Interesting. I've never really thought about it,
but I thought that the principle of the cavity wall (in cavity brickwork) was
primarily to allow any liquid water that penetrated through the external skin
of brickwork moisture to run down the inside face of the outer skin, onto the
flashing at the base of the cavity, and then drain out through the weepholes in
perpends in the brickwork.
I can see how the cavity would also facilitate air
circulation, which would promote drying out of the inside face of the outer
skin of the brickwork, which would further improve the performance of a cavity
wall (over the traditional solid masonry wall) with regards to moisture content
and dampness.
Putting aside the question of placing insulation into
the cavity, the reason for the cavity in the first place is a classic example of
the way we 'lose' knowledge over time. Where is the primary source that
explains to us the rationale behind development of the cavity wall, as
contemplated by the people who actually developed the cavity wall principle?
I encounter this conundrum regularly in the course of
my work - current favourites include:
·
A belief that you should never use
acid in any form on sandstone … in a city where there is substantial
anecdotal evidence that for several decades, all sandstone buildings were
washed down with dilute hydrochloric acid upon completion … I have been
able to trace back one source of the belief that acid should not be used to a
100 word comment article in a South African trade publication which talked
about the damage caused by acid washing of a sandstone building … reading
between the lines, my guess is that the acid in question was hydrofluoric,
which of course will have a disastrous effect on any quartz-containing
material.
·
A belief that all stone-faced
precast concrete cladding panels will fail if there is no grommet around the
fixing clips between the stone and the concrete (due to differential thermal and
moisture-induced movements)… which dates back to the first mention of
this method of fixing stone veneer facing to precast concrete in a version of
the Precast Concrete Design Manual dating from the early 1990s … the
genesis of which does not appear to be based on any published research, but on
the opinion of a single individual.
So, to return to the original question about the
insulation – there are two paradigms to be questioned:
a)
Should we fill the cavity space in
a cavity masonry wall with insulation?
b)
Is “Insulsmart” a
suitable material for use as injected insulation i.e. will it perform
adequately without adverse effects on the surrounding historic fabric?
My reading of the collective wisdom proffered to date
is that we haven’t adequately answered the first question, although
consensus appears to be that we shouldn’t fill the cavity; and that we
don’t think “Insulsmart” is a suitable material for the
proposed use due to known problems with injected foam materials, and the
potential fire hazard …
Time to get back to fee-paying work.
Cheers
David West
Executive Director
internationalconservationservices
T: +61 (2) 9417 3311
M: +61 (411) 692 696
W: www.icssydney.com
sustaining your heritage
-----Original Message-----
From: The listserv where the buildings do the talking
[mailto:[log in to unmask]] On Behalf Of deb bledsoe
Sent: Thursday, 21 January 2010 9:06 AM
To: [log in to unmask]
Subject: Re: [BP] insulsmart
I went and read the msds, specs, etc. Supposedly
non-toxic in a fire.
Material is not an irritant, you can get it on your
skin while applying.
Should not breathe the dust from cutting it. Duh.
I just remember so many stories from some ancient
thread about
completely screwing up a masonry/plaster cavity wall
by filling it.
Dewpoint in the wall changes and water builds up
inside or outside the
foam (or other insulating material) and causes issues
with the plaster,
the masonry or the foam itself, in breakdown of the
materials and/or
growth of mold.
There is supposed to be air circulating in a cavity
wall.
~deb
Jim Follett wrote:
>
> What about fire issues?
>
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