There's a Problem With Fire Bricks 

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The pain of knowing there was an easier way but you just didn't do it that way because it involved having to talk to a human being... I felt that. lmao.

Yes! Cross-hobby knowledge sharing needs to happen. Often one group has solutions to problems the other group hasn't even considered. And although being into multiple maker disciplines can lead to a lot of need for space, it can also lead to efficient use of space: everything in my garage workshop has multiple purposes.

2 years ago I was watching you make the thing. Didn’t know you could get one cut to size like that. Depending on the price of course, that really could be a big benefit.

You could use an adhesive specifically for kiln bricks to bond them together so it would move more as one. It would also help using ceramic wool on the outside surface for greater insulation. In our lime kilns we use ceramic wool, soft fire brick and then the harder fire brick on the inside for ware resistance. We also use a castable Fire brick but it’s very expensive. You should be able to find this material at an industrial concrete and brick supplier. Hope this helps

Years (decades) ago in college we built a small kiln with a removable top. The top had a steel angle iron band around it and a slight pyramidal shape to combat shrinkage. Worked pretty good for holding together over a few years of usage despite being built by a couple clueless students. Instructor gave us a grudging "it'll do" on the job. Which from him was high praise.

Suggestions to prevent issue in future. One simple way would be to swap the bricks around every so many hours of use, so the shrinkage ends up being even over time. Now unless you use special alloy steel, most steel and pure iron have similar melt temperatures, cast iron having a much lower tmelt. 99.999+% pure iron has a much higher melt temperature, but it is very hard to obtain in quantities enough for rods... nice thing about having a career in chemistry for 40 years, you learn a lot of interesting trivia... Now there are metals that would withstand much higher temperatures without softening, but they are quite pricey. Another note is that your holes need to be loose enough for expansion of the rods, or you will end up with cracked bricks, especially when they shrink onto the rods.

I don't know about fire bricks, but shrinkage has been a major problem in my life too.

When I first switched on my home made electric foundry all the joints wanted to open up and fall the thing apart. I switched it off and built a cage around it, a bit like your rods, but external. When (if) I build my next (bigger) foundry, I will keep this idea in mind. A very neat solution.

Can’t believe I started watching you 5 years ago build this, it was what got me into this kind of stuff in the first place and melt my own metal, thanks!

Absolutely agree on cross-hobby interactions. I do a lot of pyro stuff and frequently find myself gandering pottery and blacksmith resources because there's SO MUCH crossover. Shout out to all the ceramics guys keeping the cost of lithium and strontium compounds low. Love yall

Thanks for the entertaining education on fire bricks. I'm building a forge now, and didn't know the bricks shrink a little.

Wow, 2 years already... still got all the ingredients just sitting in my garage, unopened/unused... had wonderful plans 5+ years ago, but per usual, life happened. And so I chose to vicariously build with you, I'm very grateful you were willing to share along the way! Assuming life, well "actual life" doesn't stop happening anytime soon, I'll truly benefit from this shared knowledge, eventually, I'm sure, if I can just open the garage door... Again, thanks!

I love your style, easy sub. Informative with plenty of humor, just the right amount of editing splashiness

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You can also use firewool, it's like fiberglass but for furnaces, use that as an inside layer and it should help take some heat load off the firebricks

You edit and display your nerdiness/personality well. Very fun to watch!

The material you want is called Blakbond mortar made by BNZ materials. Also, not allowing for thermal expansion will spall the edges of the bricks, so looser band, plus strong mortar joints will work better. Many pottery kilns get destroyed because they are too tightly constructed. Gaps are your friend. Best of luck

Thanks for posting this and going over the subtle differences between two designs.

Potter here and this video was recommended. We've solved a lot of the problems you talk about in the first minute of the video! (Use fiber/castable refractory and your rebar solution is basically the Minnesota Flat Top kiln). I've always been interested in what else my kiln could be used for - although at ~10 Cu ft for the electric one and 30 Cu.ft for the gas one they're a bit big to fire up for small stuff. (Funnily enough the electric is a top loader (door is the lid - made of brick) while the gas kiln is a front loader (fiber door)).

Another way to keep your lid bricks from shrinking would be to line the underside with kaowool. A piece of 2" thick should keep the bricks from getting hot enough to shrink.

