[Cob] Cobhouse Design

[Shannon Dealy]

On Thu, 9 Apr 2009, howard at earthandstraw.com wrote:

> You are welcome.
>
> BTW I have seen people say to put earthen plaster under lime plaster
> which I want to caution people against.  I don't think its wise to put a 
> harder plaster over a softer one from my experience as it messes with 
> the bonding.
> The lime bonds into the straw bales very strongly.  Plaster on cut ends 
> of the straws, no mesh required nor control joints for cracking.  This 
> is true even if you plaster up a foundation, across a wood band and onto 
[snip]

This only makes sense is if you actually need a stronger bond for the lime 
plaster.  An earthen plaster in it's simplest form is nothing more than 
cob with the ingredients run through a sieve, and since lime plasters work 
just fine on cob walls (which are typically given an earthen plaster base 
coat before putting on lime), there is not a problem with doing this. 
Since your posting had a heavy context of straw bale to it, if you are 
looking for your plaster to provide significant added structural strength 
for a bale wall (and perhaps this is what you intended) then I think you 
could reasonably argue against the use of earthen plasters as a base coat 
since this would limit the lime plaster bond on the face of the bales to 
the strength of the earthen plaster underneath it.  If you are simply 
looking for a durable weather resistant surface on an already strong wall, 
the use of lime over a well bonded earthen plaster should not be a 
problem.

FWIW.

Shannon C. Dealy      |               DeaTech Research Inc.
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