[Cob] topsoil

[Henry Raduazo]

Making bricks is the best test of a potential cob material. I mix  
sand with the base material and try to find the ideal material and  
then try to get it approximately right not precisely wrong. The first  
time I did this I mixed 0, 1, 2, 3, and 4 parts of sand with one part  
soil. Every one of my blocks was suitable for building, I thought 2  
parts sand and one part clay soil was the best, but I tried for a 1  
to 1 mix because clay was free and rock dust cost $22.00 per ton and  
had to be transported one pickup truck load at a time. In the end a  
10 foot high wall shrank about 3 inches top to bottom. The double  
pane glass that I embedded in the wall with 2 inches of foam padding  
survived, but the outer pane cracked so I now have a 45 x 32 inch  
single pane of glass imbedded in an 8 ton cob wall.
	Dry cob is unaffected by freezing, but if water is allowed to soak  
deeply into the wall and freeze it will damage the wall. Normally the  
dry cob with a roof over it sheds water and wicks it away from the  
surface so quickly that by the time serious freezing occurs the wall  
is unaffected. Cob walls have thermal inertia too so that if you have  
hard rains followed by cold freeze the cob walls will resist deep  
freezing long enough to prevent damage.
	I have several walls in the Washington, DC area with no roof. We  
have lots of rain followed by freezing and as you would expect the  
walls are deteriorating over time. Other walls that occasionally get  
wet are undamaged.

Ed


On Jan 16, 2010, at 11:06 PM, Janet Standeford wrote:

> How far down should you go to get beneath topsoil in a vegetation rich
> environment? I went down 6-8 inches and found soil in a tiny valley  
> that
> had some miniature root stragglers and since it was already wet I
> squeezed some together and  found it to be nearly pure clay. It is
> sticky so I had to scrape it off the shovel and when pressed, it held
> together  until it was down to about 1/8 of an inch then it started to
> fall apart..
>
> Thought I'd run this by you guys before I use it for my samples as I
> have limited time to get these tested so can't spend a lot of time
> playing with it.
>
> By the way, does clay not freeze? The first 4-6 inches of dirt was
> frozen then it became very easy to shovel out.
>
> Hoping to make some initial sample blocks this weekend but need to  
> know
> where to find a small amount of hydrated lime and a small amount of
> portland cement.
>
> Any ideas? I am really grateful to have the support of such a great
> group of people. Some of the individual emails make me feel like
> extended family. Thank you.
>
>
> _______________________________________________
> Coblist mailing list
> Coblist at deatech.com
> http://www.deatech.com/mailman/listinfo/coblist