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Kristin_Gail

A New Kiln Conversion Project: What Would You Do?

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Kristin_Gail    12

Warnings are necessary: 1. I'm chock full of cockamamie ideas; try not to roll your eyes too much. 2. The Kiln Book and The Art of Firing are literally on their way to me in the mail, so I may understand in a week or so why my ideas won't work.  But.

 

I've just brought home a new (to me) kiln.  It's currently electric, with 5" thick soft brick walls/floor and a 4" thick fiber lid.  Internal dimensions are 27.5" wide, 41.5" long, 30" high.  I'm using it for single-fired soda (I realize soft brick and fiber don't agree with soda), fired with two Venturi burners.  And I really hope to add a bit of wood, as well.

 

I'm currently planning cross draft, with both burners on one short end, chimney on the opposite.  I'm really hoping for a more front-side/back-side look to my pots, that's why I'm hoping to do cross draft.  I have a specific idea in my head of how I'd like to do it (although am quite perplexed about the chimney), but am first open to your seasoned suggestions.

 

If you had this nice, open, unadulterated cube, what would you do?  Or what do you think I shouldn't do?

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Biglou13    202

Pictures please.

 

I understand there some kind of coating. You can use to extend the life of soft brick.

 

My prelim. Designs for my kiln is for cross draft also. But I have hard bricks......

 

What is output for Venturi burner? Home made or store bought?

 

What shelves are you using?

 

Does design have a bag wall?

 

Unless you do up draft. You'll need a chimney that will take the heat meaning HARD bricks.

 

Then you'll have to calculate flue size chimney etc etc to get proper draft.

 

I think that forced air burner is a way around these issues.

 

Ok I think the cross draft is problematic for what you have. I think up draft is your best option. I have technique for the front side back side look. And still utilize, up draft. But will discuss that with you in private.

 

I like crazy ideas...... (Crazy plausible) ideas. I like ideas outside of the box.

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Kristin_Gail    12

I don't have photos right now, but can get some today or tomorrow. (It's currently wrapped in a tarp, sitting in my driveway, awaiting its reconstruction.)

 

The two burners are from Marc Ward.  I called him to describe the kiln and my plan, and asked if I could just add another burner to the one I already have, to save money.  He agreed, so I sent mine to him and he's setting up the new system for me, including a Baso valve and possibly a pilot.  They are B-2 burners, BTUs here:  http://www.wardburner.com/burnersparts/venturiburners.html

 

I was planning to coat the kiln with ITC 100, but Marc Ward advised me not to, as he used to sell it, and reports potters called him to tell him it had ruined their kiln.  I've used it on two prior projects with no such results, but I only fired each of those kilns a handful of times.  I was planning to use EPK/Alumina Hydrate as my coating, but could be swayed otherwise.

 

I could possibly be convinced to go downdraft, but no way in the world can you convince me updraft.  That's what I have right now, and that's why I bought this new kiln.

 

The shelves are, I think, mullite.  I realize those, too, aren't supposed to hold up to soda, but I intend to use them at least at first.  Coated, of course.  Everything in the kiln will be coated.

 

My idea is to build a bag wall 9" (or another number recommended here or figured out from those books!) from the short side, with both burners coming into this firebox.  I'd like to line this firebox completely with cut pieces of those mullite shelves (which are now 13" x 26").  I'm hoping they will hold each other up if I put them in there just so; or possibly put castable in the corners to wedge them into place.

 

In the stacking space I thought I could build up the bottom with a few layers of soft brick, harvested from my current electric kiln conversion, which has 2.5"-thick walls.  Then, on top of these, to protect them, a layer of cut up shelves/castable.

 

My confusion with the chimney is that all my research has been done online - and this research keeps repeating "use x, y, and z formulas to figure out chimney diameter and height.  Unless you're using Venturi burners."  But then I can never find info on that caveat.  I did find, somewhere, that the chimney might only need to be as high as the top of the kiln - which leaves me in a conundrum about how to get the fumes out of the kiln shed (which has to have walls [with big windows] to keep out snow, as I'm in Canuckistan).

 

I have a very, very small budget for this project, but (assuming I can make the shed out of found materials) I do have room for the hard bricks necessary for the chimney and bag wall (if I'm told I can't use salvaged soft bricks for the bag wall).  Although I do wonder, if the chimney ends up being high, at what point I could switch to metal or house brick.

