Bristol Studio
Kiln Construction
Noborigama 250 |
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This kiln was built during 2002-2004.
It is the fourth wood fired kiln built by Robert at his pottery.
Learning from previous experiences,
he designed this kiln with several goals in mind. |
Firebox is at the far right.
The middle chamber is for glazed ware and the
last chamber for salt glazing. The total
volume is 400 cu ft., loading area is 250 cu ft. |
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The Design 1. Interior height 7 ft. falling off to
4 ft. at
the sides.
To allow standing upright when loading & prevent back
strain.
2. Interior side walls, straight for first four feet.
To increase volume and prevent awkwardness of stacking
a catenary shape.
3. Built around the size of 2 ft. square kiln shelves.
Staking pattern of 2 shelves wide by three shelves
deep, 4 ft. x 6 ft.
4. Firebox feed ports built chest high.
To allow stoking without bending over.
5. Loading area over 250 cu ft.
Allows for plenty of room for production ware in quantity,
approximately
1400 pieces. While permitting a dozen oversize pots on
top.
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Bricks were laid using a mixture of sand and
fireclay.
The ratio was changed, as needed, to permit a thin or thick bed for the
brick. |
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Bricks were purchased when they were most affordable. About 10,000
bricks were used building this design. These pallets of bricks sat for
years next to the studio. |
Kiln Construction
More information on this kiln can been seen at
Firing Photos |
Flues have
cut bricks on the visible face,
a "castable" refractory is used to fill in the remainder
to save time cutting bricks to shape. |
The kiln is 21 feet long with over 250 cubic foot of loading area.
There are 19 arches.
9 flues, 4 doors, 3 chambers, and 6 over feed ports & stoke holes.
Making arches over flues, cleanouts &
feed ports is not strictly necessary,
as a flat lintel would suffice.
However, building a kiln that was pleasing to the eye as well as functional,
meant putting extra effort into building these arches.
The salt chamber has the largest
single arch at 8 ft.
deep,
with a 3 ft. rise and 7 ft. span.
The chimney is 20 ft tall.
There are over
10,000 bricks
incorporated in the structure. |
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The "Salt" chamber, right, is
stepped up 16 inches from
its firebox floor. The small arch, in the front center of the photo,
is a clean-out for
the firebox of the salt chamber. |
The Kiln is 21 feet from firebox to the back wall of
salt chamber.
In the fore ground is the firebox outline. |
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| Mini-Arched "air intakes" of Firebox. |
Air intakes for Firebox line up with rows
of bricks
that support the grated firebox floor. |
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| Grated floor allows air to come in under
the entire firebox. |
Building a Noborigama, rather than an Anagama,
requires more brick and time to construct.
However the results Robert seeks
are best achieved with this style
Kiln.. |
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Determining the shape of a Catenary arch is
done by
hang a chain
(this is a "bead chain" like the ones used for pull cords on lamps).
The
shape of the arch is transferred to plywood by spraying paint over the chain to leave
its shadow.
The form can then be cut out and serve as the pattern for the arch. |
Plywood panels, with 2 x 4 struts, are covered with masonite,
making a very strong form.
The arch form Robert built was 1/3 shorter than the depth of the kiln,
this make the arch more maneuverable.
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The form is raised 3/4 inch higher than
side walls using wooden shims.
When all the arch bricks are in place the
form is released,
thus
"Throwing" the arch. |
The arch is then free standing and the form can be removed.
The form is
then shifted, re-shimmed, bricked over and
" thrown" several more times to create the full depth.
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A bonded arch
means bricks are set in a staggered pattern.
In this photo, temporary bricks hold the end of the bonded arch,
until
the form is shifted and the arch is continued. |
Arch bricks are laid with a thin coat of
fireclay to even out irregularities. |
Kiln Construction
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Robert standing under the glaze chamber arch, before a
secondary door arch was installed.
This design creates straight walls for the doorway which makes bricking in the door an easy task.
The doors (when bricked in) are 13" thick and use I.F.B.*, these light
bricks are easy to handle.
I.F.B. have a shorter life then hard brick, but their insulation value, and
ease of replacement made them worthwhile in the doors.
Exterior walls are 3 brick deep (13.5 " thick).
The hot face interior has super duty firebrick.
The middle (core) is composed of I.F.B.
The exterior layer is make of old, previously used, firebricks.
* I.F.B. = Insulating Fire Brick, a porous, light brick, with high
insulation value. |
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A facer coarse of arch bricks on top of the
firebrick arch.
Insulation blanket and cement will flush out to the top of facer
bricks. |
Each arch is comprised of a coarse of Super Duty
Firebrick, backed with 2 inches of 2300F fiber blanket and 1 inch of
insulating mineral board.
For lateral strength and protection, 2 inches of
cement is applied with block wire reinforcement. The cement was mixed
with red art clay, for color. |
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Fitting cut bricks to "die" into
curve of the throat arch.
Construction of arches is
not a complex procedure but is time consuming. |
A diamond blade on a wet saw is used to cut fire
bricks. |
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Cement blocks are used to raise the level of the Chimney
foundation
to be level with the exit flues from the salt chamber. |
A mixture of concrete was used to sheath the
exit tube
protecting it from the weather. |
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Three exit flues from the salt chamber
converge into the chimney.
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A round chimney is not difficult to
construct.
This design makes a wedge shape void on the exterior,
which is filled with
concrete.
The mortar between bricks was strictly fireclay. |
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| The exit flue tube is bricked over, and a layer of
insulation blanket and metal reinforcing mesh is applied before coating with
cement. |
Working alone, Robert was able to increase the
height of the chimney,
at a rate of 4 feet a day. |
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It should be noted that a round chimney of
the same diameter
as a square chimney, while having less total cross section, is just as efficient.
The corners of a square chimney (while increasing the over all volume)
do not assist the draft.
Flue gases spiral up in a circular motion, therefore a round chimney is
encompasses the volume in the most geometric manner. |
The chimney is topped off at 20 ft,
it has an interior
diameter
tapering from 28" at base to 18" at the top. |
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Robert Compton Pottery
2662 North 116 Road, Bristol,
Vermont 05443, U.S.A.
Phone: 802-453-3778
E-mail: Robert & Christine
04/17/08
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