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My Kiln Build

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bciskepottery    925

I decided the arch would have a rise of 4" /foot. so the arch has a total rise of 12". 

 

Jed

Are you building downdraft or updraft? Downdraft has the arch as part of the cube; updraft has arch on top of cube.

 

The size of your burner ports should at least equal the size of your flue opening; flue can be bigger (you can always put a post inside it if the draw is too much) but you will have problems if the flue is smaller.

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jrgpots    231

 

1.  Are you building downdraft or updraft? 

 

2. The size of your burner ports should at least equal the size of your flue opening; 

 

1.  I'm building a downdraft. The inside measurements are 31 (side to side) x 30(front to back) x 24 (stem wall).  With a 12" arch, the height will be 36 ".  Is that too far away from the ideal cube design.  If so, I can lower the rise.  To have the top of the arch be within the cube, the rise would be 6" or 2"rise/foot.  Is a 2"/ft rise structurally sound?

 

 

2. Each burner port is 4" x 4".  I have 2 burners.  So the flue opening is 4" x 8".  Should I increase the flue size a bit?

 

 

3. Should I put a throwbrick between the skew brick and the casted arch?  I don't know how much taller that will make the arch height.

 

Sorry for so many questions. It is a bit more challenging than I initially anticipated.

 

Jed

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Mark C.    1,807

 

 

1.  Are you building downdraft or updraft? 

 

2. The size of your burner ports should at least equal the size of your flue opening; 

 

1.  I'm building a downdraft. The inside measurements are 31 (side to side) x 30(front to back) x 24 (stem wall).  With a 12" arch, the height will be 36 ".  Is that too far away from the ideal cube design.  If so, I can lower the rise.  To have the top of the arch be within the cube, the rise would be 6" or 2"rise/foot.  Is a 2"/ft rise structurally sound?

12 inch rise on a 31inch span is a bit tall-I'm away from my stuff to tell you what I have but that seems a bit high on the rise-since you already built the form I guess you are using it?

The inner wall of the arch should  land about an 1/2 to 3/4 of an inch from inner brick wall accounting for shift. You are making a cast arch??I have zero experience with that. 

 

The cube is theoretical and for me is just a guideline-you are close enough-my car kiln is deeper  hence is not the perfect cube and works fine.

read Olsens kiln (older stuff)as well as Lou Nels book for simple rules. I used Nills newer venturi flue specs on my last kiln (salt kiln) both on the flue and chimney and it works super.

2. Each burner port is 4" x 4".  I have 2 burners.  So the flue opening is 4" x 8".  Should I increase the flue size a bit?

 

I build my flues a tad large and plan on using a split (1/2 brick long ways) to fill in.I like the smaller openings but can enlarge if needed buy taking splits out.

 

 

3. Should I put a throwbrick between the skew brick and the casted arch?  I don't know how much taller that will make the arch height.

I do not know a throwbrick?you mean a regular brick?More details. I always avoided cast arches as they have failed for friends.

 

 

Sorry for so many questions. It is a bit more challenging than I initially anticipated.

 

Welcome to kiln building my friend-you learn from each one.

 

Jed

I'll be home late week and add more but you may be done by then.

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jrgpots    231

Olsen calls the straight brick sandwiched between the skew brick and the arch, a "throw brick."  I had never noticed this before and was curious about it.

 

I built my arch support wider than you suggest.  It is 34" WIDE.  That is a 1 1/2" overlap on each edge.  Olsen gives a minimal arch rise 1 1/2"/ft and a maximum of 3" ft.  So I will rebuild the support to the right width and a 6 " rise.  That keeps the kiln in the cube shape.   My final kiln space will be 15+ cu ft. (not bad for a beginner).

 

I will widen the flue. I like the idea of adding a split if needed.

 

I was rushing to get as much built this past week because this Wednesday I will have disc replacement surgery on my neck.  I will not be able to lift anything greater than 2 lbs for 2 weeks. (I hope it is only 2 weeks).  As you know I live in the desert.  And we almost never get rain.  Yet as soon as I started the kiln it has rained here for 5 days straight.  My friend in the neighborhood told me I had to stop building the kiln before we all floated away.  We have had about 7 " of rain in 1 week.  We normally only get 9"-11" in a year.. The rain gods need to talk to the kiln gods more often. Their cooperation would be very much appreciated.

 

Mark, Bruce, Neil, Marcia.... Thanks for your help... I would have hesitated more before starting project without your back up.

 

Jed

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Mark C.    1,807

I think the throwbrick makes for a sliding surface between the arch and skew which is good idea.The arch will move over time with expansion contraction- heat- cooling cycles .

Do not rush the build as thinking it through will pay off in the long run.whats a few months in the long run if it works better.

Check out Lous book on kiln and space age materials,

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jrgpots    231

My stem wall can be 21" or 25" tall.  Would it be better to have a 21" wall and a 12 " arch ( I have already made it) resulting in a height of 33"; or use a 25" wall with a NEW arch of 7" rise which would make a total height of 32" ?

