Thumbs up for the sheer amount of effort you have put into this! From building a jig, to writing arduino code to automate this jig and making a clear video explaining all these concepts without bias - Thank you!
I just sat through a 15 minute video about bricks for no particular reason and found it one of the more interesting videos I've watched recently. 🤣🤣 good video
Haha, yeah, I wanted to know what fire bricks actually do because I don't really know about them. I sat through this 15 minute because it kept my interest. Still don't know what fire bricks are used for but I know now that the brick can tolerate thermal shock. So, I guess I learned something.
@@anthonykinrade8642 I would think it would last a generation. Leave the door on while cooling and it would take 2 or 3 days to fully cool. Same with heating, heat it up from morning until night or vice versa.
Never been so interested in wood fire ovens now,… the bricks, the temperature, the pre cast vs brick decision, and even cooking times amaze me. Great content. Now I just got to save up for one!
I built an Alan Scott design (the Bread Builders book) wood-fired oven 10+ years ago. I would guess I have fired it more than 100 times since. The hearth is fire brick but the dome and end walls are used red brick (probably 80-100 year old brick). I take 3 1/2 hours to fire to 800F 1" below the hearth or dome surface), cook the pizzas over the next hour and then it takes 24 hours to cool back to ambient. I have not had any spalling of the dome or end walls. The red bricks may have cracked, but nothing has fallen on the pizza or the hearth. I wonder if the slower cycle times accounts for the lack of spalling. Also the Alan Scott Design has a cast concrete cap over the dome to hold everything in place. I don't know of any pizza oven that cycles as quickly as your test rig. I realize that a 24 hour test would take a long time to complete multiple iterations but your current test seems to not mimic reality. A topic I would like to see explored is thermal mass. The Alan Scott design is really a high mass bread oven designed for multiple bakes in succession. Pizza does not need that thermal mass. It just needs high heat on the hearth to cook the bottom and the fire to cook the top. As a consequence of the thermal mass, I use a lot of wood to heat up the oven .
Hi Jim - thankyou for the very well thought out response, much appreciated! The test rig was designed not to try to mimic the exact conditions experienced by a brick in a wood fired oven, but to show the effects of thermal shock on different materials. Your longer cycle time is definitely going to be protecting the bricks from severe thermal shock - I'd be interested to hear your firing method and whether you build the fire in one location inside the oven, and how that particular area is faring compared to the rest of it. Your heat up time at 3.5 hours is fairly long, but it's the cool-down time that has me interested - 24 hours is very short, is that with a door sealing the oven opening? I think that Alan Scott has done a great deal of good for the wood fired oven community, however his design doesn't incorporate much insulation, and focuses on thermal mass. The thing is, you can have BOTH. If you had the same thermal mass that you have in your oven, properly insulated, it should take around 3 days to cool down, and even then it would be well above ambient. Any suggestions of an experiment/video that we could put together around the Thermal Mass topic?
@@TheFireBrickCo My ASD oven has the following features: Hearth is fire brick laying on top of 3 1/2" of reinforced concrete slab that is thermally broken from the slab support walls. Under the concrete is 5 1/2" poured in place perlite/pumice and cement insulation ; Dome is one layer of red bricks with a 3 1/2" poured in place reinforced concrete cap with 6-10" of perlite/pumice insulation over that. I start the fire at the door and push it back as the fire progresses so that by the 2 1/2 hour mark it is in the center of the dome (it is actually a barrel vault). At the 3 1/2 hour mark I rake out the embers all over the hearth and let it soak. I keep at least one piece of wood burning during this so that when i push all this to the back, I still have a fire. I add a couple of sticks of wood, at that point, swab the hearth with a wet rag on a stick and probably wait another 20 minute for things to even out. The first pizza is always a flat bread to test the heat (don't want to waste toppings). If it is too hot I wait some more, if not we are good to go. I think Alan Scott thought this oven took 5-6 hours to fire to get enough energy in the mass to cook 4-5 batches of bread. i remember being on a forum before he died and he quit the forum due to exasperation with us pizza makers complaining about how long it took to heat up. His point was this is not a pizza oven, it is a bread oven. I think he said something like " if you want a pizza oven, get a 200l barrel, cut the end out, lay it on it side and build a fire". His point was you don't need the same thermal mass for just quick cooking pizzas. I leave the door open for cool down. If I close the door (uninsulated) I am sure it wouldn't reach ambient for 48+ hours. I buried 5 thermal couples in the masonry at the time of construction so I could learn how quickly it heats up. What I found is that even with my 3 1/2 hour firing, the concrete below the hearth and above the dome was barely 200F and continued to suck heat out of the bricks after I stopped firing. I" from the surface was 800F The next one I build will be much less massive - maybe just bricks and some insulation. i was hoping you could maybe show how quickly heat builds up (or not) in bricks. Some folks have wanted to used insulation bricks for their oven but miss the point that the retained heat in the bricks is actually helping cook the pizza. I do like my hearth size -30" x 40". there is enough room in the back for the fire and room for a couple of Pizzas. It could be shorter than 40" - maybe 30x30 and do the same thing although working closer to the door is less convenient handling of the pizza. I have been half tempted to build an oven that is fire brick with an insulated metal dome. Get the hearth hot and then rely on a good fire to radiate the heat off the metal dome to cook the top. Enough for now
My is build the Same way, except I used the ones with 3 holes in it, filled with mortar. Used for about 2 years to cook pigs and lambs, no crumbling yet. Heart is fire brick
Great video. This actually makes me feel better about using regular old red bricks in my outdoor pizza oven. Mainly because it’s temporary and will only be used a few times. If I’m to build a permanent one definitely going with the fire bricks.
The old Russian stoves used for hundreds of years in the coldest parts of Russia were composed of 500 to 800 red bricks with (white) plaster over top many of them. They simply didn't have firebricks until a few decades ago and probably still don't use them in "remote Siberia." The reason these ovens lasted for 20 or 30 years is, just like he said, once they were brought up to temperature (say, the first day of October,) they were heated twice a day, every day through the winter, and the bricks were not allowed to "cool down" until, say, June 1. The thermal mass, as a whole, kept way above room temperature. I'm sure they had to do some minor repairs on the firebox every five or 10 years, but not on the rest of the brick stove.
Spot on - and they would have heated them up fairly slowly too, to avoid thermal shock at the beginning of the cycle. If you used them that way the vast bulk of that construction would last for a very long time, but eventually the brick in the firebox would need to be replaced.
Very geeky and very cool on a shockingly hot topic :)) Loved that you used an Arduino for the testing rig - real inspiring. Thanks too for the scientific approach, provides a great explanation about an ancient subject. Best wishes for your business!
@@TheFireBrickCo yes, they are very functional devices. Another one to take a close look at is the Raspberry-PI W ... 5 to 10 USD, Linux, lot's of GPIO's, tons of code and support on the internet. (Including PID stuff) ... all that and not much bigger than a credit card. Cheers!
Respect for this mans building potential. Such an awesome rig. Dont forget the steel going in and out of that oven. Another modern marvel. Thanks for putting together this video.
Awesome content. I just viewed a video recently about building a pizza oven using the pressed red bricks. A lot of the comments mentioned that these bricks would explode if used in this way. Your demonstration was good to see, so that I would feel more comfortable knowing the bricks won't explode during use but develop cracks over time. I thoroughly enjoyed your presentation!
