Mark Potter on mon 26 oct 09
Clayarters / Gasfirer's / Kiln Mavericks . . .
I need to do some improvements/repairs to the top/arch of my Alpine 24
cu ft updraft gas kiln.
I'm loosing way too much heat through the top. I have leaks there that
are just too much. I got a good firing out of the kiln recently in a
new location with new burners, but the kiln has a terrible time making
it through the last two cones in a Cone 10 firing. I've had this
problem each and every time I've fired this particular kiln. It
stalls, and I believe the reason is too much heat loss through the top.
The Alpines were manufactured with one layer of brick on the sides and
top, which was then backed up by a loose mix of vermiculite and some
kind of refractory cement. Over time this 'mix' has broken down, and
lost a lot of it's insulating abilities.
I need to dig out the top of the kiln. . and make some structural
repairs. Like all Alpines, this one has some pretty major cracks in
the kiln walls and arch. None that have been alarming, until now . . .
I'm wondering if the crack in the arch, though it wouldn't lead to a
collapse, actually was the thing that caused high temperature gasses
to divert upwards and work it's way through the vermiculite mix
insulation.
So does anyone have suggestions for the easiest/best rebuild of the
top of the kiln. Has anyone had experience rebuilding the refractories
of Alpine kilns?
I'm thinking of the following:
a) dig out all the loose mix insulation, exposing the arched brick
below. . . .
b) lay in Kaowool ceramic blanket in it's place. Back that up with
ceramic board to keep the airborne fibers at bay.
c) The cracks in the arch brick are about 1/8" wide when the kiln is
cool. I'm planning to stuff those with a mixture of ceramic mortar and
ceramic fiber.
Does this sound like a wise plan of action?. . . . or would you
recommend I dig out the entire arch and essentially rebuild the top of
the kiln?
regards,
Mark
Mark W. Potter, Jr.
131 Cottage Street
New Haven, CT 06511
www.visionage.net
203 909-0004
Marcia Selsor on mon 26 oct 09
I did some repairs including a floor replacement on kilns at the UH
Manoa while I was serving as a sabbatical replacement.
For cracks, I soaked ceramic fiber in ITC and stuffed the cracks. I
replace the peep plugs with new thrown larger cones on raku clay.
For the top, repair cracks and cover with 1-2" fiber blankets to fit
around the damper mechanism.
Spray the interior with a thin coat of ITC.
If you have to replace the arch..remove the damper assemply. Trace
with newsprint, the interior curve of the arch and build an arch
support to match it.
Firgure the correct layout...skew, #1 arch 2 straights...whatever the
combo is on the arch. Build a support for the arch frame with
forethought of how to drop it down once the arch is complete. I would
also remove the shell and put fiber blanket to replace the vermiculite.
Marcia Selsor
On Oct 26, 2009, at 9:26 AM, Mark Potter wrote:
> Clayarters / Gasfirer's / Kiln Mavericks . . .
>
> I need to do some improvements/repairs to the top/arch of my Alpine 24
> cu ft updraft gas kiln.
>
> I'm loosing way too much heat through the top. I have leaks there that
> are just too much. I got a good firing out of the kiln recently in a
> new location with new burners, but the kiln has a terrible time making
> it through the last two cones in a Cone 10 firing. I've had this
> problem each and every time I've fired this particular kiln. It
> stalls, and I believe the reason is too much heat loss through the
> top.
>
> The Alpines were manufactured with one layer of brick on the sides and
> top, which was then backed up by a loose mix of vermiculite and some
> kind of refractory cement. Over time this 'mix' has broken down, and
> lost a lot of it's insulating abilities.
>
> I need to dig out the top of the kiln. . and make some structural
> repairs. Like all Alpines, this one has some pretty major cracks in
> the kiln walls and arch. None that have been alarming, until now . . .
> I'm wondering if the crack in the arch, though it wouldn't lead to a
> collapse, actually was the thing that caused high temperature gasses
> to divert upwards and work it's way through the vermiculite mix
> insulation.
>
>
> So does anyone have suggestions for the easiest/best rebuild of the
> top of the kiln. Has anyone had experience rebuilding the refractories
> of Alpine kilns?
>
> I'm thinking of the following:
>
> a) dig out all the loose mix insulation, exposing the arched brick
> below. . . .
> b) lay in Kaowool ceramic blanket in it's place. Back that up with
> ceramic board to keep the airborne fibers at bay.
> c) The cracks in the arch brick are about 1/8" wide when the kiln is
> cool. I'm planning to stuff those with a mixture of ceramic mortar and
> ceramic fiber.
>
> Does this sound like a wise plan of action?. . . . or would you
> recommend I dig out the entire arch and essentially rebuild the top of
> the kiln?
>
>
> regards,
>
> Mark
>
>
> Mark W. Potter, Jr.
