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re: strawbales (was re: natural building colloquium east (update))
12 may 2000
anthony matonak wrote:
>...if the owner does the labor him/herself there is
>no cost of labor as is normally computed.
some schemes (eg earthships with hand-tamped tires at 20 minutes apiece)
seem so labor intensive that owner-builders have to pay themselves
close to $0.00 per hour to make them economical...
>> an 8' wall full of 150 pound per cubic foot wet concrete exerts
>> 1200 pounds per square foot of force at the bottom, right? so each
>> square foot of wall needs about 1200 pounds of strawbales near the
>> bottom... about 40 30 pound bales for each linear foot of perimeter,
>> at the bottom of the wall, extending more than 100' outwards from
>> the wall, on both sides!
>somehow the picture of 100' of strawbales built up to provide for
>a form that's only 8' tall strikes me as silly...
"outwards," not upwards (which would be a lot tippier, and make it
harder to slide the concrete down into the 100' slot :-) my sense of
the original poster's question was "how many bales would we need
to stack on the sides to build an above ground concrete wall, using
the bales as forms, with no ground stakes or through-ties." the answer
seems to be "a lot" :-) this might look like a linear stepped pyramid
8' tall and 200' wide, with the concrete in a narrow slot running
up the middle.
low tech, no connectors, lots of bales (about 10,000 for a 30' long
x 8' tall wall :-), lots of gravity, lots of schlepping, suitable for
an army of slaves who don't need care or feeding. or maybe a large
group of interns who are paying to live and work and eat at an
educational "eco-center" :-) or an army of monks or inmates who
might see this as a religious experience...
>...[a modified] procedure would go something like the following.
>first, pound in rebar 'stakes' into the ground spaced however closely
>together you figure they need to be along the inside and outside of
>the wall so they will stick up roughly into the middle of your
>strawbales when they are stacked on them. leave them sticking
>up a foot or two into the air, making sure they are in deep enough
>into the ground so they won't move, and impale the first layer of
>strawbales on top of them.
ok.
>lay plastic or steel strapping material across this single layer
>of strawbales
ie a single layer on sides of the wall...
>extending all the way from one side to the other leaving a bit
>hanging off the outside edges of the bales which will later get
>fastened to something to hold it. perhaps 2x4's oriented vertically
>and placed at every x feet horizontally would suffice to attach
>these straps to the outside of the bale wall/forms.
ok. maybe horizontal 2x4s would work better, a single or doubled
2x4 hanging flat outside on top of each layer of bales...
bale bale
bale bale
2x4 strap strap ... strap 2x4
bale bale
bale bale
2x4 strap strap ... strap 2x4
bale bale
bale bale
-------*----------------*----------
stakes * *
>a variation of that would be to build a large dome shaped mound of
>strawbales. use a layer of cob on top of it to 'round' it off. place
>your array of rebar with pins stuck into the cob spaced a few inches
>off the surface. add window and door frames where desired. spray the
>works with shotcrete as in the example above.
shotcrete again... seems techy and expensive...
>...remove the bales from the inside through the doorway (which you
>should not have covered in concrete)...
nice...
>this should give you a pretty good monolithic concrete dome without
>the cost of fancy forms.
well, the monolithic form is just an inflated cloth bag that costs
about $2/ft^2 and can be reused. it seems to me the expensive parts
of that process are the polyurethane foam sprayer and rebar wiring
and shotcrete pump...
>if you don't like using shotcrete you could probably just plaster the
>concrete on the outside by hand.
lotsa work, for a thick wall... so, what do you think of the idea
of burying bales of mushroom hay (50 cents each?) inside the wall?
nick
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