Cracking is all about the COE alumina and fire clay have relatively very little movement within their thermal expansion whereas red brick have lots of iron which is less dense and Ferris non- Crystal Inn
Thank you. Very informative! I bought red concrete bricks for my small outdoor oven, i hope it will do ok. And as you said, i will slowly acclimate the hot temperature to them before i cook them pizzas😃
I used red bricks for my forge and it worked well. It was a cool forge but after a couple uses some the bricks cracked. You probably when to use firebricks when making a forge if you don’t want to make one from a truck rotor, 1/4 or 6-8mm plate. Wield it in the shape of a box tapering down like maybe a 6x6in tapering down to a 4x4in. Or a 8x8in tapering down to a 4x4in. That is 20x20cm tapering down to a 10x10cm. Probably 3 1/2 inches deep or 8xm deep.
This is a GREAT question! I don't recommend it as I have seen them fail - refractory castable has many incredible properties but it doesn't have nearly the same level of surface hardness as firebrick. If you were to do a side-by-side test (which I really want to set up an automated rig to do) rubbing a steel tool on a firebrick and on a cast refractory panel you would see the cast surface start to wear a long time before the brick did. Again, refractory castable is brilliant material, but we don't use it for cooking surfaces.
Coolest test tig.. tests done very nicely. Enjoyed your full video though watched it without any context. Glad i watched it. Cheers mate. Keep up the good work.❤
Great question - It doesn't contain aluminum, it contains the precursor ore - alumina. Our fire bricks are completely safe to cook directly on, we have NSF4 accreditation so you can rest assured our bricks have been tested and found safe to bake directly on.
Hi, great question! Definitely don't just use normal Portland Cement based mortar - it breaks down at around 350C which you are definitely going to exceed. You'll need to find some Refractory Mortar in your region
Great video! thanks for doing this - excellent demonstration. Just a question, will covering the front of the bricks with a centimetre or so of fire clay stop this rapid deterioration?
Good question Ryan - the issue with that will be that the fire clay wouldn't bond permanently to the brick, and would delaminate over time. Otherwise it would definitely make a difference, by reducing the severity of the thermal shock experienced by the brick.
In a way, this video alleviates my concern with using regular bricks to build a pizza oven, since I really don't think it would be used for more than 5 or 6 times a year. Thank you for the really helpful information.
Thanks for the informative video, very cool testing setup! I'm building an oven but am more worried about food safety of the materials, do you know if there are any health concerns for heating standard red brick vs fire bricks to a high temp?
Hi Arthur - great question! Our fire bricks are made from fireclay, which is a naturally occurring material with a high level of alumina. I don't believe there would be any difference between a pressed red brick and a fire brick in terms of preparing food on either surface, providing the pressed red brick is unglazed (which would be an issue)
thorough and concise - good well done. whenever i get around to building an outdoor pizza oven, i think it's safe to say the investment in fire bricks are well worth it. cheers!
Ive been looking into making one as well theyre not too much more expensive than a regular brick thankfully unless youre building a really big one and even then you could get away with the structure being clay and the internal cooking part being fire brick
Hi Jasper, to minimise spalling you would probably need to ramp them up over around 5 hours or more - the big bread ovens take several days, sometimes longer to get up to temperature.
Miners use thermal shock to bore in hard rock..A fire is built against the rock face, then when it is hot water is thrown on it. The thermal shock shatters the rock nicely..
This is perfect! Next (if you guys do this again) should be testing different "species" of fire brick, i.e. refractory cement vs plaster-of-paris mix vs etc.
Interesting. But on other hand don't we build the oven so that no thermal shock is possible. By insulating it we make sure the temperature falls very slowly. As for rising temperatures since we start oven with wood it goes up gradually. You need at least 15-20 min to get there. Am I wrong?
Hi @kilmenkor! You're spot on regardin gthe cool down phase - the insulation ensures we don't see thermal shock as the oven cools. But when it comes to starting the oven up you'd be surprised how quickly you can achieve some very high surface temperatures directly above the fire, even just using wood.
Great question - correct, if you heat up pressed red bricks at a sufficiently slow rate, they shouldn't have any issues. I haven't done the testing necessary to give you a figure on the heat up rate, but a conservative figure would be 50C per hour. The big bread ovens built with the pressed red bricks would take several days to heat up from a cold start (which is why there weren't allowed to cool down very often!)
Are there concerns with the aluminium content of the fire brick being used in direct contact with food? Any acidity in the food will draw the aluminium into the food which is toxic. Is this something that you have thought about? Maybe these fire bricks are different than the usual kind in some way?
The fire bricks don't have any aluminium, they have alumina which is the precursor to aluminium. We have had all of our bricks tested by Underwriters Laboratories and they are certified to NSF-4 as food grade, completely safe to cook on!
Thank you, Thumbs Up!! Would you mind giving me your opinion on what sort of problems I'll encounter if my contracter used the SAKRETE High Heat Mortar with actual "Fire Brick" but instead of just using the mortar underneath the brick, he used it underneath and then made grout lines instead of placing the brick next to each other. Can I use that a my cooking surface? Or do I have either replace the whole thing by putting another layer of fire brick. hope this question make sense
Hi Yuri - it does make sense; your oven floor has mortar joints in it rather than being firebricks pushed hard against each other. It should pose a huge issue - I would want the mortar to be recessed slightly below the brick surface so that you don't end up getting any into your food though
Really informative vid, thanks. Is it possible to use the bricks from storage heaters instead of fire bricks in a pizza oven? Could you test them like this to see?
Great video. What about using the red brick for the body of the wall and running a 2 inch coating of refractory cement over it inside the area for the flame? Would that retard the heating cycle enough for the red to hold together and adjust. I wonder, what rate of heating can they handle. Im contemplating building a stove completely out of ref cement and bricks. Not really trying to cut costs, but if it will work then why not?
That's a very interesting question - the issue is actually the 2" coating - there aren't many refractory products that we've found that work well in that kind of installation, as the thermal cycling tends to make them de-bond from the brick surface that it's applied to. This is due to the difference in the thermal expansion coefficients of the two materials. With the right engineering and careful product selection this could be done, but without dedicating a lot of engineering time to the design you would most likely find the internal lining would fail. On top of that problem, the 2" refractory lining would most likely cost you more than just building the structure with firebrick for the firebox instead (good quality unmolded refractories like castable are quite pricey)
@@TheFireBrickCo ah, great point. I didnt think about the coating falling off due to the difference in expanding and contracting. But like i said it wasnt to cut corners. Thx for your input. After i build my 3rd bike trailer then a rabbit enclosure i will start plans on building a home on my land with earth floor. And the stove or fire brick stove on the ground. One thing at a time
You will find that almost all of the inside of a wood stove will reach the same temperature as the fire box, so you'd be well advised to stick with fire brick throughout
Very INTERESTING vidio. I am trying to identify some older bricks I bought at a garage sale. They are a pale yellow/coral , dence, heavy and very hard to cut.The issue is they have a BLACK center! About 3/4 of the center is evenly black. I was under the impression they are fire bricks but am not completely sure.I wouls like to be able to send a pic. to you but I don't see that option here.I would really like your opinion! Is there a way to send you a picture?
@@TheFireBrickCo Thanks for getting back to me. No,I haven't heard from anyone. I did not send photos as there is no option to do so here or on your web page.
