Cement under hard brick in cone 10-12 kiln

[Marcia Selsor]

If they are one brick thick, they are most likely a very high quality brick and not K2300.

I had a brand new Geil at UTB but too far from the meter to be used. I did clean out the wasps'nests in the burner ports. Trying to remember

how thick it was.

It was definitely some very high quality bricks and not the every day soft bricks I have used for kiln building.

 

Marcia

[Marcia Selsor]

Lily,

I googled Geil kilns.

I do think there is more than one course of brick or insulation on those kilns. The interior is lined with very high quality bricks.

 

"2600º F and 2800º F High Alumina (60% or more) Insulating Fire Brick backed by high temperature block insulation constitutes this kiln's interior. All models will fire to 2500º F (cone 14). "

Insulating your kiln is the best way to control the firings, and save energy making it cheaper to operate in the long run.. It is not good to go "cheap" with one layer of bricks in my option.

Marcia

[Guest JBaymore]

Every kiln design is a design and engineering problem that takes into account MANY factors in coming up with the final solution. In the case of pre-manufactured (as opposed to site-built) kiln units, there are many considerations that come into play that have nothing AT ALL to do with just the thermal issues.

 

One of these is the physical size of the unit and the transportabilty (weight). A kiln with the more typical site-built standard of 9" brick walls would be physically very large and also very heavy. Installation issues into spaces for jobbers would increase, and the shipping costs would skyrocket. So a tradeoff happens between thermal considerations and these other factors. Hence the usual thinner wall sections.

 

I am sure you have noticed that you CAN build a fiber lined raku kiln from a single layer of 1" fiber blanket suspended on a frame of chicken wire and if you pump in enought BTUs/hr... it easily gets to temperature. But is it an "optimal" insulation situation? No, of course not. But if the over-riding goals for the kiln are simple, cheap, and light.... it works. But you are trading fuel per firing for "simple, cheap, and light". In some situations that is the correct trade off. In some... not.

 

Another one of these "other factors" is the price point for the market. If one upgrades the insulation, that increases the manufacturing costs... and hence the final sale price. Combine this with potential increased shipping and jobber installation costs.... and maybe you price the unit out of the market. There is a limited market for these kinds of units to start with, and usually the market is trying to squeeze nickels to get more pennies (even institutions). So get the already high price higher... and sales drop off.

 

CAN you build a cone 10 gas kiln with ONLY 4 1/2" of IFB as a lining. Sure. Look at Bailey gas kilns for a commercial example. Will it work? Yes. Is it the best solution? Well.... you hve to put down the list of design considerations that went into the decisions to DO that.... to evaluate that idea.

 

Are there potential "issues" with only 4 1/2" of IFB for a wall section? Yup. Lots of them. For one example, the high temperature gradient from hot face to cold face and the physcial breakdown stress such a differential places on a monolithic brick. If you understand what al;l of these are... you can decide if this is an acceptable choice within you own deign guidelines.

 

Are there some general "engineering best practices" for kilns. Yes, lots. Are they totally unbreakable "rules"....... mostly "no". If you understand the nature of the matrerials you will use and the concepts behind their uses.... you can make intelligent informed decisions.

 

I use a long checklist of questions with clients when we design a kiln unit. The answers lead to the final design.

 

Just like everything else in ceramics ... the always correct answer to, "What should I do in buildfing my kiln?" is "It depends".

 

best,

 

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

[Marcia Selsor]

exactamente!!!!

 

Marcia

[Mark C.]

I like the 9 inch wall for its thermal mass

The interior can be soft brick or fiber or fiber over soft brick but the exterior for me looks best as hard brick-for me this is only an aesthetic issue. I have friends with expanded metal frames with all fiber kilns and they work fine but look strange

The thermal mass helps for a slow cool down as well.

Mark

[yedrow]

Marcia,

 

I was thinking too narrow. I believe there is an inch or so thick block insulation behind the IFB.

 

John,

 

I understand. It's all about the engineering. And, there is a lot more to this than I have been told.

