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when is a fastfire not a fastfire?

updated fri 18 may 01


David Hendley on thu 17 may 01

Valerie W. Johnson had several questions about building an
Olsen Fastfire kiln -----

The Fastfire design has been around for a long time and
has been 'fine-tuned' for best performance. If you start
changing things in the design, you will end up with a
different kiln.

Part of the design is to use kiln shelves for the floor of
the kiln. A thin kiln shelf heats up fast and sends heat
up through the floor of the kiln. If you use a thick slab
or build small arches for the floor, you no long have an
Olsen Fastfire kiln. It will probably still work, but your
firing times will increase and you may have temperature
difference problems with a hot top and cool bottom.

Likewise, if you start building the walls with hardbricks
you will drastically change the kiln. You will never be
able to fire in a few hours if you use hardbricks. It will
probably still be an OK kiln, but it will not be an Olsen

The firing times Fred lists in his book do not seem realistic
to me, as he says he can fire to cone 10 in less than 2 hours.
You can expect a firing of under 5 hours if you follow the
plans. If you start adding more mass, you will be up to 8 to
12 hour firings.
Fast firings are not necessarily good. My larger size Fastfire
will fire in 5 hours, if speed is the objective, but the finished
pots do not look so great. I stretch it out to 8 or 9 hours for
better results, but it's nice to know I have that extra power
to really goose it if I want to.

There is no reason to mortar the bricks together, and yes,
build in a damper. I would recommend a 'passive damper',
which is just a hole in the stack. Just make it so one brick
is removable, and have different sized bricks handy to block
different percentages of the hole for more or less effect.
Outside air is drawn in through the passive damper, and this
serves to decrease the draft in the kiln itself.

I bisque-fired in a Fastfire kiln for several years. It is indeed
possible to do so, but it is a big pain. It is hard to start slow
enough, so you don't have the flames directly hitting the ware
before it is warm enough to take the direct heat. It's really
boring to stay around all day, s-l-o-w-l-y feeding the fires.
Then, after the firing, all the ware is covered with ashes that
must be brushed off before waxing and glazing the pieces.

As with most things, if you go ahead and spend the money
to buy what you need, you will end up with a better kiln.
That means:
Silicon carbide shelves for the kiln floor.
Insulating bricks for the kiln, including 9" thick walls, rather
than 4 1/2" thick, as is still shown in the book.
ITC 100 ceramic coating for the inside of the kiln.
The ITC will protect the insulating fire bricks from the
fluxing effect of the ashes flying around the kiln.

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just read.
David Hendley
Maydelle, Texas

----- Original Message -----
From: Johnson, Valerie W.
Sent: Wednesday, May 16, 2001 11:58 AM
Subject: fastfire wood kiln

| Hi everyone,
| I'm new to the list, but I've been lurking about for a few days.
| I'm building a fastfire woodburning kiln (which may be converted to gas
| I get too frustrated with wood), substantially in line with the plans in
| Olsen book. I have a couple of questions:
| 1. To mortar or not to mortar the bricks? Benefits/problems with
| mortaring?. I expect to never need to disassemble the kiln. If I
| the plans don't call for expansion joints, although they discuss adding a
| fraction of an inch at the corner joints. How exactly do you do that
| without throwing the angles of the walls off?
| 2. the plans don't call for a damper in the chimney; is one needed?
| 3. I have been given some 9x18x3" hard firebrick slabs from a refractory
| supplier: would there be any problem with using these as the kiln floor?
| 4. can you /would you bisque porcelain in this kiln? if so, what would
| the schedule?
| 5. if I used hard firebrick inside the kiln and ifb outside the kiln (for
| 9" walls), would i extend the firing time past "fastfire" by a huge
| What about vice-versa; ifb inside and hard firebrick outside--would the
| benefit be a slower cooldown?
| thanks to anyone who has some advice.
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