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Mart    23

Wow Kristin_Gail, looks awesome! I wold love to turn this in to a downdraft gas kiln. :)

 

I think use of word chimney is a bit misleading.

What you really need, is:

A) a flue internal/external, depends how you like to build it

B) a hood above the kiln, that takes gases exiting via "flue" from your kiln.

 

You have:

w 27.5"

l 41.5"

h 30"

Lets see now, google's 34237.5 cu inch to cu feet gives us 29 stetsons hats or 19,81 cubic feet. Lets forget that for now.

 

You say have 13" x 26" kiln shelves. Aren't those too tight fit for a downdraft gas kiln?

Are you planning to point those burners upward. If yes, why do you need a bagwall?

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Biglou13    202

nice

 

do you have a pyrometer yet

 

very excited to see the progress

 

the only successful kiln conversions ive seen were up drafts

 

but i want to see your concept/ idea.

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JBaymore    1,432

ITC 100 HT HAS to go on new soft refractories to be really successful.  You also have to prepare the brick surface VERY well... and it needs to be WET first.  And it has to be a VERY thin coating.... the BIG mistake people make is the American "more is better" approach.

 

All of that being said........ ITC 100 HT ios NOT the "cure all / be all" that it is purported to be.  It does extend the life of soft bricks in soda a bit........ but they still die a pretty fast death.

 

That kiln looks a lot like the typical Japanese electric reduction units.  Crossdraft should work GREAT for the "directionality" you mention.

 

best,

 

.......................john

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JBaymore    1,432

Are you planning to point those burners upward. If yes, why do you need a bagwall?

 

Crossdraft is what she said, I think.  Flow along the long dimension of the kiln.... in one end.... out the other.  A mini gas-fired "anagama" so to speak.

 

best,

 

.......................john

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Mart    23

JBaymore, correct. That's what she did say :)

 

But still, if flames are blasted up from the left (see the picture above), tight fitting shelves will make the heat move form left to right and then leave from the right bottom side of the kiln.

This requires least cutting/damage. Flue comes up at the right side of the external wall, made of light insulation bricks or ceramic fiber + fire bricks and a hood + sheet metal pipe above the flue/kiln will take care the rest.

 

Building a full height brick chimney makes no sense at all, unless she got the material laying around in piles.

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Pres    896

Could this be lined with hard panel fibrefax insulation to get along with the brick-protecting it?. this thought coming from a neophyte when it comes to kilns.

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JBaymore    1,432

Why go "up" on the side.... just fire into the chamber thru the side wall in the direction of flow.  Use larger forms as a "bag wall" to disburse the flames / heat energy as necessary.

 

best,

 

....................john

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Kristin_Gail    12

Mart –

Can you help me understand the difference between a flue and a chimney?  Is the flue the hole and the chimney the column?  I had intended to either have the exit flue be at the bottom of the vertical face of the narrow side, or in the floor adjacent to this spot.  I hadn’t considered putting a vent over the kiln.  Is this still something I'd want to do, knowing I will be introducing wood?  Oh geez, now I'm thoroughly confused by your last post ...

 

The shelves are currently 13†x 26â€, but I intend to cut them so the stacks of wares are about 21†x 21â€, which leaves roughly 3†space on each side.

 

I planned to drill the holes for the burners on the bottom of the vertical face, so coming in horizontally, hitting a target brick if necessary, with a bag wall that’s adjustable in height, but I’d probably start out at 13†high (just because it’s the height of one shelf on end).  

 

My little Venturi gets to Cone 6 in my 7 cu ft kiln without too much problem (PSI gets up to about 22) on a 100-gallon tank.  While this new kiln is, right now, 19+ cu ft, my plan of building up the floor under the stacking space brings it down a few cu ft – in addition, the walls are 5†thick as opposed to 2.5†thick in the smaller kiln.  So Marc Ward and I decided I shouldn’t have too much of a problem reaching temp with two identical burners and two 100-lb tanks.  We’ll see how it goes – especially in a Canadian winter.

---

Biglou – I do have a pyrometer.  I recently finally bought a digital one, encased in a ceramic sheath.  It was a great help in the little kiln last time.

---

John – Yes, that’s what I mean about the burner direction.  I never thought of it as a mini-anagama, but I can see that now.  As for the bag wall:  You're saying don't put one in at all?  I've had a tough time with pieces blowing up when the flame hits them directly, so I'm a bit enamored with the idea of a bag wall right now, keeping my pieces nice and safe.

