Cement under hard brick in cone 10-12 kiln

[LilyT]

Hello, oh knowledgable potter people,

 

I've seen pictures of kilns built over a layer of regular cinderblocks, but

I'd also heard that regular cement loses compression strength when exposed

to high temperatures (anywhere from 300 to 1000 degrees F).

 

Does anyone think (or know whether) a kiln floor made of a single layer of hard

fire brick laid down so it's only 2-1/2 inches thick would get hot enough to

damage the cinder blocks when used for firings to cone 10-12 and then allowed to

cool slowly (12 hours or more)? Would it make a difference and be preferable to have a

thicker layer of hard brick?

 

Thanks for any input on this!

 

-Lily

[Mark C.]

Hello, oh knowledgable potter people,

 

I've seen pictures of kilns built over a layer of regular cinderblocks, but

I'd also heard that regular cement loses compression strength when exposed

to high temperatures (anywhere from 300 to 1000 degrees F).

 

Does anyone think (or know whether) a kiln floor made of a single layer of hard

fire brick laid down so it's only 2-1/2 inches thick would get hot enough to

damage the cinder blocks when used for firings to cone 10-12 and then allowed to

cool slowly (12 hours or more)? Would it make a difference and be preferable to have a

thicker layer of hard brick?

 

Thanks for any input on this!

 

-Lily

 

 

Lily I would say for me only that thats not enough. I would have soft bricks down 1st layer then hard .I have build most kilns on cement pad then on cement blocks with steel mesh that gets the floor up high with air under kiln then hard or soft bricks for floor.

As I only have made about 12 kilns (gas) I really should not have an opinion so lets see what others say who are the kiln builders. some of my kilns where made as test kilns and I do not what do talk test here. Offcenter has some kiln experience maybe he can chine in . John Baymore has tons of kiln work behind him and will know for sure.

Mark

[LilyT]

Hello, oh knowledgable potter people,

 

I've seen pictures of kilns built over a layer of regular cinderblocks, but

I'd also heard that regular cement loses compression strength when exposed

to high temperatures (anywhere from 300 to 1000 degrees F).

 

Does anyone think (or know whether) a kiln floor made of a single layer of hard

fire brick laid down so it's only 2-1/2 inches thick would get hot enough to

damage the cinder blocks when used for firings to cone 10-12 and then allowed to

cool slowly (12 hours or more)? Would it make a difference and be preferable to have a

thicker layer of hard brick?

 

Thanks for any input on this!

 

-Lily

 

 

Lily I would say for me only that thats not enough. I would have soft bricks down 1st layer then hard .I have build most kilns on cement pad then on cement blocks with steel mesh that gets the floor up high with air under kiln then hard or soft bricks for floor.

As I only have made about 12 kilns (gas) I really should not have an opinion so lets see what others say who are the kiln builders. some of my kilns where made as test kilns and I do not what do talk test here. Offcenter has some kiln experience maybe he can chine in . John Baymore has tons of kiln work behind him and will know for sure.

Mark

 

 

Ok, thanks. I have a cement pad, too, on which I plan to use the blocks. Is the steel mesh for stability?

Dang, I had seen some and didn't think to acquire it, oh well.

 

I could put soft brick first... I have some old crappy soft bricks (a nice gift!) that I can cut down

and fit as a layer underneath the hard brick... It has some glass on parts of it, but it shouldn't

get to glass fluxing temp there, I would think? Or do you think I'm kidding myself?

Guess this kiln might need some mortar after all.

 

I also have some interesting old hard brick from an iron smelting operation that I'd

thought about piecing together for a floor. It's 5 inches thick! The kids use it as

furniture and obstacles to jump their cars over in the yard. The soft brick would be more

proven though, and less work cutting...

 

Geesh, better get started with the construction.

 

thanks again,

Lily

[Lucille Oka]

Hello, oh knowledgable potter people,

 

I've seen pictures of kilns built over a layer of regular cinderblocks, but

I'd also heard that regular cement loses compression strength when exposed

to high temperatures (anywhere from 300 to 1000 degrees F).

 

Does anyone think (or know whether) a kiln floor made of a single layer of hard

fire brick laid down so it's only 2-1/2 inches thick would get hot enough to

damage the cinder blocks when used for firings to cone 10-12 and then allowed to

cool slowly (12 hours or more)? Would it make a difference and be preferable to have a

thicker layer of hard brick?

 

Thanks for any input on this!

 

-Lily

 

 

Lily I would say for me only that thats not enough. I would have soft bricks down 1st layer then hard .I have build most kilns on cement pad then on cement blocks with steel mesh that gets the floor up high with air under kiln then hard or soft bricks for floor.

As I only have made about 12 kilns (gas) I really should not have an opinion so lets see what others say who are the kiln builders. some of my kilns where made as test kilns and I do not what do talk test here. Offcenter has some kiln experience maybe he can chine in . John Baymore has tons of kiln work behind him and will know for sure.

Mark

 

 

Hey Mark, don't start discounting yourself! If you have made 12 kilns of various sizes you have a lot of information to offer. I have never made a kiln at all. You are 12 up on me and I am sure many more of us. Your input is welcomed.

 

Were you serious about going tuna fishing?? On average how much does a mature tuna weigh?

[TJR]

Lily T;

I agree with Mark that one layer of hard brick is not enough.

Here are your layers;

Concrete pad

cinder block

old soft brick[can be broken but the two halves should fit together]

hard brick layer

 

I would not put a metal layer. Iron melts at 2000F, and you are firing to 2380F.The one kiln I built with a metal layer warped.

