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Re: GSBN:Clay plastered wall passes 1-hour test!
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- Subject: Re: GSBN:Clay plastered wall passes 1-hour test!
- From: André de Bouter forum@...
- Date: Fri, 21 Jul 2006 09:22:22 +0200
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Congratulations and thankyaverymuch for for sharing the info and for all the
effort that must have gone into his project.
As for stuffing the gaps between the bales, might I humbly suggest straw-clay
rather than cob. Probably also very fire resistant but maybe more
representative of realistic construction practice than cob because less of a
thermal break. (In France some builders stuff with lime/straw and a handfull of
On edge or flat:
In France more and more builders use bales on edge even though the rumour is
that the plaster does not adhere as well as as when layed flat. In my (earth
plaster) experience it seems to me that does not matter a great deal. More
important (in both cases) is to work the plaster well into the bales
Could the fact that the second wall tested (earth plaster on bales layed flat)
holds up longer be due to the way the bales are layed?
Do we have any numbers on how well plaster (be it cement/lime or earth) adheres
to bales flat or on edge?
In France only plaster on bales layed flat have been tested:
1000kg/mÓ (0,01 MPa) for a lime/hemp (+ a small aount of sand)
plaster (=25 times the weight of the plaster)
8000kg/mÓ (0,08 MPa) for a lime/hemp (+ a small aount of sand)
plaster (=200 times the weight of the plaster)
> I want to add a couple of things to what Bill and David have said.
> Firstly, I underestimated the importance of the plaster on the cool side.
> When we applied it I was unaware of it's function regarding a fire on the
> opposite side. So it was not as thick as it should have been (only 3/4" and
> slightly less in some places) and not enough chopped straw was added. This
> what caused the crack when the wall was moved into place and coupled to the
> furnace. We had the material on hand and time to patch it but we did not.
> Thus the oxygen took the big suck from the fire and there was our weak spot.
> was a bit of a cliff hanger there at the end. Water did indeed leak out
> near that crack on the cool side during the hose test but Mike the Fire Guy
> seepage doesn't count and gave us a passing grade. I love that guy.
> Matts and Tracy certainly made the right call on the type of earthen
> plaster. We have this beautiful gray clay occuring in some caliche here in
> Texas and it is my favorite for plaster because it is hard and is very crack
> resistent. Since this is present with caliche it has lots of limestome
> aggregate in it. The fire would have exploded that limestome plaster away
> quick time, I believe. In fact, there seems to be some limestome or talc or
> chalk or gypsum particles in the red clay (I have noticed them before but
> given them much thought) and where these white particles were (they seemed
> to be
> no closer than every 12 inches or so) the red plaster had popped off and
> exposed their little white heads.
> So, notes on passing an earth plaster on straw fire test: Plaster the cool
> side well.
> Use a silica clay. And, I think, cobbing the gaps would be better than
> stuffing as it would give more attachment for the plaster.
> Perhaps with a better plaster job on the cool side and cob in the gaps we
> could have gone for the 2 hour test.
> All in all it was a beautiful thang. Thank you Bruce, David, Matts, Ben,
> Bill and both Mikes, Cougar and Nicholas and Kindra and CASBA and the God of
> Hellfire for having a little mercy...heaven knows we need that.
> Frank Meyer
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