 

Any suggestions?

 

For a forced air (power burners) downdraft kiln, what is the chamber size to flue ratio?  Just rechecking everything...

 

 

Jed

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neilestrick    1,381

Just go with what you've got. It won't make a difference. The whole cube thing is not a requirement. I've built and fired many kilns that are rectangles. It's all good. Don't over think it.

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jrgpots    231

I placed a 2 inch thick castable arch a few days ago. I have placed 4 inches of kaowool on top of the castable. On top of the wool, I have placed some expanded steel. I will be adding 4 inches of junk castable on top of the expanded steel mesh.

 

I have run into a conundrum... the door. Since my hard bricks are tongue and groves the outer wall does not form a flat surface, so what type of door will work?

 

 

Jed

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jrgpots    231

post-26461-0-69856700-1497147885_thumb.jpgpost-26461-0-44646900-1497148258_thumb.jpgpost-26461-0-91490800-1497148273_thumb.jpgHere are a few of the latest build photos.  I'm calling the kiln "ugly Henry."  This week I will add a second layer of castable to the top.  The chimney needs about 2 1/2 ft more of height.

 

Jed

post-26461-0-69856700-1497147885_thumb.jpg

post-26461-0-44646900-1497148258_thumb.jpg

post-26461-0-91490800-1497148273_thumb.jpg

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Mark C.    1,807

I'm a little confused as this detail is usually worked out in the planning phase?

You could have cut the the bricks flush or fill the space with a castable?You still can but not will be a lot harder.

When making  kilns from scrounged materials  usually door is a stack of brick-you number them and always restock them the same.

I'm making an assumption that you want a hinged door at this point??and are wondering how this may work?

Detail details details-in kiln building it best to work on them before the build.

I suggest a stack door of bricks cut to fit.

I think those chimney bricks that are standard fire brick for house chimneys will all crack that close to the heat source. (these I assume are not stamped fire bricks )I had cracking on these types 4 feet from my damper and these are much closer.Just expect that and take precautions .

Photos of the uneven surface will help us on the door issue.

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JBaymore    1,432

Typically "standard" house chimney hard firebrick are considered "low duty" firebrick.  Suitable mainly for upper chimney use on kilns.

 

best,

 

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

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jrgpots    231

I'm a little confused as this detail is usually worked out in the planning phase?

You could have cut the the bricks flush or fill the space with a castable?You still can but not will be a lot harder.

When making  kilns from scrounged materials  usually door is a stack of brick-you number them and always restock them the same.

I'm making an assumption that you want a hinged door at this point??and are wondering how this may work?

Detail details details-in kiln building it best to work on them before the build.

I suggest a stack door of bricks cut to fit.

I think those chimney bricks that are standard fire brick for house chimneys will all crack that close to the heat source. (these I assume are not stamped fire bricks )I had cracking on these types 4 feet from my damper and these are much closer.Just expect that and take precautions .

Photos of the uneven surface will help us on the door issue.

I placed the angle iron in front to give support. I will be placing a layer of castable along the edge of the opening so the sides are straight and flush. I will be stacking the brick in the door.

 

Yes, I have made many mistakes from the planning, design, and execution thereof. Hopefully, retro repair and engineering can save my button.

 

Jed

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jrgpots    231

Typically "standard" house chimney hard firebrick are considered "low duty" firebrick. Suitable mainly for upper chimney use on kilns.

 

best,

 

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

The Base of the chimney up to the damper and 4 inches above is heavy duty 4 x 4 x 12 brick. Above that is 2000 fire brick. I guess that is the chimney firebrick...? I can change this. How high above the damper do I need to use hard brick?

 

 

Jed

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jrgpots    231

The following things I have learned.

 

1. Use standard brick size. USE STANDARD BRICK SIZE!

2. Make the concrete pad 6 inches thick.

3. Make the door first. Raise the walls starting at the door jam.

4. Place the angle iron frame BEFORE the arch.

5. Use standard rise in the arch so you don't have to make special angle skew brick.

6. If casting the arch, leave the arch support in for longer than you want. This will allow à non-stressed arch.

7. One 6 inch castable layer is better than 2 or three layers.

 

8. FIND A FRIEND WHO HAS DONE THIS BEFORE. HAVE HIM/HER PRESENT FOR DESIGN, EXECUTION, AND BUILD.

 

 

JED

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JBaymore    1,432

Jed,

 

A lot of, if not most, kiln builders use hard firebrick for most if not all of the chimney.  Some aspects of the reasoning for this can be solid.