Sorry, Mark.

TJR

[LilyT]

Lily T;

I agree with Mark that one layer of hard brick is not enough.

Here are your layers;

Concrete pad

cinder block

old soft brick[can be broken but the two halves should fit together]

hard brick layer

 

I would not put a metal layer. Iron melts at 2000F, and you are firing to 2380F.The one kiln I built with a metal layer warped.

Sorry, Mark.

TJR

 

 

Hi, TJR,

Thanks for weighing in on the soft bricks, too. No gaps in the underlayer

of the floor sounds like a good idea.

In your kiln with the metal layer, the metal was in the floor? As a

sheet? under which layer? I expect my kiln will weigh 3 tons or so when finished,

so I'm curious as to how the warping occurred. I'd like to avoid that issue.

I was going to just freely stack the walls without any metal frame though

I'd at one point thought about using angle iron to 'belt' it together, but

decided against it? If you don't mind sharing more details of your

experience, I'd like to know more. One of the great things about this

forum is how generously people share their experiences... and the details

really matter.

 

warm regards,

Lily

 

although I would comment that 2795F is reported as the melting point of iron

but steel has a lower 2500F melting point. it does lose strength starting from

1000 degrees however.

[Marcia Selsor]

I agree. One layer of hard brick is not enough. I use one layer of insulation bricks or two if possible and unless building a wood or soda kiln or a car kiln, I don't use hard bricks period except in the bag wall. One course of good insulation bricks is equal to 5 courses of hard brick for heat transfer.* source from refractory manufacturers booklets.

Also, when lining up the cinder blocks, run the holes horizontal to avoid moisture from seeping up into the bricks.

You could put a layer of insblok between the hard bricks and the cinderblocks. I have built over a dozen including cast Arches and catenaries. If you can find an old AP Green refractories book, it has charts of all the combination bricks and skews required for sprung arches.

I use threaded rods across the front and back of sprung arches with nuts,car valve springs and large washers so that the arch

can be tightened from time to time .

 

Marcia

 

 

[Guest JBaymore]

There is an unfortunate persistent myth amongst many potters that "heat rises" and that supposed "understanding" results in under-insulated kiln floors. Daniel Rhodes' "Kilns" book did a lot to perpetuate this siutation with all the kilns pictured in there that have two 2 1/2" thick hard brick as the floor courses.

 

Heat energy moves from areas of higher concentration to areas of lower concentration and is not affected by the direction with regards to gravity. Basic thermodynamics. Easily demonstrated.

 

So if you have decided that the insulating value of the walls of the kiln need to come to a certain value.... the floor needs to have that same value. Otherwise the amount to heat energy that moves through the floor area will be greater than that which moves through the wall and roof sections. Thereby not only wasting heat energy but also causing the kiln to tend to fire cold on the bottom. And possibly causing damage to the underlying support structure, be that concrete or steel or ??????.

 

One layer of hard brick is absolutely not enough.

 

If you are using brickwork construction (as opposed to castable or fiber), you sort of have a design and engineering decision to make here. Standard brick series comes in 2 1/2" thickness. Unless you go to specail sized bricks, that is the size that is typically readily available. If you lay them flat, then your choices are for a 7 1/2" thick floor, or a 10" thick floor. If your walls section is 9" thick (typical) then the 7 1/2" is underinsulated, and the 10" thick is over insulated.

 

This gets a bit more involved too. HOPEFULLY you are already planning on using graded refractory construction technique in the walls and roof. This means that the inner hot face courses of brick (and the header ties) are of a grade that matches the kiln's max. use temperture, and the outer cold face layer is one that matches the brick interface layer temperature. This gives the maximum insulating value to the wall section...... because the higher rated brick has a lower insulating value.

 

So the floor construction should mimic this approach also.

 

For most clients kilns I have used the following layers, laid flat: 2 1/2" of 1600 IFB, 2 1/2" of 2000 IFB, 2 1/2" of 2300 IFB, and 2 1/2" of high duty, dry pressed hard refractory firebrick.

 

When I HAVE to cut corners for a client, sometimes I have gone with 2 1/2" of 1600 IFB, 2 1/2" of 2300 IFB, and then 2 1/2" of high duty, dry pressed hard refractory firebrick...... but this is not optimum.

 

Another approach here is to lay the floor courses on their sides.... sort of like making a typical wall sectioon but having it "laying down". Then the choices typically become 4 1/2" of hard brick, backed with 4 1/2" of 2300 IFB. Or better yet 1 " of high duty hard firebrick splits (laid flat), then 4 1/2" of 2300 IFB backed with 4 1/2" of 2000 IFB.

 

Note here that I focus on building good long lasting kilns, not cheap kilns . When you are rebuilding or repairing kilns... you are not making pots .

 

 

best,

 

 

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

[LilyT]

I agree. One layer of hard brick is not enough. I use one layer of insulation bricks or two if possible and unless building a wood or soda kiln or a car kiln, I don't use hard bricks period except in the bag wall. One course of good insulation bricks is equal to 5 courses of hard brick for heat transfer.* source from refractory manufacturers booklets.

Also, when lining up the cinder blocks, run the holes horizontal to avoid moisture from seeping up into the bricks.

You could put a layer of insblok between the hard bricks and the cinderblocks. I have built over a dozen including cast Arches and catenaries. If you can find an old AP Green refractories book, it has charts of all the combination bricks and skews required for sprung arches.

