Cob: Clay and Bool

[~Lootvik~]

If you're drawing a parallel with concrete walls, you're probably right 
John.  I know that engineers freak out when you put big rocks in a 
structural concrete wall.  What is the tensile strength of cob?  Most 
likely it varies a lot.  I think the embedded rocks are a great idea.  Like 
if you go without a plinth, they would shield from backsplash along the 
base.  Or above the plinth or just for looks.  I'd worry a lot less with 
rough-surfaced rock, than say river rock, which wouldn't bond as well.

That 3-5 ratio is a mighty big range.  Is the 3 for building with "bad" 
adobe cob re etc.?

otherfish wrote:
>Phil & Charmaine,
>Altho I don't know zip about Bool wall construction, I feel that a bit of
>logic will help in deciding how to do it.  It's pretty clear that the
>strength of cob ( and other forms of earthen construction ) derives from
>being built as massive walls.  Thaditional cob walls were THICK.  This is
>true of adobe also. Tested data of adobe walls shows that a minimum
>thickness to height ratio of 3 to 5 is fairly stable in seismic conditions
>if there are no other stability measures included in the wall construction.
>This means that you want the wall to have a proportional thickness of 1 foot
>for each 5 feet of height.  Given this as the proportion of thickness (mass)
>of wall cob that is stable, it stands to reason that if you place rocks
>within a cob wall, it will be in keeping with proven stability proportions
>if no cob part of the wall is less than this same thickness.  So if your
>wall is 5 feet high, don't have less than 1 foot of continuous cob BETWEEN
>any stones you place in the wall.  As your wall increases in height keep
>this same proportion of non disrupted cob between stones.
>
>This is supposition & not proven, but to me stands to reason.
>
>john fordice
>TCCP