what's going on..... and bond beams

[Shannon C. Dealy]

On October 3, 1996  patrick newberry said:
>
>It got kind of quite out there so ....
>It's been raining a week now and my earth plaster walls are still wet???
>
>I am wondering when the best time to start a cob building would be??
>here in georgia winters are wet and mild and summers are hot and dry.
>Do they only build in summer most places with cob????

The big question is will the walls dry out in a reasonable amount of time,
if the humidity is really high, it's raining all the time, or it's always
overcast or cold out, then the walls won't dry out and might develop mold
or mildew on the surface.  Also though I am told this has not been a
problem, I would be concerned if a really hard freeze should occur on a
freshly built section of wall since I would expect the water in the wall
to freeze, expand, and significantly weaken that section of the wall.
I would say that a simple test would be to mix up some stiff mud, form
it into a block about 4x12x12 inches, and set it outside under cover near
where you intend to build your walls.  If after 3 - 4 days it hasn't
hardend significantly, then your walls probably won't either.

>
>The bond beam, I heard one person mentioning a  cement bond beam.
>regardless of cement or wood....is this the same thing as a  top plate in
>straw bale????

A bond beam as I understand it is the same thing as the top plate in straw
bale, but I am not sure what this has to do with cob, no bond beams (or 
top plates) are needed.

>
>
>If one is doing interior walls what kind of thickness is common. 
>I'm thinking of about 20 inch thick exterior walls.
>
Cob Cottage Company uses a 12" thickness for interior walls, and a 16" to
18" thickness for exterior walls.

>I have heard that straw is NOT a necessary ingredients. Any comments????

News to me, and I wouldn't even consider trying it personally.  I like to
think of cob as a really cruddy form of fiber-glass.  The sand and clay
are the resin, and the straw is the glass.  If you leave out the straw,
then all you have is a block of resin which will have a very low tensile
strength as well as poor resistance to shearing forces.  I'd hate to think
what would happen to a cob structure without straw in an earth-quake.
Also you would lose most of what little insulation value cob has.
Basically what you would end up with is a building with good compression
strength, but virtually no strength in any other direction.  In other
words, you could park a truck on top of it, but if the truck ran into the
building it would cave in.


Shannon Dealy
dealy at deatech.com