[GSBN] Expanded Perlite as under-floor insulation (was Re: Question about SB insulation at foundation/ceiling GSBN Digest, Vol 10, Issue 29)

[RT]

> Date: Tue, 24 Jan 2012 20:17:21 +0100
> From: "forum at lamaisonenpaille.com" <forum at lamaisonenpaille.com> a ecrit:
>
> Le 24/01/2012 19:10, Laura Bartels a ecrit :

>> perlite was tamped, finishing at 7" for an R-value of 21.9.

I don't have any experience with expanded Perlite other than the stuff  
that comes in small plastic bags, used for creating soil mixtures for  
houseplants.

I'm guessing that that stuff would be typical of uncompacted expanded  
Perlite in general (ie density ~ 32 to 64 kg/m^3 (~2 to 4 lbs/ft^3), quite  
friable /hydrophilic .

In order to achieve an R-value of 21.9 for a 7 inch thickness, the Perlite  
would need to be compacted to a density of ~ 5.5 lbs/ft^3  (a guesstimate  
based on the values listed in the ASHRAE Handbook of Fundamentals -- R-  
3.3 to 2.8 for densities 4.1 to 7.4 pcf).

In order to overcome the hydrophylic tendencies of expanded Perlite and  
make it suitable for use as below-grade insulation, I know that a  
"treated" version is available, presumably in the form of some sort of  
silicone-type coating to seal the porous surface of the granules.

Wouldn't compaction (by what looks like somewhere around a half) result in  
breaking-down of the friable granules, thereby exposing the unsealed cores  
and rendering them able once again to suck up and hold onto moisture,  
thereby reducing if not negating their value as thermal insulation ?

I remember YakWoman (aka Kelly Lerner, a (Year of the) Dragon lady)  
mentioning that the Perlite might be left in the bags in which it is  
supplied in order to gain some protection from wetting.

I'm not entirely convinced of the feasibility of such (ie I would imagine  
that it'd be difficult to maintain the integrity of the bags during the  
compaction process, not to mention during shipping & handling) but then  
again, no one (including myself) has really tried to convince me.

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

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