[Greenbuilding] Cob as an alternative to spray foam sealant?

RT ArchiLogic at yahoo.ca
Thu Jan 27 16:52:54 CST 2011


On Wed, 26 Jan 2011 17:15:22 -0500, Steve <steve at greengeek.ca> wrote:

>  clay slip/perlite
> mixture sprayed into wall cavities like gunnite or shotcrete, anyone
> know if this has ever been attempted?
>
> I know it wouldn't be nearly as airtight or as insulating as spray
> foam, but it would be better than nothing and still completely
> biodegradable. :)
[snip]

( For full text of this message/thread, see:

http://lists.bioenergylists.org/pipermail/greenbuilding_lists.bioenergylists.org/2011-January/000737.html      
)


I see a ".ca" in the "greengeek" edress so I going to ass-u-me that we're  
talking a MooseLand locale ?

And if that assumption is accurate-  just wondering: Where in Canada are  
there naturally-occurring perlite deposits ?
(And "no" I don't think that the "insulation" or "plastering supplies"  
aisles at the nearest Home Despot qualify)

ie Does it make Green sense to import a "natural" (if being  
mined/pulverised/packaged/transported by massive machinery qualify it as  
"natural")  thousands of kilometers and across international borders just  
so that one can say that an insulation is "bio-degradable" ?

Not only that, the resultant mixture likely wouldn't even provide the  
minimum R-values for a wall as required by the Codes (assuming that the  
cavity is standard 2x4 or 2x6  wood-frame construction) and would not seal  
very well once it has dried and shrunk away from the framing.

So I have to wonder: "Why bother ?"  ... knowing that here in Canada, a  
more readily-available, lower environmental  impact, plentiful, "natural",  
bio-degradable, blow-able "waste" material with about the same or better  
insulation value as perlite (depending upon density of the form of perlite  
used) exists.  (Sawdust, chopped straw or even chopped up recycled  
newsprint etc  )

and re: Cob as caulking

I'm also wondering what specific sorts of "cracks" are being contemplated  
as candidates for "cob-as-caulking /sealant" ?

Given that the insulating value (such as it is ... see chart below) is due  
entirely to the straw component, we'd be talking large, dog-turd-sized  
gobs of straw/clay material being used in an attempt to "seal" the cracks.

I would venture that if a crack in the cladding or interior finish surface  
is so humongous that one would be trying to cram a dog turd-sized gob into  
it, then that "crack" requires more attention than just caulking.


====================================================
This is the chart below:

Density      Conductivity	R-value
(kg/m^3)		(W/mK)       per inch, Murrican units.

300			0.1			1.44
2100			1.4			0.103


(i) straw coated to point where it is *just* covered then form tamped
    (ie: cavity wall fill - 40 pcf  (~641 kg/m^3))

(ii) straw just covered then lightly placed
       (ie ceiling insulation -  20 pcf (~320 kg/m^3))

(iii) straw just covered, then same amount of additional clay slip added  
then form tamped
      ( ie high mass wall - 70 pcf (~1122 kg/m^3)			


Conductivity values for densities ranging from 300 -2100 kg/m^3 excerpted  
 from chart in
Gernot Minke's "Lehmbau-Handbuch" (with values in 100 kg increments  
between 300 and 2100 kg omitted for the sake of brevity. It's pretty much  
a straight-line curve between the two).

The "typical" straw'clay mix densities were provided by John Cruikshank,  
inventor of the "Sunny John"

		http://www.sunnyjohn.com/toiletpapers2.htm

I've done the arithmetic to convert the metric units for density and  
conductivity to R-values & Imperial units.
============ End of this is the chart below ========

-- 
=== * ===
Rob Tom
Kanata, Ontario, Canada
< A r c h i L o g i c  at  Y a h o o  dot  c a >
manually winnow the chaff from my edress if you hit "reply"
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