Cob Do I really need sand in my clay?

[Adam Aaron Weiss]

Sam-

I think that the main purpose of the slip coat was to prevent cracking,
but as I think back on it now I think that it only prevents surface
cracking.  The major cracks of the wall were avoided by the right amount
of clay per unit sand as you had indicated in your first message.
Therefore, the proper ratio of materials IS essential, but for aesthetic
purposed the plaster coat can be doctored to look smoother if you keep the
plaster from drying out too quickly.  This can also be accomplished by
misting the walls with something like a windex bottle full of water.

Adam

On Wed, 30 Jul 1997, FROG wrote:

> 
> >In answer to your question about the cracks, I think it has more to do 
> >with the rate of drying than the ration of materials.  That is to say if 
> >you let the clay dry too quickly the wall will crack.  In Germany where 
> >I worked building houses out of a straw and clay mixture, and plastering 
> >them with a sand/clay plaster we wet the walls down with a brush and a 
> >slip coat to stop the cracking.  Good Luck.
> 
>      Adam:
>      
>      Do you do this after the earth plaster has completely dried?  The slip 
>      coat sounds primarily like a crack filler.  Yes?  Do you add sand to 
>      your clay slip coat?
>      
>      Thanks
>      
>      sam
>      
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