Thanks so much for this info Ben! I've been scouring the internet for fire bricks in South Africa and they are scarce as well as extremely expensive. When using pressed red clay bricks for an oven, should I preferably use refractory cement as mortar? I'm thinking that standard cement/mortar will crack and break long before the bricks do. And to your knowledge, would clay paving bricks be a better choice than the pressed red bricks?
No problems! Without knowing a whole lot about the pavers I couldn't say for sure whether they would be any better than the pressed reds you have available. Definitely use refractory mortar if you can get your hands on some!
Hmmm I'll just re-word that to see if I understand you correctly. Firebrick as the hot face, followed by high temperature insulation (50mm of ceramic fibre blanket would be the ideal) then 30mm of render, with the 'bristol blue engineering' brick on the outside? If that's the approach then it sounds good.
Well done! Thanks for the video excellent information. P.S. The Higher content of Alumina in the firebrick the better quality the fire brick will be. It's also more expensive the fire brick but will handle more heat!
Thanks!! You are correct on both counts - however they will also be more thermally conductive which can be a problem for the oven floor (burning the crust). We find the 38% mark is the sweet spot - high enough for great quality brick, but low enough that they aren't going to burn a pizza the second it hits the oven floor
Hi using fire bricks only can Refractory cement be used to build the pizza oven with fire bricks ? I did a test using reg cement in my metal fire pit and the pcs:s exploited...as if any moisture will expand...so I want to make my own pizza oven but safely.
It depends what you mean by 'Refractory Cement' - we use a Refractory Mortar mixture to put between the bricks in our Wood Fired Oven kits, which is a blend of Ciment Fondu, fine crushed refractory aggregates and some proprietary additives. But Ciment Fondu by itself would not be advisable
Now THERE is a good question - firepits don't get nearly as hot as a wood fired oven as they're open, so you have fresh, cold air coming in over the bricks cooling them down somewhat. That's for the sides at least. For the base, it's still going to get very hot beneath the fire. The downside of firebricks in that application is that they are porous, so they'll soak up rainwater if left exposed.
What sort of disclaimer do you provide for ovens dropping grit onto the pizza? I've thought of starting a wood fired pizza shop but what if a customer bites into tiny fragments of firebrick?
That's a good question - it's not something that we have ever heard of happening with one of our ovens thankfully! I'm guessing that most restaurants would need to have some kind of public liability insurance cover?
Do all fire bricks need to be rectangular for a manufacturing reason or can the bricks be cast into different shapes like a circle, a pyramid, or a more complex shapes with holes? Can fire bricks be manufacture into large shapes like a giant meter x meter square that is 10 cm thick?
That's an excellent question - the bricks are pressed into dies to form the shapes, so the more simple a shape is, the easier (and more cost effective) it is to press that shape. Complex geometry can make the initial cost of producing the press dies incredibly expensive! You also have to think about handling and the likelihood of breaking a part - a piece of the size you gave would most likely be made from refractory castable rather than being pressed in a die. Does that help?
I first heard no value of how bricks differ since the times I cleaned out my Moms oil boiler that heated radiators. Fire bricks are easy to clean, creosote just slides off to the poke. Thanks
@@TheFireBrickCo Are you able to slow down the rate of rise of the temperature to more closely emulate the real application? The test setup shown takes the samples from an ambient of 12 C to an ambient of 600 to 900 C in 30 seconds. That is a rate of rise of temperature of 1200 to 1800 C/minute. The video states that a normal wood fired oven gets to about 400 C in 2 hours which is 3.3 C/minute. The test setup ramps the temperature up 360 to 540 times faster than the real application. The video is correct in referring to it as a thermal-shock test. In the real world, that would be like dumping red hot coals into a cold oven. No one does that. A test at several times the real world ramp rate would be a realistic worst-case test of the materials, i.e. a thermal-cycle test. It may also require more than the 240 cycles to cause the damage the video claims will occur, spalling. This can be a fun programming challenge since it will require closed-loop control of the oven temperature. Since the ramp rate was several hundred times what would be experienced in the real application, it is not surprising that some damage occurred to some of the samples. However, gross cracking is not the type of damage that was supposed to be demonstrated (spalling or flaking of the surface). It is commendable that the firebrick survived the test with only cosmetic damage but I would imagine the cost is higher than for the other materials.
I'm sure in the right set of circumstances you could make a brick explode (say, a concrete brick that's soaked in water, if you got that really hot, really quickly you might get a steam explosion of some kind)
Older pressed bricks seem to have a better tolerance for high temperatures than more modern ones, but they still share the same basic properties as a solid pressed brick, they're just not created with really high temperatures in mind.
Very useful and instructive. I'm just building a masonry stove and tossing up between fire and pressed brick, I get what you're saying. Excellent presentation by the way, good, clear and down-to-earth: very Oz. Thank you!
Now you're getting right up there! You could use a high alumina fire clay brick but it would need to be in excess of 70% alumina. Beyond that you start looking at Zirconia bricks and other high end refractories
When you next get to work with one, when it's up to pizza temperature try scraping the coals aside and have a look at the bricks - they'll be glowing orange.
@@TheFireBrickCo oh. From what others have said since I asked, they said granite, a metamorphic rock created from molten rock, would be fine. But I have no experience. Has it spalled for you? I did put a slab of marble into the fire to see what would happen and it was still smooth, but it was only 1 fire.
Would you say it would be a longer-lasting design to use red brick on the sides of the over and use fire brick where the wood will burn and the platform you will cook the food on? Or would the bricks on the side also have issues the heat change? Fire brick is 3-4 times as expensive which is why many people stay away from it and use red brick and then pavers for the shelves in a tier oven build.
A point that you did not bring up is that there is a density difference, which means that the fire brick should have more thermal mass thus hold heat longer. Do you have data on this?
Hi Bill - this is a good point too, the density of a 38% alumina firebrick is going to be around 10% greater than a pressed clay brick. Not huge, but considerable. This video was really focused on the longevity of the oven as opposed to performance. Good observation!
Thanks for this information. I have wanted to build a brick oven for quite some time and any new information I find is very helpful. Thanks again! Very much appreciated information! 💞
Fire bricks are a colloquial term for Refractory Bricks - but most often it refers to a group of refractory bricks made with 'fire clay', a naturally occurring clay with a high alumina content. There are a myriad different types of Refractory Bricks - lightweight insulating bricks, through to incredibly dense chromium based bricks. You're looking for a dense refractory brick made from fire clay.
Another consideration is that lighter bricks have better insulating qualities. This is important if one is building a furnace for metal casting, pottery, etc.
Not bad mate, not bad at all. Speaking here as a professional lab rat and amateur pizza oven builder. I would only do two things different. One I would find some way of not heating your red bricks to dull red at one end and dark at the other. Dull red is, what, 700C? Whereas the other end of the brick is not red at all. So at least 200C temperature differential from one end to the other. That's a pretty big differential setting up internal stresses. Perhaps a plate in your furnace so the flame can't impinge directly on the brick? Secondly, I would limit the max temperature to around 550-600C. Several reasons. One: high alumina firebrick is usually weaker at the lower temps than it is at say 1200C Naturally, I can't lay me hands on the appropriate phase diagram right now. (Spewing I didn't pinch a copy of the company refractory manual when I retired.) Two: its a fairer test of the capacity of any brick to run it to the temperatures it would actually see in service. 2 minutes up and down is pretty radical. My oven is made form fired clay pavers - it generally gets 2 hours up, held at pizza temps for a couple hours, then overnight cool off leaving the fire to burn down with the door on it. It has one cracked brick in the arch (cracked right through like I'd sliced it that way) and no visible spalling. It's ten years old. Don't get me wrong - firebrick is definitely better, and I 100% agree with your reasons for that. Damn, I'd love to get my hands on your test rig. I'd really like to compare homebrew mortar with alumina based mortar/castables and CAC based cements. Because, in a pizza oven, I can't see the alumina based castables ever reaching the 1100C needed to make mullite.
