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Used fire brick changed my plans

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I still can't believe I am typing this, but I found about 1000 hard fire brick behind a co-workers garage. ... He told me to come get 'em. I asked what he wanted for them. ... He simply said come get 'em.  So now I have a problem; I have to build a kiln. ... I know. I know.  You fine folks would be happy to help remove this burden from me, and that is very kind and (uh-hem) expected.   But I've reeeally wanted a larger kiln for a while now.  Nat gas power burner.  Circa 30 cubic feet.  Gas company is crunching their numbers to get me 600k btu/hour to my shop.   Normally fire cone 6.  Might go back to 10 also.  If you had to build a thousand-brick kiln that you could fire with both nat gas and wood, what would you build? (Local waste disposal company said I could have all the wood I wanted, just come get it)  ... Gosh it's great to have these kinds of problems for once!  I used to feel like this looking at the Sears catalog before Christmas!  


OK. Question for you guys who've seen a brick or two in your time:

 Empire DP (Known. Check.)

Scratching head on 3 other types (googled to no avail other than Davis Fire Brick Company, Oak Hill, OH):

Davis - Savage

Davis - OHC

Davis - Hi Grade


Ring a bell with any of you guys?  Guessing since they were paired with Empire DPs (colleague salvaged them all from same location 11 years ago), crossing fingers that they all have about the same rating.  I'll definitely place Empires in hot face areas.  Not sure how many Empires there are.  If I have enough, great.  If not, I'll place the others where they can be removed/replaced without having to contort myself too much or as non-hot face floor.  Going to pick them up this weekend.


I'll stop this one here, and maybe start another about the kiln when I get them all home safe and sound.


Thanks y'all.


Edited by Patrick
misspelled word

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First off I need more info about you to answer you question as I have seen a brick or two.

These are all hard brick so that limits

you somewhat 

What I need to know is what kind of pottery are you?

hobbyist? production potter?

How much kiln experience do you have (not counting electrics)

part time potter?

Pots or sculpture maker?

playing with clay  or something else?

whats your age? wood or gas question for this answer is why I'm asking

how many electric fires are you now doing a year?(kiln size )

Edited by Mark C.

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I appreciate your directness.

Hobbyist since 2015. The word "production" regarding pottery means different things to different people, and I won't assume I know what you mean.  While all my eggs will not be in one basket, my goal is to become self-supporting with pottery and keep doing that until I quit breathing. ... And this is not an "if" but a "when". (The self-supporting pottery ... and come to think of it, the quit breathing too.)

Kiln experience is with electric to propane conversions.  Also fired barrel & pit. Currently have a 3 cubic foot and 8 cubic foot conversion kilns. Bisque and glaze firing each once a month, but have green ware and bisque constantly on the shelves.  More of a time thing than a "wares ready to be fired" thing.

Currently part time/as time allows, as I have full time employment in an unrelated field.  Financial groundwork is being laid to allow a transition to self-employment.

Pots.  Big pots.  And little pots.  Generally functional pots.  Had little interest in "art" when I started, but my unshakable curiosity is dragging me into that world.  But I understand the significance of such things as "mugs sell".

Playing? No.  Too flippant a word.  See line 2.  What do you mean by "something else"?

44y/o 180 lb. No physical limitations. Wood/metal work is a given (torch/welder/saws/et.al.).

Electric fires per year? None.

Propane to Nat gas is a no-brainer from a $/btu standpoint.  I see nat gas as reliable/predictable/reproducable.  I currently see wood firing (which I will self-teach because I'm a fool like that) as a "All work and no play makes Jack a dull boy"  kind of thing.

So.  Did that give you enough information to locate me in your paradigm? (I'm smiling.  I hope you are too.)


Edited by Patrick

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Just a few more questions-thanks for that info as it really helps

Are you in an area where you can build a wood kiln or a gas kiln in the rural areas without much bother or are city permits etc going to kill such a project.

For example a Natural gas hookup usually means permit oversite-vs a wood kiln usually means go ahead as no gas is needed and many rural areas do not care (not talking about cities)

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While waiting for a few more answers I'll add this

So hard brick really suck up BTU in any kiln.My 35 cubic homemade car kiln is lined with soft brick almost everywhere. That way its very efficient to fire.

