How to build a straw-bale wall
Straw bale walls can be built very much like
brick walls, stacking the bales on top of a concrete foundation with a
damp proof material (heavy plastic) between the concrete and the bales
to stop any moisture getting from the ground into the wall. They are held
down firmly by high tensile fencing wire or rods which are attached to
a ‘top plate’, something strong like a wooden frame or steel reinforcing
sheet which holds the bales firmly onto the foundation. If using wire,
it is passed through a curved piece of ‘poly-pipe’ which is set into the
foundation.
Diagram of a straw-bale wall, many Australian
designs simply use reinforcing mesh as a top plate and high tensile fencing
wire as a tie down
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Footing for a curved wall. Note the starter bars
set in the
concrete. Curved poly pipe has also been set
in the
foundation to allow wire to be passed over the
wall and through the foundation for tightening |
An amazing hand-operated tool called a Grippler
is used to tighten the fencing wire around the wall, using little gripping
devices called Gripples. It is simple for anyone to use and can be purchased
from stock&station agents |
Then the walls are covered with chicken wire (netting)
which is knitted from one side of the bales to the other with binder twine
using big (75cm long) needles. Finally the wall is plastered with a cement
render.
Above: Attaching chicken wire to the bales
using big bale
needles to thread the binder twine.They can be
made
cheaply by a welder.
Right: Rendering the west wall of
the studio at The Food
Forest |
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Bales can be stacked on the flat or on their edges.
In some constructions the roof rests on the walls and in others there is
a pole-frame supporting the roof. If you want to be sure your walls stay
dry it is easiest to build a pole frame and roof first.
The job is best done with friends, the fellowship
and energy of the group giving enormous energy to the project and everyone
sharing their skills with others. Having at least an amateur carpenter
in the bunch helps enormously if you are going to incorporate windows or
doors into the construction.
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| Pole-frame construction gives you a roof to build
under...very handy if it rains |
It is good to have a least one carpenter
Bales can be sculpted to fit!
on site, a house is much more than 4 walls! |
Rendering is one of the most satisfying parts
of the operation and is remarkably easy. It is well worth getting a plasterers
trowel (which is rectangular and bigger than a brickie’s trowel) and a
hawk (a square piece of wood with a handle under it) to carry the mortar
from the barrow to the wall. For the faint-hearted you can don a tough
pair of rubber gloves and smear or throw the mortar onto the wall. This
works well but is slower than using a trowel. We use a mixture of 6 parts
plasterers sand, one part lime and one part cement. The cement render sticks
to the straw and to the netting which forms a strong ‘ferro-cement’ layer.
With two more coats of render, each a bit more than 1cm thick, the total
plastered layer ends up being about 3-4cm thick. The first layer should
leave the netting partly visible and to save costs we use ordinary
grey ‘blended cement’ in the mortar.
The second layer is used to give you pretty much
the exact shape you want and for this and the final layer we use a light
coloured cement (like Brightonlite), which allows the colour of the sand
to come through. Some plasterers sand is yellowish, which leaves you with
a very light sandstone colour, as seen in the pictures of our walls; alternatively
you may want to go for a dark red or brown sand. You can also use a shovelful
of earth from your own property, as long as it is finely screened; can
give you a wall which virtually merges into the landscape. The final layer
on garden walls needs to incorporate a waterproofer which can be mixed
into the render or sprayed onto the wall after it is finished. We actually
put a layer of plastic between the netting and the straw on the top
of garden walls as an extra insurance against water entering the wall.
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| Soil from your property can be used in the mortar
mix |
Waterproofing around windows and posts is important |
A waterproofing agent is applied to or incorporated
in the outside layer of render |
You’ll have no problems with termites, insects
or fire with a properly built straw-bale wall but water in the straw is
fatal so the wall must always have good drainage around it and the foundation
must be proud of the surrounding ground. Having high powered sprinklers
which spray the wall for long periods of time is a poor policy!
Where wooden uprights emerge from the wall to
carry a trellis, a non-hardening mastic joint should be made so that there
is not even the tiniest crack for water to sneak through, the goo is available
from hardware shops.
A trick we developed to save costs and resources
in building garden walls is to use the bales on edge rather than ‘on the
flat’. The foundation can be narrower and less bales are used. The
top plate is 300mm wide trench mesh which is bought in 6m lengths. It can
be bent into curves up and down and partly cut and joined into curves from
side to side, giving you absolute flexibility in the shape of the wall.
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Finishing the final coat of render with
a
gloved hand gives a strong, smooth finish |
Trench for footing of
garden wall |
Windows add interest and can be opened
or
closed depending on circumstances |
You can even build a moongate in your wall by bending
trench mesh into a circle or elipse and strawbaling around it. Little windows
built into the wall add enormous visual interest allowing for selected
views while the wall cuts out unwanted sights and noise. The walls around
our studio make you quite unconscious of a thundering great shed only 20
m away and eliminate traffic noise from the busy Gawler Bypass.
You can now do a one-weekend course in strawbale
building to learn the tricks strawbale pioneers had to discover over
years of building and to meet architects and engineers who are comfortable
working with strawbales. Courses are run in most states and you can find
out about them via permaculture associations and networks.
I believe that attending a workshop or helping
on a strawbale site is the best way to get a realistic idea of whether
you would want to build in this medium. Happy building!
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| Gerald Wittmann, an engineer specializing in
straw-bale construction chatting to a workshop participant at The Food
Forest |
Straw-bale architect Bohdan Dorniak |
Experienced straw-bale builder Lance Kairl
demonstrates a rendering technique |
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here to return to the Straw-bale menu at the top of the page |