Thankyou Mick! I'm definitely no scientist - I would agree with almost everything you said there; it would be really good to be able to do a longer term test with a slower heat ramping time and cool down time to give a more accurate result. On what you said about the differential thermal stresses - I think that's one of the things that fire bricks are designed to handle better than the pressed bricks, so in a way it's a good representation of that. The thermal shock test rigs that I've seen in refractory labs (which are SO DARN COOL) actually take the samples and lower them into a furnace - so the exposed end of the brick experiences a roughly uniform temperature (unlike our furnace with no baffle - that's an excellent idea). However I think even with a baffle we would still set up a significant differential between the hot end of the sample and the opposite end which is secured in the holder, so there would still be a really significant temperature differential in the sample, just across a different section of the brick. I reckon I will set up the rig again some day - I have so many things I want to test! But it would be good to set up a better rig - I'm thinking of modifying an electric kiln...
Interesting! I've not come across them at this point - however if they're anything like the pumice I have come across in the past they would have a fairly soft surface, and would be very lightweight which is not quite what we want for the lining of a wood fired oven. What you're looking for is a very dense material with a hard wearing surface (that is capable of handling the high temperatures and thermal cycling that you see in a Wood Fired Oven)
Question, I built a giant wood fired brick bbq (before seeing your video). It’s all build with similar size bricks burnt with 3 holes that are filled with mortar. It also has 4 inch concrete counter and then more of the brick that goes all the way into the chimney. Inside the bigger size oven opening I layered fire yellow bricks, on the concrete counter and inside oven and only about 4 feet high (inside oven). That brick is about 5 inches fat. Do you think I’m safe?
Hi GOran, what you don't mention is any kind of insulation materials to protect the concrete counter (concrete doesn't survive much past 350C). The bricks with the three holes in them will definitely fail over time, and possible quite rapidly as they are an extruded brick
@@TheFireBrickCo I understand that it will deteriorate in time, but with once a month use I don't think it will be that problematic. Heart of the BBQ has a 5 inches (12.5cm) fat fire bricks, both sitting on top of concrete counter and inside and around about 3-4 (90-120cm) feet high plus the chimney all brick. Opening is quite big, cook box interior is 4 ft (120cm)wide and 2-3 ft (60-90cm) deep and its quite high. Enough place for heat to disperse. I don't thing my counter will ever reach 350C.
Well,thank you very much.iv just built an oven in my garage with 100 year old glazed brick and youv really set my mind at ease that they’re not going to explode .🙏🫶✌️🏴
I wonder if you may have been too kind on the bricks by testing only a thin sliver, which will heat up very quickly but fairly uniformly. A whole brick exposed to rapid temperature cycling on just one surface would presumably see greater stresses from differential expansion of surface and interior, leading to more spalling of the surface. Did you also test whole bricks? (Great video!)
That is a good point right there Tim - We haven't done further testing at this stage but I think you are likely spot on - a full brick would be stone cold in the center while the hot face has reached 300C, leading to much greater thermal stresses. Id say we would actually get bits of brick popping off if we tried it in the test furnace!
What about the actual slab the pizza sits on what do you recommend. I've seen guys just use a patio stone which seems suspect to me... Unless there's mesh through it?
Good question - the bricks themselves are (as in, a single brick by itself), but when mortared together as a structure you want to avoid them freezing while waterlogged as the subsequent freeze-thaw expansion/contraction cycle will cause significant cracking in the mortar joints as the bricks move relative to each other.
Excellent. This was very helpful for me to make the right decisions for my design of an oven I am going to build. Btw, lol, I like the sounds in this video.
@@TheFireBrickCo Does it also apply to terracotta tiles. I suspect Yes. Thinking about a Pearlcrete Pizza Oven on top of an insulated j hook rocket stove.
Nice Demo Mate. I have a Wood fire BBQ (for a better word) which I built from ordinary bricks I had laying around. Its been in service for over 5 years but it only gets used 3 times a year as I have a Normal gas BBQ. I had never thought about a house Fire place.I guess they do last a while. I can recall some old Pubs with fires every night. Blood Fire heats up the whole Pub!
Adobe, clay or 'cobb' materials can be quite heat resistant, but they have issues of their own. My conversations with people who are big fans of cobb ovens have all reinforced my understanding that they just don't last very long. They're incredibly cheap to build, but they tend to fall apart fairly quickly. They also really don't like getting wet, at all, as the clay never reaches temperatures high enough for it to become a ceramic material. It's a good question though, I might have to dust off the Rig and do some more testing!
Thumbs up for all your videos! So, you are using bricks with 38% alumina; if I use bricks with 30% alumina will it be ok? What are the pros and cons with more alumina? It would be nice if you could test bricks with different alumina 30% 40% 50% 60% alumina.
Good question! There's a bunch of good info out there to be found on the differences between different alumina content in fire clay bricks, but to give you the very basic answer - the higher the alumina content, the higher the temperature that the brick can withstand. This comes at a cost to their ability to withstand thermal shock though, and they get much more expensive as you go higher. In a Wood Fired Oven environment a 30% alumina brick will likely be fine, but the lower alumina bricks also tend to be of low quality in their production process.
So, you ran your test through 240 cycles. And as you mention, in fireplaces the spalling is in the hottest areas, not on the surface of all the bricks. I'm assuming this would be the same in a pizza/bread oven - so in the dome directly above the fire and the floor directly below it. Less spalling (maybe) in and above the actual cooking area. My concern has always been about the comments saying "regular" bricks will explode. You say that's not gonna happen. If I fired it up a few times per month, regular bricks seem like they ought to last a good while before I have to worry about getting brick dust and bits into my food! Thank you so much for this video!
Firebricks, or bricks that's been harden by fire, got it . . . What about the binding of the bricks when making an oven? Do I use cement? Or mortar? Or something that's specialized in heat resistant and thermal shock?
Hmmm not quite - technically almost all bricks are 'hardened by fire' - a fire brick is made with a very different type of clay to most building bricks. You would need to use refractory mortar to lay the bricks for a wood fired oven - check out our building series for more info
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Thumbs up for the sheer amount of effort you have put into this! From building a jig, to writing arduino code to automate this jig and making a clear video explaining all these concepts without bias - Thank you!
Thankyou so much Subbu - I really appreciate the encouragement!
No kidding!!!
I just sat through a 15 minute video about bricks for no particular reason and found it one of the more interesting videos I've watched recently. 🤣🤣 good video
Glad you enjoyed it!
Haha, yeah, I wanted to know what fire bricks actually do because I don't really know about them. I sat through this 15 minute because it kept my interest. Still don't know what fire bricks are used for but I know now that the brick can tolerate thermal shock. So, I guess I learned something.
Me too, loved it
Me too.
Yeah he did a nice job with the test rig too.
Congratulatórios , you just went from "I think" or "I was told" to actual real proof, Hats off on your effort and rigurosity.