Back in the 1970s, I worked at a lead smelter. We used a coke-fueled blast furnace. We used some kind of mud to seal the cracks between the fire bricks. Got it on pallets of 50lb bags. We'd throw a few shovels full in a 5 gallon bucket and mix it with water; no special ratio. It sealed the cracks well. It wasn't adhesive, so it came off pretty easily when we shut down the furnace. For a small oven like yours, you'd be able to use a chipping hammer that welders use to chip the flux/slag off of welds. There's gotta be somewhere you and your friends can chip in and buy some of what ever that was. I never knew what industrial supply we got it from.

I dont do any foundry related stuff but i watched this whole video, love this guy

I made my lids from fiber refractory board. It's more durable than wool, bit less than brick. However being a solid sheet, doesn't have this issue. You can coat the surfaces with kiln wash to hard face them to reduce damage, or repair erosion over time. Making a mount that prevents any sliding contact is a good idea, and usually allows for putting a bit of wool around the edges as a seal, which prevents wear and heat leakage. The mount also holds the hot door while you unload the crucible.

Built a few kilns. Actually really surprised I only just stumbled on your channel since you do so much of the stuff I used to do. I like your idea about sharing experiences between disciplines. That's the way to learn new ways of doing crazy interesting stuff. Here goes with some of my experience with kilns. The biggest I've built was about 18 feet by 20ish feet. Basically big enough to park a 1 ton GMC Suburban inside with room to spare. Steel framed box suspended from a gantry. The gantry was on trolley rails. Took four guys to move it. It had two steel framed beds it could be dropped on so, basically... while one was firing the other was loaded and unloaded and serviced if it needed it. It needed it often. Structural mild steel really doesn't like glass firing temps and wool never seals up as well as I would have liked. The beds had 1/4" X 6" leveling blades bolted into the firebrick bed frame so that the top edge could be periodically lined up in a perfectly level plane a couple of inches above the fire brick surface. Then clay grog (basically non-scoop kitty litter) was poured in to fill the difference. That made it possible to use a screed to scrape the grog out perfectly flat and level. Economical to build and easy to maintain but not the most energy efficient beast. 200w 480v three phase power through mercury relay switches and a programmable controller. Ooph. Great fun to work around in the summer. Most were a lot smaller. 2' X 2' X 3' mostly. Great for almost anything. All of these used alumina foam firebrick on the inside and compressed ceramic fiber panels (basically space shuttle heat tiles) outside of that. There was a 2" L angle welded frame to buckle the firebrick together with threaded stainless rod to compress it together. Mild carbon steel threaded rod rots quickly and rotten threads make crappy fasteners. The ceramic fiber panels were fitted over that with a thin sheet of ceramic wool between to fill the space. Just adding that insulated it so well the outside was good and warm after a day long fire, but you could touch it without burning your hand. High fire nichrome coils were fitted into grooves in the firebrick walls and ceramic rod was run through the coils to prevent sag. Pieces of nichrome wire were used to fasten the ceramic rods to the walls (inside grooves) so that the coils were sitting about half in and half out of the wall surface. It's best to leave the coils as far into the kiln space as possible. The part in the groove tends to concentrate heat and when a coil burned out it would burn out facing the groove. The rods kept the coils from sagging so that wasn't a huge problem that they weren't stuffed into deeper grooves. Each of these had three coils for convenience but a couple of kilns I built like this used zoned heating so I could use a Terra cotta flower pot with a removable plug in the bottom drain hole, as a crucible for glass casting in the top of the kiln. A little high alloy steel rod and a ceramic cone set in the drain hole and after the glass had time to properly melt and fine (outgas) the rod could be pulled up gently by a cheap spring until the ceramic cone slipped out of the drain hole and let the glass melt flow into the mold. I even set up nichrome wire in random ladder-like arrays under the pot so that different colors of glass would drip down through it and become a bit better mixed but not fully blended together... Made awesome organic looking effects in the castings. Just measure the volume of the mold using sand... weigh the sand... put that weight of CoTE compatible glass into the flowerpot, plus 15%-25% for the glass that would cling to the pot and not pour into the mold... Ramp the kiln up so it didn't shock the mold and wait until the bubbles in the melt rose and mostly popped... pull the drain plug and start the cooling and annealing program. By using seperate controllers and zoned heating coils, the mold could be kept at a lower temperature than the crucible to keep the mold castable from breaking down while getting the glass melt hot enough to outgas and flow better. Hexagonal Boron Nitride makes a great high temp mold release for glass as well as a lot of metals and in case you want to put an actual top or side loading door on your kiln, this is what you want to use to lubricate any moving parts (hinges, pivots for a split top door, etc) It's a greasy white powder ceramic with the same molecular structure as graphite but much better heat stability. There... Probably as much as anyone is going to want to read from me for a minute. ✌️

