[Cob] National Park Service earthbag construction

[mudhome at netzero.net]

At 09:55 AM 2/24/2004 -0600, Amanda Peck wrote:
>I do see what you mean.  That one bag going up around a window form looks 
>pretty bad, bag flapping at the corner, doesn't look like it's tied in 
>well.  I'd think that the forms should be left in until that area is 
>completely covered--with layers of wire over the top?  I'd be very very 
>happy to be seeing that wrong, and it's really fine.
>
>(this picture:  http://www.calearth.org/cvillage/DlxArch.htm )

Actually, I hadn't even noticed the corner in that picture, though Doni and 
Kaki's method of tucking in the corners (they call it "diddling") is much 
of what makes their bagwork look so good. What I was trying to point out in 
that picture is that taking the forms out must be fine - so how much 
Portland cement is in there to make it fine? With nothing in the bags 
except sand and clay (at best) I don't believe a long bag looping up over 
an opening can work, even if the form is left in till the end. When there's 
no cement the arches have to made of many bags rammed into wedge shapes 
with the top one acting as a keystone, THEN a long bag may be laid over the 
top to help lock them together (or openings can be corbelled in SOME 
situations). Cement could be used only in the arched bags but, because some 
of them continue on to become part of the general, wall I think all the 
earth used in those structures is stabilized with cement.


>I wondered about the vaults too.  Figured that it probably had something 
>to do with LEAKS!

Hmm... I would have thought anything for leaks would go over the bags 
rather than under them, as I thought was happening based on pictures like 
this:

http://www.calearth.org/3vaults_files/E1WomenBuilders.jpg

>or possibly that the vaults in the Ceramic House book are made of bricks, 
>not something floppy like the earth bags,

Yes, his ceramic houses (whether vault or dome) were built of adobes in the 
traditional Persian style, then fired from inside (preferably filled with 
ceramic pieces that needed to be fired anyway). There is no mention of bags 
in Ceramic Houses & Earth Architecture (copyright 1986).

>and it was "don't do this at home" time to make longish vaults out of 
>earthbags.

Well, I had thought that the only trouble with "trying earthbag vaults at 
home" would be that the whole vault would have to be supported during the 
process. After all, a vault is just an extended arch, and the shapes 
certainly seem easier to figure out and guide through construction than 
catenary domes. But your message sent me looking back over things and, 
while I found statements that imply earthbag vaults, such as--

CalEarth's "3 vault house" page saying:
"The universality of the material and design has caused these houses to be 
considered for the moon and Mars by NASA scientists interested in in-situ 
utilization of planetary resources."
and "The environmentally friendly design uses on-site earth"

and from the page selling the "Earth One Superadobe Home Blueprints" (in 
case anyone is unaware, Khalili calls earthbags superadobe):
"Vaulted earthen construction eliminates the need for timber."
"Environmentally friendly earthen materials"

and NOTHING saying that the vaults are not made entirely of earthbags... 
when I examined the vault pictures closely, ignoring all the spots where 
you can't actually tell how thick the tops of the vaults are because they 
meet endwalls and everything is plastered over, I was shocked. NONE of the 
vaults are thick enough to be made of earthbags!!!!! Earthbags form the 
sides and buttress them, but that does not meet my definition of "earthbag 
vault"!

AND, in her earthbag book Building with Earth Paulina Wojciechowska says 
"To my knowledge, a vault wider than 5 feet (1.5 meters) has not yet been 
successfully constructed using earthbags. Most vaulted roofs are 
constructed from other materials and joined to the earthbag walls using a 
bond beam."

So it seems you were right (perhaps even more so than you realized) and I 
was living with blissful delusions.

Sarah