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## outer wall of wood kiln - r-20

### Eva Gallagher on sun 19 sep 04

I thought that I would be getting some secondhand R-23 insulating fire
bricks that I would use for the outer walls of the chamber and floor of my
train kiln. Now I am told that they actually are R-20 from A.P. Green.
(Service temp is 2000F) The hot face of the kiln will be of secondhand R-26
(they have channels cut out for electric elements from a home-built electric
kiln that was never used - so the R-26 is a bit thin in spots. Probably 3
inches instead of 4 1/2". I will fill the holes with a homemade castable.
Will the R-20 get too hot? As these R-20 bricks are a very good buy I would
also like to use them under hard bricks in the floor. Rhodes in his kiln
book does show R-20 behind a 4" hard brick. However for the floor can I use
just a 2 1/2" thickness hard brick backed by R-20?
Was just wondering if anyone had done this.

Eva
Deep River , Ontario

### Louis Katz on tue 21 sep 04

Here is how i would work out my solution to your question. But I would
trust experience over these simple calculations.
--------------
I don't think you will have a problem with the walls but it might be
close. If you assume that the temperature gradient is linear (it won't
be this assumes that the k-25 and k-2000 have the same insulating
value) and you have a 6 inch wall (forgeting the brick past the inside
of the grooves and the inside of the kiln is 2350 and the outside is
250 degrees your temperature differential thorugh the whole wall is
2100 degrees.
2100/ 6. You loose 350 degrees for each inch of wall thickness. Since
you have 1.5 inches of inside layer you get
2350 -(1.5 x 350) =2350- 525= 1825.
Now, these brick are not as insulating as R-20 (these are not R values
as in fiberglass but max temperature ratings) .
Once the holes are filled I think you will come close to the same
insulation value as a 1.5" K-20 or better so I think you are o.k.
The hard brick floor sounds iffy, but if someone has done this I would
believe them. Usually floor brick do not get reduced. This will help
but I remember being told that if you build a 9 inch wall of k-20 on
the outside and hardbrick on the inside you will exceed the rating for
the k-20's. Also the 2000 degree brick will probably not be the bottom
of the insulating wall. You can't set this directly on cement (more
insulation and will probably blow up) You may end up on cinder block (
more insulation) . More insulation will raise the hot face of the
r-20's when the kiln has been at temperature for a while. I might risk
it anyways but that is risky no?I would look for some more hard brick
or some k-23's for under the floor.

I would be careful with what you stuff the element grooves with. If it
is all clay you make end up with a spalling problem as solid clay
expands more than insulating firebrick.

With all of this said and done K-23 's are frequently fired to 2350
degrees F and hold up reasonably well although after a few years there
is some shrinkage. The Bray had a well used kiln built this way that
was near 20 years old of hard use. It had been repaired in many places
and the arch had been replaced.

louis

On Sep 19, 2004, at 9:36 PM, Eva Gallagher wrote:

> I thought that I would be getting some secondhand R-23 insulating fire
> bricks that I would use for the outer walls of the chamber and floor
> of my
> train kiln. Now I am told that they actually are R-20 from A.P. Green.
> (Service temp is 2000F) The hot face of the kiln will be of secondhand
> R-26
> (they have channels cut out for electric elements from a home-built
> electric
> kiln that was never used - so the R-26 is a bit thin in spots.
> Probably 3
> inches instead of 4 1/2". I will fill the holes with a homemade
> castable.
> Will the R-20 get too hot? As these R-20 bricks are a very good buy I
> would
> also like to use them under hard bricks in the floor. Rhodes in his
> kiln
> book does show R-20 behind a 4" hard brick. However for the floor can
> I use
> just a 2 1/2" thickness hard brick backed by R-20?
> Was just wondering if anyone had done this.
>
> Eva
> Deep River , Ontario
>
> _______________________________________________________________________
> _______
> Send postings to clayart@lsv.ceramics.org
>
> You may look at the archives for the list or change your subscription
> settings from http://www.ceramics.org/clayart/
>
> Moderator of the list is Mel Jacobson who may be reached at
>
>
Louis Katz
http://www.tamucc.edu/~lkatz

