Cob: strawbale/cob on the inside

[Matthew HALL(SED)]

Dear Tom
>
>The stumbling block in my mind has always been how to adequately protect an 
>external earthen plaster from cracking/spalling in the repeated freeze/thaw 
>cycles we regularly have at either end of the winter.  Through November, and 
>then again for about 7 weeks in early Spring, we often have humid days (as 
>snow/ice melts) and freezing nights. This regularly cracks commercial bricks 
>that haven't been fired at high enough temperatures to resist taking up 
>moisture.  Given that, it makes me feel doubtful that a wide roof overhang 
>and a high foundation would be adequate to protect unfired earth.  I'd 
>appreciate any ideas ....
>
>Tom Fetter.
>
Soil (cob etc) that has been stabilised with around 10% portland cement can actually be a lot more
durable than fired commercial bricks. You may wish to consider this when you think about rendering
your outside wall, although it does increase the cost quite considerably. Also, you may wish to
consider using animal hair or even natural fibres in the mix (about 5% by volume) to reduce the
cracking effect of the brittle render. The tensile forces still occur but are more evenly
distributed and so the cracking is not quite so deleterious, i.e lots of tiny cracks not a few huge
ones. 
Matthew_________________________________________________________________
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>
>


____________________________________________________________________
Matthew Hall - PhD Research Student
Centre for the Built Environment
Unit 9 Science Park
Sheffield Hallam University
Pond Street
Sheffield S1 1WB
England

Tel: +44 (0) 114 225 3200
Fax: +44 (0) 114 225 3206
E-mail: M.Hall at shu.ac.uk