 

A lot of kilns have the chimney, or at least a good amount of the chimney, outside in the elements.  Hard firebricks withstand the 'ravages of the elements' FAR better than insulating firebricks.  Repeated wetting and freeze/thaw cycles will cause insulating firebricks to break down and start falling apart....as well as steadily slowly losing their insulating value.  So this is the 'good part' of the reasoning to use them.  Hard firebrick are typically less expensive than insulating firebricks... so this to is another good reason to use them.

 

Personally for a cone 10 type gas kiln I'd make the first 3-4 feet of the vertical chimney a high duty hard firebrick.  Then about 3-4 feet of a medium duty.  Anything above that can be low duty "home fireplace" firebricks. 

 

It is generally OK to stack hardbrick on top of insulating firebricks... since the cold and hot crushing strength of the IFB is pretty high ... like in the 150 pounds per square inch range. 

 

People don't often think about chimney weight.  We recently build a 25' tall hadbrick chimney that was 9" x 18 inside.  That loading is over 8000 pounds on the 18" x 27" base footprint (3.375 sq. ft).... or 2370 pounds per square foot that the support area has to hold up (for years).   If you only look at the area of the brick support wall of the chimney.......... that comes to about 3556 pounds per square foot........ or 24.7 pounds per square inch on the actual brick surfaces.

 

The support PAD under a tall hardbrick chimney becomes and issue to look at under really tall chimneys.  If not though out well... can sag or crack.

 

best,

 

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

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Mark C.    1,807

Kiln pads as John has covered well mean you always need more steel and concrete than other types of foundation work.

I have made a few of your mistakes back when I was a kid -I have seen all of these before by others -the chimney was one I see all the time.

You will need more high fire(bricks that have a name stamp on them) (not low temp unmarked chimney hose bricks from the building /lumber stores with no name stamp on them).You will find the damper area gets really hot and needs to be made with high fire bricks. You also need to have the damper supported on an edge inside the flue area on all sides. I cannot see what you have going on there?

I am not a fan of castable on a hot face-mainly because I have seen so many failures. 

Its good you are learning from the build.

The standard size brick for kilns is the key.

Get some more good brick and go up another 4-5 feet in stack before using the low fire chimney brick

You should also get standard brick for the door-hopefully you designed the space for them.

You could wet diamond saw the tongue and groves off-its a bear of a job but I have done worse.

 

good luck

 

PS after another 5 kiln builds you will have all the details down-at least that was my experience

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jrgpots    231

Jed,

 

 

 

 

Personally for a cone 10 type gas kiln I'd make the first 3-4 feet of the vertical chimney a high duty hard firebrick.  Then about 3-4 feet of a medium duty.  Anything above that can be low duty "home fireplace" firebricks....

 

 

best,

 

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

John,

 

I will be using power burner. So I was going to have the chimney end about three feet above the arch top. Is that too short?

 

Jed

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jrgpots    231

Here are a few more things I have learned.

 

1. Wear long sleeve shirts when cutting or grinding hard brick. I developed a contact dermatitis that looked and felt like poison ivy which lasted 2-3 weeks.

 

2. Mig welders do better with a 20 amp circuit breaker.

 

3. Old IFB brick pieces can easily be turned to grog by putting them in a cement mixer and covering the opening with a garbage bags to reduce dust. Three hours of tumbling in the mixer does the trick.

 

JUST THINK WHAT WILL LEARN ONCE I START FIRING THE KILN.

 

Jed

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JBaymore    1,432

 

Jed,

 

 

 

 

Personally for a cone 10 type gas kiln I'd make the first 3-4 feet of the vertical chimney a high duty hard firebrick.  Then about 3-4 feet of a medium duty.  Anything above that can be low duty "home fireplace" firebricks....

 

 

best,

 

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

John,

 

I will be using power burner. So I was going to have the chimney end about three feet above the arch top. Is that too short?

 

Jed

 

 

 

Nope....not too short.  With correctly sized forced air burners...... you could just have the hole in the floor in the back of the kiln (except for safety reasons).  Take the chimney up an amount that deals with where the very hot gases and the crap coming off bisque and glaze firings is routed away from people, building openings and so on.

 

You should see some of the noborigama and anagama in Japan........ with sheeets of flames coming out the rear of the klin .... right at ground level from the exit flues.  Would give an OSHA or insurance company inspector a coronary ;) .

 

best,

 

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

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jrgpots    231

I would love to see that in person....maybe someday.

 

I had plans on placing a tile roof on the kiln. I have never seen it done. Is it possible?

 

Jed

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Mark C.    1,807

Since the kiln is forced air the stack is not as important-but it does need to be made from material that will take the heat. You could wrap those low fire chimney bricks in wire or steel so when they crack they stay put.

I have seen stacks on inside kilns use round fiber board types in tin pipe work for many years. I even have some from a friends kiln when he moved away. I call them flue liners.-they cannot get wet since they are compressed fiber.

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jrgpots    231

No, I will change out the chimney bricks for super duty bricks. Any ideas where the cheapest super duty brick can be purchased?

 

Jed

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