search  current discussion  categories  kilns & firing - wood

## wood kiln question

### Lee Taylor on tue 2 nov 10

On Oct 31, 2010, at 7:28 PM, stan gibson wrote:

> Hey there potters...Building a big cross draft wood fire kiln,
> placed back into a hill, the whole thing surrounded by a concrete
> retaining wall..Will be 4.5 inches hard brick backed by 4.5 inches
> soft brick with periodic header courses of hard brick extending to
> the outside wall... drain pipe at the footing, back filled with
> rock...

Stan, Paul,=3D20=3D20

I am completing a similar kiln and have used homemade castable for the=3D20=
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arches. However, I think that the castable behind soft brick would be ov=
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erkill=3D20
(and over cost!). I think sand with a small amount of portland cement wo=
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uld=3D20
be plenty strong and cheap. I don't think that heat on the outside of a =
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soft=3D20
brick wall is much to be concerned about. With a soupy mix the slurry wo=
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uld=3D20
run all the way down to the bottom of the wall. Would this clog the drai=
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ns?=3D20=3D20

What kind of stress do you have on the walls? is there a sprung arch or=3D2=
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catenary? Where will the weight and expansion stress from the arch be=3D20=
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carried on the walls? I'd love to see some photos or plans!=3D20=3D20

I've tried to attach a couple of photos of the "box" part of my kiln. Yo=
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u will=3D20
see that it is backfilled with rocks and red clay. It hasn't been fired =
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yet, so=3D20
probably I speak from naivete!

The other thing that you may want to check out is the hard brick headers =
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into=3D20
the soft brick. I'v been told that the expansion ratios are different be=
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tween=3D20
hard and soft brick. You may want the walls to move independantly of=3D20=
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eachother.=3D20=3D20

Sounds exciting! I'd be glad to share by phone some of the advice I rece=
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ived=3D20
from a number of experts on kiln building during the design phase of my k=
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iln. I=3D20
had a lot of help from many generous potters. 540-463-7785.

Lee Taylor
Lexington, Virginia

### Paul Herman on thu 4 nov 10

Hello Stan, Lee and all,

and I think I'll just post it to the list anyway. It's based on
diatomaceous earth (DE), which I buy as "Floor Dry" (absorbent) down
at the Napa auto supply store in Reno, NV. I'm not sure how widely
distributed this product is, but it is available around the western US
as far as I know.

Insmud recipe:

2 coarse diatomaceous earth (4-6 mesh)

2 fine diatomaceous earth (16 mesh)

1 fireclay

Mix it up with water stiff or sloppy, pour it, ram it, or trowel it on.

If you are using it on the outside skin of a kiln, add a little

Lee, if you use this home made stuff the cost isn't so bad. Also, if
protecting the concrete from excessive heat is a concern, then
insulating castable would be the best material to use, IMHO. If you do
extended firings, the heat will have time to work it's way through a
soft brick layer, possibly firing the concrete wall.

I've always tried to build things in a robust manner, and have been
accused of "overkill" plenty of times. So what is so bad about
building things more robustly than the absolute cheesy minimum?

good firings,

Paul Herman

Great Basin Pottery
Doyle, California US
www.greatbasinpottery.com/

On Nov 2, 2010, at 6:51 AM, Lee Taylor wrote:

> On Oct 31, 2010, at 7:28 PM, stan gibson wrote:
>
>> Hey there potters...Building a big cross draft wood fire kiln,
>> placed back into a hill, the whole thing surrounded by a concrete
>> retaining wall..Will be 4.5 inches hard brick backed by 4.5 inches
>> soft brick with periodic header courses of hard brick extending to
>> the outside wall... drain pipe at the footing, back filled with
>> rock...
>
> Stan, Paul,
>
> I am completing a similar kiln and have used homemade castable for the
> arches. However, I think that the castable behind soft brick would
> be overkill
> (and over cost!). I think sand with a small amount of portland
> cement would
> be plenty strong and cheap. I don't think that heat on the outside
> of a soft
> brick wall is much to be concerned about. With a soupy mix the
> slurry would
> run all the way down to the bottom of the wall. Would this clog the
> drains?