I use threaded rods across the front and back of sprung arches with nuts,car valve springs and large washers so that the arch

can be tightened from time to time .

 

Marcia

 

 

 

 

Hi, Marcia,

Thanks for the additional information! I love knowing the 5:1 factor

of soft to hard brick insulation. I have in my mind that insulation slows

down the heat transfer, so this makes me realize that a single layer

of hard brick will be HOT. especially with some longer firing times.

I did run the cinder blocks with the holes horizontal,

although my only thought was for air cooling, and not about moisture seepage.

Good point about moisture. Exactly how bad is it to have wet bricks? Wet

hard brick? Is there a danger of cracking or explosion? Or is it fuel inefficiency?

I live in an area where there's rarely freezing temperatures and I

know about keeping the soft IFB from freezing while wet. But I was planning

on having grass around the kiln to decrease any fire hazard.

Threaded rods, nuts, car valve springs, and large washers are a great

off the shelf construction idea. My roof design currently is flat (30" alumina

shelf supporting 1 or 2 IFB layers, tbd) because I was worried about the work of

keeping an arch in position, (also the cost of special brick to be purchased

new) but the threaded rods would make it easier. What are car valve springs

and how do you attach them? Are they used because the arch needs to

expand and the rods wouldn't comply?

Again many thanks for your comments, they're so helpful!

 

warmest regards,

Lily

[OffCenter]

Lily, other people have already posted lots of great info, so I only want to add that you may want to look at some of the non-brick options. I'm in the early planning stages of building a small salt kiln that uses very few bricks and instead will be built of panels made of 1 inch fiberboard (2600 degrees for hotface) backed by ~6 inches of fiber (around 2400 degrees) backed by fiberboard (2000 degrees). (Solicited John B's advice in another thread.) The hotface will be covered with ITC and the outside with cement/fireclay mix. Except for using some Kaowool back in the 70's when I built kilns in Colorado, I don't have any experience with all the wonderful new materials available now, but it may save you time and money to check with someone who does know about them to see if, for example, a layer of fiberboard could be substituted for one of the layers of brick in the floor and ceramic fiber for a layer of IFBs in walls or arch, etc. Don't forget to check out ITC, too. I don't know much about it but I asked and there is a thread on this forum with lots of feedback about it.

 

Jim

[Marcia Selsor]

Lily,

Wet bricks can crack if not blow up.

 

 

Grass can dry out and be a fire hazard. I think pea gravel would be better imho.

The nuts, car valve and threaded rod are for the kiln frame particularly bracing the side angle iron at the base of the sprung arch. Solid welded frames will restrict the expansion of the hot bricks and the frame can bow becoming looser over time. The car valve springs allow the arch to expand and contract as it is needed. So you are doing a Minnesota Flat top? I built one for a car kiln but replaced it with an arch after a while. In a university environment, the kiln was fired often, several times per week. The flat top did start losing bricks. I think arches are much stronger. again just my opinion. We all have one.

 

Marcia

[LilyT]

There is an unfortunate persistent myth amongst many potters that "heat rises" and that supposed "understanding" results in under-insulated kiln floors. Daniel Rhodes' "Kilns" book did a lot to perpetuate this siutation with all the kilns pictured in there that have two 2 1/2" thick hard brick as the floor courses.

 

Heat energy moves from areas of higher concentration to areas of lower concentration and is not affected by the direction with regards to gravity. Basic thermodynamics. Easily demonstrated.

 

So if you have decided that the insulating value of the walls of the kiln need to come to a certain value.... the floor needs to have that same value. Otherwise the amount to heat energy that moves through the floor area will be greater than that which moves through the wall and roof sections. Thereby not only wasting heat energy but also causing the kiln to tend to fire cold on the bottom. And possibly causing damage to the underlying support structure, be that concrete or steel or ??????.

 

One layer of hard brick is absolutely not enough.

 

If you are using brickwork construction (as opposed to castable or fiber), you sort of have a design and engineering decision to make here. Standard brick series comes in 2 1/2" thickness. Unless you go to specail sized bricks, that is the size that is typically readily available. If you lay them flat, then your choices are for a 7 1/2" thick floor, or a 10" thick floor. If your walls section is 9" thick (typical) then the 7 1/2" is underinsulated, and the 10" thick is over insulated.

 

This gets a bit more involved too. HOPEFULLY you are already planning on using graded refractory construction technique in the walls and roof. This means that the inner hot face courses of brick (and the header ties) are of a grade that matches the kiln's max. use temperture, and the outer cold face layer is one that matches the brick interface layer temperature. This gives the maximum insulating value to the wall section...... because the higher rated brick has a lower insulating value.

 

So the floor construction should mimic this approach also.

 

For most clients kilns I have used the following layers, laid flat: 2 1/2" of 1600 IFB, 2 1/2" of 2000 IFB, 2 1/2" of 2300 IFB, and 2 1/2" of high duty, dry pressed hard refractory firebrick.

 

When I HAVE to cut corners for a client, sometimes I have gone with 2 1/2" of 1600 IFB, 2 1/2" of 2300 IFB, and then 2 1/2" of high duty, dry pressed hard refractory firebrick...... but this is not optimum.

 

Another approach here is to lay the floor courses on their sides.... sort of like making a typical wall sectioon but having it "laying down". Then the choices typically become 4 1/2" of hard brick, backed with 4 1/2" of 2300 IFB. Or better yet 1 " of high duty hard firebrick splits (laid flat), then 4 1/2" of 2300 IFB backed with 4 1/2" of 2000 IFB.