Thankyou Gregorio! Much appreciated!
This video has given me the confidence to build my domestic pizza oven from the cheaper red pressed bricks and replace them when necessary. Thanks!
Good stuff Anthony! Jump back in here and give us an update in a while to let us know how it's going over the years.
Replace them? You mean rebuild your entire oven right? I’m all for using red brick for an oven but replacing means rebuilding to me.
Yes, exactly what I meant! Rebuild it when required.
@@anthonykinrade8642 I would think it would last a generation. Leave the door on while cooling and it would take 2 or 3 days to fully cool. Same with heating, heat it up from morning until night or vice versa.
That's short minded if not stOOpid... enjoy the redbrick crunch on your pizzas.
Never been so interested in wood fire ovens now,… the bricks, the temperature, the pre cast vs brick decision, and even cooking times amaze me. Great content. Now I just got to save up for one!
Thanks heaps Shaun!
I built an Alan Scott design (the Bread Builders book) wood-fired oven 10+ years ago. I would guess I have fired it more than 100 times since. The hearth is fire brick but the dome and end walls are used red brick (probably 80-100 year old brick). I take 3 1/2 hours to fire to 800F 1" below the hearth or dome surface), cook the pizzas over the next hour and then it takes 24 hours to cool back to ambient. I have not had any spalling of the dome or end walls. The red bricks may have cracked, but nothing has fallen on the pizza or the hearth. I wonder if the slower cycle times accounts for the lack of spalling. Also the Alan Scott Design has a cast concrete cap over the dome to hold everything in place.
I don't know of any pizza oven that cycles as quickly as your test rig. I realize that a 24 hour test would take a long time to complete multiple iterations but your current test seems to not mimic reality.
A topic I would like to see explored is thermal mass. The Alan Scott design is really a high mass bread oven designed for multiple bakes in succession. Pizza does not need that thermal mass. It just needs high heat on the hearth to cook the bottom and the fire to cook the top. As a consequence of the thermal mass, I use a lot of wood to heat up the oven .
Hi Jim - thankyou for the very well thought out response, much appreciated! The test rig was designed not to try to mimic the exact conditions experienced by a brick in a wood fired oven, but to show the effects of thermal shock on different materials.
Your longer cycle time is definitely going to be protecting the bricks from severe thermal shock - I'd be interested to hear your firing method and whether you build the fire in one location inside the oven, and how that particular area is faring compared to the rest of it.
Your heat up time at 3.5 hours is fairly long, but it's the cool-down time that has me interested - 24 hours is very short, is that with a door sealing the oven opening? I think that Alan Scott has done a great deal of good for the wood fired oven community, however his design doesn't incorporate much insulation, and focuses on thermal mass. The thing is, you can have BOTH. If you had the same thermal mass that you have in your oven, properly insulated, it should take around 3 days to cool down, and even then it would be well above ambient. Any suggestions of an experiment/video that we could put together around the Thermal Mass topic?
@@TheFireBrickCo My ASD oven has the following features: Hearth is fire brick laying on top of 3 1/2" of reinforced concrete slab that is thermally broken from the slab support walls. Under the concrete is 5 1/2" poured in place perlite/pumice and cement insulation ; Dome is one layer of red bricks with a 3 1/2" poured in place reinforced concrete cap with 6-10" of perlite/pumice insulation over that.
I start the fire at the door and push it back as the fire progresses so that by the 2 1/2 hour mark it is in the center of the dome (it is actually a barrel vault). At the 3 1/2 hour mark I rake out the embers all over the hearth and let it soak. I keep at least one piece of wood burning during this so that when i push all this to the back, I still have a fire. I add a couple of sticks of wood, at that point, swab the hearth with a wet rag on a stick and probably wait another 20 minute for things to even out. The first pizza is always a flat bread to test the heat (don't want to waste toppings). If it is too hot I wait some more, if not we are good to go. I think Alan Scott thought this oven took 5-6 hours to fire to get enough energy in the mass to cook 4-5 batches of bread.
i remember being on a forum before he died and he quit the forum due to exasperation with us pizza makers complaining about how long it took to heat up. His point was this is not a pizza oven, it is a bread oven. I think he said something like " if you want a pizza oven, get a 200l barrel, cut the end out, lay it on it side and build a fire". His point was you don't need the same thermal mass for just quick cooking pizzas.
I leave the door open for cool down. If I close the door (uninsulated) I am sure it wouldn't reach ambient for 48+ hours.
I buried 5 thermal couples in the masonry at the time of construction so I could learn how quickly it heats up. What I found is that even with my 3 1/2 hour firing, the concrete below the hearth and above the dome was barely 200F and continued to suck heat out of the bricks after I stopped firing. I" from the surface was 800F
The next one I build will be much less massive - maybe just bricks and some insulation.
i was hoping you could maybe show how quickly heat builds up (or not) in bricks. Some folks have wanted to used insulation bricks for their oven but miss the point that the retained heat in the bricks is actually helping cook the pizza.
I do like my hearth size -30" x 40". there is enough room in the back for the fire and room for a couple of Pizzas. It could be shorter than 40" - maybe 30x30 and do the same thing although working closer to the door is less convenient handling of the pizza.
I have been half tempted to build an oven that is fire brick with an insulated metal dome. Get the hearth hot and then rely on a good fire to radiate the heat off the metal dome to cook the top.
Enough for now
My is build the Same way, except I used the ones with 3 holes in it, filled with mortar. Used for about 2 years to cook pigs and lambs, no crumbling yet. Heart is fire brick
Great video. This actually makes me feel better about using regular old red bricks in my outdoor pizza oven. Mainly because it’s temporary and will only be used a few times. If I’m to build a permanent one definitely going with the fire bricks.
This is exactly the intent behind this video - glad to hear it was helpful!
The old Russian stoves used for hundreds of years in the coldest parts of Russia were composed of 500 to 800 red bricks with (white) plaster over top many of them. They simply didn't have firebricks until a few decades ago and probably still don't use them in "remote Siberia." The reason these ovens lasted for 20 or 30 years is, just like he said, once they were brought up to temperature (say, the first day of October,) they were heated twice a day, every day through the winter, and the bricks were not allowed to "cool down" until, say, June 1. The thermal mass, as a whole, kept way above room temperature. I'm sure they had to do some minor repairs on the firebox every five or 10 years, but not on the rest of the brick stove.
Spot on - and they would have heated them up fairly slowly too, to avoid thermal shock at the beginning of the cycle. If you used them that way the vast bulk of that construction would last for a very long time, but eventually the brick in the firebox would need to be replaced.
Very geeky and very cool on a shockingly hot topic :)) Loved that you used an Arduino for the testing rig - real inspiring. Thanks too for the scientific approach, provides a great explanation about an ancient subject. Best wishes for your business!
Thank you!! Haha, it was such a fun process, I loved it. I'm dusting off the Arduino right now actually for another project....
@@TheFireBrickCo yes, they are very functional devices. Another one to take a close look at is the Raspberry-PI W ... 5 to 10 USD, Linux, lot's of GPIO's, tons of code and support on the internet. (Including PID stuff) ... all that and not much bigger than a credit card. Cheers!
Respect for this mans building potential. Such an awesome rig. Dont forget the steel going in and out of that oven. Another modern marvel. Thanks for putting together this video.
You're very welcome!
