Always considering building a kiln

[CactusPots]

My kiln is the best thing I ever built.  The main thing I'm not satisfied about it and would do differently is to not use fiber for the hot face.  At this point it has been sprayed multiple times.  Originally with the ITC product.  Lately with a 3000 degree kiln mortar.  It's holding up OK in some places, shrinking away in others.  It would probably be a disaster if I did functional kitchen pots. Since my planters aren't even glazed on the inside, there hasn't been an issue.

Which brings me to my question.  Has anyone ever considered using kiln shelves for the hot face?  They would be held in place the same way the fiber is with button and wire.  Actually, mine uses some kind of notched rod and small cup with a screw on cap.  You get the idea.  Probably use 3/4 inch mullite shelves that are used so to be pre shrunk.  Interesting idea or stupid?

[Mark C.]

The thermo mass would weigh a lot and the shelves are not good insulators at all.Soft brick work the best

Your fiber sounds like modules which work fine. If you get to much of a layer of spray(ITC and Mortar) the weight will tend to make the surface spall off. (tear and fall)

I have soft brick with a layer of fiber  on top on the vertical  two side walls  next to bag wall and the fiber is now starting to fail but the soft brick have a sprayed clean surface behind so its just a new hot face ready to go.

Mark

[CactusPots]

The insulation is all fiber.  The kiln shelves as hot face would be only that.  My current is 6" of built up roll fiber.   The lid is modules, they don't pose much of a problem.   The sheet metal outside face never gets much hotter than 300 degrees.    I think the 3/4 inch face would be stable.  Basically, in a 36 cf kiln covering the walls would be about the same as the shelves used as furniture.  Since I've got silicon carbine and one set of advancers, I'd just be putting the shelves back in, thermal mass wise.    I'm guessing you've never heard of someone doing this.  That's my game, thinking outside the bucket.     "Wisdom is found in a multitude of advisors".

[neilestrick]

Using kiln shelves like that will cause them to warp or crack due to the uneven heating. You'll have a big mess in no time. Soft brick are the best balance of durability and insulation.

[CactusPots]

I respect your expertise, but you're talking theoretical,  right?  You've never seen this tried?  Don't need insulation, and don't want the thickness of soft brick.  I don't see why a 3/4 inch shelf would be wildly uneven backed by fiber.  It's not that much material to heat.  

[liambesaw]

I used a kiln shelf as a bag wall, worked fine.  Maybe try a few shelves in there and see how it works before committing to lining the entire kiln.

[neilestrick]

42 minutes ago, CactusPots said:

I respect your expertise, but you're talking theoretical,  right?  You've never seen this tried?  Don't need insulation, and don't want the thickness of soft brick.  I don't see why a 3/4 inch shelf would be wildly uneven backed by fiber.  It's not that much material to heat.  

It would be wildly uneven because the hot face would be very hot, and the cold face would be very cold by contrast, against the fiber which doesn't hold or conduct heat much at all. Kiln shelves expand as they heat up, just like everything else. One side expanding a lot compared to the other is going to cause problems in a slab like that. It's one of the reasons we have people posting here on the forum all the time about big platters and tiles cracking.

@liambesaw Alpine used to use kiln shelves as bag walls. The uneven heating of one face toward the burner port and one face toward the ware cause them to warp badly. Because they were notched into the door jamb, they would break the bricks in the jamb as they warped. It's one of the first things I changed when I started working there.

[Magnolia Mud Research]

I sugges that you visit Hank Murrow's website
http://www.murrow.biz/hank/kiln-and-tools.htm 
and read about his fiber kiln;  the design was published in the September 2001 Ceramics Monthly;

then maybe contact him for his insight on fiber kilns. 