This explains so much as a glassblower cause I've seen these built so differently depending on application in my field like most glass furnaces use the arches or the foundry style if the furnace is constantly hot vs annealing ovens which use less heat and less time hot are just cubes.

In between the bricks can be placed soft graphite gasket material. Exhaust system gaskets have a graphite ring, as an example. Graphite is one of those things you can't easily burn. It could save you on the electric bill and rate of cooling. I worked on one whose steel band was held closed with a turnbuckle on a spring. I might need a super-hot oven in the future, and any good-sounding ideas will be tried.

In the top 2 explanations of the month right here . I wondered how that worked.

Is there a certain limit to how much those bricks could shrink? If there is, in theory one could fire them in a way to pre-shrink them and then they could be set from there. (Maybe that's not the case, but it would be interesting to find out.)

I learned from TKOR and now im here just before i craft it

Bless Phil Rogers soul. Potter here, not an expert but just by observation, when potters build their kiln, especially wood fired kiln (Those big ones) we use at least 2 layers of bricks. Usually a primary layer of firebricks followed by a backing layer of clay bricks. We also use ceramic insulation cloth between the layers to further insulate the kiln. That being said though, I have not experienced a kiln repair as of yet and cant comment much on the shrinkage issue as our kilns usually "Settle" over time and its geometrical shape usually solves any problems with potential cave ins and such. Edit : Definitely forgot to mention that ball clay is used as mortar too.

2:00 Funny you say that, because I was worried I was getting into too much at once. Forging, pottery, pyrolysis and distillation, composting. It all seems very exciting but it's just so much all at once. I appreciate all the videos you people make that I can watch during the work week and put into practice on my days off.

Paul, your tighting band does not give direct pressure to the inside bricks. The band is giving pressure only at the corners. Shorten the corner bricks and shape them to get some overall octagonal design so the band can exert some pressure to the bricks in the middle. Or just add a wegde to the middle ones between bricks and band.

I'm a pyro, if anyone needs me for something This is the first video of yours that I have watched, and I'm dying at the words on screen

Thanks for your entertaining presentation. I saw a few videos where they were making their own firebrick with a mixture of refractory cement, vermiculite and sand. With that you can cast a custom-shaped piece of any size. Perhaps include reinforcing iron within the piece?

I used to work for a metals recycling company. We mostly had refractory brick for the furnaces. When we line the furnaces we intentionally add 1 few mm in between the brick with a bitumen pads so when we ramp up the temp to ~1000 C (~1900 F) the pads would burn off. Since we ran the furnaces at more or less temp constant 24/7 until the next relining we don't really have issues with the lining itself (except for the occasional worksmanship or material infiltration issue). We do have shrinkage cracking on the spouts we use to tap the furnaces and yes we usually use pottery clay to patch up/cover up those problems. We found that low moisture clays worked best for that application

I've worked in the steel Industry for years. My craft is in maintenance, not production. From what I gathered, keeping the furnace hot mitigates shrinkage of the refractory brick. The lentil entry to the reheat furnace fell in recently. They used metal to hold up the refractory, and the metal failed. The furnace had to be idled to ambient temperature for the reconstruction. Consequently, much of the other refractory had to be replaced.

Inspiring as usual, thanks!

Another great video! Great comment about masonry arches. Cheers from Alaska

Loved the video man! Enjoying watching your production evolve! Also I really want a kiln lol. I need a workshop...