The arch is K28s and some k26s-same as above the  firebox . Hard brick are used only in the burner areas. The outside of kiln is all hard brick except the door on car which is fiber. The car is floor is a mix of a few hard brick under post loads but mainly 3 layers of soft brick on a  sheet of steel on steel car.

If that same kiln was all hard brick the price to fire it would be sky high.

The soft brick lining is the key and not using k23s which will spall over time at cone 10 repeatedly . I know this as I lined this kiln once with k23s-back in 1978. They failed over time and I since rebuilt it with better soft brick.

Now if you are making a 6 figure salary every year until you retire then this all does not matter.  Or since you are close to playing the ponies in KY you may have won big as well and its a moot point. But if you are going to try to make any type of living with clay this will very much matter very much in terms of fuel costs.

No lets talk wood-it has to be hard brick and the (Empire DP) need to go in the firebox. wood  pots for a living is NOT for the weak of heart mind or body.

If you have a large social potter network in your area it can be done-that means many helpers as wood firing takes lots of time up firing the kiln-as well as preparations and clean up-about 100 times more than say a simple gas kiln .

Hard brick everywhere in a wood kiln is whats called for so you are in luck.

The next topic is the kiln chimney which no matter what kiln is made  from whatever fuel you  use you need hardback for the stack and that will eat up more than you think.


You mentioned cone 6 and I will add I know of no one personally doing cone 6 with gas or wood so I cannot help you there .Its less fuel  but you still need soft brick in a gas kiln or hardbrick in a wood kiln no matter what temp.

One thing about these Davis bricks you need to find out more about them and that is not as hard as you may think since they had so many types they must have been well known somewhere at some time. I collect  hard bricks in my travels and have never run across Davis but I'm out west and they are east coast.Dig deeper to get the answers to the different types stamped on the sides-I also assume they are standard size??? 4.5 x 2.5 x9 inches-right???

Now lets talk kiln size as I have seen many a person build to big a kiln again and again.

A 30 footer is for a high output or if thats not the case not many fires per year. Its better in my experience to fire more often (learning) than less often and wondering whats going on??

Production potters like me who make their livings at this making functional wares tend to use kilns from 24 cubic feet to 50 cubic feet with 30 being about in the most used range.I used to fire my gaze 35 cubic car kiln about 35 glaze fires per year and now am down to about 27 glaze fires along with a 12 cubic gas kiln also fired about 27 times a year as well. But I'm slowing down and these numbers are getting less

I have a friend doing the same as me with aGeil 27 cubic car kiln and another who is using about a 36 cubic car kiln and another with a front loading 30 cubic kiln.These are all high output production folks doing shows full time and stocking galleries and selling wholesale. POT pots pots.

I suggest a 24 cubic as the largest with the info I have above.

Get some soft brick and line the gas kiln-that pile is about right for a 24 cubic and chimney  natural draft with some bag wall material left over for the future-You will go thru some bricks as the bag walls eat hard brick over the years and if you fire alot you will need to replace these walls-if you have a wood kiln every more so.

I suggest  a layer of hard on the floor then two layers of soft on top of that  except under the post spots-then go hard all the way down. 

Also lets talk shelve size as most think of this afterwards  as an afterthought  and really its the 1st decision any one should make building a kiln.

I  have been round and round with folks asking about building kilns with is so again I will add the most common size for gas kiln shelves is 12x 24-build the kiln around this common size most economical shelve size-why because they are the most available size and most cost effective and they fit most wares  well on three point stilting plan and are easiest to load and move around size wise


Plan your shelve size add a little room to breath and then the bag walls and firebox area and this will determine wall placement.

Also remember brick size and make them work together .

Also consider flue size and burner ports-the more burners the more even fire unless you are going forced air-if forced air- chimney size need not be as tall.

There have been a few builders asking 1,000 question the past year and I suggest searching  from the main page to find these posts-That way you can avoid their mistakes and not take our word for things gone astray.

