Dave Finkelnburg on wed 9 jan 02
Julie,
It is great you are starting on a kiln adventure! Good for you!
Here are my biased thoughts on your project.
First, you write, "....fire brick seems to be preferable to fiber...."
I don't necessarily disagree (I have three brick kilns), but I'd give this a
little more thought. I assume that by fire brick you mean insulating fire
brick (IFB). You surely don't want to make the kiln out of hard brick,
except possibly for some floor brick for wear purposes.
Here are the issues I see with fiber versus IFB.
Mostly, IFB is easy to work with. Anyone can stack brick, you don't
even have to use mortar (it's actually even better not to mortar most of the
time). You can easily cut IFB with a cheap gypsum-board hand saw. Aside
from some dust exposure during construction, use of IFB doesn't have any
health risks. IFB is relatively cheap.
On the other hand, fiber is always more energy efficient than any
insulating fire brick. The fiber weighs less for the same amount of
insulating capacity. Less weight means less mass you have to heat in the
process of doing what you really want--heating your ware.
Fiber kilns can be much more portable than brick kilns, because of the
light weight.
Fiber kilns will cool faster, which can be a real plus if you are short
on time to get a load out of the kiln. If you want slow cooling, you can
always fire down. I get to wait forever plus two-and-a-half days for my
30-cubic foot (stacking space) IFB downdraft kiln to cool to 380-degrees F,
whether I want to or not. :-(
There are two real drawbacks to fiber, in my opinion. One is a health
issue, the other a construction/knowledge issue. Health first. My
understanding is American-made refractory fiber insulations, when fired to
stoneware temperatures, become capable of producing dangerous airborne fiber
particles. I hear that a new fiber in Europe may solve this problem. Until
I am certain this is not a health issue, I will not use fiber in a hot-face
application in my own kiln. Where I have used fiber (on top of my 4.5-inch
sprung arch), I have encapsulated it with sodium silicate to prevent fiber
dust from blowing around. NOTE: fiber outside a layer of IFB is not the
health concern I am worried about. Such outside fiber doesn't get much
hotter than 1,000-degrees F, probably a lot less.
The second issue is plugging all the holes between the inside of the
kiln and the outside, when only fiber is the kiln lining. It helps if you
can find someone who understands how to work with fiber. Fiber shrinks
during firing. The shrinkage is permanent. The solution is to seriously
compress the fiber before using it. Feriz Delkic, among others, sells
already compressed ceramic fiber "modules" for kiln use. I believe Mel
Jacobson compresses ceramic fiber by driving on it with a car. Some use a
hydraulic jack. You get the idea--this is a construction issue.
Hank Murrow has a wonderful fiber kiln design. It's the best I've seen.
It's also a bit more complicated to build than dry stacking IFB.
In my opinion fiber is the best kiln material, really state of the art,
but it takes planning, knowledge, and money to build a really good, safe
fiber kiln.
By the way, when you get "The Art of Firing," pay special attention to
Nils' comments on flue dimensions. He has it right. Often exit flues in
gas kilns are seriously oversized, which makes the damper hard to control.
Good luck with your project!
Dave Finkelnburg, just in from shutting off the burners on a
beautiful winter night in Idaho
From: Julie Milazzo
>Hey everyone, I'm writing to hopefully get some information on building a
>gas kiln
Cindi Anderson on thu 10 jan 02
Thanks for your information, but your two statements seem conflicting to me.
Can you explain this more?
If fiber is more energy efficient, then it should cool slower. But maybe it
is like the difference between thermal mass and insulation. A log house for
example is lower in "insulation" but since it has "thermal mass" it is
actually net more energy efficient. Is that what you're saying here?
Does everyone concur that fiber cools fast? And if that is true, does it
cool too fast?
Thanks
Cindi
Fremont, CA
----- Original Message -----
From: "Dave Finkelnburg"
To:
Sent: Wednesday, January 09, 2002 9:01 PM
Subject: Re: building a gas kiln---Long
> On the other hand, fiber is always more energy efficient than any
> insulating fire brick. The fiber weighs less for the same amount of
> insulating capacity. Less weight means less mass you have to heat in the
> process of doing what you really want--heating your ware.
> Fiber kilns will cool faster, which can be a real plus if you are
short
> on time to get a load out of the kiln. If you want slow cooling, you can
> always fire down. I get to wait forever plus two-and-a-half days for my
> 30-cubic foot (stacking space) IFB downdraft kiln to cool to 380-degrees
F,
> whether I want to or not. :-(
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