Bud!!!!!... that was SOOOOO interesting!!... never cast a bloody thing in my life.. with heat i mean.. but your presentation was so good.. i stayed and watched it all. Good job on the presentation.. and very good skills there man!! Liked it a lot!

Refractory blanket works well for lids. It's light weight too, but it helps to be rigidized. An area the size of your kiln there would be quite affordable. The plus side is it's flexible, affordable and can be rapidly heated with no cracking issues. The down side is the dust is extremely irritating and potentially carcinogenic so it's a good idea to seal or rigidize, and it cools down very quickly compared to fire brick which can be an issue if you want to control the rate of cooling. I suspect you're probably well versed on the stuff. 304 stainless steel works very well for those kinds of temperatures. The issue with steel, like the threaded rod, is that heated iron will react with any CO2 generated by the firing and cause corrosion which can damage the bricks, an issue with both electric and gas pottery firing, and if the steel is galvanized the zinc fumes are toxic. 304 stainless has a ridiculously high melt point though at high temps it will oxidize but without the corrosion issues you get with iron. I come at it from a pottery perspective, now building my 2nd kiln, and could not agree more about sharing info between crafts as I've gleaned most of my deep in the weeds detailed info about gas, gas burners and construction materials from DIY forge builders.

Outstanding video! 👍🏻🎅👍🏻 Glad I clicked, liked and subscribed! 😂

Fun and informative. Thanks!

I actually love aluminum borro silicate brick. I cast bronze hammer heads, (so far)...super easy to mill and cut.

IDEA: take the lid apart, and then put the shrunken sides of the bricks on the outside and the unshrunken bricks on the inside.

For industrial heat treatment furnace design (giant methane pizza oven style) all our furnaces had height-adjustable doors that were metal frames with bricks inside of the doors; I would venture using this as the primary access for a non conveyor style kiln/oven/furnace would work fine too and eliminate a lot of issues like what you are dealing with. On the flip side you have some degradation of efficiency at the joints for that style door, have to maintain positive pressure inside and may or may not need some kind of ventilation to pull fumes from the entrance (like I said, we used methane so some different considerations)

Steel rods - good start, if you shape them into an inverted arch inside the bricks and then post-tension them (steel stretches like a spring for when they are cold and larger) if the bricks can take that much stress. Post pensioning them from that inverted arch shape also pulls the outside bricks down, or the inside bricks up. And as pointed out mild steel may not be the best steel to use.

I worked in an industrial foundry where the furnaces and heat treat kilns were larger than your living room. The furnace roofs are all made in arch shapes for this reason. A little shrinkage is taken up by the arch shape. Almost everything was high density fire brick arches supported by steel framework.

Cool. Thanks for sharing.

I’m building a kiln this summer, as big as I can. I have as much clay as anyone could use in a lifetime. Tbh though, you can make your own fire bricks with plaster of Paris and sand, I don’t know the exact formula because I haven’t needed to make one yet. Fortunately for everyone interested, you can also add fiber glass to your mix to add some support in the mix. If you have ever seen the inside of a old coke oven, the walls and ceiling are basically glass.

I used to be a professional potter. We had a gas fired kiln and fired in reduction. We used the entire natural gas service line that ran in the building for 4 burners and an additional 40K gallon propane tank run wide open on an additional two burners. We would fire to cone 11, which is hot for pottery. Total firing time was about 12 hours and then 12-18 to cool to ~350-500 degrees when you could start unloading and burning your gloves off. The roof of the kiln was built as a Roman arch. The floor and front door were on iron wheels on tracks so you could load and pull out the pots like a giant cart. The door was sealed with kaowool which is basically synthetic asbestos that hasn’t been banned yet. And if you pump in enough gas, any air leaks won’t matter. But kilns don’t last forever and it needed to be rebuilt every 5-7 years.

i have built lids for my blacksmith forge and i used 3/8" Ceramic Hardboard coated in a ITC-100. ITC-100 is a coating that seals and protect the ceramic fibers, and it reflects/ re-emit the infrared heat as the heat up. they have held the heat for years, and have traveled from a dry climate to a humid one and are still very usable. my blacksmith forge uses 1" Ceramic Hardboard to insulate and the boards are extremely light weight.