Awesome content. I just viewed a video recently about building a pizza oven using the pressed red bricks. A lot of the comments mentioned that these bricks would explode if used in this way. Your demonstration was good to see, so that I would feel more comfortable knowing the bricks won't explode during use but develop cracks over time. I thoroughly enjoyed your presentation!
Thankyou Pete! Much appreciated!
@@TheFireBrickCo but are red building bricks food safe?
Yes they all are food safe
Cracking is all about the COE alumina and fire clay have relatively very little movement within their thermal expansion whereas red brick have lots of iron which is less dense and Ferris non- Crystal Inn
At last someone who knows what they are talking about. Great video.
Thanks George!
Thank you. Very informative! I bought red concrete bricks for my small outdoor oven, i hope it will do ok. And as you said, i will slowly acclimate the hot temperature to them before i cook them pizzas😃
See how you go DJ, feel free to report back here in a few months with how it's all going!
I used red bricks for my forge and it worked well. It was a cool forge but after a couple uses some the bricks cracked. You probably when to use firebricks when making a forge if you don’t want to make one from a truck rotor, 1/4 or 6-8mm plate. Wield it in the shape of a box tapering down like maybe a 6x6in tapering down to a 4x4in. Or a 8x8in tapering down to a 4x4in. That is 20x20cm tapering down to a 10x10cm. Probably 3 1/2 inches deep or 8xm deep.
Sounds about right!
What is your opinion building Oven floor refractory concrete
This is a GREAT question! I don't recommend it as I have seen them fail - refractory castable has many incredible properties but it doesn't have nearly the same level of surface hardness as firebrick. If you were to do a side-by-side test (which I really want to set up an automated rig to do) rubbing a steel tool on a firebrick and on a cast refractory panel you would see the cast surface start to wear a long time before the brick did. Again, refractory castable is brilliant material, but we don't use it for cooking surfaces.
@@TheFireBrickCo Thank you very much for your response and have a nice day
Coolest test tig.. tests done very nicely. Enjoyed your full video though watched it without any context. Glad i watched it. Cheers mate. Keep up the good work.❤
Thank you!!
The firebrick has a lot of aluminum in it? Is that safe for food?
Great question - It doesn't contain aluminum, it contains the precursor ore - alumina. Our fire bricks are completely safe to cook directly on, we have NSF4 accreditation so you can rest assured our bricks have been tested and found safe to bake directly on.
Hi, do you have recommendation on what to use for the mortar? Would bog standard Portland cement do? Cheers
Hi, great question! Definitely don't just use normal Portland Cement based mortar - it breaks down at around 350C which you are definitely going to exceed. You'll need to find some Refractory Mortar in your region
Any idea what kind of bricks 🧱 do we need to used for fire oven?
Thanks 🙏
We recommend using fire bricks for a wood fired oven, as you'll see in the video 😊
Thank you. I was making a wood fired oven in the garden and i came across your video. Now i know what is thermal shock and flaking.
You are welcome!
Great video! thanks for doing this - excellent demonstration. Just a question, will covering the front of the bricks with a centimetre or so of fire clay stop this rapid deterioration?
Good question Ryan - the issue with that will be that the fire clay wouldn't bond permanently to the brick, and would delaminate over time. Otherwise it would definitely make a difference, by reducing the severity of the thermal shock experienced by the brick.
@@TheFireBrickCo Good point, didnt think about delamination. Thanks for that :)
In a way, this video alleviates my concern with using regular bricks to build a pizza oven, since I really don't think it would be used for more than 5 or 6 times a year. Thank you for the really helpful information.
No problems Chomp!
Thanks for the informative video, very cool testing setup! I'm building an oven but am more worried about food safety of the materials, do you know if there are any health concerns for heating standard red brick vs fire bricks to a high temp?
Hi Arthur - great question! Our fire bricks are made from fireclay, which is a naturally occurring material with a high level of alumina. I don't believe there would be any difference between a pressed red brick and a fire brick in terms of preparing food on either surface, providing the pressed red brick is unglazed (which would be an issue)
@@TheFireBrickCo
Isn't aluminum bad for our health ?
@@maxgarbani6644 well it is probably bad if you eat it, but not if it is inside the bricks.
Can you use the red clay bricks for the dome with refractory cement in the in side😐? Thanks on advance
Unfortunately not, the cement would just flake off over time unless you made a very thick layer (at least 2") which would be quite expensive
@@TheFireBrickCo thank you for responding!
thorough and concise - good well done. whenever i get around to building an outdoor pizza oven, i think it's safe to say the investment in fire bricks are well worth it. cheers!
Glad it was helpful!
Ive been looking into making one as well theyre not too much more expensive than a regular brick thankfully unless youre building a really big one and even then you could get away with the structure being clay and the internal cooking part being fire brick
Thank you for the video. I am building a small "to GO' pit and needed to get educated on fire brick technology etc.
You're very welcome!
Very nice demonstration , very technical.
Thankyou!
So to prevent red brick flaking, how slowly should it be heated? Would they flake if it was brought to temp over an hour?
Hi Jasper, to minimise spalling you would probably need to ramp them up over around 5 hours or more - the big bread ovens take several days, sometimes longer to get up to temperature.
Really enjoyed this demonstration. Will you be releasing studies on Brick mortar?
Hi Michael, it's definitely on the cards! We will be setting the rig up again soon...
the right mixture of sand and clay works very well....
Miners use thermal shock to bore in hard rock..A fire is built against the rock face, then when it is hot water is thrown on it. The thermal shock shatters the rock nicely..
That is a TERRIFIC illustration of it!
This is perfect! Next (if you guys do this again) should be testing different "species" of fire brick, i.e. refractory cement vs plaster-of-paris mix vs etc.
Thanks! Great idea!
Also maybe you could test bricks with different alumina. 30% 40% 50% alumina
How did you cut the samples so cleanly? Are they from the same bricks on the table?
Good question - diamond blade on a wet cutting brick saw. Yep they were cut from those very same bricks!
Interesting. But on other hand don't we build the oven so that no thermal shock is possible. By insulating it we make sure the temperature falls very slowly. As for rising temperatures since we start oven with wood it goes up gradually. You need at least 15-20 min to get there. Am I wrong?
Hi @kilmenkor! You're spot on regardin gthe cool down phase - the insulation ensures we don't see thermal shock as the oven cools. But when it comes to starting the oven up you'd be surprised how quickly you can achieve some very high surface temperatures directly above the fire, even just using wood.
Can the firebricks be used in an outdoor fire pit?
They can, but you would want to make a cover so that the bricks don't soak up water out in the rain
So if I slowly heat up the bricks and slowly cool them down, red bricks would be just fine? How slow is slow enough?
5 years..
Great question - correct, if you heat up pressed red bricks at a sufficiently slow rate, they shouldn't have any issues. I haven't done the testing necessary to give you a figure on the heat up rate, but a conservative figure would be 50C per hour. The big bread ovens built with the pressed red bricks would take several days to heat up from a cold start (which is why there weren't allowed to cool down very often!)
Are there concerns with the aluminium content of the fire brick being used in direct contact with food? Any acidity in the food will draw the aluminium into the food which is toxic. Is this something that you have thought about? Maybe these fire bricks are different than the usual kind in some way?
The fire bricks don't have any aluminium, they have alumina which is the precursor to aluminium. We have had all of our bricks tested by Underwriters Laboratories and they are certified to NSF-4 as food grade, completely safe to cook on!
