or mix sand and clay together
for a respectable cob mix you will have a totally free building
material. Lime, cement, or purchased sand does add to the overall cost,
but compared to other building methods (and the tools and equipment
needed) Cobwood and Agstone are an inexpensive and easy to use
alternative material.
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