LT
 

[CactusPots]

I've seen that website.  Let me tell you about the kiln I designed and built 15 years ago.  It's 36 cubic ft fiber downdraft.  Stacking is 2 sets of 18x18 shelves with a 6 inch gap between the stacks.  There are 4 propane venturi burners on each side.  The flue box is interlocking castable refractory with a venturi at the entrance and another at the entrance to the stack.  This creates enough pull to create draft at 200 degrees.  The chimney is only to the height of the kiln,   sheet metal lined with fiber.  Full reduction shows no flame out the top. The walls and door are 6" roll fiber and the lid is 12" modules.  All in all, it fires great, uses about 36 gallons of propane on a 12 hour fire to cone 10.  I own and read every book on kiln building, visited every kiln I could before building this.  I'm very satisfied with my design, but always think things could be better.  Fiber is without a doubt the best insulation, but I don't think it's the best hot face.  I don't know what is.

[Mark C.]

Hot face is all relative to where it is in a kiln and what type of kiln. The inside a bag wall hot face takes more beating than say the back wall hot face.Also where its reduction or salt or soda also factors in as does cone 11 or cone 6. They all will have  effects on hot face.I have mad elots of kilns . I once built a fast fire Olsen wood kiln with  lots of kilns shelves  (the roof) some as hot face. It turned out badly.I have fibered roofs and walls and made fiber kilns and hard brick and soft brick-heck mt salt kiln in a combo hard and soft brick fiber roof kiln.

For reduction kilns I like soft brick in the interior hard brick exterior.I use k28 and k26 mostly as the k23 will spall over time at cone 11.Yop see a lot of time /wear after many hundreds of firing.You also get to see what holds up in the long run. I have rebuilt my car kiln 2 times since its 1979 build.

The two side walls behind the bag wall are soft brick sprayed faces  with my own milled zircon spary and covered with 1 inch high temp 8# fiber. Its failing in a few areas now after 15 years of tons of fires -the soft brick is prestine.My all fiber door (6 inch) is still holding well after almost 40 years

I feel kiln shelves are far from the best product but I always like outside the box thinking so if you try it let us know how the outcome is.What I can say is silicone carbide will warp. Mullite based shelves will warp -advancers will be problematic drilling holes as my are near impossiable to cut. Maybe the english dry pressed high alumina shelves which I use in my salt woulkd be best. They are 1 inch thick and pretty stable-I used them for a  few decades in my reduction kiln.-Mine where thru Tacoma Art/Clay Center

I'm not sure what the gain would be using them as a hot face. It just takes more BTUs to heat them. The beauty of fiber is it is refelctive with heat. The few down sides is it quick cools badly and cannot take abrasion.

[neilestrick]

Fiber will give you the lowest firing costs, as it has very little mass and doesn't absorb heat like bricks. The down side is that it is not very durable. You have to decide which is more important. For me, the lack of durability and safety issues associated with fiber put it at the bottom of my list. I much prefer soft brick. It's easier and safer to build with and maintain.

[CactusPots]

Neil,  I agree.   That is precisely why I'm pursuing this topic.  Otherwise, I'd consider my fiber kiln to be the very best way to build a kiln.  The area where the kiln is showing it's lack of durability is the hot face.  The door seal is holding up well.  The door itself is another advantage to fiber because of the light weight.  I'd be surprised if technology doesn't come up with a material that has all the advantages I'm looking for in a facing material to cover the fiber and remove the disadvantages.

A single layer of soft brick as a hot face is a possibility if the thickness was accounted for in the original design.  Not good enough for an upgrade of an existing kiln.  I'd wonder how you would secure the 4 ft or more single stack of bricks.  You could get compression from the lid, maybe that would be enough.  More likely run some kind of tie to the outside skin like the fiber is doing now.  ?

There is something to be said for lowering fuel consumption outside of initial costs.

[Mark C.]

What is the hot face doing that showing lack of durability .Usually its to do with to thick a coating applied or the wrong density or thickness. or temp rating. Whats up with yours?

 

2600 for hot face is best-2400 will  fail sooner by far.

[neilestrick]

I've seen kilns that have one layer of soft brick, backed up by rigid fiber insulation (not fiber blanket). It worked just fine. For stability, you mortar the brick, but otherwise build it like a traditional brick kiln with a sprung arch and angle iron holding it all together. Then you add on the fiber board and secure it with more metal.

My thinking is that as soon as you add another material other than fiber, you negate the benefits of fiber- low mass- so why mess with fiber at all at that point.

