The original version of this article appeared in "the CobWeb" issue ten,
Spring 2000. See the order form on the
Cob Cottage Company web site
if you are interested in subscribing.
When I talk with people about natural building, their first question is often:
"How much does it cost?". Unfortunately, most people don't seem to understand
my usual answer: "As much as you decide to spend".
To make my meaning as clear as possible, I decided to demonstrate
what could be done for free.
I needed a tool shed/storage building, so I decided to make it a
demonstration project with the following set of rules:
- Materials where possible must come from the property.
- Where materials cannot be obtained from the property, they must be
available for free.
- Only hand tools may be used
- Every tool used must either not be necessary
(in other words it was just used for convenience), or a reasonable
substitute must be able to be improvised using only materials on the
The intent of these rules is that not only will the building cost
nothing to make, the tools required to make it must be available for free
The following materials have been used in the construction of the building
- The earth on the site is used as-is for making cob.
It is actually not a very good cob soil without the addition of sand, but it works.
Using the shake test, draining the excess water, then allowing it to dry
shows a high clay and silt content (about 35% clay, 15% silt), and the remaining
sand was rather poor quality and very fine.
- Grass is collected from around the building site to use
in the cob mix. I use a variety of different grasses, weeds, and other
fibrous plants - pretty much whatever
is there as long as it doesn't have thorns. The plan is that
grass will also be used to make twine to fasten together the roof
structure and for thatching the roof.
These pictures show the grasses and other plants that are used as fiber
in making the cob. The picture of the field is rather deceptive in that
it just appears to be grass, but a closer examination shows there are a
wide variety of plants, pretty much all of them end up in the mix, though I
generally try to avoid using the ferns because of their rather low tensile
strength. Avoiding the inclusion of blackberry vines and other thorned
plants is also important when doing barefoot cob mixing (ouch!).
- Rocks were dug up from above the site to build the foundation.
- Logs and branches for the roof structure are all
from trees that were blown down or found in slash piles.
- Glass jars
- I don't have time to try making glass right now,
so I am using glass jars for windows. Jars
can be acquired for free from friends, relatives, and waste
- I am using water from a well on an adjoining property, Other
sources available include a stream running through the property, digging a
well, channeling runoff water into a small pond, or mixing cob while it is
raining - the last approach can work quite well, but if you work to slowly
or it rains to hard, you will end up with to much water in the mix.
The tools actually used in the construction of the building so far (all of
which are shown in the picture above) are as follows:
- This is my most important tool, and unfortunately the
hardest to make a substitute for from materials on hand. The only
options I can think of are to fashion a stone blade, or do without.
The difficulties involved in not having a cutting tool would give me a
real incentive to learn how to make stone knives. The machette is used
- Cutting grass to a reasonable length for making cob
- alternative: tear the grass into smaller pieces with bare hands, or
only harvest shorter grasses.
- Cleaning the ends of grass for thatching - alternative: leave
the ends rough.
- Cutting wood for the roof structure - alternative:
break small stuff with hands and feet, use a fire to burn through larger logs.
- Trimming the cob - alternative: be more careful about applying the cob,
so no trimming is necessary, or let the cob dry until hard, then chip
away excess with a rock.
- used to cut grass for the cob mix and thatching.
Grass can also be harvested by just pulling it out of the ground instead.
- used to dig out/level the building site, dig the foundation
trench, move the soil into the cob pit, and dig up rock for the foundation.
A strong stick or pointed rock works well for breaking up the
soil, and a flat rock or bare hands can be used to move the soil around.
Interestingly, when digging up rocks that are packed together, a strong sharp
stick actually works far better than a shovel.
- used for transporting rock to
the building site. Large rocks could be either carried or rolled to
the building site, and small rocks could be carried in a twig basket or
- 3/4 inch steel screen on wood frame
- Used to quickly separate rocks larger than 3/4 inch from smaller
rocks and soil. You could just pick the rock out by hand.
