[Strawbale] airtight plaster

[RT]

On Sat, 09 Jun 2012 09:56:48 -0400, Dave Howorth <dave at howorth.org.uk>  
wrote:
[snip]
> I'd welcome any advice or pointers to materials about making
> straw bale walls airtight.
>
> I'm planning to use the indoor plaster as the main airtight barrier. It
> will probably be clay plaster, though lime is a possible alternative. I
> know a bit about tapes to use at window and ceiling junctions and so
> forth. My main concern at the moment is about how to use clay plaster to
> make an airtight barrier that stays airtight. So things like minimising
> cracking and so on.

David;
This will be brief because I'm just on my way out the door.

I'd say that achieving air-tightness of the plaster is not so much about  
minimising cracking as it is controlling where the cracking occurs and  
then implementing a strategy to ensure air-tightness at those controlled  
crack locations.

That means breaking up the plaster into panels of a reasonable size so  
that shrinkage cracking within the field of the panel will be eliminated  
(assuming that the proper mix proportions will be used for the plaster and  
that proper curing of the plaster will be carried out etc.)

Anywhere where there is a control joint, including a flange behind the  
joint in the plaster (or dissimilar planes/ materials) to ensure  
continuity of the air barrier between the two (300 mm wide strip of  
builder's poly or Tyvek or sheet metal or rubbery sheet membrane etc) and  
detailing the interface as a self-locking mechanical joint rather than  
relying upon goop is an effective technique.


-- 
=== * ===
Rob Tom					AOD257
Kanata, Ontario, Canada

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