 

Note here that I focus on building good long lasting kilns, not cheap kilns . When you are rebuilding or repairing kilns... you are not making pots .

 

 

best,

 

 

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

 

 

Hi, John,

 

Oh, my, guilty, guilty, guilty as charged on all counts! I'm thinking of building

 

cheap and thin, lol!

 

Good point that heat radiates, but I do think that the bottom of my propane

 

kiln exterior (converted electric kiln 2" soft brick wall) is cooler than the top.

 

Could that be due to the hot gases rising?

 

(As a aside that I don't understand, that kiln is updraft and fires evenly with less than a cone

 

difference, but I do not place anything in the bottom 5 inches because as it's the

 

firebox. Maybe direct gas heat transfer plays a larger role than radiation at low

 

temperatures in kilns? Also it's only 7 cu ft so maybe it's easier to fire evenly?)

 

Ok, so my whole kiln is only single(4-1/2") wall thickness, hard brick on the bottom.

 

I was only thinking this might get too hot outside. Your ideas of matching temperature

 

for insulation value has a lot of design beauty which I appreciate. I have k26 and

 

k23... and I had read that itc can protect k23 brick even at cone 10 etc, so I'm

 

going to try that in a single layer (4-1/12), and see if it helps give better insulation.

 

Also, lol, that's the brick I have. But I think I should at least be stacking the

 

hard brick lower walls vertically with hard brick 2-1/2" thick for the hot face, and

 

IFB for the cold face. I guess I'm designing a less optimally insulated kiln

 

that is on the order of my conversion kiln (2" IFB) so Marcia's and your point

 

that hard brick is only 1/5 as insulating means a 4-/12" hard brick layer is about

 

half the insulating value of 2" soft brick... means I should redesign the hard brick

 

layers and the floor at the very least. Hard brick hot face and soft brick outer face

 

(2-/12), so the kiln will be less underinsulated in those areas as compared to the

 

4-/12" soft brick, but there will be no gross heat 'leaks'.

 

My kiln was going to be small (16cuft) and cheap, but I see where this will

 

run into inefficiencies that might be very annoying. Such as wasted fuel.

 

Unfortunately I have to keep it's outer dimensions small because of my

 

pad size, too.

 

Thank you thank you for all the great details from your kilns, I

 

hope it's not too annoying to you that I won't be able to do as good a job

 

optimizing (due to cheapness and fear of my pile getting so big the neighbors

 

will start to worry). I find the details and your thoughtful descriptions of the

 

issues super helpful because it helps me calculate a minimal design

 

efficiency better. ie exactly how suboptimal I will be.

 

Yeah, it's true that messing around with kilns is not throwing pots, but

 

there's an OCD part of me that likes it, too :-). And I dream about a perfect

 

place someday where everything can be optimized, but that's not going

 

to happen in this lifetime I realize now, so it's "get to it the best one can

 

while one can do the getting..." (an engineering approach of avoiding

 

catastrophic failures)

 

 

 

 

 

 

warmest regards,

 

Lily

 

 

 

 

Another less than perfect feature is that I will be throwing wood directly onto

 

the floor, more like sidestoking. Amidst the propane flames. Maybe I should

 

make a mini grate on that area of the floor to get better air circulation.

 

 

[Marcia Selsor]

Kilns at high altitudes

 

Just an added note. When I was at Banff (6000+ ft above sea level) there was a fast freddie wood kiln that repeatedly stalled at 1900 degrees. The kiln was an exact copy of Olsens guidelines. When the director called Olsen about it, Fred said he forgot to mention chimneys at high altitudes. You need more draft when at high altitudes. Not sure where Jim or Lily are building, but keep that in mind for your construction.

 

Marcia

[LilyT]

Lily, other people have already posted lots of great info, so I only want to add that you may want to look at some of the non-brick options. I'm in the early planning stages of building a small salt kiln that uses very few bricks and instead will be built of panels made of 1 inch fiberboard (2600 degrees for hotface) backed by ~6 inches of fiber (around 2400 degrees) backed by fiberboard (2000 degrees). (Solicited John B's advice in another thread.) The hotface will be covered with ITC and the outside with cement/fireclay mix. Except for using some Kaowool back in the 70's when I built kilns in Colorado, I don't have any experience with all the wonderful new materials available now, but it may save you time and money to check with someone who does know about them to see if, for example, a layer of fiberboard could be substituted for one of the layers of brick in the floor and ceramic fiber for a layer of IFBs in walls or arch, etc. Don't forget to check out ITC, too. I don't know much about it but I asked and there is a thread on this forum with lots of feedback about it.

 

Jim

 

 

Hi, Jim, yes those are great ideas! How my kiln was born was that

I just happened to get a bunch of bricks from a friend of a friend at

half price, and locally (nearest pottery supply place is 200 miles)

so that was my starting point. Now that I'm in the middle of the design,

and hefting the 3 tons of brick, heheh, I see that your design is much

better for reasons of heat mass, stability, and probably building and

ease of use, too. (I love the designing stage, and it's a good thing,

because there's so much to think about)

I've been convinced I need to redesign some portions, so maybe I will

see about using some fiberboard in place of IFB, since I'll probably need

more of one thing or another. How is it that you are supporting your

structure? (it doesn't sound like it's self supporting like a stack of brick

would be, but I'm 100% ignorant here?) Does it get glued together?

or put in a frame?

