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QotW: Do you protect your kiln floor with a kiln shelf to start your shelf build, and if so do you use a full or pair of 1/2 shelves?


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Hi folks, once again no new questions in the question pool - 

Soooo I will pose another question this week. 

As all of you probably know, I have a new kiln and will be going through the test firings and first firings and other things. This is big step, as I have not used a vent or computerized kiln before to fire my own work. I have assisted in firing and seen the dyna trol system in use. My new one has genesis, and quad elements a power vent, and 3 inch brick. However, that is not anything to do with the question. . . somewhat.

I have always fired my kilns with a base shelf usually placed on 1/4-1/2 inch stilts. I started out with full shelves in the bottom. The full shelf broke after several firings, and I started using 1/2 shelves. Then I started to use 1/2 shelves with different height stilts under them. My reasoning was two fold, one to start the shelf build with the bottom allowing overlapping plate lips, and second to give more air circulation at the bottom of the kiln. Now I have decided that the bottom will have two 1/2 shelves, but do not think I need to use a staggered first layer, as if I leave them flat I could possibly up 3 pieces to a layer, even though one would bridge the two shelves.

My practical question for the QotW: Do you protect your kiln floor with a kiln shelf to start your shelf build, and if so do you use a full or pair of 1/2 shelves?

 

best,

Pres

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Original owner had just bought a new set of half shelves; she gave me four of the old set. Two serve as the base, on half inch risers; the better of the other two sees service as top shelf when I have a short stack. The fourth one is falling apart; it might serve as a bottom if the other ones disintegrate...
I'm liking half shelves for staggering the load - helps even out the heat. The extra posts take up some room, but overhanging can make up for it.

Am looking forward to joining you in new kiln land one of these days Pres. I have a plan!

Edited by Hulk
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Full or two half shelf’s protecting the bottom, always at least half inch off the floor, more like 1”. Staggered stacking as practical as after red heat there is really not much convection happening and even if there was the air is so thin it does not hold any real heat and to prove it to yourself pull a peep and feel the blast of hot air leaving. Oh, you won’t actually because the atmosphere is so thin.  So the staggered stacking is created with an eye to make the wares able to “see” as many elements as practical for even heating. Sort of like standing in the sun or under a shade tree. 
And to add, the first layer is rarely staggered unless I have something very tall and I really have never experienced difficulties. Congratulations  on the new kiln, you have done this for so long my guess is you will figure cool ideas to try.

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My electric (bisque only) is a full on bottom and up on some smaller broken kiln shelve pieces at the stacking points .That space is 1/2 inch off floor. Its about 10 cubic feet.

I only use 1/2 shelves from there up-I do have a full shelve  if needed I  just do do not use it ever.

its a manuel kiln with a fire rite auto turn up switch that ramps it up automatically .Timer and cone sitter for shut down

The kiln is outside and has no vent system-Its not fired more than 6-8 times a year -I tumble stack the top of it usually-really stuff it full.

Most bisques are in my 35 cubic car kiln every other week-way cheaper to fire

Edited by Mark C.
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Putting a shelf at the bottom, whether two halves or one full, is a must for two reasons. One, it helps to reduce heat loss through the floor so the kiln fires more evenly. Second, it protects the floor. It's much cheaper to replace a shelf than a kiln floor if something goes awry. Kiln shelf: $60. Kiln floor w/ freight delivery: $450. I've always just used pieces of kiln shelves as posts under the bottom shelf. It doesn't need to be any more than 1/2 inch. You'll get plenty of air flow from a downdraft vent with just 1/2".

If you use a full shelf at the bottom and use 1/2 shelves above it, then you have to use 4 posts under the full shelf, which runs the risk of the shelf not sitting evenly on all 4 posts. You do not want the shelf to rock, or it can warp or crack. If it's rocking at all, use very thin wads of clay dipped in kiln wash or alumina to even everything out. Be sure to use clay that is rated for the highest temp you'll be firing, or make wadding from kaolin and alumina.

I never stagger shelves unless I have to, and have never had issues from it, even in my big 21 cubic foot kiln. I've always found that staggering just wastes space. Unless you're firing very quickly, you shouldn't have evenness problems across a shelf.

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@Hulk Don't get rid of those broken shelves, they work well as @neilestricksays to use as bottom stilts, or other stilts. I have always used them as a "riser" for a stilt when I didn't have enough 1/2" stilts.  @neilestrickI had to get more of the patens in to the loads, and as there was not enough space for two across the stagger helped, then would fire the chalices on the top shelf.

I had wondered about large bottom shelves, and probably did things wrong as I used 5 in the octagonals to support the full bottom shelf. It is good to know that 1/2 inch gets me enough to have downdraft ventilation. I leave a small space between halves for air circulation.

@Bill Kielb When I was in my first year of teaching, '73, I was talking to another teacher and an administrator. We were standing near the kiln at the end of the ^06 glaze firing that the ceramics teacher had turned up and opened the vent on the old square Amaco. You folks all remember those polyester pants that were in vogue back then? Well, I stood there in the warmth not realizing that I was near the vent hole. Yep, melted them to my leg.  Never again. Wore cotton after that. The old kiln?  5 years later I started dong electric raku out in the center court, for the next 3 years. 

 

best,

Pres

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I put a full shelf on the bottom, on 4 x 1/2“ stilts. I use half shelves above that. My kiln is on a square stand, not on a metal plate, so the stilts also line up with points on the metal stand underneath the kiln so I don’t crack the bottom with uneven weight. So far so good.

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39 minutes ago, Pres said:

I was near the vent hole. Yep, melted them to my leg.  Never again. Wore cotton after that. The old kiln?  5 years later I started dong electric raku out in the center court, for the next 3 years. 

 

We have had similar mystery things happen especially after red heat. Folks often don’t realize that infrared radiation is a thing. Had a sectional L&L as I recall but could have been any. A kiln that did not have continuous sheet steel wrapping each section, it left a brick on brick interface between the sections. I remember seeing a red glow between the sections to which I really didn’t give it a bunch of thought at the time, pretty small light leak. Until the molded plug for the kiln began burning up. Turns out that neat red  infrared stripe went right across the back of that plug and over time the plug overheated and began failing. Ordered a new cord end and in the meanwhile stuck some foil tape on the plug to reduce its temp by 30 -50 degrees or more until the new one arrived days later. Just a small innocent red stripe!

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I use 1 inch stilts under a shelf that has split in half,  I want to make sure I have enough circulation for my Enviorvent to function well.  The bottom is always a little colder so I don't mind starting the load a little higher in the kiln.   Denice

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