DEBBYGrant@AOL.COM on tue 2 oct 01
I am asking this for a friend who is not on the list. She is rebuilding her
salt kiln using soft brick instead of hard and of course she knows that they
will break down faster. I suggested that she might try spraying the kiln
with ITC in order to preserve the integrity of the brick but she is not sure
that this would be cost effective. I, myself, have sprayed my electric
kiln with ITC and have found that the elements have lasted much longer.
I would be interested in getting some opinions, especially from some
other salt glaze potters.
Debby Grant in NH
Craig Martell on tue 2 oct 01
Hello Debby:
If your friend doesn't treat the soft brick with something the kiln is
going to have a very short life. Salt is hell on wheels with soft
brick. Eats it right up!
I've never used ITC on a soft brick salt kiln. I have coated k-23's and
k-26's with ITC and fired them about 10 times in my hard brick salt
kiln. So far they are fine. I've been told that there will be problems
after around 40 firings. This is not borne out by fact and observation
though. I've never seen a soft brick salt or soda kiln that has more than
40 firings.
The least your friend could do is spray the brick with a wash of 75%
alumina and 25% kaolin. Then, fire it to bisque temp before going ahead
with a vapor glaze load.
regards, Craig Martell in Oregon
Earl Brunner on tue 2 oct 01
Well, I hope someone else with a bit more experience jumps in here, but
salt is VERY corrosive to soft brick if there is not some kind of
protective coating. Mel and friends have done some rather involved
testing with ITC on different refractory materials, He could certainly
give some good insight here.
DEBBYGrant@AOL.COM wrote:
> I am asking this for a friend who is not on the list. She is rebuilding her
> salt kiln using soft brick instead of hard and of course she knows that they
> will break down faster. I suggested that she might try spraying the kiln
> with ITC in order to preserve the integrity of the brick but she is not sure
> that this would be cost effective. I, myself, have sprayed my electric
> kiln with ITC and have found that the elements have lasted much longer.
> I would be interested in getting some opinions, especially from some
> other salt glaze potters.
>
> Debby Grant in NH
>
--
Earl Brunner
http://coyote.accessnv.com/bruec/
bruec@anv.net
vince pitelka on tue 2 oct 01
> I am asking this for a friend who is not on the list. She is rebuilding
her
> salt kiln using soft brick instead of hard and of course she knows that
they
> will break down faster. I suggested that she might try spraying the kiln
> with ITC in order to preserve the integrity of the brick but she is not
sure
> that this would be cost effective. I, myself, have sprayed my electric
> kiln with ITC and have found that the elements have lasted much longer.
> I would be interested in getting some opinions, especially from some
> other salt glaze potters.
Debby -
Before your friend goes any further I suggest she contact Tracy Dotson at
ThePottery@aol.com - Tracy has built hundreds of kilns, and has tried some
softbrick salt kilns lined with ITC, and the results were very discouraging.
Those kilns have been rebuilt with hardbrick. If your friend's kiln is
going to get very light use, and if he/she can limit the maturation
temperature to cone 8 or 9, then you might get good life out of it.
If your friend decides to go ahead with the softbrick, make sure that the
floor and the lower 24" of wall are entirely hardbrick. No softbrick and no
coating (so far) can withstand the stress of salt firing in those areas.
Best wishes -
- Vince
Vince Pitelka
Appalachian Center for Crafts
Tennessee Technological University
1560 Craft Center Drive, Smithville TN 37166
Home - vpitelka@dtccom.net
615/597-5376
Work - wpitelka@tntech.edu
615/597-6801 ext. 111, fax 615/597-6803
http://www.craftcenter.tntech.edu/
Pete Pinnell on wed 3 oct 01
A few years ago, a couple of my graduate students did some testing of ITC, along with several home made coatings, in our soda kiln. Soft bricks were coated and lined up on top of the bag wall, along with a couple of plain soft brick to act as a control. In the short run, the home made coating held up best, and the ITC coated brick was no different from the uncoated ones. In the long run, (after 5 firings), there was no difference among the bricks: all fell apart.
The problem, I believe, is one of porosity. The coatings (such as ITC) are not vapor barriers, so while they may not react with the soda they still allow it to pass through into the underlying brick, which fluxes and falls apart due to the difference in thermal expansion between the fluxed brick and the unfluxed brick which underlies it. If these coatings were glassy, they might be able to provide real protection. Just thinking aloud- has anyone tried using an Alumina Phosphate refractory as a coating? It would certainly be non-reactive with soda, and perhaps the phosphate glass would act as a vapor
barrier. In theory, that might work, provided the CTE is compatible to that of the brick.