Ah, yes, I'm also trying to follow the ITC discussions... thanks for mentioning

them though, because it's hard to find things using this forum's search

function so it's nice to get a heads up.

 

Thanks for chiming in about these options, too. Maybe in the future my kiln will get

that outer layer of insulation I can't afford to give it now, and it will be one

of these materials, once I get out of the stone age. (Gee whiz this discussion

makes me realize how old my mindset is getting - I'm so much more comfortable

working with old, simple, physical materials.)

 

 

 

 

Warmest regards,

Lily

 

[LilyT]

Lily,

Wet bricks can crack if not blow up.

 

 

Grass can dry out and be a fire hazard. I think pea gravel would be better imho.

The nuts, car valve and threaded rod are for the kiln frame particularly bracing the side angle iron at the base of the sprung arch. Solid welded frames will restrict the expansion of the hot bricks and the frame can bow becoming looser over time. The car valve springs allow the arch to expand and contract as it is needed. So you are doing a Minnesota Flat top? I built one for a car kiln but replaced it with an arch after a while. In a university environment, the kiln was fired often, several times per week. The flat top did start losing bricks. I think arches are much stronger. again just my opinion. We all have one.

 

Marcia

 

 

Ok, I will keep the bricks dry to avoid blowing up. I guess I will candle the

kiln carefully, since I wasn't planing on a moisture barrier under the cement

which is already in place. Maybe under the cinder blocks? Does anyone's

cinder blocks under single layer of IFB get hot enough to melt plastic at the bottom?

(I have a moisture barrier at the base of my mud oven but the base of

that is 3 feet tall). oh, wait. sheet metal, I can do that, I think Mark suggested

steel mesh up earlier, maybe this is another reason to think about a flat

sheet of it.

 

I'm not sure what a Minnesota Flat top is (I'm really quite ignorant, sorry!)

All I plan is to span the top with single width kiln shelves like a lid. I

am quite certain the arches are stronger, but if I see sagging I plan to be

able to easily unstack the top and flip the shelves over. No mortar in

this kiln unless there's instability near the bottom. (In which case I'm

planning to use a thin fireclay mix) In your Minnesota Flat Top, how did

the top lose bricks?

 

What was the old saying about "plan for your project to take 5 times

longer to actually accomplish than you think"? I see that it's because my

original plans need to be adjusted. I am trying to stick with simple

construction techniques for this one because I don't trust that I will

be able to complete a technically complicated one, such as an arched

roof, and still get the other steps of the kiln completed.

 

Grass can dry, it is true. It is already in place (yes, I'm building the

kiln in the middle of my lawn) but if I can't maintain it, I will replace

it with pea gravel or something like that, good idea.

 

thank you for your opinions. Without your generous and invaluable

sharing of opinions formed by experience, my own trial and errors would

lead to much less future pottery. The fact that you break down the

opinion into reasons and how it all inter-relates makes it that much

more useful.

 

warmest regards,

Lily

[LilyT]

Kilns at high altitudes

 

Just an added note. When I was at Banff (6000+ ft above sea level) there was a fast freddie wood kiln that repeatedly stalled at 1900 degrees. The kiln was an exact copy of Olsens guidelines. When the director called Olsen about it, Fred said he forgot to mention chimneys at high altitudes. You need more draft when at high altitudes. Not sure where Jim or Lily are building, but keep that in mind for your construction.

 

Marcia

 

 

hi, Marcia,

Yes, good point, you would need more draft to supply more oxygen at high altitudes.

I will be using propane so that supplies it's own draft fortunately. Especially

because I will be firing it at 6 psi. I am also only at 750 ft elevation anyhow.

But I will keep extra brick on hand in case the chimney needs to get taller

despite my rationalizations, lol. Or maybe I'll bring a blower just in case.

BTW, one of your comments led me to find a posting on clayart where

someone used 'spiral pipe' glued together with ITC. Do you know what

spiral pipe is? Is it even ceramic? or metal?

 

warmest regards,

Lily

[Mark C.]

Hello, oh knowledgable potter people,

 

I've seen pictures of kilns built over a layer of regular cinderblocks, but

I'd also heard that regular cement loses compression strength when exposed

to high temperatures (anywhere from 300 to 1000 degrees F).

 

Does anyone think (or know whether) a kiln floor made of a single layer of hard

fire brick laid down so it's only 2-1/2 inches thick would get hot enough to

damage the cinder blocks when used for firings to cone 10-12 and then allowed to

cool slowly (12 hours or more)? Would it make a difference and be preferable to have a

thicker layer of hard brick?

 

Thanks for any input on this!

 

-Lily

 

 

Lily I would say for me only that thats not enough. I would have soft bricks down 1st layer then hard .I have build most kilns on cement pad then on cement blocks with steel mesh that gets the floor up high with air under kiln then hard or soft bricks for floor.

As I only have made about 12 kilns (gas) I really should not have an opinion so lets see what others say who are the kiln builders. some of my kilns where made as test kilns and I do not what do talk test here. Offcenter has some kiln experience maybe he can chine in . John Baymore has tons of kiln work behind him and will know for sure.

Mark

 

 

Hey Mark, don't start discounting yourself! If you have made 12 kilns of various sizes you have a lot of information to offer. I have never made a kiln at all. You are 12 up on me and I am sure many more of us. Your input is welcomed.

 

Were you serious about going tuna fishing?? On average how much does a mature tuna weigh?

