permaculture

[EFMonaco <EFMonaco@compuserve.com>]

John wrote...
>My original question here still applies:

>> The use of fiberglass fibers in a mix adds tensile strength to the mix
 and eliminates the need for wire mesh.<<
...
>> Trowling cement containing fiberglass fibers is no problem, you hardly
  know it's there.<<

>I can't trowel it onto thin air, though...I still need something to form
the shape that I'm troweling onto - so, what do you recommend?<

John,
I don't know the particulars of your situation, but I'd probably use the
galvanized lath,
sold for stucco applications.  It's rigid enough to hold itself up while
you trowel on the
cement.  It will resist corrosion long enough.  I might also try plant
fibers 
like bamboo or vines; or a plastic mesh wrapped multiple times around some
kind of form, which you could improvise.  

>How about using engineering fibers while plastering a mesh armature, which
can rust if it's going to but with the fibers the rusting won't affect
strength much if at all?<

This could work.  If the mesh were on the inside of the tank and the cement
coated on
the outside, then if it rusted and exploded the concrete, it would occur on
the inner-most
layer of the tank, and there still would be pleanty of strength left.

>For DIY work and relatively small projects (which is what I'm interested
in) forms are lots of extra work, lots of extra materials and money and
very limiting as to what shapes can be formed compared to just shaping the
armature and then plastering it.  Plus for stuff that's one-off, the forms
are pretty much useless after the structure is done.  So I'm not going to
make forms - by that point I might as well do regular poured steel and
concrete, possibly made easier by use of cempo/energrid/rastra or faswall
type units.<

Ah, to form or not to form!  Forms are a pain in the ass but, they give you
the best job.
I think the dislike of forms is why humans invented masonry.  Form with
bricks and mortar.
I haven't tried this but how about driving bamboo poles into the ground in
a radial pattern, 
then connecting them with more bamboo, basket style, or the lath, or
plastic mesh?
Take it up in lifts so the thing gains stability before it gets too high.

>Can you clarify sources and uses of fibers - I've heard of 'engineering
fibers' that can be added to any mix, is that what you're referring to?<

I'm not well versed in "engineered fibers", but here's my take on them:
If you know (or have calculated) what tensile forces you're trying to
resist in a 
structure, conventional structural analysis and reinforced concrete design
practice would have you place steel reinforcing at the locations where
these
tensile forces act so as to resist them.  This frequently gets into a lot
of steel,
which is expensive, so there's always an effort to reduce the amount of
steel in
the design.  One concept is redundancy, where the thinking is that the
forces you're
tryint to resist will spread out to other parts of the structure and will
be resisted there, 
so you can reduce the overall amount of steel by a percentage, be it 10 or
20, 
depends on codes.
When fibers came along, everybody knew that they resisted tensile forces,
so
this would also reduce the amount of steel.  But by how much?  So a set of
models
and formulas have arisen to predict and calculate how much resistance and
force
these fibers would provide, depending on how many you use and what the
materials
are.  This doesn't mean much in a non-engineered structure like a house or
a home
project.  Like all general rules (such as putting joists 16" on center), if
you stay in the
general guidelines, things tend to work out okay.  The "engineering" only
comes into
play when you're trying to work at the limits.
My experience with fibers is that they are fiberglass and come in two
sizes: long and short.
You can buy bagged mixtures of cement and fibers sold generically as
Surface Bonding
Cement.  There are also trade names like Surewall and Sacrete.  Home Depot
has it.
If you order delivered readymix concrete in a truck, you can specify fibers
be added to the
mix.  They usually ask if you want short or long.  I have used short for
slabs.  They speak in
terms of "bags", same as cement.  One, two, or three bags per yard (cubic
yard, CY). 
Usually, one bag per CY is pleanty.  If you're mixing mortar to trowel on,
by the wheelbarrow,
I'd add a shovelful per wheelbarrow.  How's that for engineered
specificity!
If you're mixing it yourself, you have to find the bags.  Perhaps a
concrete form or accessory
place would have it; or you could ask your local readymix plant where to
get it.  Sometimes
they'll let you have a bag or two if you ask, but they probably buy it in
bulk (not in bags).  I know
Home Depot doesn't have the fibers, and I haven't tried to find them
separately.
Best I can do, hope that helps.
Gene Monaco