There are all sorts of refractory materials available to build kilns with, but the cost is prohibitive for your average studio potter. Industry can justify the cost because of the volume of work they produce.

What is the max temp rating of the fiber you used in your kiln?

[CactusPots]

The kiln was built 15 years ago, I'm not sure of the specs any more.  I trust my local ceramics supplier to have provided the appropriate materials for what I was doing.  Mark is right, where the coatings are thickest, they move away from the fiber because  fiber does shrink.  I think that's the biggest issue with it as a hot face.  Also,  it's fragile to bump into.  It's hard not to occasionally stick it with the corner of a shelf.  Of course that would ding soft brick as well.  

I think low mass is both a blessing and a curse.  Heating a hard brick kiln strikes me as wasteful.    Like deliberately choosing a Hummer as a daily driver.  I get it that there are advantages and effects that the hard brick kiln produces with it's super slow cooling.  Adding mass to the work in a fiber kiln is a compromise.  The kiln fires best with a full load, I've already eliminated a lot of internal mass with silicone carbide shelves.

I do appreciate you guys helping me consider the finer details.  I do think you're right about the kiln shelves warping.

[Magnolia Mud Research]

1 hour ago, CactusPots said:

he kiln was built 15 years ago, I'm not sure of the specs any more.  I trust my local ceramics supplier to have provided the appropriate materials for what I was doing. 

The use of ceramic fiber in the form of rigid shapes has increased significantly in the last 10-15 years, but not necessarily advertised directly to studio pottery suppliers. 

For example: ZIRCAR Refractory Composites, Inc.,
has these variants of ceramic fiber on their opening web page, http://www.zrci.com/  :  Rigid Boards, Rigid Cylinders,  Moldables, Papers and Felts,  Blankets, Textiles, Die Punched Parts, Rigidizers and Coatings, Machined Shaped.  There are others with similar forms.   

The most efficient (energy) way to achieve "slow cooling" in a fiber kiln is to down fire. The energy to keep the ware 'warm' during the down fire period is significantly less than the energy to raise hard and/or soft fire bricks to the peak temperature.

 A fiber kiln does demand closer attention to the cooling temperature profile than does the brick kiln.  For those of us who learned to fire with hard brick, switching to fiber requires we relearn something, just as we had relearn to drive a pickup with an automatic transmission. 

LT
 

[Mark C.]

I have sprayed many a fiber lining and by far most folks put to much material on the fiber-I did long ago but have learned that a really thin light coat is best. It will not peel if it has no weight. As to the back surface shrinking that is most likey not the highest temp fiber as it shrinks alot. weather you spay fiber or brick this is best.

I have found the best fiber at Hi-temp in Portland they sell thru e-bay as well. They sell all typoes so its best to know what you need

The good stuff is here-The density and top end temp is what you need for a cone 10 hot face.

https://www.ebay.com/itm/Ceramic-Fiber-Blanket-2600-1-x-24-x-25-8-Dens/132166304299

Most ceramic suppliers do not have you covered as most folks do not need or know what is needed for various applications .I have yet to find a ceramic supply house that has enough choices to make work what I need.

In the ceramic world other supppliers than traditional suppliers need to be tapped.

You want this k2600 for a hot face-behind that surface you drop down to k25 and then k24 as its cheaper and really works fine behind the hot face.

The thing you will find is this k2600 does not shrink as much as say k2400. When fiber lining I always allow for some loft (not pulled tight) to make room for the shrinking.The loft idea is a bit of a waving surface that contracts over time.

I own tons of k2400 fiber ( I got it at a bargain long ago as it was 4 feet wide)and use it way back away from hot face.I alway have a new roll of the good stuff as well as at least 500 soft bricks for repairs-never know and I'm a long ways from good supplies.I'm a kiln materials hoarder for sure.

I now tend to favor soft bricks over fiber with hard brick only where needed in kiln making.The spqre fiber is for my two fiber kiln doors. one is a salt kiln.

[Babs]

Do the board fibre. Same amount of effort or less than kiln shelf installed where it wasnt designed for....may ...maynot work.

Hardboard fibre made for purpose. Not transporting kiln..fine