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Info on Cob cistern and Cob Swauna (sweat:sauna)Vernon B. Johnston vajohnston at nas.comMon Oct 27 20:42:26 PST 1997
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i'd appreciate any info on cob and cisterns.=20
this is kind of an aside - maybe pat newberry might know best: does=20
anybody know why it is inappropriate to mix straw with clay if one is =
making=20
bricks for a fired structure 'a la nader khalili'? i was wondering about =
methods for air-entrapment with ceramic structures - i thought maybe =
firing a=20
cob structure might result in a strong, water-resistant but relatively=20
light-weight semi-porous (ie. higher r-value) ceramic structure. or does =
the=20
straw expand too much when it is burning, causing the clay/adobe to =
crack?=20
the reason i mention this is that i was wondering whether the steam=20
from the sweatlodge might saturate the cob with so much moisture that =
the=20
building would slump after a while, reducing the strength of the dome. =
i've=20
never built anything with cob, i was just curious whether you thought =
this was=20
a valid consideration. i'm trying to get a feel for how the material =
behaves=20
over time. i would imagine (based on no experience whatsoever) that cob =
in a=20
humid environment would act like wax in warm environment - that it would =
basically melt, but really slowly. what do y'all think?=20
thanks=20
lars fields
We are very interested in your cob cirstern. When you are able, please =
post
more info on this! Thank you for your post about the cob sweat, it was
quite informative.
Pete
Your Welcome! I am enjoying the process of building with earth =
immensely. It makes me feel good. As for the cistern, I was =
considering various structures to collect the rain water in. I don't =
believe they were overly pricey ($500 to $2000) considering the value =
that I place on water, but if I could come up with an alternative to =
plastic, concrete, or galvanized then that money could be spent on =
something else - something pleasurable like traveling to sunny warm =
climates in the winter, or dinner and a good movie, or...??? What I =
thought might work would be a cob cylinder raised off of the ground just =
like a cob home. It seems to me that 12 inches or so thick would work =
just fine. The concerns that I had were: (1) would any severe freezing =
cause an ice expansion inside the container to break my tank, and (2) =
how do I keep the water in the tank. =20
In my area the temperature may drop to 15 degrees F, and on occasion =
to zero. I remember reading somewhere (when I find it again I'll post =
the reference) that with the mass of the water and with the mass of the =
structure it should be all right. Anybody else have any answers, =
experience, or ideas? I am willing to bet that the straw which acts =
like little rebars will be sufficient, especially if I "knit" well with =
lots of long straw.=20
The other reason that I am willing to bet it will be fine is the =
synergy created by the use of cement mortar to line the inside of the =
tank. Not only do I get a decent liner to keep my water in, I get =
increased tensile strength. Anyway, that is what I decided to line the =
Cob tank with - about a half inch or so of cement mortar, either hung on =
chicken wire or metal lath. I know that Lars did not want to use =
concrete, but perhaps this liner would be minimal enough to be =
acceptable.
With those two concerns answered in my own head I did comfortable =
enough to build the periphery foundation for the cistern. But... what =
really made me feel good about the project was a section in a book =
entitled "Ferrocement Water Tanks: and Their Construction" by S.B. Watt. =
Don't worry! This book has more to it than ferrocement. It seems as =
though the Dogon people in Mali were in need of water storage for the =
water that they got from their roofs. What they used were the old =
granary bins which had capacities to 10 cubic meters or more. Before =
the used them for water storage they lined them with 1 cm or so thick of =
cement mortar mixed 1:3 (cement:sand by volume) over chicken mesh that =
was stapled to the inside of the bin. =20
These granary bins were right along side of their homes so their =
location was perfect. Also...they were constructed of an adobe material =
with was reinforced with grass fibres. Sounds like cob to me!!!
When they build a new storage tank, the Dogons rounded the bottom =
of the basin using a soil-cement mixture of about 1part cement to 10 =
parts soil. What I did was after I built my rock foundation (up about a =
foot to keep run-off from penetrating the tank and to protect the cob =
from run-off and rain) I dug out a concave shape in the bottom of the =
structure. I will then build it up smooth with cob and/or cement:soil =
mixture.
Hope this answers some of your questions about my cob cistern. Now =
to the Cob Swauna.
