kruzewski on tue 12 jun 01
Hi,
A friend of mine has just built a woodfire kiln which is an interesting
conglomeration of several design ideas.
He has been advised by a local woodfirer to pre-fire his kiln empty to
dry out the bricks. Although we all live in North Wales, which has a
fairly damp atmosphere, he has protected the bricks against the rain etc
and doesn't feel they are particularly damp.
He will be once firing in the kiln, pre-heating the kiln with a small
wood fire (there is no gas) the day before the main firing which will go
up to high stoneware.
Does he need to fire the kiln empty the first time?
Your advice will be much appreciated.
Jacqui, North Wales - where it's cold - 53 degrees - and cloudy and I've
put on the central heating. Where IS Summer - will it ever arrive?
dan mickey on tue 12 jun 01
> He has been advised by a local woodfirer to pre-fire his kiln empty to
> dry out the bricks. Although we all live in North Wales, which has a
> fairly damp atmosphere, he has protected the bricks against the rain etc
> and doesn't feel they are particularly damp.
> He will be once firing in the kiln, pre-heating the kiln with a small
> wood fire (there is no gas) the day before the main firing which will go
> up to high stoneware.
PREFIRING A KILN ESPECIALLY WOOD IS ALOT OF EFFORT, AND TIME. i FEEL THAT
SINCE THE FIRING IS A RAW OR GREEN FIRING, IT WOULD BE O.K. TO NOT PREFIRE
THE KILN. nOW THIS ALL DEPENDS ON SOME FACTORS:
1. HOW MUCH IF ANY CASTABLE/ MORTER WAS USED AND HOW CLOSE TO THE FIRING
DATE WAS IT USED?
2. DID THE BRICK GET DIRECTLY RAINED ON OR HOW LONG WERE THEY EXPOSED TO
MOISTURE? HARD BRICK LEFT OUTSIDE, EVEN COVERED, CAN HARBOR ALOT OF
MOISTURE.
3. WHAT IS THE TYPE OF WORK GOING INTO THE KILN, I.E. ANY LARGE WORK.
IF THE ANSWER TO #1 IS LITTLE CASTABLE/MORTER AND WAS DONE AT LEAST A WEEK
BEFORE THE FIRING THEN ITS SAFE TO NOT PREFIRE
IF THE BRICK WAS EXPOSED FOR SAY A YEAR I WOULD BE WEARY OF IT NOT BEING
PREFIRED.
IF THERE IS ALOT OF REALLY LARGE WORK GOING IN GREEN, SAY HUNDRED POUND
VESSELS, THEN ITS GOING TO TAKE A LONG PREHEAT ANYWAY.
ALL SAID BETTER SAFE THEN SORRY. I KNOW OF KILNS THAT HAVE BEEN CAST THEN
FIRED TWO WEEKS LATER TAKING A LITTLE LONGER THAN NORMAL PREHEATS, SAY 12-20
HOURS, RATHER THAN 8-12 HOURS.
PERSONALLY I PREFER REALLY LONG PREHEATS WHEN RAW FIRING, MAYBE ITS JUST
SAVORING THE CALM BEFORE THE STORM, BUT I DO NOTICE A DIFFERENCE IN THE WORK
FROM AN 8 HOUR WARM UP TO BISQUE, COMPARED WITH A 16 HOUR WARM UP TO BISQUE.
GOOD LUCK
SHANE MICKEY
_______________________________________________________
Send a cool gift with your E-Card
http://www.bluemountain.com/giftcenter/
Tony Ferguson on tue 12 jun 01
Forget the prefire. Load it up and fire it.
Otherwise if you must, put a propane burner on it.
Sleep when you're dead.
Tony Duluth, MN
=====
--Tony Ferguson, fergyart@yahoo.com315 N. Lake Ave. Apt 401Duluth, MN 55806(218) 727-6339Looking to see, buy or barter artwork go to:http://acad.uwsuper.edu/www/aferguso/fergyart.htm
Steve Mills on wed 13 jun 01
No, even with wet bricks we've never pre-fired; the warm-up just takes a
bit longer, depending on size. Our latest is about 16 cube setting area.
Steve
Bath
UK
P.S. It's dry down here at the moment, though not for long!