 

 

Lucille

I'm very serious about tuna fishing . I have been chasing albacore tuna since mid 90s on one of my Boston Whalers-I have 3 major passions one is underwater photography (fish photos for 30 years now) The other is tuna fishing and the other is clay. Life is short and I have two many interests. On Friday we left at 5 am and got back to dock at 8.30-covered 190 miles burned 105 gallons of gas used 220#s of ice and caught 27 tuna-The run was 60 miles off Eureka to the southwest and about 45 miles over.

I'm a moderator a tuna web site and am know on the web as Onokai-

I'm cleaning tuna yesterday as we bleed them and ice them as soon as we land them.We can them we vacuum pack/freeze them we eat them year round-right now have salmon and halibut all fresh caught in the freezer. I have only stuck to clay posts here as thats my main business but not my only passion.

I have had a lot of positive feed back from many on this site thanks for that.

This boat photo was taken of my boat on friday while tuna fishing offshore

the other is what a fresh albacore looks like with me holding it head on.

 

Mark

[OffCenter]

Lily, glad you got a deal on the bricks. I haven't been able to find one, even though I've come close on a couple of occasions. That is one reason I started thinking about using alternative materials. The more I looked into it, the more I liked the idea. The problem is that I don't have much experience with anything except bricks. I even experimented a little with making my own bricks which led to the idea of making sections of kiln instead of brick shapes, then why not just get away from bricks and build it of ceramic fiber, ceramic board, castables, etc. To answer your question, it would be a supported by cinder blocks (maybe without the concrete pad) and the panels held together by nichrome and ceramic nuts and bolts and by a steel frame. One advantage is that it would be super easy to change out the hotface ceramic board when it becomes degraded.

 

In short, I'm fascinated by the possibilities of leaving the brick behind and building kilns with modern materials. I even like the idea of kilns that are works of art themselves. For example, take a look at the kiln on the cover of Ian Gregory's "Alternative Kilns" attached.

 

Jim

[LilyT]

Lily, glad you got a deal on the bricks. I haven't been able to find one, even though I've come close on a couple of occasions. That is one reason I started thinking about using alternative materials. The more I looked into it, the more I liked the idea. The problem is that I don't have much experience with anything except bricks. I even experimented a little with making my own bricks which led to the idea of making sections of kiln instead of brick shapes, then why not just get away from bricks and build it of ceramic fiber, ceramic board, castables, etc. To answer your question, it would be a supported by cinder blocks (maybe without the concrete pad) and the panels held together by nichrome and ceramic nuts and bolts and by a steel frame. One advantage is that it would be super easy to change out the hotface ceramic board when it becomes degraded.

 

In short, I'm fascinated by the possibilities of leaving the brick behind and building kilns with modern materials. I even like the idea of kilns that are works of art themselves. For example, take a look at the kiln on the cover of Ian Gregory's "Alternative Kilns" attached.

 

Jim

 

 

Dang, that's a good looking kiln. Very modern looking, also. Does it reportedly fire well?

Mine will be as ugly as possible, alas. It will be a heap of mismatched brick in

a chunky rectangle-ish pile (not a cube).

 

 

Modern kiln construction seems like a very different proposition. More like one

of the textile arts than a construction project in some ways. It sounds like it would

be extremely efficient - looks like serendipity brought you to a much higher level

of kiln construction! I wasn't even seriously thinking of building a kiln actually, but

someone said very pointedly to me that he knew of some bricks available and I

should go look at it, lol. Guess I might have been talking a bit much about kilns...

so then I thought of all sorts of good rationales to justify another kiln (like being

able to fire my husband's large pots, like how I love firing with wood and being able

to get some interesting stacking in a cleaner kiln.

 

I hope you post pictures of your kiln project along the way and give us reports on

how the finished kiln fires. More food for thought!

 

Are ceramic nuts and bolts pure ceramic? What an interesting idea! Does ceramic

have good tensile strength?

 

warmest regards,

Lily

[Marcia Selsor]

Lily, glad you got a deal on the bricks. I haven't been able to find one, even though I've come close on a couple of occasions. That is one reason I started thinking about using alternative materials. The more I looked into it, the more I liked the idea. The problem is that I don't have much experience with anything except bricks. I even experimented a little with making my own bricks which led to the idea of making sections of kiln instead of brick shapes, then why not just get away from bricks and build it of ceramic fiber, ceramic board, castables, etc. To answer your question, it would be a supported by cinder blocks (maybe without the concrete pad) and the panels held together by nichrome and ceramic nuts and bolts and by a steel frame. One advantage is that it would be super easy to change out the hotface ceramic board when it becomes degraded.

 

In short, I'm fascinated by the possibilities of leaving the brick behind and building kilns with modern materials. I even like the idea of kilns that are works of art themselves. For example, take a look at the kiln on the cover of Ian Gregory's "Alternative Kilns" attached.

 

Jim

 

Nice looking kiln. I met Ian Gregory several years ago at La meridiana. Not that year but previously he had built a floating kiln that fired as it sailed across the pond. I only saw the pictures. Kiln design can become an obsession..but a good one.

Marcia

 

 

 

 

[TJR]

Lily T;

I agree with Mark that one layer of hard brick is not enough.

Here are your layers;

Concrete pad

cinder block

old soft brick[can be broken but the two halves should fit together]

hard brick layer

 

I would not put a metal layer. Iron melts at 2000F, and you are firing to 2380F.The one kiln I built with a metal layer warped.