Lars, your concern is whether the cob structure will "melt" due to =
the action of the steam. That is not a concern of mine. The amount of =
time the Swauna will NOT be in use will allow a lot of airing out and =
drying time for the cob. Also, I do plan on the cob to be fairly dry =
and tight before the first sweat. Cob structures that have not been =
plastered, have an adequate roof ,and have been exposed to the elements =
seem to hold up just fine. Sweats generally are not used on a daily =
basis, but if they were I feel the structure would be fine. There is =
the possibility of plastering the inside, but I have not given that much =
consideration. Thanks for the question. It does get me thinking!
By the way, when you start to build a cob sweat/sauna, don't start =
to corbel your wall in too soon. I spent almost 6 hours readjusting my =
walls because I started to go in too soon. We need room for the our =
backs and head, so after you start building sit in it to get a feel for =
what it would be like. And... for sure, make sure that if you haven't =
been in a sweat before, do it before you build.
Thanks - Vernon vajohnston at nas.com
=20
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<HTML>
<HEAD>
<META content=3Dtext/html;charset=3Diso-8859-1 =
http-equiv=3DContent-Type>
<META content=3D'"MSHTML 4.71.1712.3"' name=3DGENERATOR>
</HEAD>
<BODY bgColor=3D#ffffff>
<DIV><EM>i'd appreciate any info on cob and cisterns. <BR><BR>this is =
kind of an=20
aside - maybe pat newberry might know best: does <BR>anybody know =
why it=20
is inappropriate to mix straw with clay if one is making <BR>bricks for =
a fired=20
structure 'a la nader khalili'? i was wondering about <BR>methods for=20
air-entrapment with ceramic structures - i thought maybe firing a =
<BR>cob=20
structure might result in a strong, water-resistant but relatively=20
<BR>light-weight semi-porous (ie. higher r-value) ceramic structure. or =
does the=20
<BR>straw expand too much when it is burning, causing the clay/adobe to =
crack?=20
<BR><BR>the reason i mention this is that i was wondering whether the =
steam=20
<BR>from the sweatlodge might saturate the cob with so much moisture =
that the=20
<BR>building would slump after a while, reducing the strength of the =
dome. i've=20
<BR>never built anything with cob, i was just curious whether you =
thought this=20
was <BR>a valid consideration. i'm trying to get a feel for how the =
material=20
behaves <BR>over time. i would imagine (based on no experience =
whatsoever) that=20
cob in a <BR>humid environment would act like wax in warm environment - =
that it=20
would <BR>basically melt, but really slowly. what do y'all think?=20
</EM> </DIV>
<DIV><EM><BR>thanks <BR>lars fields</EM> </DIV>
<DIV><EM></EM> </DIV>
<DIV><EM>We are very interested in your cob cirstern. When you are able, =
please=20
post<BR>more info on this! Thank you for your post about the cob =
sweat, it=20
was<BR>quite informative.<BR><BR>Pete</EM> </DIV>
<DIV> </DIV>
<DIV> </DIV>
<DIV><FONT color=3D#000000 size=3D2>Your Welcome! I am enjoying =
the process of=20
building with earth immensely. It makes me feel good. As for =
the=20
cistern, I was considering various structures to collect the rain water=20
in. I don't believe they were overly pricey ($500 to $2000) =
considering=20
the value that I place on water, but if I could come up with an =
alternative to=20
plastic, concrete, or galvanized then that money could be spent on =
something=20
else - something pleasurable like traveling to sunny warm =
climates=20
in the winter, or dinner and a good movie, or...??? What I =
thought=20
might work would be a cob cylinder raised off of the ground just like a =
cob=20
home. It seems to me that 12 inches or so thick would work just=20
fine. The concerns that I had were: (1) would any severe =
freezing=20
cause an ice expansion inside the container to break my tank, and =
(2) how=20
do I keep the water in the tank. </FONT></DIV>
<DIV><FONT color=3D#000000 size=3D2> In my area the =
temperature=20
may drop to 15 degrees F, and on occasion to zero. I remember =
reading=20
somewhere (when I find it again I'll post the reference) that with the =
mass of=20
the water and with the mass of the structure it should be all =