 

Mark,

 

I'm still real clear about having lots of thermal mass. As I understand: High thermal mass kilns cost more to operate, but they also give a more even cooling cycle. I know that we have had terrible blistering bouts with this kiln (most white clays blister at least some), and I've been wondering if the problem isn't too rapid a cooling cycle.

 

Joel.

[Mark C.]

Joel

The blistering is on the naked clay parts or under glaze or both? whats the clay body?

and what Temp is it fired to?

 

As far as thermal mass my favorite wall is soft then hard-the soft super insulates on the way up and the hard holds the heat after gaining some on the way up and releases slowly during the way down to some degree. My side walls on car kiln have fiber over the soft brick so the wall mass is cool on the up side and warm on the downside.The whole wall is 11-12 inches with that fiber over a standard two brick layup.

 

Mark

[yedrow]

The blisters can vary in size, up to almost centimeter, but mostly smaller. There appears to be a layer of glaze on the body surface. The worst body is a variation of B mix, but we have problems on all white stoneware bodies so far. The glazes that blister most are mostly, but not always, glazes that include rutile. There are no constants it seems. I used 25# of Standard's standard body and it didn't blister, but that isn't enough to draw conclusions from. Porcelian doesn't blister beyond margin of error numbers. I've consulted with Jeff Zamek about it but we didn't get to a solution (the company made changes). The only solution I could find was to change to a red clay, and that works. However, people like copper reds (groans) and a red body doesn't play well with red glazes. Otherwise I'm happy with the red body for the most part.

 

Joel.

[Guest JBaymore]

Yedrow,

 

How are you bisque firing that white clays? Electric kilns? What is the programmed cycle (ramps and holds exactly). Does the electric kiln have a local pickup ventilation system? Describe exactly how you stack those bisques.

 

best,

 

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

[yedrow]

We don't stack real tight, but reasonably tight. However, the bisquing schedule has changed over the last couple of years. We try to keep the ware exposed to at least 1 element, preferably 2. We now have a different kiln, but we were using an L&L with slow bisque. We really did try many variations in bisque firing since that was the most likely cause. We're now bisquing to 06 but when we were using the B mix knock off we were bisquing to 05. I'm afraid I don't remember the ramps and holds in any detail. Presently we're using a 19 cu. ft. Olympic, that uses a kiln sitter (bar cones) with a 3 hr. delay at the beginning of the firing schedule. Oh, and large cones fall pretty much within half a cone or better, at least since last I saw.

 

The blistering on the B mix was so bad that we could fire the ware twice (90 cu. ft. Geil downdraft kiln) and get blisters that were as bad in the second firing, as they were in the first.

 

I soaked the gas kiln and also dropped down at different firings between 50 and 200 degrees, trying to find a place to soak that would allow the bubbles to heal.

 

Joel.

[Mark C.]

I have seen a lot of B-mix blistering over the years.

I do not use but 200#s max per year of B-mix which is drop in the bucket but my fellow potters who live nearby use it and its gone south many times. When it blisters it was all over even on unglazed bottoms. Seems like it was a formula issue for them

Firing a hotter bisque helped but a change at the factory really helped more.

B -mix right now has some issues I'm told by users and since its one of the most popular bodies I'm sure John Pacini is working on it at laguna west I know they changed water sources and that took a while to resolve as it affected some clay .

Lets see what John Baymore has to add about blisters.

 

I have a wild story about Daves Porcelain and a few tons that blistered and how I dealt with it with John Brooks Lagunas owner but I think I've already told it on this board and it will not help you now.

Mark

[yedrow]

The way I stopped it immediately was to cube out the 25# block into 2-3 inch cubes and dip two ends into a bowl of RIO. That however is very time consuming. But, when you're stuck with 10k of clay you have to do something.

 

Joel.

[LilyT]

Wow, I miss just *one* day of posts since I have to attend to some other things in life (darn it) and there's a gazillion to read!