- used to keep walls vertical. A plumb bob could be
fashioned with grass-twine and a stick or rock to use in it's place.
- used for mixing the cob. The cob mixing is done in a shallow
pit with a tarp which makes it easier, but traditional cob just
used the pit.
- protects hands, but are not a necessity.
- brings water to the site. I could probably fashion a bucket from local
materials, but it is simpler in this area to just make cob while it is raining,
and/or dig a small pit next to the cob pit to channel rain water into.
The building is designed to meet the requirements of both the "accessory
building" code definition, and the limitations of the materials used.
Key design decisions for the building:
- It is a round building which is structurally the most stable (important
because I am using thin walls due to size constraints), and requires
the least wall construction for the amount of enclosed space.
- The main window faces Southwest for the best lighting on this
site.  It was created by setting rows of glass jars in a cob matrix.
Additional small windows are scattered around the wall using individual
- The door faces Northeast, since that direction is the most protected
from wind and weather. This will be important, since it may be difficult
to block air flow around any door I can make within the rules outlined above.
The cob for the doorway has been given a bevel to make it
easier to get a reasonably tight fitting door. The door has not been
built yet, but some possible options for the door construction include:
a woven grass mat, woven twigs with a thin mud plaster, or a light clay panel.
- The roof will have a 45 degree slope and be thatched using local grasses.
- The building foundation is done "rubble trench" style, and consists of a
trench dug down below the frost line (about 1-1/2 feet below the interior
floor height), lined with rock to channel water in the bottom
away from the building, then filled with coarse gravel.
The stem wall is made of large rocks mortared with mud.
But it's not a house!
While this building is not intended to be a house, there is nothing about it
that would preclude such a use. Though the interior is only about 80
square feet, this is more than enough space for a bed for two people, a
place to hang clothes, a tiny wood stove, an area to prepare
food, and a small sink. All of these could be made from cob, wood, and/or
fired clay. Aside from an outdoor composting toilet, this
is all you need -- anything more is a function of choices you make.
(Laundry and bathing facilities have not been overlooked, they are not necessary.
It is quite feasible to do laundry in a sink, and to bathe yourself using a
wash cloth and sink.) It is important to remember that many homeless
people get by with far less.
Some lessons learned (or re-learned)
When the building is complete, this article will be updated, but in the
mean time there are a few lessons that I have learned.
- If I could only have one tool, the machette would be my first choice,
with a hose or bucket to haul the water running a close second, since
these are the most difficult to manufacture or do without.
- It is possible to have grass/straw that is to long for cob.
In the past, my cob work has used straw from bales, which (so far) has never
been to long to use, so I haven't given much thought to the length of the
I may have already known this, but I had to (re)learn it with my first
batch. I put the harvested grass directly into the cob on my first
batch, it's average length was probably around two feet (with many stalks
over three feet long), and
having it so long made it virtually impossible to break the batch up
into the "cobs" for placing onto the wall once I was done mixing. I was
ultimately forced to use the machette to hack managable pieces out of the
batch. After this experience, I used the machette to cut the grass
into pieces about six to twelve inches in length for all future batches.
- My high clay/silt cob mix once dry will soften much more quickly than
an "ideal" cob mix when soaked in water (a few hours as opposed to days),
which shows how much of a difference a good high sand mix makes for water
- When using glass jars for a window, first clean the jars, then put a lid
on them, and don't remove the lid until you are done with the building.
It is virtually impossible to avoid getting mud inside the glass jars when
handling them while building a window, so I now have to clean the insides of
all the jars built into my windows, which will be alot more difficult than
cleaning them in a sink. You may have noticed from the pictures that
the bottoms of the jars are covered in dirt -- it's all on the inside!
For information on related topics:
- Life Statement
- articles on small houses, lifestyle, saving money and more, written by the
author of this article.
- Cob Cottage Company
- the people who are primarily responsible for the revival of cob as a
building material world wide. If nothing else you will find much nicer
looking examples of cob as a building material.
Return to the Cob Cottage Company home page.
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