In message , kruzewski writes
>Hi,
>
>A friend of mine has just built a woodfire kiln which is an interesting
>conglomeration of several design ideas.
>
>He has been advised by a local woodfirer to pre-fire his kiln empty to
>dry out the bricks. Although we all live in North Wales, which has a
>fairly damp atmosphere, he has protected the bricks against the rain etc
>and doesn't feel they are particularly damp.
>
>He will be once firing in the kiln, pre-heating the kiln with a small
>wood fire (there is no gas) the day before the main firing which will go
>up to high stoneware.
>
>Does he need to fire the kiln empty the first time?
>
>Your advice will be much appreciated.
>
>Jacqui, North Wales - where it's cold - 53 degrees - and cloudy and I've
>put on the central heating. Where IS Summer - will it ever arrive?
--
Steve Mills
Bath
UK
John Baymore on wed 13 jun 01
He has been advised by a local woodfirer to pre-fire his kiln empty to
dry out the bricks. Although we all live in North Wales, which has a
fairly damp atmosphere, he has protected the bricks against the rain etc
and doesn't feel they are particularly damp.
He will be once firing in the kiln, pre-heating the kiln with a small
wood fire (there is no gas) the day before the main firing which will go
up to high stoneware.
Does he need to fire the kiln empty the first time?
Jacqui,
Hi.
If the kiln utilizes some commercial castable refractories that are to be=
fired in place, they MAY have some specific instructions about drying and=
firing. That is the first consideration. If they do..... do NOT ignore
them. It will compromise the longevity of the installation. Follow the
instructions to the "T". The manufacturer knows it's product.
Other than that..........
It takes a HUGE amount of heat energy to make the state change converting=
liquid water at 212 F (100C) to gaseous water vapor. A REALLY wet kiln
will tend to stall until it is mostly dried out due to a lot of heat ener=
gy
being "sucked off" to change all the water to steam.
A lot depends on how MUCH water was utilized in construction, and how wet=
the bricks were in general from storage or wetting down to control dust
during construction. If the kiln was covered with a back up of
....say....... a ton and more of a homemade or commercial castable or
something like that ....... it is going to sit and belch a lot of steam a=
t
some point (usually around 1800F-2000F) for a long time before it gets
really hot inside. Ditto if each IFB was dipped in a bucket of water to
control construction dust. And so on.
If you used a LOT of water......... I'd advise dry firing the kiln. Unle=
ss
you have so many teams of stokers that an extended firing all at once is
not really an issue. If you have only a couple of people firing....and t=
he
expected cycle is say......24-26 hours..... and a stall of an additional =
4-
5- 6 hours would make the work load objectionable....then dry fring the
kiln moves the extra time to a point where it does not impact people (and=
their judgement) as adversely. =
If the bricks were stored under cover, and only a little leveling and
bonding mortar was used here and there........ you probably won't notice
anything. Not much different from a kiln sitting outside in an open kiln=
shed for a long time without being fired....... picks up atmospheric
moisture about the same. Technically...it will take more heat energy tha=
n
a recently fired "dry" kiln....... but probably nothing really noticable.=
The one place that problems CAN come up from this kind of thing is the
"combination of factors synergy" problem. IF..... the kiln design is
marginal so that combustion is not really as good as it should be, and
IF........ the wood supply is a little damp or not cut small enough, and
IF....... the kiln refractories selection is a little underinsulated, and=
IF....... the stokers are not experienced...... then the wet kiln
refractories can be the "straw that broke the camel's back" when combined=
with one or more of the former situations. Sometimes a couple of factors=
can combine to cause a problem where if only one of them was present.....=
.
it wouldn't have been a problem. Just keep this general concept in the
back of your mind.
So the odds are good you can just load up and fire away.... expect a sta=
ll
at some point commensurate to the amount of water used as the kiln drys
itself out....and then it'll climb once again. =
Enjoy the firing.
Best,
...................john
John Baymore
River Bend Pottery
22 Riverbend Way
Wilton, NH 03086 USA
603-654-2752 (s)
800-900-1110 (s)
JohnBaymore.com
JBaymore@compuserve.com
John.Baymore@GSD-CO.com
"Earth, Water, and Fire Noborigama Woodfiring Workshop August 17-26,
2001" (Full- now on waiting list.)
| |
|