Our test was done in a soft brick soda kiln we built from Thermal Ceramics K-25's, which have the highest Al2O3, lowest SiO2 content of any of the commonly available soft bricks. It started to fall apart within a dozen or so firings, with brick crumbles falling onto anything not covered by a shelf. We replaced the firebox with hard brick after about 40 firings, and managed to keep the kiln limping along for a couple of hundred firings. By the time we tore it down, the arch was about half it's original thickness. On average, we used one to two pounds of soda ash, dissolved in water, per firing. Had we
done the typical "dump in 20 pounds of salt" technique commonly used in salt firing, I doubt the kiln would have made it through a semester.
On the positive side, the lower mass of the kiln meant we were able to get firings in and out much faster, and the work had a fresher, brighter look than the "burnt cookie" appearance one often gets from hard brick kilns. It also used quite a bit less gas, of course.
BTW, we just built a new soda kiln and a new salt kiln: both are hard brick, and uncoated.
Pete Pinnell
University of Nebraska, Lincoln
Nils Lou on wed 3 oct 01
ITC sprayed on the inside of an IFB brick kiln will hold off the
deterioration for only a short while, so I don't recommend doing that as
it isn't cost effective. I am thinking that the only way to use IFB in
salt is to completely coat the entire brick so the corrosive vapors don't
get behind the coating and create spalling damage. I and my students will
be building an IFB salt kiln this fall with fully coated bricks here at
Linfield College in Oregon. We will let the list group know the results.
Inherent in the process is how the salt is introduced. Much less damage is
done by spraying in a saturated salt solution than simply dumping in solid
salt which liquifies before vaporizing. --nils
On Tue, 2 Oct 2001 DEBBYGrant@AOL.COM wrote:
> I am asking this for a friend who is not on the list. She is rebuilding her
> salt kiln using soft brick instead of hard and of course she knows that they
> will break down faster. I suggested that she might try spraying the kiln
> with ITC in order to preserve the integrity of the brick but she is not sure
> that this would be cost effective. I, myself, have sprayed my electric
> kiln with ITC and have found that the elements have lasted much longer.
> I would be interested in getting some opinions, especially from some
> other salt glaze potters.
>
> Debby Grant in NH
>
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>
Bruce Girrell on thu 4 oct 01
Nils Lou wrote:
> Much less damage is
> done by spraying in a saturated salt solution than simply dumping in solid
> salt which liquifies before vaporizing. --nils
A potter friend of ours went to France and returned saying that they use
cups full of salt placed so that the flames from the burners impinge on the
salt (not sure what the cups are made of). That would also eliminate the
dumping of salt into the kiln. Seems reasonable to me, but I've never had an
opportunity to try it. What, if any, would be the drawbacks to the
vaporization of salt from cups?
Bruce Girrell
second salt firing post in two days - what's happening here?
Steve Mills on fri 5 oct 01
This is precisely the method I use. I was taught it by a French Potter
Yves Crespel who works in Brittany. The containers I use are simple
cylinders about 2.5 inches in diameter with a little bar of clay across
the top as a splatter guard, and are fired to stoneware before use.
Otherwise they absorb the salt into the porous body and collapse into a
molten blob very firmly attached to the shelf!! In the 10 plus Cu.Ft.
Kiln I use, we put 2 between the firebox and the pot chamber, each
containing about 1 Dessert spoon of common salt, no more! The coverage I
get is excellent because I don't lose so much salt vapour out of the
stack; it melts earlier!
Try it!
Steve
Bath
UK
In message , Bruce Girrell writes
>Nils Lou wrote:
>
>> Much less damage is
>> done by spraying in a saturated salt solution than simply dumping in so=
>lid
>> salt which liquifies before vaporizing. --nils
>
>A potter friend of ours went to France and returned saying that they use
>cups full of salt placed so that the flames from the burners impinge on t=
>he
>salt (not sure what the cups are made of). That would also eliminate the
>dumping of salt into the kiln. Seems reasonable to me, but I've never had=
> an
>opportunity to try it. What, if any, would be the drawbacks to the
>vaporization of salt from cups?
>
>Bruce Girrell
>second salt firing post in two days - what's happening here?
--
Steve Mills
Bath
UK
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