I can  add more as needed time for my bath to soak my broken arm

Heres me building my 1st car kiln in the 70s-I was in my twenties and have the hat on-this was many kilns ago and untold tons of clay before me-heck I was throwing stoneware back then-still need a plumb bob and string to do it right


Edited by Mark C.

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Digging the photo Mark! Maaan, you made the 70's look good! LOL.  ... And leave them ponies alone unless you wanna be poor! (or a pony breeder - they do pretty well)

Spent a lot of time chewing on this today, and I think I'll stick with just gas for this kiln.  I'd rather have a kiln that did one thing well than two things inadequately.

Getting a gas kiln up and running (zoning, permits, codes, etc concerning gas company and local ordinance and building/gas codes) is an absolute non issue.  I've dotted my i's and crossed my t's there.  I'll be building it under a standalone shed.  Firing gas would also be a non issue.  A wood kiln would not be against any ordinances either BUT (and it's a big fat but!) our lovely little community is still small enough where if the right person took the initiative about excessive smoke, an ordinance could quickly come into existence, and I wouldn't know about it until our one police office knocked on my door. (He's a really nice guy.)  Not interested in suppressing that wonderful feeling in my guts every time I started firing a wood kiln.  

Still beating the bushes for info regarding the Davis brick - might end up being a try and see kind of thing.  No biggie.

Here some of my thoughts & figures on the kiln so far.

Mark, we are on the same page regarding 1st pick a standard kiln shelf size (12x24 - check.) and size the kiln to that.  Ergo, 27 cubic feet (3x3x3).   

The reason the 6" wiggle room on each side is I really like the Abernathy kiln idea.  "Put heat where you need it."  Makes sense to me.  In my previous post, I mentioned "power burner" and to be more accurate should have said forced air burners, which I have decided to build.  Several reasons for this: (1) I'll have 7" WC on the gas.  Blowers would give me more flexibility than not.  (2) No chimney required, although I will make a flue box with damper for another option for tweaking atmosphere - unless you all have a better idea.  Might be unnecessary - not sure.

(OBTW: Has anybody ever tried a forced-air wood fired kiln? No chimney needed?  I've heard of some using underground silicon carbide pipe to get more air to certain parts of anagamas.  Just brainstorming.  Almost seems like heresy though.)

Hard brick vs IFB:  I agree with just about everything you said, Mark.  The fuel cost calculations I did in planning this out used the btu/hour/cubic foot for different kiln material provided by the generosity of Marc Ward at Ward Burners.   He stated that he was conservative in his figures - rather have the available heat and not need it than need it and not have it.  I am assuming he knows what he's talking about.  Estimated fuel costs for my current price of natural gas (I can almost hear some of you laughing already) for a 14 hour, cone 6 firing with 9" hard brick, 27 cu ft kiln would be in the range of $34-$44. Dropping it down to 7 hours would be a little over $20.  The same times with a 9" IFB, 27 cu ft kiln would be $31 and $15 respectively.  I don't think I would consider that difference "sky high".  --  In theory, there is no difference between theory and practice.  But in practice, there is. --  And I know there are a LOT of variables to this not mentioned.  OBTW: Propane costs for 9" hard brick, 27 cu ft, cone 6, 14/7 hours would be $155 and $103.  Propane with 9" IFB, 27 cu ft would be $90 and $72.  Yeah. My jaw hit the floor too. My current prices for nat gas per btu is $0.000006.  Propane is $0.000029. (Same number of decimals in both. 5x higher.)  If I have erred in my calculation (aside from the FACT that calculations are in no way obligated to conform to reality), please let me know.  If anybody wants the spreadsheet I made to beat my head against all this with, let me know.

