[Greenbuilding] Cob as an alternative to spray foam sealant?

[Lance Collins]

A problem with giving advice on the use of natural materials 
(especially soil : loosely called clay in many posts) is that their 
properties are so variable.

When I was making mud bricks I experienced almost no shrinkage with 
most of my sub-soil,  but I have a patch a few metres from my 
principal source which does shrink noticeably.   My soil made 
excellent mud bricks but as far as I could work out with simple tests 
is only about ten percent clay.   Look up the composition of clay on 
wikipedia and see what a large number of various compounds constitute clay.

The key to success is experimentation (and a bit of luck).

Regards
Lance


At 08:04 AM 29/01/2011, you wrote:
>Frank, shrinkage depends on a number of factors and can range from 
>between 5% all the way up to 50% for certain types of clay. 
>Furthermore, the amount of moisture in the mix will affect the 
>degree of shrinkage. That being said, as a 'rule-of-thumb' you can 
>expect about 10% shrinkage in the clay content of your mix. If the 
>clay is mixed with cellulose matter such as wood chips or straw, 
>these will swell and shrink independently depending on the moisture in the mix.
>
>My suggestion would be to try using two or three coats / 
>applications with each successive layer filling the cracks and 
>shrinkage that occurs in the previous.
>
>Regards
>Steve
>
><http://www.naturalbuildingsite.net>www.naturalbuildingsite.net
><mailto:naturalbuilding at shaw.ca>naturalbuilding at shaw.ca
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