> 131 Cottage Street
> New Haven, CT 06511
>
> www.visionage.net
> 203 909-0004
>
Marcia Selsor
http://marciaselsor.com
douglas fur on mon 26 oct 09
Mark
Two method which come to my mind-
Excavate and add fiber. *I'd check with your local refractory dealer. When
I built a kiln for friends the APgreen dealer told me about some low temp
back up fibers "furnace blanket" and boards that were cheaper and better
insulation (insulation value tends to fall as refractorieness rises so
getting the lowest temp rating that will do the job usually gets you the
best insulation)*
Excavate and add castable-
*A castable would tend to seal leaks. I'd make a mix with
perlite+sand+fireclay+portland cement*
I've also seen some alpines that seemed "too"* tall and were just hard to
fire evenly.
*By this I mean that they get away from a cubic shape and are more like two
cubes stacked on the inside.
I've also seen some people add more fuel to heat the top but then must open
up the damper to balance the combustion and the gasses rush out not spendin=
g
enough time in the kiln to heat the top. So the contrarian gambit of
reduced fuel and a tight damper can be successful.
DRB
Seattle
Vince Pitelka on mon 26 oct 09
Mark Potter wrote:
"So does anyone have suggestions for the easiest/best rebuild of the
top of the kiln. Has anyone had experience rebuilding the refractories
of Alpine kilns?"
Mark -
I did a lot of work on the three Alpines we had at UMass-Amherst when I was
clay studio technician there after grad school, including refractory repair=
s
on the arches. The cracks sound very repairable, and the rest is easily
rebuilt. Once you have repaired the cracks, and have replaced the
insulation above the arch, you won't have to worry about losing heat. You
can use fiber blanket to add additional insulation, but I prefer a
less-expensive solution mentioned below, and in any case the fiberboard
would be redundant and unnecessary.
The best way to repair cracks in a softbrick arch is to inject
high-temperature refractory cement or repair mortar into the crack. For
that, you will need to get some empty caulking-gun tubes. You can get them
at good paint stores, especially the ones that supply paint to commercial
painting contractors. If you can't find an empty caulking gun tube, just g=
o
to Lowe's or Home Depot, and buy several caulking gun tubes of cheap
water-base whatever - anything in a caulking gun that is water-base. The
important thing is that the residue will wash out once you inject the
contents of the tube into the garbage (or some more devious use). You will
need to use compressed air to push the plunger disk back out the open end o=
f
the tube, but do so very gently so you don't create a cannon, and aim into =
a
closet or something so you don't lose the plunger disk. You will also need
the standard caulking-gun frame that fits the standard tubes.
Ever three inches or so along the crack, drill a 1/4" hole with a masonry
bit. The hole depth should be half the thickness of the arch. If you are
going to remove all the insulation from the top of the arch, then do this
from above. Fill the caulking gun tube with high-quality refractory cement=
,
put the plunger disk in place, and put the tube in the caulking gun frame.
Liberally spray water in the vicinity of the crack on both sides top and
bottom. That's so that the refractory cement has a chance to cure before i=
t
dries completely. Poke the tip of the caulking gun firmly into one hole,
and inject as much refractory cement as it will take. Do the same at every
additional hole. Work additional refractory cement into any gaps in the
crack and smooth with a wet sponge. No need to mix in ceramic fiber for a
narrow crack like this.
For insulation over the arch, you can use ceramic fiber if you want, but yo=
u
can create an efficient insulation layer very easily for pretty cheap as
explained below, and it will help reinforce the arch. You will need some
sort of insulating filler, and there are a number of choices. Do you have
any IFB scraps around? If so, you can crush them on a concrete pad outdoor=
s
with the end of a 4x4 fence post or a piece of heavy pipe. If you don't
have crushed scrap IFB, you can use perlite, those little expanded silica
spheres used in potting soil, often available by the bag from landscapers.
Or, if you can find any these days, you can use vermiculite. Or, if the
kiln is in a well-ventilated place, you can use sawdust (not fine sawdust).
By volume mix 40 parts insulating filler, 30 parts cheap sand, 20 parts
fireclay or any dry crushed scrap clay, and 10 parts Portland cement. Mix
in a mortar tub with a hoe, using just enough water to make a rammable mix,
and pack in place on top of the arch. You can do this immediately after yo=
u
do the repairs on the cracks in the arch, but wait at least 36 hours before
applying any heat in order to let the Portland cement cure. After 36 hours=
,
you can close the door, light the burners, and leave them set on low for 24
hours or so on low to help things dry out a little. Even if the insulating
layer is not completely dry at that point, you can fire the kiln, because
with 40% insulating filler and 30% sand it is extremely well ventilated .
If any cracks develop in the insulating layer, you can fill them with a mix
of 80 parts insulating filler and 20 parts scrap slurry.
Have fun -
- Vince
Vince Pitelka
Appalachian Center for Craft
Tennessee Tech University
vpitelka@dtccom.net; wpitelka@tntech.edu
http://iweb.tntech.edu/wpitelka
Snail Scott on tue 27 oct 09
On Oct 26, 2009, at 10:00 PM, Vince Pitelka wrote:
> ...if you can find any these days, you can use vermiculite...
Has it gotten scarce? -Snail
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