 

 

 

 

Marcia - sorry I somehow missed you earlier post before… wow, floating kiln sounds crazy! how fun would it be to load a stack of pots onto a moving surface? And didn't you warn me about wet kiln bricks… I guess wet fiber works fine :-)

 

 

 

 

I completely agree that well insulating the kiln will help it fire better and significantly save fuel. (especially because I will be firing with 5 gallon propane tanks because that is the size I can easily haul around myself) I unfortunately have size limits on the total kiln. I did manage to google and find a similar kiln size made of a single layer of IFB that fired to cone 10 with only 20 gallons of propane, so I'm hoping that this will be doable even if expensive in fuel (that's $85 for 16 cu ft, ) It allows me access to a kiln under my control on my property, so more pottery will get done (I hope). Perhaps my next kiln :-)

 

 

 

 

Jim - you might be surprised to find yourself in the building stage before you know it. You certainly seem to have all your plans ready to go. Good luck on a successful project when you do.

 

 

 

 

Mark C - That is one good looking kiln (I noticed it on another thread, yes). I would be pleased to hear more about what you have done, I will call you as I said. I also would like to know why you would need to keep heat away from steel underneath the kiln (is that what you meant? I might have misunderstood), since it wouldn't actually melt until way above cone 10, would you have issues if it softened somewhat? Also ITC on kiln posts sounds like a good idea… I'd like to hear more.

 

Your comments about thermal mass are interesting. I originally wanted lots of hard brick mostly for thermal mass (as well as resiliency

 

 

 

 

John - That was well said clarifying that everything is a choice where you gain something and lose something else. It's that un-expressed tradeoff that we all struggle with. I need something small, not too hot on the outside, and fireable with a limited number of bbq sized propane tanks:-). I mentioned above that I hope that 4 tanks is the right order of magnitude. I am also hoping to supplement with wood obviously which I can get for free and also need for the atmospheric effect. I may need a blower or a taller chimney in that case, but maybe not, I did ok with no chimney on an updraft to cone 10 with propane and wood. I hope to improve my fuel efficiency by coating the kiln on the inside with ITC and mudding the outside to minimize cracks.

 

You certainly are aware of more of the tradeoffs than I am, I'd be interested in your further thoughts along this line if you have the time to go into it. What you already mentioned about the physical breakdown stress across a single layer of brick… so how significant is this? Would it decrease brick life by say 50% ? What kind of breakdown do you see from this? Cracks? Overall crumbling? How long does a kiln last anyway - some of the examples people speak of have 100's upon 100s of firings

 

and then may be rebuilt using the same bricks just patched up a bit.

 

And I think you'd mentioned hard brick splits for the floor hot face, backed by IFB as the outer layer. This should speed up the heating of the floor of the kiln so it potentially would be less uneven in firing? Do you or anyone see any downside to using silicon carbide shelves lining a soft brick floor of the kiln? Cracking?

 

 

 

Joel - I've had blistering similar to what you describe, down to extra blistering on a refire that was supposed to heal it. It happened with various clays at different times over 3 years but always with the cone 5 b-mix. unfortunately I was not in control of the firings nor was there information on the exact firing conditions, but they were standard programs on commercially available electric kilns. I'll be interested to see if your inquiry finds a specific answer that might apply to me :-). Oh, I see you just posted again… did you wedge all that RIO into the clay?

 

 

 

 

Thanks everyone!

 

Looking forward to hearing your opinions and analyses!

 

 

 

 

-Lily

 

 

 

 

 

[Guest JBaymore]

We don't stack real tight, but reasonably tight. However, the bisquing schedule has changed over the last couple of years. We try to keep the ware exposed to at least 1 element, preferably 2. We now have a different kiln, but we were using an L&L with slow bisque. We really did try many variations in bisque firing since that was the most likely cause. We're now bisquing to 06 but when we were using the B mix knock off we were bisquing to 05. I'm afraid I don't remember the ramps and holds in any detail. Presently we're using a 19 cu. ft. Olympic, that uses a kiln sitter (bar cones) with a 3 hr. delay at the beginning of the firing schedule. Oh, and large cones fall pretty much within half a cone or better, at least since last I saw.

