logan johnson on wed 30 mar 05
Hi Gang!
I need some advice on giving some advice to a newbie wanting to build her first raku kiln the least expensive way possable. I've seen some raku kilns built from freestanding bricks but can;t remember what kind of bricks were used. Can anyone tell me how to make a free standing brick box with a hole for the burner at the bottom under the shelf. ( I know I would have to offset the butted joints) I was also thinking of using a piece of expanded metal lined with Kaowool ( with a hole cut in it ) for the lid. I thought for single person use a lid my friend could lift off the lid herself. How mant corses of brick would we need ? Do we use all soft fire brick or a combination of soft & hard fire brick? What am I forgetting to ask about? I don't want to give her wrong info so I comming to the pro's that know before I suggest anything to her.
H E L P !
Thanks In Advance!!
Logan Johnson Audeo Studios
www.audeostudios.com
"Carpe Argillam!!"
Craig Clark on thu 31 mar 05
Logan, here are a few suggestions. I am predicating this on the
belief that you are going to be building a small kiln, as in not much
more than a 2ft cube or so. If you are going to go the route of using
brick my advise is to use soft brick. One course will be sufficient. Use
soft brick for superior insulating capacity. You can pretty much stack
and unstack them as you see fit. Just figure out how many you will need
to make the desired size box.
The idea of using expanded metal lathe as a skeletal structure from
which fiber blanket is hung will work fine for making a lid.. One thing
to consider is a couple of pieces of light duty angle iron, or channel,
that will span across the top of the lid to prevent sag.
When choosing the blanket go for either a 6 or 8 lb density. You
will be happier in the long run. Also, if you are able, get the two inch
thick blanket.Use both sodium silicate as an adhesive between blanket
layers if you are going for more insulation and a good nichrome wire
with high fired "ceramic buttons" to hold the blanket in place.
Keep in mind that the construction of a raku kiln can indeed be a
creative endeavor. Folks have made raku kilns from just about every
structure imaginable at one point in time or another. A few examples of
what folks have used have been Volkswagon Beetles, Vans, BBQ Smokers,
old pipes, metal boxes of various shapes and sizes, etc...just about
anything that insulating fiber blanket can be hung from. To start, a
small simple cube is the best way to go. It will be the most efficient
and the easiest to build and fire.
A quick note of caution. When folks have using various exotic
frames, such as VW Beetles, for a kiln, they have painstakingly remove
all of the guts of the vehicle. Al the plastic, wire, headliner, etc.,
Basically anything that would burn. Same, same with any other "odd" sort
of form or object. Old pipes or industrial containers in particular may
have potentially noxious residue in the pores of the iron, or steel that
will vaporize and become harmful when heated.
If you do not already have the bricks then you may find that using
fiber blanket for the entire kiln will be the less expensive route to
go. If you go to your handy dandy local refractories supplier you can
get a great price on the stuff. Don't go to your ceramics store. They
will most likely be charging you a considerable mark up. Just google
refractories for your area (use the closest large city as a reference)
and give those listed a call. Here in Houston I go to Able Supply.
If you use the blanket for the entire kiln I suggest that you go
with at least a 2 inch thickness of insulation if you plan on keeping
the kiln for any length of time. The only drawback is that the thicker
the insulation the more the original construction cost will be. For a
small kiln you won't need more than 2 boxes of blanket and that won't
cost you much more than about $120 or so which ain't to shabby. Plus the
cost of the lathe, wire, sodium silicate, burner and your time.
Just use a single natural draft venturi burner to fire with. They
run about 40 bucks and can be had at a number of locals. Once again, if
you use the internet to go to the source of what you are looking for you
will end up saving some money.
Ward Burner Systems is an excellent source for much of what will help
you with raku kiln building and firing. They are very helpful and
forthcoming with information. One of the best in the business for
potters, in my opinion. Here's the link http://www.wardburner.com/index.cfm
Hope this helps
If you have any specific questions just contact me off list
Craig Dunn Clark
619 East 11 1/2 st
Houston, Texas 77008
(713)861-2083
mudman@hal-pc.org
Denny on fri 8 apr 05
Logan,
I once had a call from a person with a new raku kiln, a garbage can lined w=
ith ceramic fiber for the chamber, resting on 4 rows of hard firebrick for =
the combustion chamber. Her kiln was not getting up to temperature, even af=
ter a long time. Only after some probing did I learn that her friend had gi=
ven her the hard firebrick. Seems they had dug the brick up from the garden=
path the day before. Perhaps the ultimate in economical brick?? I indicat=
ed to her that the kiln was not likely to get up to temperature until all t=
he water had been boiled out of the brick she was using. It would be a long=
wait.
