Cob Yoda's cob house

[cobcrew at sprynet.com]

On Wed, 3 Dec 1997, Will Firstbrook  WCB of BC <wfirstbr at msmail.wcb.bc.ca> wrote:
>[SNIP]
>Yet some of our ideas may be very difficult to implement. 
It ain't easy bein' green.  But that's what the list is for, right?
>
>One of the area's that seems tricky is my eldest son's room. 
[SNIP]Any Ideas on how this could be done?
Cob roofing is our favorite topic.  We are planning both a 11' hallway with a cob 
barrel vault and a 15.5' cob dome.  For our larger dome, we are thinking of using 
cut Hebel aerated concrete block (very light weight, good insulator, about 3-4x 
stronger than the best cob mix we have made.)  Note: we have not found any round 
windows that are screened and open.  Anyone have any ideas
about round windows where you need ventilation and have lots of mosquitoes?
>
>Three possible techniques come to mind:
>[SNIP]
>3. Maybe the wattle and daub technique of getting lots of sticks tied
>together in the shape of the structure then using them as a form to
>massage the cob into.
This is the one we're going to do.  We have a ton of bamboo cut and ready for 
use.  Might not be available in BC.  Hope to use a mesh system, with large pieces 
interspersed with smaller ones.  About 4" square, tied with "black wire".  
Thinking about 6-8" total thickness.  Shape is key - catenary or egg shaped helps 
distribute lateral forces and will help with the snow load.
>[SNIP]
>Yet cob does not make a good roofing material even with a lime finishing 
plaster.
Well, what is the difference between all those cob ovens and a small dome?
There are many adobe brick domes world-wide; cob offers some advantages over
adobe brick, I think, in terms of the extra straw component adding to the 
tensile strength and fewer cold joints.  Carol Crews (sp?) in New Mexico has a 
hybrid cob/adobe structure with an adobe dome roof (not catenary).  She has 
suggested a special sealant (silica-based) that waterproofs but still allows 
water vapor to enter/exit the material.  If we run into difficulty, we have
considered covering the cob with:
1)  A silo top ($1,500 new from Minnesota).
2)  Ceramic tile or synthetic tile or tiles made from recycled tires.
3)  A tin roof (best option for rainwater collection)
4)  Some form of thatching.
>
Best of luck with your project.  We have been getting some of our design
ideas from an adobe book, "Adobe and Rammed Earth Buildings" by Paul McHenry,
Jr.  There are several pages on adobe domes and barrel vaults.  And hey, if
we have to make some bricks, we'll do it!

Our details are at http://home.sprynet.com/sprynet/cobcrew
Mike.