Sorry, Mark.

TJR

 

 

Hi, TJR,

Thanks for weighing in on the soft bricks, too. No gaps in the underlayer

of the floor sounds like a good idea.

In your kiln with the metal layer, the metal was in the floor? As a

sheet? under which layer? I expect my kiln will weigh 3 tons or so when finished,

so I'm curious as to how the warping occurred. I'd like to avoid that issue.

I was going to just freely stack the walls without any metal frame though

I'd at one point thought about using angle iron to 'belt' it together, but

decided against it? If you don't mind sharing more details of your

experience, I'd like to know more. One of the great things about this

forum is how generously people share their experiences... and the details

really matter.

 

warm regards,

Lily

 

although I would comment that 2795F is reported as the melting point of iron

but steel has a lower 2500F melting point. it does lose strength starting from

1000 degrees however.

 

 

Lily;

The kiln in question was built at the University of Manitoba on a Sculpture court, outside the sculpture studio. There was a drain in the middle of the court yard pad, so snow and ice and water were involved.[i am in Canada]We used a large expanded metal box that had girders for the sides. The idea was to raise the kiln above the snow. The girders were 6 inches thick. The kiln never remained square and never fired right. We tore it down and built on cinder blocks. We also used to use these extruded terra cotta blocks to put kilns on. You might find them at a brick yard although I haven't seen them used in a while.

To save energy, you can make your kiln floor out of G26 softbrick rather than hard brick if you are not worried about wear and tear on the floor.

TJR.

[LilyT]

Lily T;

I agree with Mark that one layer of hard brick is not enough.

Here are your layers;

Concrete pad

cinder block

old soft brick[can be broken but the two halves should fit together]

hard brick layer

 

I would not put a metal layer. Iron melts at 2000F, and you are firing to 2380F.The one kiln I built with a metal layer warped.

Sorry, Mark.

TJR

 

 

Hi, TJR,

Thanks for weighing in on the soft bricks, too. No gaps in the underlayer

of the floor sounds like a good idea.

In your kiln with the metal layer, the metal was in the floor? As a

sheet? under which layer? I expect my kiln will weigh 3 tons or so when finished,

so I'm curious as to how the warping occurred. I'd like to avoid that issue.

I was going to just freely stack the walls without any metal frame though

I'd at one point thought about using angle iron to 'belt' it together, but

decided against it? If you don't mind sharing more details of your

experience, I'd like to know more. One of the great things about this

forum is how generously people share their experiences... and the details

really matter.

 

warm regards,

Lily

 

although I would comment that 2795F is reported as the melting point of iron

but steel has a lower 2500F melting point. it does lose strength starting from

1000 degrees however.

 

 

Lily;

The kiln in question was built at the University of Manitoba on a Sculpture court, outside the sculpture studio. There was a drain in the middle of the court yard pad, so snow and ice and water were involved.[i am in Canada]We used a large expanded metal box that had girders for the sides. The idea was to raise the kiln above the snow. The girders were 6 inches thick. The kiln never remained square and never fired right. We tore it down and built on cinder blocks. We also used to use these extruded terra cotta blocks to put kilns on. You might find them at a brick yard although I haven't seen them used in a while.

To save energy, you can make your kiln floor out of G26 softbrick rather than hard brick if you are not worried about wear and tear on the floor.

TJR.

 

 

Hi, TJR,

It sounds like your kiln was suspended by the mesh? (correct me if I'm wrong) It's always surprising to me how the center of a span can be difficult to keep from sagging (even a small force is difficult to resist) - is this what happened to your raised kiln? So, out of curiosity, how much did it snow in Manitoba and how far up did the kiln have to be?

I like the idea of putting less mass in the floor to save energy, but I am planning on being pretty harsh with the floor (soda and

wood); and also I'm trying to justify it by saying that it will allow a slower cooling cycle without firedown. It's a rationale though,

because I'm pretty sure it would be slow enough to prevent dunting anyway even with a single layer of IFB. I have a kiln that likes to drop at 600F-900F per hour.

I love so much hearing about everybody's experiences. It makes me feel like I'm spent the first 40 years of my life only doing boring stuff! How did I not notice all this fabulous building and creating was going on all around the world? I sat in indoor classrooms and

studied books all my life.

 

warmest regards,

Lily

[OffCenter]

Lily, glad you got a deal on the bricks. I haven't been able to find one, even though I've come close on a couple of occasions. That is one reason I started thinking about using alternative materials. The more I looked into it, the more I liked the idea. The problem is that I don't have much experience with anything except bricks. I even experimented a little with making my own bricks which led to the idea of making sections of kiln instead of brick shapes, then why not just get away from bricks and build it of ceramic fiber, ceramic board, castables, etc. To answer your question, it would be a supported by cinder blocks (maybe without the concrete pad) and the panels held together by nichrome and ceramic nuts and bolts and by a steel frame. One advantage is that it would be super easy to change out the hotface ceramic board when it becomes degraded.

 

In short, I'm fascinated by the possibilities of leaving the brick behind and building kilns with modern materials. I even like the idea of kilns that are works of art themselves. For example, take a look at the kiln on the cover of Ian Gregory's "Alternative Kilns" attached.

 

Jim

 

 

Dang, that's a good looking kiln. Very modern looking, also. Does it reportedly fire well?

Mine will be as ugly as possible, alas. It will be a heap of mismatched brick in

a chunky rectangle-ish pile (not a cube).

