Cob (Fwd) Re Sand arch

[Patrick Newberry]

john fordice sent this to me, and I'm posting it to the list.
Don't forget folks, reply to the list, if it makes sense, and in this case, I 
think it does.


>to goshawk (pat?)

yes pat=goshawk

>your arch is intriguing
>is it earthbag construction except filled with sand (sandbag construction?)

A rose by any other name would smell as sweet. Right!
I initially learned it as superadobe from Nader Khalili, then in an effort to 
be more generic, I started referring to it more as earthbag construction and 
yes sometimes I even call it sandbag construction. Actually the bags are more 
the size of feed bags.


>you probably already posted this , but I lost the thread.  could you please 
>give a nutshell descroption of the whole thing?   the ability to make an 
>earthen arch roof that has withstood weather is worth repeating to the lost


Here is how I build the earthen arch that as withstood multiple years of wet 
weather. (we get about 50 inches a year here)

Prepare by building a wooden form the size of the arch you wish to build. 
Arches and vaults need forms, domes do not. Place the form in it's location 
jacked up by a few bricks

1. get your bags. I like them to be about 18 inches wide. 
2. fill with earth. If I was building a house, I'd make the mixture similar to 
rammed earth, moist, not wet. 
3. pound the bags, simliar to pounding tires but easier. 
4. place barbed wire between levels of bags.
5. build up and to the near the top of the form.
6. build "key stone" bag by filling the last three bags at once and tamping 
down hard with the pounder. 
7. remove the bricks, then the form
7. If exposed to weather, e.g rain, I plaster the structure with stabilized 
earth. 

A little note: I find that plaster over the earth filled bags is different than 
plastering directly on the earth. With the arch in question, I can tell there 
is a small space between the earth and the cement/plaster. This is caused by 
the bag inbetween. If you tap on the cement plaster shell/stucco you can hear 
it. I believe that  this is what allows for the different expansion and 
contraction rates of the two materials to not cause problems as was found when 
plastering cement stucco over the older adobe structures in the west and then 
having chucks of the wall fall off. This was plaster directly to the earth and 
thus the problems.



That's it,
Pat,
http://www.gnat.net/~goshawk
"There is No Hope, but I may be wrong."