[Cob] Washington DC cob: The experimental wood chip and paper clay wood shed

[Henry Raduazo]

	I have finished The experimental wood chip cob and paper clay  
plaster wood shed   Useable space enclosed 4 1/2 feet by 26 feet (two  
13 foot bays.. Total cost of materials under $100. Freebees (cost  
items that I got for free) four 2" x 8" x 15 foot beams and two bales  
of straw.
	Using wood chips to make cob instead of straw seems to be a success.
	I want to scale this up a bit by making a full sized wall before  
winter. The wall will be made of tiller mixed wood chip cob having no  
rock dust or other filler in the mix (only clay and wood chips).  
Currently my work day is Thursday, but I can do a couple of Saturday  
or Sunday work parties if there is any one in The Washington DC area  
interested in learning how to mix cob with a rototiller.
	My thanks to Gergo Szekley, Onyemobi Desta Anyiwo, and Alex Matsov  
who were kind enough to donate their time to make this experimental  
wood shed possible.

	The following article is a rough draft with no pictures. I can send  
a photo version to anyone who wants to see the pictures. Since I am a  
little dyslexic, I am particularly interested in someone who wants to  
proof read this and send it back to me.
'
Ed


Experimental wood-chip cob and paper/clay plaster wood shed

	Why experiment? Someone once told me I know what I know and I know  
what I don’t know, but I don’t know what I don’t know and that is the  
problem.
	The definition of “Natural Building” is building made with the  
materials which are natural to a particular location. For example I  
want to plaster my cob wall. Traditional earth plaster uses cow dung.  
Here in the Washington, DC area cow dung is not natural. With all the  
government agencies here shredded paper is natural and after a few  
simple experiments I know that paper is a good short term substituted  
for dung. I don’t know how long lasting or how durable it will be.
	Recently I tried pulping 15 -20 year old science fiction books. They  
would not pulp. I tried shredding and soaking and mechanical  
agitation. When they did break up there were few good fibers in the  
mix and many pieces of paper. It seems that acid paper oxidizes over  
time, and as it oxidizes the wood fibers become stiff and brittle. I  
didn’t know that and I didn’t know that I didn’t know it.
	This can have consequences in the real world. When I build a house  
or any structure where I have more than a few days invested in it I  
do not want unpleasant surprises. I do lots of experimental buildings  
so that I discover these possible glitches before they happen on my  
own house. It is imperative to do lots of experiments.
	Here in the DC area straw is also not a natural material. I can get  
it for $7-$10 a bale, but I can get truckloads of shredded wood  
delivered to my door free. More important though is the fact that  
shredded wood has greater strength than shredded straw, is more rot  
resistant, and I believe it will turn out to be more susceptible to  
machine mixing. Cob in it’s current configuration is not an  
economically viable alternative to stick building in the us. This may  
change. The US is an un-developing nation and as wages decline and  
material costs go up who knows?
	I think that we can speed up the path to viability by devising  
various machine mixing alternatives. Imagine, for example, a cement  
truck delivering 5 yard batches of truck mixed cob to an owner/ 
builder building cite on Saturday and Sunday and then returning to  
mixing concrete on the other five days of the week. This might be  
viable where tarp mixing is not.
	There is little or no natural stone and round wood is usually cut up  
into firewood sized pieces or not suitable for building here in the  
DC area, but building materials are discarded every trash day so if  
you cruse around in a truck on trash day you can get blocks, bricks,  
urbanite and random pieces of lumber.
	The wood shed started with four 2” x 8” x 15 foot boards left over  
from a deck project. I was lucky to get them before they were cut up  
and thrown in a dumpster. My foundation is a combination of  
cinderblocks and urbanite supporting slightly rotted 4” 4” timbers. I  
could have used round wood or stone instead if it were available.
	The walls are two L-shaped wall segments and one T-shaped wall  
segment made of rototiller cob. One of my first experiments was to  
make cob with a cheap front tine rototiller. I have now made more  
than 40 tons of cob with a tiller. It is no longer experimental. The  
only problem I have found is that wet cob can only be stacked 6  
inches to a foot each day. Then you need to wait a few days for the  
cob to dry. This time I am using shredded wood chips instead of  
chopped straw. The wood seems to be quite fibrous and much stronger  
than straw. The few leaves in the mix do not seem to affect the  
strength.
	The darker wet area in this picture shows a day’s work. At about two  
feet from the top of the wall I put in dead man anchors as hurricane  
ties to secure the roof beams. I used two different types the first  
is a 2” x 4” section attached to a strip of oak and an alternative  
