[GSBN] penetration of plaster in bales...

Mon Oct 26 19:04:42 UTC 2009

 I'm just back from the colloquium in Oregon where I had very limited access to the internet or phone. Someone mentioned to me at the colloquium that I had been quoted as saying that earthen plaster could be sprayed two inches deep into bales - or something like that...and I couldn't recall having said that...but who knows, I've said a lot of things over a lot of years. Perhaps this is the reference that was being referred to here. 

About the testing at Oak Ridge National Laboratory (ORNL) that I was involved with, I can describe a few things about the wall and the results. First, the plaster was a cement, lime, sand mix the exact proportions of which I don't remember off the top of my head. I could conceivably have that in my notes from back then - though I haven't any time to look for them as I leave in the morning for a week and a half in Baltimore for code change hearings and more. The more relevant information was that the plaster was applied with gunite machine - used for building swimming pools and stabilizing embankments, etc. - which blew the mix on with more force than most stucco machines I've had experience with. This resulted in penetration of the plaster into the bales greater than usual, based on simple observation at the time. I did not measure it, but my memory is that it was on the order of 1-1/2 to 2 inches deep. This led me to think about whether the depth of the fully insulative part of the bale wall was reduced by perhaps as much as 3 or 4 inches. 

Also, I recall that these bales were fairly typical 2-string wheat straw bales, that were laid flat in the wall panel. We were pretty careful in building this wall, though I don't think any more than most conscientious bale builders are. We weighed and measured each bale and recorded the moisture content using our old Delmhorst BH1 meter. I remember that the bales were actually closer to 19 inches wide than the more typical 18 inches - and this was noted and considered in the calculation of R-value for the tested panel. 

We did, in fact, compact them as much as we could by stomping around a bit on them as we went up. We also were thorough about stuffing the gaps, but I don't think we used the now more common practice of stuffing the gaps between bales with loose straw and then capping that with a cob-like mix of straw and clay. Then the completed wall panel was stored at the lab for a long enough period of time for it to dry out - I can't recall exactly how many months it was but it was an agreed upon time that we felt would give the plaster time to cure and the moisture to approach equilibrium.  

The other point that I make over and over when I talk about this test is that at the time this test was done, this was the most advanced whole wall or roof assembly testing facility in the US. And the result of this test showed that in practice, this bale wall system was almost exactly twice the tested (in the same facility with the same criteria) steady-state R-value of a 2x6 wood frame wall with fiberglass insulation (as perfectly installed as possible, since it was built by the insulation manufacturer). In other words, this straw wall panel provided twice the insulation value of what was considered at the time to be the best standard practice "high" insulation wood frame wall. If my guess about the actual thickness of the straw-only part of the wall thickness is accurate, then the approximately  R-27 (I have not looked this up to see what the exact number was) might have actually been for 15 or 16 inches of straw, not 19 which was the number used to come up with the R-value per inch. Which was the point that I was probably trying to make when I uttered whatever it was that led to this whole conversation in the first place.

Hope that helps.

David - trying to remember what I said - Eisenberg

-----Original Message-----
From: caroline meyer white <fredmeyer8 at yahoo.com>
To:  with public archives) Global Straw Building Network(private <GSBN at greenbuilder.com>
Sent: Mon, Oct 26, 2009 10:14 am
Subject: Re: [GSBN] penetration of plaster in bales...

Your questions are exactly something I am about to do a little bit of testing on, here in Bath. I have been reading through what they had available of thesis's and dissertations on loadbearing straw. Everyone, except the Germans presenting at ESBG has done there testing on plastered straw, and yes, it is obvious that the strength and stifness of the plaster is governing the performance. Since most of the work has been done in Canada or the US, it was either lime/lime-cement/cement plaster, and with our fancying clay?clay-lime plaster in Denmark, I am still looking for more on that. 

But the question that was raised here, was then, what about the connection between the plaster and the straw, both initially, but also over time.. If the lower part of the wall had minor moisture damage, and say, the connection weakened over time, and therefore after some years you wouldn't have that strength as depending up on.

So we are making a few tests where we have different degrees of connection between straw and render, to see what results that will bring. 

In doing this little literature read-up, I thought about making a website or some other point of sharing research documents, -those which would be interested in offering it of course, so that when we need to see what has actually already been done, and what did they come up with, we could first go and have a look there.. A lot of the questions that are arising have already been answered.

Cheers

Caroline

Caroline Meyer White 

Friland 23 
8410 Rønde 
tlf + 45 40 76 1980 

New email which I am changing to: hojtpaastraa at gmail.com 

Kender du: engodsag.dk ? 

Eller paksbab.org ?

--- On Thu, 10/15/09, MattsMyhrman at aol.com <MattsMyhrman at aol.com> wrote:

From: MattsMyhrman at aol.com <MattsMyhrman at aol.com>
Subject: Re: [GSBN] penetration of plaster in bales...
To: GSBN at greenbuilder.com
Date: Thursday, October 15, 2009, 6:58 PM

In a message dated 10/14/09 1:02:13 PM, contact at lamaisonenpaille.com writes:

- some plastering techniques are able to shoot plaster up to 5 cm (2'')
into a dense bale wall as David Eisenberg told me was done for the wall
made for the thermal testing at Oak Ridge.

David needs to tell us more about the test wall.  I remember hearing that in some way or other it was poorly constructed.  For example, were the bales really dense?  Was each course settled into place by having some sturdy people stomp along the wall?  Was the penetration really this deep, and if so, was it only at the spots where the rounded ends of two bales butt up against each other, i.e., the holes that are usually stuffed with straw to prevent thermal
 nose-bleeding?

Matts (Butt What About...) Myhrman    

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