 

 

Modern kiln construction seems like a very different proposition. More like one

of the textile arts than a construction project in some ways. It sounds like it would

be extremely efficient - looks like serendipity brought you to a much higher level

of kiln construction! I wasn't even seriously thinking of building a kiln actually, but

someone said very pointedly to me that he knew of some bricks available and I

should go look at it, lol. Guess I might have been talking a bit much about kilns...

so then I thought of all sorts of good rationales to justify another kiln (like being

able to fire my husband's large pots, like how I love firing with wood and being able

to get some interesting stacking in a cleaner kiln.

 

I hope you post pictures of your kiln project along the way and give us reports on

how the finished kiln fires. More food for thought!

 

Are ceramic nuts and bolts pure ceramic? What an interesting idea! Does ceramic

have good tensile strength?

 

warmest regards,

Lily

 

 

Lily, unfortunately, I'm only at the one-step-beyond-daydream stage. I have a lot to learn before I even do the plans for the kiln, let along actually start building it. Who knows, though, I may look back and be glad that not finding used bricks or being able to afford new ones caused me to find a better way. Googling has led me to a few things that are sort of ceramic nuts and bolts, so things like that are available but probably just a very large button made of fireclay/kaolin with nichrome wire (I think that is what Ian Gregory recommends in his books.) would be the best way to go. The kiln pictured is beautiful but is only functional for raku.

 

Marcia, what an interesting idea--performance kilns!

 

Jim

[Mark C.]

Before you say no metal naysayers I hope you know it from EXPERIENCE because that is where I'm speaking from

Here Lily is my 12th kiln and only kiln with metal (except my car kiln floor which has metal under layers of soft brick for 35 years and 1800 to 2000 fires on it) still WORKING

This is a salt kiln here at the house I made 10 years ago with expanded super heavy duty 3/4 inch steel-as we wanted to have cooling air under the cinder blocks and also knew salt would attack it over time. This metal is looking good until I die which may come sooner than I want dealing with negativity here from a few.

Here is the link and a photo-the expanded mesh is on top of cinder blocks-Its super heavy stuff. I normally do not use metal but it as with many things in life it has its place and here it works wellNow if somebody what's to get on my case about this (metal use)

 

I cannot tell you how many kilns I have seen that are made that do not work right from the onset and are not well thought out-I'm sure John has seen this as well.

This ones fires for 35$ to cone 9-10 and I should say I learned kiln building in the 70's (bad learning years I hear) and did not step away from clay or kiln building then (the 70's) but continued with building and learning to this day as I make my living from selling functional pottery for the past 40 years. I need kilns that work and work every day. Its not a dream for me its tomorrow and the day after.

Now before the questions start coming in why cone 9-10 thats because I like that temp for my stoneware salt pots to be.

Yes it could be cone 08 or cone 6 or whatever cone you want but at 35$ a fire I like cone 10 and I have tons of cone 10 stoneware already paid for and on site.

This kiln has steel around it and its heavy steel thick enough to rust my whole life and hold up-Its been painted with high heat silver paint and is rusted now in a some spots. We do not care-I have used stainless steel in some spots like the stack and gutters on kiln roof as I had them and like stainless as well as brass. I have a few tons of brass in the yard from diving over the years and I like copper as well and also have lots from old steamships. I have salvaged for fun.So lets talks about metal I'm all in and all ears.My best friend a super wielder and I have my own buzz box as well but he is the man with steel.As you can see steel has its place.This kiln has a door that swings open and then 360 degrees around and goes way onto the other side. The top is fiber which was a test I'm doing and no I will not talk on the net about it as I learned it in the 70's

The door is fiber as well and is holding up ok-hard bricks to just above the burner ports then k28 from there.

Lily if you want to talk kiln building just call me -I'm on the west coast-that way we can cut to the chase without interference-I'll gladly share what I have learned back in the 70s.As well as anything else kiln related including hows this ones holding up.

I'm removing my phone# here- after you pmed me-talk to you Lily on Tuesday-thanks

PS the table on right is all stilts sprayed with ITC which was a test for us in the salt back then (10 years ago) test results are a phone call away.

The thing about steel in the floor is to keep heat away from it-I did that by starting with soft brick layer then a 12x12 jumbo hard brick layer (I had them as I'm a brick hoarder) then a regular hard brick layer. As a brick hoarder I always have cases of new soft bricks (250 last count) in various k temps as well as a pile of new hard brick-so If I need to repair a kiln I can without going to a distant supply house as none of these item are stocked within 300 miles of me

I have learned a lot from this test kiln

 

 

Mark

http://ceramicartsda...381entry18381

[yedrow]

Okay, this is kind of blowing my mind. I've only used one atmospheric kiln. It was made by Geil, and I'm pretty sure it is one course of IFB thick. I don't think the car bottom is more than one course (along with a complete covering of ^11 shelves) I'm going to check tomorrow, but I'm all but certain the walls aren't more than one brick thick. I will note that after about 10 years and around 500 firings the thing had a wall caving in. We were told it was an engineering issue and given parts to repair it. Now I'm wondering if it was built too light. From what I've read way too light. I also want to convert an electric kiln into a gas kiln (plowing the fields of my own ignorance here). I'm again fairly certain that the walls on this are one hard brick thick, with about two inches of fiber and the element holders over that. But this kiln is a rugged machine that was build for industrial use. It isn't made of sheet metal, it is a monster. I've been assuming that it was a ^10 electric kiln but now I'm uncertain.

 

Joel.