tie is a 2” x 4” attached to steel wire and embedded in the wall  
either works.
	At this phase the average work day is only two hours because all you  
can do is mix one batch of cob and put it on the wall then quit while  
it dries out. On a larger wall this would not be a problem.
Gergo  was able to walk in the wood-chip mud barefoot. wood splinters  
do not seem to be a problem. Note the wood fiber size in the photo  
below:
	Five easy days of work and we are finished with the walls and ready  
to start on the roof.  One of my goals has been to come up with a  
cheap, easy to build, biodegradable roof to go on biodegradable cob  
structures. I have built several children's play houses having paper,  
clay, sand and boiled linseed oil composite roofs. So far problems  
have been caused by people walking on them and and breaking the  
composite material causing leeks but otherwise the system has been  
quite successful.
	The first step is to drill holes in the roof beams and secure bamboo  
rafters every six inches. Then cover this with a woven bamboo mat.
	 Bamboo for this project is harvested locally and can usually be  
found anyplace where the wether is rated at zone 7 or warmer. My  
policy is to never plant bamboo since it is an invasive non-native  
plant. The bamboo that I need is exactly the bamboo that people  
normally want to get rid of.  Culms of bamboo shoot up to 40 feet  
tall in 3 months, and look beautiful, but I only want to use culms  
that are at least three years old and a little ratty looking. Older  
bamboo is stronger and more bug resistant. The best bamboo to build  
with will have a nice green, yellow or black stem depending on the  
variety, but it will be starting to loose its leaves because the  
xylem and phloem will have started to get clogged up by silica  
deposits. Culms are cut and split fresh using a bamboo splitter from  
the Hida tool company. I prefer the 8-way splitter for 2 1/2 inch  
bamboo and I prefer to use only “clear” sections of bamboo.  That is  
the portion of the culm that has no branches. People who do not have  
access to bamboo should consider willow instead. If you cut down a  
stand of willow trees they will send up water shoots that can be  
woven in a manner similar to split bamboo.
	The woven mat has a warp and a weft. The weft is made with the  
thickest bamboos running vertically. The warp is thinner bamboo  
strips which are woven horizontally in and out between the weft.  
Every foot or so I weave a piece of twine into the mat to tie the  
first and last weft members together. This is to prevent them from  
pulling out when you lift the mat to position it on the roof. The  
uneven ends seen above are sawed off, The mat is lifted on to the  
roof and tied to the bamboo rafters with galvanized wires or nylon  
string.
	The next phase is plastering. I use a layer of heavy straw, a burlap  
fabric layer, a second layer of heavy straw, and a finish layer of  
fine paper plaster.
	Heavy straw is made by chopping straw with a lawn mower and bagging  
it. I then put and inch or so of water in the bottom of a pit and mix  
dirt into the water till I have a layer of heavy mud in the bottom of  
the pit. I then dump in a bag of chopped straw and I till the straw  
until I have a layer of thick mud. Sometimes I need to add a second  
bag of straw to sop up the mud. I want a sticky but workable mass  
that can be thrown up on to the bamboo mat and massaged into the warp  
and weft to form a flat surface.
	I then unroll a sheet of burlap on to the mud and massage a second  
layer of the heavy straw on top of the burlap to form a second flat  
layer. I guess the bamboo and the two layer of mud are 1 1/2 to 2 1/2  
inches thick. The burlap acts as a tensile reinforcement to keep the  
final roof from cracking when people walk on the roof. The burlap can  
also help to form the drip flange. I like to roll the burlap edge and  
heavy straw together to form a coarse drip flange all around the roof  
structure.
	I then let this dry at least a couple of days before applying the  
paper/clay finish.  The recipe that I use for the paper clay is one  
bucket of heavy clay slip (screened), one bucket of paper pulp,(wrung  
out a little) and one bucket of screened sand. This may vary  
depending on how clay rich your soil is.
	Paper pulp is made in advance by soaking newspapers or other paper  
for a couple days then coarsely tearing it up, then placing it on a  
tarp or in a bucket and walking on it till it turns to pulp (no large  
pieces of unseparated paper).
	The slip can be made either by foot mixing water and clay in a large  
barrel or by mixing smaller batches in a drywall bucket using a paint  
mixer and a high speed drill till it forms peaks, then pouring it  
through a 1/8 inch mesh screen. I also pour the sand through the same  
screen and mix the ingredients together to a smooth consistency. this  
mix is then applied to the coarse straw/clay and to the drip flange  
and troweled smooth.
	After this has completely dried I paint the roof with boiled linseed  
oil.
	The roof shown at the beginning of this article is 7 foot by 30 foot  
and cost under $100.00.