Thank you, Thumbs Up!! Would you mind giving me your opinion on what sort of problems I'll encounter if my contracter used the SAKRETE High Heat Mortar with actual "Fire Brick" but instead of just using the mortar underneath the brick, he used it underneath and then made grout lines instead of placing the brick next to each other. Can I use that a my cooking surface? Or do I have either replace the whole thing by putting another layer of fire brick. hope this question make sense
Hi Yuri - it does make sense; your oven floor has mortar joints in it rather than being firebricks pushed hard against each other. It should pose a huge issue - I would want the mortar to be recessed slightly below the brick surface so that you don't end up getting any into your food though
Really informative vid, thanks.
Is it possible to use the bricks from storage heaters instead of fire bricks in a pizza oven? Could you test them like this to see?
I'm not certain but I had a feeling that storage heat bricks were very similar to fire bricks?
Great video. What about using the red brick for the body of the wall and running a 2 inch coating of refractory cement over it inside the area for the flame? Would that retard the heating cycle enough for the red to hold together and adjust. I wonder, what rate of heating can they handle. Im contemplating building a stove completely out of ref cement and bricks. Not really trying to cut costs, but if it will work then why not?
That's a very interesting question - the issue is actually the 2" coating - there aren't many refractory products that we've found that work well in that kind of installation, as the thermal cycling tends to make them de-bond from the brick surface that it's applied to. This is due to the difference in the thermal expansion coefficients of the two materials. With the right engineering and careful product selection this could be done, but without dedicating a lot of engineering time to the design you would most likely find the internal lining would fail. On top of that problem, the 2" refractory lining would most likely cost you more than just building the structure with firebrick for the firebox instead (good quality unmolded refractories like castable are quite pricey)
@@TheFireBrickCo ah, great point. I didnt think about the coating falling off due to the difference in expanding and contracting. But like i said it wasnt to cut corners. Thx for your input. After i build my 3rd bike trailer then a rabbit enclosure i will start plans on building a home on my land with earth floor. And the stove or fire brick stove on the ground. One thing at a time
So could you use standard bricks for most of a wood stove or oven and just use fire bricks for the lining of the fire box?
You will find that almost all of the inside of a wood stove will reach the same temperature as the fire box, so you'd be well advised to stick with fire brick throughout
Heavier bricks have higher thermal mass which is better for fireplaces used for heating, such as Tulikivis.
Spot on Robert!
Very INTERESTING vidio. I am trying to identify some older bricks I bought at a garage sale. They are a pale yellow/coral , dence, heavy and very hard to cut.The issue is they have a BLACK center! About 3/4 of the center is evenly black. I was under the impression they are fire bricks but am not completely sure.I wouls like to be able to send a pic. to you but I don't see that option here.I would really like your opinion! Is there a way to send you a picture?
We got your photos and I think the team got back to you, hopefully you find out what they are!
@@TheFireBrickCo Thanks for getting back to me. No,I haven't heard from anyone. I did not send photos as there is no option to do so here or on your web page.
@@TheFireBrickCo I do have a photo, however . Is there a way to send it to you?
Thanks so much for this info Ben! I've been scouring the internet for fire bricks in South Africa and they are scarce as well as extremely expensive.
When using pressed red clay bricks for an oven, should I preferably use refractory cement as mortar?
I'm thinking that standard cement/mortar will crack and break long before the bricks do.
And to your knowledge, would clay paving bricks be a better choice than the pressed red bricks?
No problems! Without knowing a whole lot about the pavers I couldn't say for sure whether they would be any better than the pressed reds you have available. Definitely use refractory mortar if you can get your hands on some!
building a oven.bristol blue engineering on outside then insoluton then fire bricks with 30mm of render on.blues ok to use?.
Hmmm I'll just re-word that to see if I understand you correctly. Firebrick as the hot face, followed by high temperature insulation (50mm of ceramic fibre blanket would be the ideal) then 30mm of render, with the 'bristol blue engineering' brick on the outside? If that's the approach then it sounds good.
Well done! Thanks for the video excellent information. P.S. The Higher content of Alumina in the firebrick the better quality the fire brick will be. It's also more expensive the fire brick but will handle more heat!
Thanks!! You are correct on both counts - however they will also be more thermally conductive which can be a problem for the oven floor (burning the crust). We find the 38% mark is the sweet spot - high enough for great quality brick, but low enough that they aren't going to burn a pizza the second it hits the oven floor
Thank you for the info. I am just about to start my oven so this will be so useful. Much appreciated.
Glad it was helpful!
Hi using fire bricks only can Refractory cement be used to build the pizza oven with fire bricks ? I did a test using reg cement in my metal fire pit and the pcs:s exploited...as if any moisture will expand...so I want to make my own pizza oven but safely.
It depends what you mean by 'Refractory Cement' - we use a Refractory Mortar mixture to put between the bricks in our Wood Fired Oven kits, which is a blend of Ciment Fondu, fine crushed refractory aggregates and some proprietary additives. But Ciment Fondu by itself would not be advisable
Very interesting video. Just curious, how much better would normal brick hold up in an open fire pit as opposed to an enclosed oven? Thanks
Now THERE is a good question - firepits don't get nearly as hot as a wood fired oven as they're open, so you have fresh, cold air coming in over the bricks cooling them down somewhat. That's for the sides at least. For the base, it's still going to get very hot beneath the fire. The downside of firebricks in that application is that they are porous, so they'll soak up rainwater if left exposed.
What sort of disclaimer do you provide for ovens dropping grit onto the pizza? I've thought of starting a wood fired pizza shop but what if a customer bites into tiny fragments of firebrick?
That's a good question - it's not something that we have ever heard of happening with one of our ovens thankfully! I'm guessing that most restaurants would need to have some kind of public liability insurance cover?
Do all fire bricks need to be rectangular for a manufacturing reason or can the bricks be cast into different shapes like a circle, a pyramid, or a more complex shapes with holes? Can fire bricks be manufacture into large shapes like a giant meter x meter square that is 10 cm thick?
That's an excellent question - the bricks are pressed into dies to form the shapes, so the more simple a shape is, the easier (and more cost effective) it is to press that shape. Complex geometry can make the initial cost of producing the press dies incredibly expensive! You also have to think about handling and the likelihood of breaking a part - a piece of the size you gave would most likely be made from refractory castable rather than being pressed in a die. Does that help?
I am planning to use firebrick for the oven floor, but can I use clay bricks for the walls and roof of the oven? Or it will still crack it?
Unfortunately they will experience just as much thermal shock in the walls and ceiling as they will in the floor, if not more
I first heard no value of how bricks differ since the times I cleaned out my Moms oil boiler that heated radiators. Fire bricks are easy to clean, creosote just slides off to the poke. Thanks
No worries!
how will your brick oven gets a rapid change in temp after heating?
The rapid change comes as the oven heats up, not when it's already been heated.
@@TheFireBrickCo Are you able to slow down the rate of rise of the temperature to more closely emulate the real application?
The test setup shown takes the samples from an ambient of 12 C to an ambient of 600 to 900 C in 30 seconds. That is a rate of rise of temperature of 1200 to 1800 C/minute.
The video states that a normal wood fired oven gets to about 400 C in 2 hours which is 3.3 C/minute.
The test setup ramps the temperature up 360 to 540 times faster than the real application. The video is correct in referring to it as a thermal-shock test. In the real world, that would be like dumping red hot coals into a cold oven. No one does that.
