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GSBN:re: Exterior cladding question
Chris Magwood wrote:
I'm in the midst of designing a building for the Town of Haliburton,
Ontario, which will provide a new space for a charitable group in which
they will run their food bank and thrift store operations.
One option I'm looking at is the use of compressed earth bricks.
I don't have any doubt that the earth bricks can be used as an exterior
cladding. What I'm wondering is this: If I lay up the bricks as an
exterior load-bearing wall, can I stack the bales directly against this
The issue is permeability. Obviously, the compressed earth bricks are
going to be less permeable than the plaster, based on the thickness (10
inches) and the density. But do you think this will be problematic?
Will the earth bricks be capable of taking up migrating moisture and
letting it go to the outside at a reasonable rate? I'm pretty good at
detailing a bale building by now, so there won't be any gross air
leakage, just what makes it through the plaster. I would treat the
earth bricks with silicate paint,
I'm guessing that non-digest version GSBNers will have responded to this
by now but ...
Quite frankly, I don't think that the potential moisture-related problems
with the straw, but rather, that it will be with the earthen brick.
The unfired clay is probably going to soak up any available moisture like a
super sponge and hang on to it like [insert your politcally-incorrect
If moisture finds its way into the brick, either via from moisture
migration from the interior or from rain wetting on the outside or via
capillary rise from the ground
(or any other number of ways that water seems to have of foiling our
exclude it), then unless we have a drastic change in our Ontario climate
due to Global Warming, it's almost guaranteed that that moisture will
freeze and when it does,
more than likely the brick will spall and otherwise self-destruct.
There is a reason that old Ontario buildings did not use even fired clay
near grade in loadbearing (ie non ventilated/drained) masonry walls.
Typically, there would have been a rusticated stone base extending to a
of 2ft or more above grade before the brick would begin.
Haliburton probably isn't much different than Kanata in that there is no
shortage of stone but there is a scarcity of soil overburden.
It could easily be argued that in Haliburton, stone would be a more
suitable "natural" material, at least for the lowermost two or three feet
of the wall closest to grade, especially if the clay has to be imported.
And if the brick has to be fabricated on-site, it'd be questionable if
there'd be any savings in labour, over stone.
I'd look at doing an insulated sandwich wall, possibly with stone (or
urbanite, modern day locally-harvested "stone") as the outer skin, earthen
brick as the inner skin, with something like Roxul mineral wool in
between, and then start with bales on top of that, preferably
not until a height where the roof overhang ensures that the bale wall and
its earthen brick cladding will not be exposed to rain wetting.
I would be sceptical of the efficacy of a painted-on film (ie silicate
paint) as the only thing keeping the earthen brick dry. I would also
imagine that the earthen block would soak up at least 4x the amount of
chemical sealer than would say, a fired clay brick.
Given that the building is being funded by a charitable group whose
are providing services to cash-challenged parties, it would seem imprudent
those badly needed (for community service) funds and put them into a
material configuration that is iffy in this climate and which is almost
certain to eat more of those scarce funds for ongoing maintenance on a
regular basis (ie re-coating with sealer every five years
or so and repairing frost damage).
~~~ * ~~~
Robert W. Tom
Kanata, Ontario, Canada
(winnow the chaff from my edress in your reply)