This story emphasizes an important point: keep your kiln brick dry. A br=
ick raku kiln will be slower to fire at first, than a ceramic fiber lined k=
iln. If the brick has absorbed much water, it will have to be dried out bef=
ore the temperature will climb much.
In a Raku kiln, I would want brick 3 or 4 rows high for the burner and comb=
ustion chamber. The combustion chamber is a key part of the kiln and needs =
to be 6 to 8 inches high, below your first kiln shelf. (See Marc Ward=E2=80=
=99s excellent website for a good discussion of this and Raku kiln burners =
& building as well. www.wardburner.com) On top of that, you need additional=
rows of brick based on the height of the ware to be fired. Say, for pots u=
p to 10=E2=80=9D ht., 4 more rows of brick are needed, plus a couple more f=
or heat/airflow around the pots. End result: Start with 10 rows of brick he=
ight (25=E2=80=9D) are needed for pots to 10=E2=80=9D tall. Some may get by=
with fewer rows, but they are handling issues of airflow in unconventional=
ways. The footprint of the brick kiln can be a based on the size of the ki=
ln shelf on the bottom, and the diameter of the pot, balanced against the 9=
=E2=80=9D length of the firebrick. Outside dimension of 22.5=E2=80=9D on a =
side (2-1/2 brick) yields 13.5=E2=80=9D inside, which would work well for, =
say a 12=E2=80=9D diameter kiln shelf. Leaving good room for heat/airflow a=
round the shelf. So, with a footprint of 8 brick, by 10 rows high, includin=
g the floor, you need 82 good bricks for the walls and floor of the kiln. (=
The next increment would be 27=E2=80=9D outside dimension, a 10 brick perim=
eter by 10 rows high, for a total of 108 bricks. Use a 15=E2=80=9D dia. kil=
n shelf.) As you indicated the kiln lid can be made as a lift-off ceramic=
fiber insulated assembly. Rule of thumb for flue area is to equal the inle=
t area for the burner. A piece of kiln shelf can be used as a damper contro=
l for the flue.
Hard brick will take longer to fire the first load and will require more fu=
el. Yet, hard brick is available in some areas as used brick and can be che=
aper than soft brick (insulated firebrick, or IFB.) Soft brick (if dry) wil=
l fire faster, but can be more expensive initially. Soft brick will get bro=
ken more often and show the wear and tear of handling, firing, and life as =
an active kiln, so keep several good new spares on hand. It would be wise t=
o make the base, or floor, of IFB, to minimize heat transfer to the substra=
te.=20
The whole kiln could sit on concrete blocks, laid on their side for airflow=
. This will help keep the floor of the kiln from absorbing water from the g=
round, or from a cement slab.
I built a steel angle frame base for my raku kiln, laid in a floor and 3 =
rows of IFB, then used a fiber lined =E2=80=9Ctop hat=E2=80=9D for the rest=
of the kiln. The whole thing is on wheels and lives in the nice, dry barn =
when not in use. Write to me off list and I will send you a drawing of the =
steel base.
The high cost of IFB may give you second thoughts and would lead you to inv=
estigate building a fiber-lined kiln. See Branfman=E2=80=99s excellent book=
=E2=80=9CRaku, A Practical Approach.=E2=80=9D Don=E2=80=99t start Raku fir=
ing without it.
Once you investigate new brick cost in your area, the fiber Raku kiln kit=
s from Marc Ward look like a very good deal. And I highly recommend that yo=
u use a Ward venturi burner with an adjustable regulator and gauge. Sure, p=
eople sometimes use =E2=80=9Cweed burners=E2=80=9D successfully. After the =
first load, weed burner efficiency drops way down as the propane tank cools=
. An adjustable regulator gives good control and fuel economy at the cooler=
early part of the firing, and lets you crank up pressure once the ware is =
heated up.
One of the best things I bought for my Raku system was the Ward two-tank co=
nnector kit. For about 38 bucks, problems of propane tank freeze-up are sol=
ved, taking the hassle of a long firing session away.
I hope this helps, Logan
Denny Means
crookedtreepots@earthlink.net
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