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GSBN:Exterior cladding question



Hello all,

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. It's a great
project, as the building has an honourable end use and will be located
right in the centre of the town, next to the art gallery and a park.
They are also keen to make it as sustainable as possible.

One of the requests of the town council is that the building be
designed to "fit in" with the existing local architecture. The art
gallery used to be a train station, so it's a nice building to echo.
But part of fitting in in this part of Ontario is a having a brick
finish. I've done some brick and stone facades in front of bale walls
before, but I'd rather not do them again.

One option I'm looking at is the use of compressed earth bricks. I had
a chance to see them being produced and even to lay some up during the
ISBBC in Denmark this summer. A local builder has recently purchased
one of these machines, and I've already decided to use them in the
floor.

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
wall? I'm a convert of the Tom Rijven school of dipping bales in clay
slip, so I would dip the back side of the bale and press it against the
earth bricks, then give the interior the usual coat of earth plaster.

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, which shouldn't hamper the
transpiring of moisture much.

I don't really want to do a typical brick veneer with an air space
between the bales and the bricks. Having done it before, I know that
it's nigh on impossible to maintain an even air space with a bale wall
unless you get into using wooden spacers or other material and time
intensive fixes. It seems to me that a patchwork of air gaps surrounded
by bales contacting the bricks would be worse than no air space at all.
So my option is use the bricks, or don't use any cladding and just make
the exterior plaster nice and square.

Let me know what you think...

Chris