Had not seen you in awhile, nice to see you seem to be doing well. I was around when you built that oven. Ended up going withthe propane tank/KAO Woll deal. Not run it for a bit-new property, getting things going but I now have a workshop and pghoto studio. Will see how mine holds up in a few weeks-have to order a new crucible because my others got left behind [[sigh]]. Good to saee you tho Amigo.

who is this man and why is he so casually hilarious? is he my new ave?

wonder if you can get the clay for making those bricks you could make youre own and make them to size and shape , not loosing any material by cutting it you have pottery ovens so you should be able to bake them a few pieces at a time (excapt maibe a one piece lid and bottom )

I can geek out on refractory block 😂

Oh neat, you're not dead. I'd thought your channel went dark over the last year. Turns out, YT felt like unsubbing me randomly and despite I almost exclusively watch content like this, the all-mighty algorithm only now decided "oh, hey. I bet he'd like this!"

Bravo for making you own kiln/ furnace thing!!! Gaps can help you. Reduction kilns aren’t that tight. They get the reduction by burning more combustible material than there is oxygen ( extra gas,wood, or oil )There is always positive pressure in the kiln so small gaps don’t matter. A sagging lid isn’t so bad and it looks like yours was a far way from falling in. I’ve seen way worse that last for 20yrs in that condition. Kiln manufacturers use a type of kiln mortar and seal the inside of the lid and between each brick as well as using octagon shaped tops to keep compression more equal like you said. Bravo for you ingenuity and exploration!

I use ceramic wool with a steel shell :) Great video!

_"It's not the aliens that didn't build them!"_ Best use of two negatives in a single sentence.

agreed i got to talken with glassblowers and bronze smelts and learned alot from them. i still not good at maken molds for complex castings but learned how to make a furnce hot enuff to make molten steel with just 150 dollars in parts.

Yeah, there's a lot to learn by trying to be more Interdisciplinary. I recently watching a video on a *bakery* that uses a woodfire oven. It operates like an kiln and in some ways even an old forge. Thinking about it, reflow soldering to make modern electronics basically uses a glorified toaster oven. {insert "It's All Connected, Man!" meme here}

I am casting my own bricks and molding a 1piece rocket stove using chicken wire for rebar. Recipe includes refractory cement, sand and mostly vermiculite and perlite.

"Where were you..." reminds me of a scene from Always Sunny where Charlie is siphoning wine into jars from tomato sauce "Where were you 10 minutes ago when I was coming up with this plan, man?"

Potter and fellow pyromaniac here. Us Potters are naturally cross disciplinary and love talking shop. I'd love to talk and prepare notes!

They dont shrink per say kinda but more important is they expand when heated andcontract when cooling so if you make an adjustable clamp for your furnace you can tighten when you cool and loosen when you fire have to look at the specs on expansion rates for the brick you chose if your using an exposed flame you want the brick to be a hard brick or a superduty

There is something we use at cement plants called plastic refractory, we call it ram. It's like playdough that cures hard almost like castable. probably wouldn't have helped here but thought I'd put it out there.

I just went for a hot box because of you! Lol

Interesting, useful, and entertaining. Humans, not aliens, built things that lasted? Give me a moment to process this counterintuitive, but proud moment.😊

The blast furnaces I have seen in foundries (for steel) had rounded tops, sort of like a coffin lid. IDK what was done to the bricks to fit them, but essentially it was a long, gentle arch. That would stop the cave ins, and work with your square furnace.

Frankly, it was both bad engineering, and the bricks. When I make my kiln I'll be sure to "dome" the top. And do wedge-shaped bricks for the sides with compression bands that can be adjusted. And thank you for this info. You helped me a lot with these few words.

First time seeing your channel, the comments on yellow letters are great lol

I never thought this bit of my brain would ever find function but for a little while in my teens I helped with the manufacture of electric ceramic furnaces for industry, they are almost always double skin with the bricks and the layers are deliberately offset as much as possible, so the corner of the bricks at the back is in the center of the bricks at the front. Takes a little more engineering up front but I think it might have been for this reason. I also remember refractory cement only being used on the outside layer and to bond the inside to the outside but the brickwork wasn't my job, I was wire brushing and painting everything metal red then enamel

@1:07 - They already make such a device for kitchens. It's called a turbo-chef oven and it's exactly as you described.

