John Baymore on sat 22 apr 00
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=22We are looking for a recipe for a Hot Faced Castable that is (hopefully)
inexpensive, and suitable for constructing small experimental salt /wood
kilns.=22
Any help would be greatly appreciated. Please feel free to either email me
directly or to post answers and/or links.
(snip)
Kimi,
Sorry about the time lag. I am very busy and I figured some other kiln
builder types would give you an answer or two before this.
First of all... need to think about the =22inexpensive=22 qualifier when you
combine it with the words =22salt and wood=22. A LOT then depends on what
exactly you mean by the term =22suitable=22. If =22suitable=22 means that =
the kiln
will withstand long term usage with minimal deterioration.... then you
probably are moving away from the word =22inexpensive=22 =3Cg=3E. If this =
kiln
truly is =22experimental=22 and that implies that it will not be around very
long...... very few firings..........then you can make the hot face out of
a lot of possible high temp home-made castables.
Wood and salt (I am assuming you plan on firing with wood but lightly
salting the wares too) as a combination are probably the most damaging
combination for most refractories. If the kiln is to last long term, then
the refractories need to be =22up to snuff=22.
If I remember correctly (and I probably don't =3Cg=3E), Louis Katz mentions =
in
his Thai pottery video that the kilns there are built out of the same clay
as the pots. And that they are rebuilt VERY often because of the poor
refractoriness of the bricks. They fail quickly.
For the most basic low tech primitive idea...... ram up (in solid wooden
forms) blocks made of a barely plastic mix of 100 lbs. fireclay mixed with
about 3 cubic feet of sawdust into big =22bricks=22 (like 1 foot by 1 foot =
by 1
foot). Let them dry to leather hard and use those to construct a temporary
kiln. Fun to build with big leatherhard blocks. Just making a big vessel
to hold heat and pots =3Cg=3E=21 Shape them as if you were making a big
handbuilt piece.......cut/shape with big knives, pruning saws, and surform
tools. Use a thick slop of fireclay and water to stick things together and
caulk the cracks. Cover the outside into a big organic looking thing with
the same type fireclay mixture, but way heavier on the sawdust proportion.
You can also ram the same mix into forms to act like a =22ram-able=22 =
mixture,
but make sure that you pack it in densely to fill voids (your forms will
have to be strong) and that you don't let the surface of where you join
=22runs=22 of the material dry out between =22rammings=22.
=22Inexpensive=22 as used by many potters often relates only to the =
materials
involved themselves. If your labor time is worth anything, and replacement
of the original materials is considered, then it is possibly more
=22inexpensive=22 to use more costly materials the first time and not have =
to
rebuild or repair the kiln as often. It is also often more cost effective
to use more costly materials to start with if the less costly materials can
result in much in the way of lost wares in firings.
One quick suggestion is that whatever you make the hot face walls
of......... spray it LIGHTLY with ITC 100 HT coating. Remember, this
application is a case where the American tenet of =22more is better=22 is =
not
necessarily true. Follow the mfgr's directions EXACTLY. You need
enough.....but you don't want too much. That will help the material you
select resist the effects of the slagging action of the salt/wood ash
combination, not to mention decrease the penetration of stong reducing
gases back into the home-made castable. A gallon is about =24140 US and
covers a lot of surface area. So while it might be pretty high tech......
it'll get the =22most=22 out of the low tech underneath it. And it isn't =
all
THAT much money.
However, this coating will tend to decrease the buildup of a layer of
salt/ash-glaze on the kiln interior. This layer of =22kiln glaze=22 helps =
to
fume salt and soda compounds back into the chamber in a non-coated kiln.
This layer of glassy material buildup is part of why as a wood kiln or salt
kiln ages, the firing results get better. The soda fumes tend to react
with the pots more and less with the huge surface area that the walls of
the kiln comprise. The coating idea is a bit of a trade off in this
regard.
This email computer is not the one where I have all my recipes for stuff.
If no one beats me to it in the next day or so , I'll go look up a couple
of home-made castables that are more =22formal=22 than the really low tech =
one
above. My guess is that someone else will also send you some thoughts.
If you build a kiln structure well and with suitable high grade materials,
it can last a long time without the protective surface coating. I have a
20 year old noborigama which is in very good shape, including the fireboxes
and inlet/outlet flues. It was built out of very good refractory materials
to start with.....'cause I didn't want to have to rebuild it.
Don't be afraid to =22play=22 if the kiln is truly temporary. You can learn=
an
awful lot about kilkns and firing by building and tearing down =
=22temporary=22
kilns.
Hope this is of help.
BEst,
....................john
John Baymore
River Bend Pottery
22 Riverbend Way
Wilton, NH 03086 USA
603-654-2752 (s)
800-900-1110 (s)
JBaymore=40compuserve.com
John.Baymore=40GSD-CO.com
=22Earth, Water, and Fire Noborigama Woodfiring Workshop August 18-27,
2000=22
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