 

The blistering on the B mix was so bad that we could fire the ware twice (90 cu. ft. Geil downdraft kiln) and get blisters that were as bad in the second firing, as they were in the first.

 

I soaked the gas kiln and also dropped down at different firings between 50 and 200 degrees, trying to find a place to soak that would allow the bubbles to heal.

 

Joel.

 

 

Joel,

 

It is pretty well known that most "finish firing" defects start out life in either the wet to dry ware handling phase or the bisque phase. They just don't show up until you unload the finish firing . The second firing is just giving the time for the problem to develop more....and says it is likely a bisque issue. (Or a clay body formulation / compounding "oops" issue.)

 

It is not just the end point cone on the bisque that matters, it is also the cycle that got that heat work done. You could say "the rate of climb when".

 

And it is PARTICULARLY the amount of oxygen flow in the bisque. That is one of the reasons I asked about how you stack and if the kiln has local pickup venting. (Answer is............ ?) If you had said yes to the latter, I would be exploring some questiona about that venting and how exactly it is installed, and having you look at the condition of a few key locations on the venting. For a 19 cubic foot electric kiln..... you need a GOOD high volume local pickup venting system to move enough air through it... (not one basically designed for the small 7-9 cubic foot-ish hex kilns.)

 

Were you getting the problems with the older L+L and if so.... how big was that one? And was it equipped with local pickup ventilation?

 

To clarify here........ I thought you said it was ALL your "white" bodies... not just B-Mix. Is that true or did I miss something? Also has this happened with myultiple shipments of your clays... or is it all coming from one large shipment that you have been using?

 

Does this happen on every single piece of the white clay? Does it happen in one particular type of form more than others (like say bowls)? Does it happen on thick pieces more than on thin pieces? And so on.

 

Did the problem start when you "changed the bisquing schedule"?

 

best,

 

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

[neilestrick]

The last gas kiln I built was completely supported on a metal frame and legs. I built a lattice of angle iron to support the floor, full span from side to side, and it worked great. I could move the entire kiln with a pallet jack if needed. I fired it for 4 years, and the floor hadn't sagged one bit. Unfortunately I had to tear it down when I moved my shop, at which point I went electric. Cinder blocks are definitely cheaper and easier to build on, but my situation required that I be able to move the kiln if needed. I had a rolling door built from 4" angle iron, which had 4.5" of soft brick backed up by 1" fiber board. Burners were forced air, so I did not need to build a tall chimney. This was helpful because the kiln was one the first floor of a two story building, and venting was easier that way. Plus I prefer forced air to venturi burners. The kiln fired to cone 11 in 9 hours, dead even.

 

 

I used to be the production manager for Alpine Kilns. Like Geil, they are only built with one layer of soft brick, backed by several inches of other insulation. In Alpines, the bricks were mortared together. I don't know if that's the case with Geil. Geil sounds like they're using block/ board insulation for the backup layers. Alpine used large particle size vermiculite, held together with just a touch of portland cement, to keep it from settling in the walls. I often saw Alpine kilns that were 40 years old and still firing strong. This method of building was much faster and cheaper than laying a full 9" of brick.

[OffCenter]

I don't know how often it is used or how many times it has been repaired, but The Alpine at Valdosta State U. was put in the Fine Arts Building in 1968 and is still used today.

 

Jim

[yedrow]

Lily,

 

I put the RIO on it and pugged it a couple of times.

 

John,

 

My apologies. I forgot to mention the vent system, probably because we don't have one, heh. The L&L kilns range from roughly 15 years old, 10 years old, and 5 years old.

 

So far it has been on all non-porcelain white bodies with the exception of about 25# of Standard's standard body. The level of blistering varies from slight pocking to pocks almost a centimeter across. Also, when firing the red body, it is heavily reduced with black coring through the whole of the (redart in recipe). BTW, I have no control of the schedule these days. The B mix knock-off was the worst and it is worth noting that the supplier couldn't reproduce the blistering in his older Bailey kiln.