Unresolved desires:

First: I want a catenary arch (in the same way I've wanted a Jeep CJ since I was 15 years old)!!  In Olsen's book he talks about ways to build arches with straight brick by angling, supporting edges, and wedging.  I get it. ... But does it work?  It's not the same as arch bricks.  I get that too.  But if done right (whatever that means), what will happen in 2 years, 10 years, 20 years? Or is this good for sprung, bad for cats? Or vice versa? Or neither? Or both?  (Mr. Baymore? Ms. Selsor? Bueller? Bueller?)  I'll probably try it just to see what happens.  How would that work with Abernathy's burner ideas? Dunno.  If I became convinced I could do a catenary arch kiln with straight bricks that wouldn't fall apart in 5 years, would I build it instead of a sprung arch Abernathy? Hmm. I think I'd want to give it a try.

Second: I want to work with homemade castable refractories.  Some research is out there (thank you, Mr. Lowell Baker).  And a catenary arch would seem like a good opportunity to cut my teeth.

Given all that, here's where I stand right now:  Unless someone with more catenary arch experience convinces me otherwise, I'll probably build something like an Abernathy with a sprung arch - all hard brick.  Use insulated castable for large door blocks. That will give me the wiggle room to see how well certain castable recipes do, and my second desire will be satiated.   Make pots and learn to fire that one.  Until I get that one up and going, I'll make do with my smaller kilns.  Later, I can let the lusts for a wood fired kiln and a catenary arch kiln battle it out in my head and heart. (Man, these are great problems to have!)

Tis where I'm at.

Still no takers on Davis fire bricks?

Mark, quick healing for your arm, friend.


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Ah, memories! All hardbrick catenary arch, 2" of castable over, castable blocks designed to overlap for door. 

DON'T Do It!! Been there. Castable crumbles at edges, falls into any inevitable gaps that happen when kiln expands with heat. Bricks try to close, but crumbs !!

After that, we tore off the arch and rebuilt with one course of high duty soft brick (all straights works for cat, not sprung), covered with 2" of fiber, covered that with brass sheeting. Left the back all hardbrick but will replace it too when I add a hinged softbrick door.

Rebuilt door stack by cementing soft brick in "puzzle blocks" to defeat, mostly, gaps. Still a pain, but better. 

I think you still need a bit of a chimney with a forced air downdraft, just to keep outflow up higher. 

Always listen to Mark C.

Best of luck

Edited by Rae Reich

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If you have access a friend with a high-fire kiln, take one of your salvaged brick and have it fired in your friend's kiln and see what happens to the brick.    Probably be a good idea to first weigh the brick, heat it in an oven for a couple of hours, and weigh again to determine just how much water is currently absorbed within the brick.  Then send it to your friend's kiln for a test run.    You don't want to find out that the salvage brick are really a low temperature rated brick. 


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I have built many a catenary arch kiln. That said I'm done with them. Why -the two ends are a pain to get sealed as the arch always expands and shrinks so it never ending battle to seal.

I  hate brick up doors as thats the cheap way out and it is a royal pain twice every fire. Especially as you mentioned a sprung arch . If you make a sprung arch you already have the steel framework to make a swing door on to-look up my old posts on salt kiln-there you can view a better door. You can make it from fiber soft brick or hard brick-your choice

I know of NO professional production folks using a brick up door. I even know a few hobby folks with swinging doors.

Castable is also a extremely poor idea for door blocks as Rae nailed in above post. Castable is made for a non movement use-use on top of your arch if you must . 

My first kilns where cat arches and castles with straight bricks-I made about 3-4 of them before learning the hard way that the energy needed to build a better kiln is about the same as a not so great kiln-same time spent but different outcomes.I even gave away my last unopened castable bags and that was in the 80s-done with that stuff as well.Live and learn Rae above.

I think the hard brick gas kiln firing costs you will find are out of line.Those charts are great but you what they say about great on paper but can it fly?

I have said my piece on insulation bricks-I learned with the others here  who tackled their 1st kiln that once one has an idea its hard to tun them around from jumping off the cliff of bad ideas. I have about 10  brick kilns under my belt but that means little these days it seem.

Neilestrick also has many a kiln build behind him and he is the go to forced air burner guy-I'm a natural draft guy-yes I have built and used forced air but now really like the gentle natural draft kilns I have made which work whether there is power or not.I have a stand by natural gas generator so even that is not an issue anymore for us.