Old geezer craftsman here, I just have to complement the prominence of the fire extinguisher on your tool shelf.

wonderful video x

For my forge lid I go over all the joints with Kaowool reinforced refractory furnace cement. I use a furnace cement that comes in a Caulk tube just to make it extra easy.

Consider longer threaded rods and tighten onto springs at one or both ends of each so the tension remains more or less constant with expansion and contraction. My 2c.

Thanks now I wanna see a kiln milled out of a giant fire brick xD

i got impressed when you said 2000 degrees, i assumed you meant Celsius lol, i understood my mistake when you said it doesn't get hot enough to melt steel

The insinuative firebricks you are using, notoriously shrink when heated. Whilst, glossy refractory bricks have microsilica (amorphous) added in addition to expansile minerals which maintain a balanced neutral linear change with heat. 0:22 this is a small sample of firebricks, 7th row down refers to the volume change. In the industry Andalusite brick is a good abrasive resistance when in contact with the flame but it will deform with temperature due to glassification of the aggregate (movement of crystalline silica), so they put in mortar gaps. Interlocking bricks are also used, which can be used without supporting structures. When not in contact with materials or flame turbulance, I would use kaowool which can expand and contract freely and be supported on the cold side.

If I had the space, I'd become a hot-boxing specialist.

Very nice 👍

Glassblower here, I would have never been able to learn had I not build my own kiln.

A few decades ago, an acquaintance of mine and I tried iron smelting, and built our smelter out of alumina kiln bricks, mortared with clay from my garden. That was a terrible mistake. At the yellow-white heat inside, the clay dissolved into the alumina like acetone into styrofoam. The structure developed severe cracks. After the first firing, it still seemed to be reasonably stable, but during the second run, it began to lean and seemed to be on the verge of collapsing.

Should add we don’t perfectly cut bricks to deal with the opening the door problem as glassblowers. We just replace the door. You figured it out but for a top loader you’ll need to reinforce the bricks. You also need to use cement. Honestly build a better structure for the whole thing with replacement of the bricks in mind. For a furnace I have a few designs that are nice I can share. If you want something more flexible a couple years ago I thought up a design for a front loader with a crucible hole on the top.

You could also use the ceramic fibre insulation that comes in rolls, easy to handle and form into shapes

Kaowool is a really nice insulation for that application just provide a support frame with handles

Thanks m8, good info.

I used to work for a company that made cremators. They recommended to their customers that they rebuild the cremators every 10,000 hours. I also worked for one of the world's largest fire brick & kaowool manufacturers, and a large part of their sales was bricks & kaowool for rebuilds. These bricks are only good for so long, then they need replacement.

Idea for the lid. Cut the all thread so that it sticks out 2”-3” of the bricks. Put a washer against the bricks, a spring, capture the spring with another washer and nuts on each side.

Tig welder tungsten rods. High temp, rigid, not massively tensile, but great for alignment. Easy to find, and because it's a very common mass production part, pretty cheap. Random idea inspired by this vid.

If you want to go the super cheap route you could always make your own top out sand and plaster of Paris that way you can make it custom fit for your furnace

I wonder if you could mix up a batch of " Star Lite" material. and put it on a thin steel sheet of steel even a piece of wood for a lighter lid. It will shrink and will need some patching at first but after it is burned in, it is pretty stable. It just won't work outside where it could possibly get wet. It is pretty amazing stuff. I have used it in place of Satinite many times for gas forges. Something to look into at least.

4:10 that flickering is killing me brother.

I’m 18 seconds in… it’s definitely my fault.

When I built pottery kilns many years ago we pinned them together with stainless steel rods. Snip them with big side cutters and instantly get a perfect bit. I never thought to ask "why stainless?" I only did it for a short while and it was just what they used.

A buddy of mine who used to build heat-treating kilns would cut a channel in the sides of the bricks that would be deep enough [and wide enough] to accept half the width of a 1/4"x1" flat bar. That bar would slot through and be kept in place by the strap. Maybe this is something you could try, because the threaded rod will only hold the bricks along a single axis. It'll still gap out in the middle.

At first I thought someone was trying to use fire bricks in place of masonry bricks, so I was intrigued.