Jeff Abney on mon 6 dec 10
I'm building a propane downdraft kiln (approx. stacking space 25 cu.
ft.) using a plan by Graham Sheehan. The kiln is built from soft brick
(IFB), but as I prepare to build the chimney, I have a mix of soft and
hard fire brick that I'd like to be able to use. I know that I don't
want to put soft brick above the level of the kiln shed roof, and I
have been advised by a knowledgeable person to build the entire
chimney from hard brick (which will add a lot to my cost.) The plans
call for soft brick at the base of the chimney, and then "any kind of
brick" higher up on the chimney. In the kiln plan and accompanying
video Sheehan even uses some common red brick on the higher parts of
the chimney where heat isn't such a factor. I have been told, however,
that I should not put hard brick on top of soft brick. Is this an
absolute disaster waiting to happen, or can I safely build the hot
part of the chimney from soft brick and then use hard brick (or even
some red brick) to finish off the chimney above the roof? Any help
appreciated!
Jeff in Georgia
Michael Wendt on tue 7 dec 10
Jeff,
I found I could build thinner walled structures with IFBs by
standing them
up on edge. Why not a chimney this way?
The dimensions of the brick lying flat are:
9" l x 4.5" w x 2.5" h. so this requires 10 layers to
create 25"
of chimney height.
In contrast, using them on dege requires 6 layers 4.5" high
to
create 27" of chimney height.
Assume you want a flue close to 9" x 9" insude dimension.
I would lay the bricks up like this:
=3D=3D =3D
ll ll
=3D=3D =3D
where the =3D=3D represents a single brick on edge crosswise.
ll represents a single brick on edge 90 degrees to the =3D=3D
=3D represents a single brick stood up vertically tying two
rows together.
I usually rout shallow 1/4 " lands into the edges of the
long wall bricks
so that I can run screw type hose clamps around the unit to
hold it
together.
These become 9" tall brick modules you can stack easily to
any height.
Each module requires 10 bricks and creates a 8.5" x 8.5"
(72.25"^2)
internal cross section that is utterly air tight and very
well insulated.
I would finsh the installation by bracketing the chimney on
all 4 corners
with 1" x 1" x 1/8" angle iron clamped every few feet with a
hose clamp.
If this would work for you, I highly recommend it.
regards,
Michael Wendt
Brandon Phillips on tue 7 dec 10
I built my stack above the dampers with the brick on edge. I used
fireplace brick from local brick supplier(cheap.) I mortared them with a
fireclay/grog mixture which has held up just fine, no spreading or gaps.
Could easily be done with soft brick as well. I used soft brick on the
top part of a stack on an old kiln awhile back, it held up just fine.
Still using those brick in my current kiln. Here is a link to photos of
my stack. http://supportyourlocalpotter.blogspot.com/2009/02/stack.html
Brandon Phillips
supportyourlocalpotter.blogspot.com
> I found I could build thinner walled structures with IFBs by
> standing them
> up on edge. Why not a chimney this way?
> The dimensions of the brick lying flat are:
> 9" l x 4.5" w x 2.5" h. so this requires 10 layers to
> create 25"
> of chimney height.
>
> In contrast, using them on dege requires 6 layers 4.5" high
> to
> create 27" of chimney height.
> Assume you want a flue close to 9" x 9" insude dimension.
> I would lay the bricks up like this:
Steve Mills on wed 8 dec 10
I regularly use house brick for the upper part of a Kiln Chimney where I ca=
n=3D
't use metal tube.=3D20
Here in the UK house brick is usually well loaded with sand, and fired to a=
b=3D
out 1100oC, so is well able to handle Chimney temperatures and heat shock. =
M=3D
y Ash Cooker is also house brick and as sound as a bell after a lot of use!
In your case I would use Hards to Kiln roof level and House brick from then=
o=3D
n, just remember Chimneys need bracing like a Kiln does!
Steve M
Steve Mills
Bath
UK
On 7 Dec 2010, at 03:54, Jeff Abney wrote:
> I'm building a propane downdraft kiln (approx. stacking space 25 cu.
> ft.) using a plan by Graham Sheehan. The kiln is built from soft brick
> (IFB), but as I prepare to build the chimney, I have a mix of soft and
> hard fire brick that I'd like to be able to use. I know that I don't
> want to put soft brick above the level of the kiln shed roof, and I
> have been advised by a knowledgeable person to build the entire
> chimney from hard brick (which will add a lot to my cost.) The plans
> call for soft brick at the base of the chimney, and then "any kind of
> brick" higher up on the chimney. In the kiln plan and accompanying
> video Sheehan even uses some common red brick on the higher parts of
> the chimney where heat isn't such a factor. I have been told, however,
> that I should not put hard brick on top of soft brick. Is this an
> absolute disaster waiting to happen, or can I safely build the hot
> part of the chimney from soft brick and then use hard brick (or even
> some red brick) to finish off the chimney above the roof? Any help
> appreciated!
> Jeff in Georgia
David Finkelnburg on wed 8 dec 10
Jeff,
You don't say which soft brick (IFB) you are using, nor how you will
stack it, nor how high the hard brick would be above it. All this
information is necessary to answer your question for certain. If you work
out the weight of the column of brick above the bottom IFB, and the
horizontal area of the IFB, you can do the arithmetic and see if your IFB
would be overloaded.
In general, though, the compressive strength of IFB is about 1.5 MPa so
say 217 pounds/square inch (psi). If your bottom course is four IFB each 9=
"
x 4.5" on the flat side, they have a horizontal area of 162 square inches.
That times 217 psi shows they will, in theory, support a stack that weighs
not more than 35,154 pounds. A structural engineer (and your building
inspector) would allow for wind load and earthquakes, passing trucks and
other sources of ground vibration. I am NOT a structural engineer.
However, dense firebrick weighs between 120 and 140 pounds/cubic foot.
Four firebrick at 140 pcf, also 9x4.5, stacked 20 feet high =3D 22.5 cubic
feet and weigh 3,150 pounds. Mortar is less dense so it can be ignored.
Btw, I ran hard brick from the kiln pad up because that's what I had
available (free). I ran light angle up all four corners of the stack and
welded strap to tie the corners together, though loose enough to allow for
thermal expansion of the brick.
Good firing!
Dave Finkelnburg
http://www.mattanddavesclays.com
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