I have set up a jig on an old radial arm saw that cuts soft bricks into #3 arch bricks (blade is 14 inch diameter and has carbide teeth) and have made my own and loaned out this saw a few times for others making their sprung own arches.Its NOT OSHA approved.Doing it myself  like brick making or cutting my own shapes or working with new materials all has taught me lots about kiln building-what works and what does not work well.

I have also tested a few firebrick pieces at cone 11 for other on this board in the past on unknown bricks.Yet to melt one

There was thread on old brick manufactures about a year ago (again use the search function from man page)It was chart link if I recall-I should have printed it -oh well

Yes you can make a sprung arch from straights but again it will not hold up to the test of time-a row now and then is another story but the whole thing is just problems waiting to get you. 

I realize these bricks where FREE but spending some $ on the other kiln parts will get you down the road better.

I'm curious about your fuel costs after a few fires as I know they will be high. Most costs are figured in therms as that whats the gas meter measures -Mine are about $1 per therm-as it varies every month.thats for all the costs-the meter (commercial flat rate) the delivery costs etc-I divide the therms into the total gas bill to figure therm costs.I have never figured BTU costs

I have a photo I'll post again of my old 40 cubic foot cat arch firing at night-it shows the door issues well during a reduction firing-all made from straight bricks from a rotary kiln-they where all free like yours but where 3 times the size.Gas was cheap back then and still it cost a lot to heat those 9 inch hard brick walls.Great glazes as they too days to cool down.We needed those days to work jobs to pay the gas bills.

Heres a large cat I made in the very early 70's

any heat loss around the door?? It was a pile the bricks door by the way-I loved this kiln until the gas bill showed up-(I did laugh at that gas use chart by the way) so you may have heard me.


kiln fireifish.jpg

Edited by Mark C.

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Looks just like mine did - only bigger! You can stand 3' away from it in the rain and be dry on one side! An awesome sight in the front yard in my city neighborhood. Neighbors became accustomed to it and never complained. They were always invited for kiln openings. 

They never even notice the Geil. But I miss the Roarrrr!

Edited by Rae Reich

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Did you break the numbers down to types? while piling???-nice pile-looks too be about 1,000

Have you called the oak hill chamber of commerce for brick details? or any current brink makers in Ohio for data on your Davis brand-Many brickmakers have data on other manufactures most likely as well -since Davis was around from early 1900s to the 70s in one form or another I'm sure that there is data out there -just not easy to grab on the net-will take some phone calls and digging.I would focus on Ohio refractory suppliers and manufactures-also ask every place you call for a lead to call next.


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An all hard brick kiln is really going to waste a lot of gas. It's a ton of mass to heat up. There's a reason people don't build kilns out of hard brick unless they have to (wood, salt, soda), and even they they use soft brick for the outer layer. If I were you, I would think about investing in some soft brick, too. If you're not going to be doing salt/soda, you could use the soft brick for the interior (so you'd need fewer) and hard brick for the exterior. 

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5 hours ago, neilestrick said:

An all hard brick kiln is really going to waste a lot of gas. It's a ton of mass to heat up. There's a reason people don't build kilns out of hard brick unless they have to (wood, salt, soda), and even they they use soft brick for the outer layer. If I were you, I would think about investing in some soft brick, too. If you're not going to be doing salt/soda, you could use the soft brick for the interior (so you'd need fewer) and hard brick for the exterior. 

Yes I agree on all points above . Your fuel cost will be to the moon with hard brick.

Look around for a good deal on a pile of soft bricks -places like e-bay -potters attic -check with industrial jobs as they often have left overs after doing boilers and ovens.

I always have about 500 soft bricks on hand as well as a pile of hardbricks for bag walls.

Edited by Mark C.

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1 hour ago, Mark C. said:

Yes I agree on all points above . Your fuel cost will be to the moon with hard brick.

Look around for a good deal on a pile of soft bricks -places like e-bay -potters attic -check with industrial jobs as they often have left overs after doing boilers and ovens.

I always have about 500 soft bricks on hand as well as a pile of hardbacks for bag walls.

And they're lighter!!  But be careful of abrasion when transporting/stacking. 

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