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2.5" kiln wall?

updated sat 24 nov 01


Lajos Kamocsay on wed 21 nov 01


I'm reading Olsen's Kiln book. The thinnest wall he's talking about is =
4.5". Is a 2.5" wall made from soft insulating brick too thin? If I look =
at Aim and Olympic 7 cu ft gas kilns, those have 2.5" walls.
I'm thinking about builing a small gas kiln, ~7 cu ft. I was planning on =
using fiber insulation over a 2.5" wall. Can it be done?


Dave Finkelnburg on thu 22 nov 01

As you say, Olympic (among others) has built kilns with a 2.5-inch IFB
wall, so obviously it can be done. Is it a good idea? Only, in my very
biased opinion, if you add fiber or some other material outside, as you have
suggested you will.
It is possible to predict the outside wall temperature of the IFB with
fiber over it, which will indicate the maximum temperature the fiber will be
exposed to. If you want, you can E-mail to me off list the maximum
temperature you intend to ever fire to (will be higher than cone 10) and
I'll try to make that calculation for you with the brick software I have.
Good potting!
Dave Finkelnburg in, thankfully, rainy Idaho

From: Lajos Kamocsay
I'm thinking about builing a small gas kiln, ~7 cu ft. I was planning on
using fiber insulation over a 2.5" wall. Can it be done?

vince pitelka on thu 22 nov 01

Lajos -
I think that a 2.5" wall is a bad idea under any circumstances, especially
in a homemade kiln. I don't even like to see it in commercial low-fire and
midrange toploader kilns, but the reason it works in that situation is
because they are round, and the outer stainless steel shell clamps the
bricks together, maintaining a tight wall.

I do not remember whether your original post specified a round or
rectangular kiln. If you are building a round kiln like the standard
toploader, with some sort of outer shell clamping everything together, I
suppose you could make this work. But if you are building a rectangular
kiln, stacking the bricks in a normal offset fashion with staggered
stretcher courses, but on edge (giving 2.5" wall thickness), the wall will
have very little stability, and will likely break down over time from normal
expansion and contraction. When you lay bricks flat giving a minimum of
4.5" wall thickness, you get a very stable, locked wall.

You will not save very much money by going for a 2.5" wall. Pay a little
more and use a 4.5" wall with the fiber on the outside, and have a stable,
long-lasting kiln. For greatest stability, I recommend you use 1"
fiberboard, with a sheet metal shell on the exterior to prevent abrasion and
relase of fibers.
Best wishes -
- Vince

Vince Pitelka
Appalachian Center for Crafts
Tennessee Technological University
1560 Craft Center Drive, Smithville TN 37166
Home -
Work -
615/597-6801 ext. 111, fax 615/597-6803

F.Chapman Baudelot on fri 23 nov 01


My old Olympic 7 cu.ft. updraft had 3" walls, not 2.5" and could hardly be=
called ultra-efficient.

I am no guru, but I would have thought it better to put the ceramic fibre=20
UNDER the refractory brick rather than on top.

By the way, I have had zero responses to my query about gasoil=20
(diesel)-fired kilns. However, the Catalan outfit which makes them have=20
been extremely helpful, and I will most probably order their 100 litre=20
model with controller etc. and install it in my patio. It has 6" of=20
ceramic fibre insulation protected by 1" of refractory and is all in one=20
piece avoiding heat loss. Europeans seem to be much more conscious of the=
need to save energy of any kind, and of course it is much higher priced=

Fran=E7oise in Almer=EDa, Spain, where it NEVER rains, except for the=20
occasional flood.