Chris Trabka on tue 27 jul 04
And the Lessons Continue
Kiln Building 101, 201.
Moving from California to Michigan (1996), I decided that I would not move
the kiln; I would build one. Clayart responses directed me to Nils Lou=92s
then out-of-print book on a Minnesota Flat Top kiln. Through the inter-
library loan system I was able to get it. I made a few changes to the basic
design. Instead of two forced air burners, I opted for 12 venturi burners
(six per side). I prefer simple systems. My glazes are high reduction
copper reds, celedons, and rutile blues =96 they do not re-fire. And the
electricity does go out at the worst possible time (lost it several times
during a firing).
The modified kiln plan was created on graph paper. A steel structure would
support the sides of the kiln would so the venturi burners could be
positioned under the kiln (firing up into the chamber). Steel was purchased
to specification, and a welder was hired. He welded up the supports for the
walls, the car and the angle brackets for the roof =96 it took a day. During=
the following week the kiln was built. The welder returned to =93finish=94;
welding the corner braces onto the frame and the support for the top of the
door.
After seven years of use the kiln started showing signs of use and a rookie
kiln builder. It was time to make some =91minor=92 repairs. Some of the bric=
ks
in the roof had broken and were crumbling. The bricks on the walls near the
door were all broken, and it was time to =91fix=92 a few other issues.
The Oxyprobe was removed and put in a safe place. A wooden frame to support
the roof was built. The roof was raised off the walls using a car jack; it
was only necessary to raise it two-inches. It was time to =93de-stack=94 the=
walls (and sort broken and whole brick). At the end of the day, it was
different to see the roof of the kiln supported by wood, the chimney but no
walls or door.
One of the changes I made was to increase the number of bricks that connect
the interior walls with the exterior walls. The first time I built the
kiln, I had only connected the walls about half way up. Some separation
between the two walls had developed =96 most noticeable near the top. This
time each course would have some bricks that connected the inside wall and
the outside wall.
The =93re-stacking=94 started. I was able to reuse many of the broken bricks=
when a partial brick was required (I sacrificed a $20.00 =93pull saw=94 to c=
ut
the bricks). In the process, I was able to see the effects of ITC100 on
the bricks. The ITC100 seemed to =93penetrate=94 about four-inches into the
brick. Where the brick had contact with the ITC100, the brick seemed harder
and more durable.
After the walls were restacked, the door was rebuilt. This time I used a
50/50 mixture of fireclay and sand between the bricks on the door.
Hopefully the bricks will not separate or break as much as they did on
the =93old=94 kiln.
A =93gasket=94 of fiber was put on top of the walls and the roof was lowered=
onto the walls. The first three rows of the roof needed replacing (I
had =91over-tightened=92 the bolts holding the bricks in place and some of t=
he
bricks at the corners had been crushed). The bolts on the rods keeping the
roof in compression the roof were loosened. The damaged bricks on the first
three rows were removed and replaced. The rods were put back in place and
tightened. The roof was again a solid structure but it was not aligned to
the front walls of the kiln. To properly shut and seal the door the front
of the roof and the front walls needed to be aligned. The =93new=94 roof was=
raised off the walls. Using some ropes and pulleys it was coaxed into
alignment. After saying =93close enough=94 I used a grinding stone on the
bricks to =93shave=94 a little bit of the roof (so the door would fit better=
).
A gallon of ITC100 arrived the next week and it was sprayed on the =93new=94=
kiln (per instructions; first moisten the bricks by sprayed 5 gallons of
water on them; next thin out the ITC100 with water; finally spray the
inside of the kiln). After a week of waiting for the kiln to =93dry=94 out
(it=92s Michigan, it=92s summer, it=92s humid =96 I could have waited three
months); it was time to force things a little. With just the pilot lights I
warmed the inside to about 300 and kept it there for a full day. After it
cooled, I felt the inside it was still damp! Using the main burners (all
12) set to very low I raised the temp to about 500 and then let it cool.
Finally things started to dry out.
The kiln was loaded for a glaze firing, the main burners were set to candle
overnight. The next morning the kiln was 500F. By noon the temp was at
1200F. Started the normal reduction firing cycle. By 5:00pm I noticed this
firing was going to run a bit on the long side. At 10:30pm cone 10 fell and
all was shut down. Now the wait =96 every 12 hours the temperature drops by
half (based on the numbers on the Oxyprobe). Four days later I can open.
The firing was great; all the glazes looked the same as the last firing of
the =91old=92 kiln.
What would I change in the design; having built it twice:
I would increase the size of the steel on the corners, the book says to use
2-inch, I would increase it to 3-inch.
I would add some steel onto the sides of the door to reduce the side-to-
side movement in the bricks during the firing/cooling cycles.
I would consider widening the door to span the entire width of the kiln and
eliminate the partial walls that float free.
I would consider placing a sheet of steel between the rods and brick in the
roof. The outside rows of brick started to push into the rods (and break)
after some years of use.
What would I not change in the design:
The car =96 it is so much easier to load and unload than my prior kiln that
had a door.
The venturi burner system =96 it is simple and the temperature is even top t=
o
bottom front to back.
The =91flat=92 roof =96 there will be/has been much said about the virtues o=
f an
arch. I doubt that an =91arched=92 roofed kiln was be as easy to =91fix=92 a=
s my
flat roofed one.
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