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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 .

------------------------------------------------------------------------
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

/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.

------------------------------------------------------------------------
Please visit the Papercrete Information page 
<http://www.northcoast.com/%7Etms/papercrete.html>, or the Dirt Cheap 
Houses page <http://www.northcoast.com/%7Etms/cheap.html> to see more 
photos and learn more about really alternative building.

------------------------------------------------------------------------
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© Copyright 1999-2003 Taylor Publishing


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