---

There’s a little sketch of a crossdraft soda kiln I found somewhere, and I’ve been picturing this sketch as I tried to plan this reconstruction project.  I should have my husband sketch out my idea for me. 

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JBaymore    1,432

I planned to drill the holes for the burners on the bottom of the vertical face, so coming in horizontally, hitting a target brick if necessary, with a bag wall that’s adjustable in height, but I’d probably start out at 13†high (just because it’s the height of one shelf on end).

 

Precisely what I was talking about. 

 

 

As for the bag wall: You're saying don't put one in at all? I've had a tough time with pieces blowing up when the flame hits them directly, so I'm a bit enamored with the idea of a bag wall right now, keeping my pieces nice and safe.

 

If you are going to bisque in that unit, then you likely will want a bag wall in it then to lessen the chance of such issues.  If the ware is already bisqued, and if you are glazing it (using water based stuff) you'll need to let the glaze water dry out before firing. For glaze firings you can use pots for a bag wall and for bisquem use bricks..... best of both worlds.

 

But if it is bisque ..... it should not be an issue.  Put specially designed pieces in this location that you use for a bag wall....without wasting the space re-firing bricks over and over.  This is a common practice amongst us wood firers.  You will have to use a good refractory body that can take the higher temperature there... like cone 12-14 .  And any glaze will have to be tolerant of one side being REALLY hot and the other much cooler.  (American Shinos don't move and LOVE direct flame impingement and heat.)  Very directional effects.... which you are looking for.

 

In that size and design kiln you will not get much impact from adding  "a little wood".  If you want some of the kind of effects that you can get in a wood kiln.... without having to burn a lot of wood.... put in some charcoal ports in that kiln for doing youhen (fire change) charcoal work.  This is the way that a good portion of the Bizen pottery in Japan is fired even though it is ALSO done in a wood fired kiln (mainly for the heat energy part of things). 

 

Take unglazed ware up to cone 10-12.  Best for this is high iron bearing bodies.  At the peak of firing, let it cool exactly 100 C off of the peak.  Then take hardwood charcoal (not briquettes) and thru prots you have left in the kiln walls / roof for this exact pupose,..... bury the wares in this charcoal.  Seal the kiln and then let it cool.  Play with the air management on the cooling cycle and also the clay bodies.

 

Hope this is of help.

 

Oh.... a "flue" can be a hole into and out of a chamber.  A chimney is just that, a chimney.  Sometimes you can call a chimney a flue also.

 

best,

 

........................john

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Kristin_Gail    12

It isn't perfectly to scale; he didn't include the walls; and there's still this huge unknown about the flue/chimney.  Also, I'm pretty sure y'all already understand what I described anyway.  But I did have the husband sketch this for me:

 

Big_Anthony_side_sketch.jpg

Maybe I should have the flue go down into the first layer of salvaged bricks, but still out the side ... ?

 

I'm still so perplexed as to how I can build a roof over this thing.  Crossing my fingers my books arrive soon and contain the answer.

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Kristin_Gail    12

Thank you so much, John.  I'm especially thankful for the charcoal info.   I had just intended to throw in some splits from out wood pile, but wasn't sure when, etc.  

 

Also:  I'm single-firing in this kiln, as I have no other kiln to use for bisque.  Hence the broken pieces when the flame hits them.

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Mark C.    1,800

I like the drawing except for the flue exit. I feel the lower the better. Can you get it down to floor level or another way to say it the same level as burners-so heat circulated a little longer before exiting?

 

as far a a roof . I assume you mean outside?

Just a framework to hold a metal roof will work fine.

Mark

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Biglou13    202

What is purpose of brick "riser" under shelves, why the floor build up?

Did you get my pm?

 

What problems are you having with up draft?

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Kristin_Gail    12

Mark - Oh yes, I can put that flue wherever it needs to go!  Lower the better?  Yes, then.  I'll do that!

 

Chimney:  I don't understand how high I have to build the chimney, although I get the feeling it doesn't need to be very tall.  If this is the case, and the chimney ends just above the kiln, how will smoke/gasses get out of the little shed?  If I make the chimney tall enough to clear the shed, won't this make too much draw?  Can I make the exit flue a few feet long, to get out of the shed, then turn 90 degrees and go up once it gets outside?

