Cob Bond Beam?

[Patrick Newberry]

>     Many straw bale builders use a concrete bond-beam at the top to level
> things out and hold things together.  What would be the difficulties with
> making that bond-beam from cob, instead?

On a post and beam strawbale stucture the last section did not quite 
reach the roof, so I used cob instead of flakes of straw and it 
worked quite well. 

But with a load bearing roof, you need to tie the roof down some how. 
Ancher bolts would work too well in cob. Rather you might have to 
bury some boards with heavy gauge wire or such attached to the 
board. The board is laid on top of the straw the covered with the 
cob (not that hard to level) and the wire would run out the top of 
the cob bond beam and then be attached to the roof. I've heard it 
called a "dead man" before.
 

> 
>     Does cob have enough strength in tension?  Could you reinforce it with
> rebar to achieve the same result which rebar does in concrete?  Would the
> cob resist the flexion produced by further uneven settling?  Concrete
> appears to do so; why?  Because of the rebar?  Does concrete crack anyway,
> a little bit, but it's under the eaves and so doesn't matter?

Rebar and cob don't stick together very well, how ever I do know of 
one fellow whom coated the rebar with cement then embedded it in the 
cob and the cement coated rebar and cob seemed to work together 
fairly well. 

> 
>     Taking this idea a bit further:  what about building a straw bale wall,
> post-and-beam outfill, and using cob to take up the spaces which you can't
> manage to stuff adequately with loose straw or partial bales?  I have in
> mind especially the space between the highest run of straw bales and the
> rafters.


As I noted above. Much much better IMHO than loose flakes of straw.


Pat
Mauk, Georgia
http://www.gnat.net/~goshawk