### Gary Navarre on tue 21 sep 04

---------------------------- Original Message ----------------------------
Subject: Outer wall of wood kiln - R-20
From: "Eva Gallagher"
Date: Sun, September 19, 2004 9:36 pm
To: CLAYART@LSV.CERAMICS.ORG
--------------------------------------------------------------------------

I thought that I would be getting some secondhand R-23 insulating fire
bricks that I would use for the outer walls of the chamber and floor of my
train kiln. Now I am told that they actually are R-20 from A.P. Green.
(Service temp is 2000F) The hot face of the kiln will be of secondhand
R-26 (they have channels cut out for electric elements from a home-built
electric kiln that was never used - so the R-26 is a bit thin in spots.
Probably 3 inches instead of 4 1/2". I will fill the holes with a homemade
castable. Will the R-20 get too hot? As these R-20 bricks are a very good
buy I would also like to use them under hard bricks in the floor. Rhodes
in his kiln book does show R-20 behind a 4" hard brick. However for the
floor can I use just a 2 1/2" thickness hard brick backed by R-20?
Was just wondering if anyone had done this.

Eva
Deep River , Ontario

Eva, Crew,
In my last kiln I used high heat duty refractory clay firebrick on the
inner shell, medium duty on the second layer over fiber blanket. The
final layer was something like R-20's. The kiln was too hot to touch
untill I added the third layer. On my next kiln I might put a layer of
redbrick over that for protection. Under this kiln I'll have more or
less 3ft. of crushed rock, about 6" of well tamped sand/clay substrate
soil, maybe a layer of redbrick, and the floor of high heat duty clay
firebrick. In my last kiln I laid the floor on the ground with little
gravel and it worked fine with a long preheat.
Now I have the foundation hole dug out to roughly 2"x10'x18' and a
4'x4'x1' under the firebox. I've added a rough drawing of the second
chamber to a new album in fotki, here is the link:
http://public.fotki.com/GindaUP/navarres_hobagama/
Keep going!

G. in Da U.P.
Navarre Pottery
Norway, Michigan, USA

### steve harrison on tue 21 sep 04

Hi Eva,
Yes you can use RI 20 as back up insulation behind your RI 26 and dense
hard brick. That is what they are designed for. They are a very soft,
light weight, fragile brick, so handle them carefully.
Best wishes
Steve Harrison

Hot & Sticky Pty Ltd
5 Railway Pde
Balmoral Village
NSW 2571
Australia

http://ian.currie.to/sh/Steve_Harrisons_books.html

On Monday, September 20, 2004, at 12:36 PM, Eva Gallagher wrote:

> I thought that I would be getting some secondhand R-23 insulating fire
> bricks that I would use for the outer walls of the chamber and floor
> of my
> train kiln. Now I am told that they actually are R-20 from A.P. Green.
> (Service temp is 2000F) The hot face of the kiln will be of secondhand
> R-26
> (they have channels cut out for electric elements from a home-built
> electric
> kiln that was never used - so the R-26 is a bit thin in spots.
> Probably 3
> inches instead of 4 1/2". I will fill the holes with a homemade
> castable.
> Will the R-20 get too hot? As these R-20 bricks are a very good buy I
> would
> also like to use them under hard bricks in the floor. Rhodes in his
> kiln
> book does show R-20 behind a 4" hard brick. However for the floor can
> I use
> just a 2 1/2" thickness hard brick backed by R-20?
> Was just wondering if anyone had done this.
>
> Eva
> Deep River , Ontario
>
> _______________________________________________________________________
> _______
> Send postings to clayart@lsv.ceramics.org
>
> You may look at the archives for the list or change your subscription
> settings from http://www.ceramics.org/clayart/
>
> Moderator of the list is Mel Jacobson who may be reached at
>

### Ivor and Olive Lewis on wed 22 sep 04

This sort of problem can be solved using a few simple sketches, a hand
calculator, an ability to extract data from graphs together with the
information and kiln design processes illustrated in J. DeBoos, S,
Harrison & L.Smith, "Handbook for Australian Potters". Part 5 Kilns,
Kiln Design pp 267-279 ISBN 0-454-00448-6. 1984.
I am uncertain if this kind of knowledge is published elsewhere but I
believe the book may have been reprinted and there may even be a
recent edition. I just have the "First".
Best regards,
Ivor Lewis.
Redhill,
S. Australia.

.