 

The last batch of B mix fired okay for a portion of the order, but then went south quick and stayed that way. This was about two years ago and we only had the two ~ 9 cu. ft. L&L's with Bartlett controllers. We have been mixing test batches to see if it goes away, and though reduced, it continues. As you ask these questions I'm getting a picture that this is indeed not a glaze firing problem. From what I'm gathering, you are going to suggest that the atmosphere in the bisquing kilns is supersaturated with impurities and they can't get out in sufficient volume. Thus, when we glaze fire there are still sufficient volatiles to bubble up through the glaze. If this is the case, what I don't understand is the "half-life" of these materials. It occurs to me that each firing should result in a geometric loss pattern. For instance, if X volume of impurities is the amount necessary to cause issues in the glaze firing, then that number would necessarily be large enough to survive the RoR outgassing effect of the glaze firing. Then, when fired a second time, one would expect a geometric reduction in incidents. And, the amount of impurities would be relatively high so they can 'survive' the heating period in the glaze firing. With most of the clays this was the case. But the B mix blistered just as much after three firings.

 

Also, not all pots would blister, but the difference seemed to be an issue of area, meaning; the larger the pot, the more likely a blister, and the blistering on smaller pots might not include pocks that ruined the piece. With the B mix we would lose/re-fire about half the load at the worst. But with others it was more like 5%. We all throw pretty thin and fairly consistent between potters, so we didn't have a wide enough range to get an idea if thickness mattered. It seemed as if horizontal surfaces suffered more than vertical ones, but the difference wasn't that large.

 

We are testing a new white body and we may be getting a good result. We'll unload a second firing of it tomorrow.

 

Joel.

[yedrow]

In Alpines, the bricks were mortared together. I don't know if that's the case with Geil. .

 

 

Neil,

 

The Geil is mortared together too.

 

Joel.

[Guest JBaymore]

Yedrow,

 

The first thing I'd do is do a bisque load of the bodies in question that is stacked very lightly compared to your normal practice. I'd also lengthen the bisque firing ramping (slower rate of climb) in the 425 F to 700 F (oxidize organics) range and then slow it down once again in the 900 F to 1300 F range (oxidize sulphur compounds).

 

Scatter cones all over the kiln. In that 19 cubic footer... I'd have 20-25 cone packs. (That alone might surprise you and give you very useful information.)

 

If you can get fresh air into the kiln unit any way possible during the whole firing...... do that. This is probably the most important thought here. Leave spy ports open, leave doors/lids cracked a tiny bit the whole time, and so on. (Best... get good active venting on the kiln.)

 

Deliberately in ONE small spot in the center of the test kiln load, load a nesting stacking of bowls with them being as tight and dense as you can in that bung of bowls....small one in a slightly larger one, slightly larger one around that, and so on and so on. Big pile of waht amounts to "solid clay" . Keep track of THESE specific pieces in the following glaze firing... and see if they tend to "blister" while maybe (hopefully) the other work in this test bisque firing does not. Or at least blister less.

 

Mix these bisqued pieces into the glaze fire loads with your "normal" bisque fired pieces. Somehow label/ keep track of which pieces are which. Monitor results.

 

Yes... that is very unscientific of me to suggest changing multiple variables all at once. But I'm guessing that you would not like to make these changes one at a time for multiple bisque loads . If you have a smaller kiln to bisque in........ that approach would be a better option to pin this down. I'm using a shotgun here where a rifle might be all that is necessary..... but the shotgun throws a lot of pellets .

 

 

best,

 

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

[yedrow]

Thanks John!

 

If this new body is still having the same problem I'll suggest we do everything you suggested. That is great information, especially stacking the bowls. Thank you so much for your willingness to share your expertise!

 

Joel.

[neilestrick]

I'd also try taking your bisque up to cone 03 and see if that helps. It'll need an extra second in the bucket when glazing, but should help to get everything burned out.