permaculture

[Elfpermacl@aol.com]

In a message dated 9/28/98 11:20:23 AM, you wrote:

<<Thanks for the information about cisterns. I have a cabin in the mountains
in Northern New Mexico which has no water system yet. I would like to try to
catch rainwater instead of drilling a well so your detailed description of
cistern building should be very helpful. 

After reading your specs on cistern building, I have a couple of questions.
I hope you can help me with them.

I'm not familiar with the term ferro-cement. When you talk about
ferro-cement, are you talking about regular cement that contains rebar or
remesh? Are you talking about pure cement as opposed to conrete which I
think of as having rocks and cement?

You described the use of rebar and remesh in the cistern. I assume you are
using some forms to build your cistern walls. Is that correct?

Do you treat the cement walls with anything to make it less toxic to humans
or fish?

Finally, I was wondering what a person does about snow when using a
rainwater catchment system? Do you have to use a special guttering system
that will hold up under heavy snow loads? If the snow melts and you catch
the water, are there special problems associated with the debris in the
melted snow water?

I have viewed the video on rainwater catchment systems in the Austin area.
It had much useful information but it seemed to be oriented toward the use
of expensive fiberglass tanks, and it said nothing about catching rainwater
in areas with snow. What other sources are avaialble for information on this
topic?

Thanks in advance for your comments.

Tom Matthews 
>>

Thought-provoking questions, Tom:

The toxicity one gives me pause.  I know that in remineralization, we always
advise people using cement kiln ash to have a heavy-metal test done as the
toxic content can far outweigh the fertility benefits.  I have not heard
anyone question the safety of cement before, but the heavy metal issue has to
be a real one.  Hopefully, the high lime content of ferrocement mortar mixes
will reduce the rate at which heavy metals are dissolved by water.  Of course
the more acid your rain, the more toxic your water.  There doesn't seem any
way around that one.

Ferrocement is a technique using woven wire, often chicken wire in several
thicknesses (offset so that the holes don't line up) imbed in a special cement
mix which is more like a mortar than a cement, probably.  The mortar is
trowled on both sides of the wire simultaneously or a form is used (see post
to Marsha I sent out a few minutes ago.)  The National Academy of Sciences did
one of their neat little studies on ferrocement in the books for development
series available through BOSTID.  Unfortunately, someone stole my copy so I
don't have it to refer to.  There is also a good book that is/was (?)
available from Intermediate Technology in Development (addresses at UN plaza
in NY and in London, as I recall off the top of my head),  called Rain Water
Catchment in Rural Africa which go into the matter.  

In your climate, of course, you need footings below the frost line and
everyone needs a thick base to withstand pressures that is reinforced , much
like the base you would use for a masonry stove.  Rob Roy describes this, I
believe, in some of his books.

For concerns about the snow load in a retrofit from what I assume is a gable
roof, look at the gutter pictured by Mollison in some of his books.  It is in
Permaculture II, I believe, but nobody has that now I suppose.  We have a copy
of it in one of the design course pamphlets we publish (by permission) but I
don't recall which one.  It is one roll of sheet metal curved so that the
water drips binto the channel but leaves shoot on by.  Where I originate, in
Massachusetts, it gets as cold as you'd like with heavy snow loads and
everyone has gutters.  If you have a well insulated roof, the snow just sits
there making more insulation.  You probably need tanks big enough to catch the
spring melt when it comes, depending on your precipitation cycles.  Generally
you can get climate figures for the past 7 to 10 years--you want month by
month and not means or any of that crap.  You want absolute numbers.  Figure
that the worst case scenario is about half as bad as things will get as we get
into major climate destabilization and size  your cistern accordingly.
(Obviously you don't need to hold the annual rainfall in your cistern as you
will use water between rains and only need to top of enough to last the
greatest interval without rain.)  Galvanized is way superior to aluminum,
health-wise, for gutters.  In warm climates, split bamboo with septa scraped
away are the way to go.  

So talk to any contractor who installs gutters in cold-climate homes and they
will tell you how they do it.  I seem to recall brackets that were lag-bolted
into a face-plate of 2-inch stock, but don't take my vague recollection on
this--it is routine for tens of thousands of roofers in the cold parts of
North America.

For Mother Earth, Dan Hemenway, Yankee Permaculture Publications (since 1982),
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