right. =20
Anybody else have any answers, experience, or ideas? I am willing =
to bet=20
that the straw which acts like little rebars will be sufficient, =
especially if I=20
"knit" well with lots of long straw. </FONT></DIV>
<DIV><FONT color=3D#000000 size=3D2> The other =
reason that I=20
am willing to bet it will be fine is the synergy created by the use of =
cement=20
mortar to line the inside of the tank. Not only do I get a decent =
liner to=20
keep my water in, I get increased tensile strength. Anyway, that =
is what I=20
decided to line the Cob tank with - about a half inch or so of cement =
mortar,=20
either hung on chicken wire or metal lath. I know that Lars did =
not want=20
to use concrete, but perhaps this liner would be minimal enough to be=20
acceptable.</FONT></DIV>
<DIV><FONT color=3D#000000 size=3D2> <FONT =
color=3D#000000>With=20
those two concerns answered in my own head I did comfortable enough to =
build the=20
periphery foundation for the cistern. But... what really made me =
feel good=20
about the project was a section in a book entitled "Ferrocement =
Water=20
Tanks: and Their Construction" by S.B. Watt. Don't =
worry! This=20
book has more to it than ferrocement. It seems as though the Dogon =
people=20
in Mali were in need of water storage for the water that they got from =
their=20
roofs. What they used were the old <FONT color=3D#000000>granary =
</FONT>bins=20
which had capacities to 10 cubic meters or more. Before the used =
them for=20
water storage they lined them with 1 cm or so thick of cement mortar =
mixed 1:3=20
(cement:sand by volume) over chicken mesh that was stapled to the inside =
of the=20
bin. </FONT></FONT></DIV>
<DIV><FONT color=3D#000000 size=3D2><FONT =
color=3D#000000></FONT> =20
These granary bins were right along side of their homes so their =
location was=20
perfect. Also...they were constructed of an adobe material with =
was=20
reinforced with grass fibres. Sounds like cob to=20
me!!!</FONT> </DIV>
<DIV><FONT color=3D#000000 size=3D2> When they build a =
new storage=20
tank, the Dogons rounded the bottom of the basin using a =
soil-cement=20
mixture of about 1part cement to 10 parts soil. What I did was =
after I=20
built my rock foundation (up about a foot to keep run-off from =
penetrating the=20
tank and to protect the cob from run-off and rain) I dug out a concave =
shape in=20
the bottom of the structure. I will then build it up smooth with =
cob=20
and/or cement:soil mixture.</FONT> </DIV>
<DIV><FONT color=3D#000000 size=3D2></FONT><FONT =
size=3D2> =20
Hope this answers some of your questions about my cob cistern. Now to =
the Cob=20
Swauna.</FONT></DIV>
<DIV><FONT size=3D2></FONT> </DIV>
<DIV><FONT color=3D#000000 size=3D2> Lars, your =
concern is whether=20
the cob structure will "melt" due to the action of the =
steam. =20
That is not a concern of mine. The amount of time the Swauna will =
NOT be=20
in use will allow a lot of airing out and drying time for the =
cob. =20
Also, I do plan on the cob to be fairly dry and tight before the first=20
sweat. Cob structures that have not been plastered, have an =
adequate roof=20
,and have been exposed to the elements seem to hold up just fine. =
Sweats=20
generally are not used on a daily basis, but if they were I feel the =
structure=20
would be fine. There is the possibility of plastering the inside, =
but I=20
have not given that much consideration. Thanks for the =
question. It=20
does get me thinking!</FONT></DIV>
<DIV><FONT color=3D#000000 size=3D2></FONT> <FONT =
size=3D2>By the=20
way, when you start to build a cob sweat/sauna, don't start to corbel =
your wall=20
in too soon. I spent almost 6 hours readjusting my walls because I =
started=20
to go in too soon. We need room for the our backs and head, so =
after you=20
start building sit in it to get a feel for what it would be like. =
And...=20
for sure, make sure that if you haven't been in a sweat before, do it =
before you=20
build.</FONT></DIV>
<DIV><FONT size=3D2></FONT> </DIV>
<DIV><FONT size=3D2>Thanks - =20
Vernon <A=20
href=3D"mailto:vajohnston at nas.com">vajohnston at nas.com</A></FONT></DIV>
<DIV><FONT color=3D#000000 size=3D2> =
</FONT></DIV></BODY></HTML>
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