 

Biglou - Oh crap, I forgot to answer your PM!

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Kristin_Gail    12

Found it!  Chimney height with atmospheric burners:

3 times interior height + 1/3 linear draw

3(24) + 1/3(41.5 + 5 + 9) = 72 + 18.5 = 90.5" = ~ 7' 6"

[With 24 being majority of interior height after I build it up).

 

Okay, then.  It'll go through the roof.  Perfect!

 

Wait.  Have I done my math wrong, or is that 144 bricks x $8.65 per brick = Whoa, how much are those forced-air burners again?

 

--------

 

Can anyone comment on this Rigidizer stuff?  Should I be applying that to the ceiling?

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Mark C.    1,800

If you go sideways more than just the wall thickness make your chimney taller than that formula

You cannot make it to tall in most cases-but it can be not tall enough-many etrror on this side as bricks run short as well as funds come chimney time.

Just allow plenty of room around and combustable roofing and use metal falshing as you stack will be hot.-You can use hard or soft brick up to the roof -then hard brick in the weather or a stainless steel salvage pipe??

I suggest you go up not sideways and you will need a damper build into stack as well-Your art of firiing book will show this.

As far as coatings I would add you will get better soft brick life from one-the lid is fiber already shrunk so I woold be wary of you epk and alumina coating on roof-as I do not know how well it will stick?

I can say that my collidial silica and milled zircon spray light will stick but Have NO SODA experience with it only salt. The ITC sprayed light will also stick-but old fiber may start to flake in a soda atmosphere

I would coat the floor and walls with the aluminai/epk mixture and do something else on ceiling

You can look up in the search function my coating recipe as I'm working hard at shows-apple juicing/fall chores right now.

Mark 

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Chantay    101

I have read about and heard from another potter about washing the inside of the kiln (for soda/salt) with a glaze.  I think Robin Hopper did this using a shino.

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Mart    23

Why do you like to spend energy (BTU, kWh) for heating up that bag-wall? :)

Will this work, if you send flames straight up?

This is a 3 min quick sketch, I hope it makes sense. What do you guys think, will this work? (I forgot the salt/soda opening)

 

post-19541-0-70166600-1380005268_thumb.jpg

 

Now you will have a bit less than 29 stetson hats of space but still more, than on the drawing you had. I am not telling, your idea is wrong but it looks like something you want to use when building a wood fired kiln.

Every brick you place inside the kiln, needs to be heated up. There is no way around it. 

 

NB! Kristin, pay really close attention to page 21 in The Art of Firing ;)

post-19541-0-70166600-1380005268_thumb.jpg

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neilestrick    1,381

Why do you like to spend energy (BTU, kWh) for heating up that bag-wall? :)

Will this work, if you send flames straight up?

This is a 3 min quick sketch, I hope it makes sense. What do you guys think, will this work? (I forgot the salt/soda opening)

 

attachicon.gifCD_kiln.jpg

 

Now you will have a bit less than 29 stetson hats of space but still more, than on the drawing you had. I am not telling, your idea is wrong but it looks like something you want to use when building a wood fired kiln.

Every brick you place inside the kiln, needs to be heated up. There is no way around it. 

 

NB! Kristin, pay really close attention to page 21 in The Art of Firing ;)

 

A bag wall is often necessary to make the kiln fire evenly. In a kiln that size it probably won't need to be more than 4.5" (1 brick on its side) tall, so that's only 3 bricks for the bag wall. In a kiln that already has over 200 bricks, that's only 1.5% more bricks, so it might cost another 50 cents in gas costs at the most to heat those up. You'd probably waste more gas trying to even out the temperature without them.

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neilestrick    1,381

Personally, I'm not a fan of burners coming up from the floor, for two reasons. First, it makes them difficult to adjust. I don't particularly like having to lay on the floor to adjust my burners. Second, they can get crud falling into them, and cleaning them out can be difficult because they're under the kiln. Go in from the side, with a short bag wall, and save yourself some grief.

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Mark C.    1,800

I'm also not a fan of burners up thru the floor-My updraft has them and when something falls into them its a pain to fish it out. Also without a bag wall there are HOT spots that do not need to be there. Many manufactures use this system as the sacking splace is bigger-not better just more for less bricks used. The corners where that flame comes up are always hot spots. The bag wall keeps this heat way more even.Neil summed it well above.Bag walls make for more even firing and less hot spots.

Mark

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