A test at several times the real world ramp rate would be a realistic worst-case test of the materials, i.e. a thermal-cycle test. It may also require more than the 240 cycles to cause the damage the video claims will occur, spalling. This can be a fun programming challenge since it will require closed-loop control of the oven temperature.
Since the ramp rate was several hundred times what would be experienced in the real application, it is not surprising that some damage occurred to some of the samples. However, gross cracking is not the type of damage that was supposed to be demonstrated (spalling or flaking of the surface). It is commendable that the firebrick survived the test with only cosmetic damage but I would imagine the cost is higher than for the other materials.
Very informative video. Now I’m wondering where the idea of exploding bricks comes from?
I'm sure in the right set of circumstances you could make a brick explode (say, a concrete brick that's soaked in water, if you got that really hot, really quickly you might get a steam explosion of some kind)
River rocks, and cinder blocks will fracture rapidly. River rocks ive seen/heard explode.
Great video. Do you use your fire brick for floor also or do you have a recommendation on a floor refractory for a home wood fired oven?
We definitely use them for the floor - the floor cops thermal shock just as badly as the dome so you want to use the right material there too.
What about 110 year old bricks from a chimney? Would they do the job
Older pressed bricks seem to have a better tolerance for high temperatures than more modern ones, but they still share the same basic properties as a solid pressed brick, they're just not created with really high temperatures in mind.
Very useful and instructive. I'm just building a masonry stove and tossing up between fire and pressed brick, I get what you're saying. Excellent presentation by the way, good, clear and down-to-earth: very Oz. Thank you!
Thankyou very much!
So what would you recommend for 1700-1900°C?
Now you're getting right up there! You could use a high alumina fire clay brick but it would need to be in excess of 70% alumina. Beyond that you start looking at Zirconia bricks and other high end refractories
as someone interested in making my own pizza oven, this video helped me a lot! Kudos!
You are very welcome! Thanks for the encouragement!
How often will the bricks glow in my oven?
When you next get to work with one, when it's up to pizza temperature try scraping the coals aside and have a look at the bricks - they'll be glowing orange.
Can I use red building brick if I line the firebox with rectangular slabs of granite, or marble from counter top cut-offs? Will it be food safe?
I couldn't recommend that - granite or marble will spall even more than pressed red brick in a firebox environment!
@@TheFireBrickCo oh. From what others have said since I asked, they said granite, a metamorphic rock created from molten rock, would be fine. But I have no experience. Has it spalled for you?
I did put a slab of marble into the fire to see what would happen and it was still smooth, but it was only 1 fire.
Would you say it would be a longer-lasting design to use red brick on the sides of the over and use fire brick where the wood will burn and the platform you will cook the food on? Or would the bricks on the side also have issues the heat change? Fire brick is 3-4 times as expensive which is why many people stay away from it and use red brick and then pavers for the shelves in a tier oven build.
Unfortunately the bricks on that make up the oven walls will experience a great deal of thermal shock too
This was very informative and probably will save me some heartache when I finally get around to building that pizza oven. Thanks for making it!
No problems Marty!
A point that you did not bring up is that there is a density difference, which means that the fire brick should have more thermal mass thus hold heat longer. Do you have data on this?
Hi Bill - this is a good point too, the density of a 38% alumina firebrick is going to be around 10% greater than a pressed clay brick. Not huge, but considerable. This video was really focused on the longevity of the oven as opposed to performance. Good observation!
Thanks for this information. I have wanted to build a brick oven for quite some time and any new information I find is very helpful. Thanks again! Very much appreciated information! 💞
Thankyou for the encouragement!
What about pavers? Are they made differently to bricks?
Thanks!
Good question - I believe a pressed paver is quite similar to a pressed solid brick, just a different shape (and sometimes a glaze I think!)
Hey, are refractory and fire bricks same? And if not is it okay to use refractory bricks in your woodfire oven?
Fire bricks are a colloquial term for Refractory Bricks - but most often it refers to a group of refractory bricks made with 'fire clay', a naturally occurring clay with a high alumina content. There are a myriad different types of Refractory Bricks - lightweight insulating bricks, through to incredibly dense chromium based bricks. You're looking for a dense refractory brick made from fire clay.
It doesn’t get any clearer than this. Could you do something similar with improper mixes of fire cement? Or how about clay mixes for tandoor ovens?
OOooooh Mark now you're giving me ideas!
Another consideration is that lighter bricks have better insulating qualities. This is important if one is building a furnace for metal casting, pottery, etc.
Yep for sure! For a wood fired oven you would want a dense firebrick to store heat in.
Not bad mate, not bad at all. Speaking here as a professional lab rat and amateur pizza oven builder.
I would only do two things different. One I would find some way of not heating your red bricks to dull red at one end and dark at the other. Dull red is, what, 700C? Whereas the other end of the brick is not red at all. So at least 200C temperature differential from one end to the other. That's a pretty big differential setting up internal stresses.
Perhaps a plate in your furnace so the flame can't impinge directly on the brick?
Secondly, I would limit the max temperature to around 550-600C.
Several reasons.
One: high alumina firebrick is usually weaker at the lower temps than it is at say 1200C Naturally, I can't lay me hands on the appropriate phase diagram right now. (Spewing I didn't pinch a copy of the company refractory manual when I retired.)
Two: its a fairer test of the capacity of any brick to run it to the temperatures it would actually see in service.
2 minutes up and down is pretty radical. My oven is made form fired clay pavers - it generally gets 2 hours up, held at pizza temps for a couple hours, then overnight cool off leaving the fire to burn down with the door on it. It has one cracked brick in the arch (cracked right through like I'd sliced it that way) and no visible spalling. It's ten years old.
Don't get me wrong - firebrick is definitely better, and I 100% agree with your reasons for that.
Damn, I'd love to get my hands on your test rig. I'd really like to compare homebrew mortar with alumina based mortar/castables and CAC based cements. Because, in a pizza oven, I can't see the alumina based castables ever reaching the 1100C needed to make mullite.
Thankyou Mick! I'm definitely no scientist - I would agree with almost everything you said there; it would be really good to be able to do a longer term test with a slower heat ramping time and cool down time to give a more accurate result.
On what you said about the differential thermal stresses - I think that's one of the things that fire bricks are designed to handle better than the pressed bricks, so in a way it's a good representation of that. The thermal shock test rigs that I've seen in refractory labs (which are SO DARN COOL) actually take the samples and lower them into a furnace - so the exposed end of the brick experiences a roughly uniform temperature (unlike our furnace with no baffle - that's an excellent idea). However I think even with a baffle we would still set up a significant differential between the hot end of the sample and the opposite end which is secured in the holder, so there would still be a really significant temperature differential in the sample, just across a different section of the brick.
I reckon I will set up the rig again some day - I have so many things I want to test! But it would be good to set up a better rig - I'm thinking of modifying an electric kiln...
Pumice bricks are underrated and capable of withstanding pine fires which are capable of melting steel. Cheaper than magnesia bricks also.
Interesting! I've not come across them at this point - however if they're anything like the pumice I have come across in the past they would have a fairly soft surface, and would be very lightweight which is not quite what we want for the lining of a wood fired oven. What you're looking for is a very dense material with a hard wearing surface (that is capable of handling the high temperatures and thermal cycling that you see in a Wood Fired Oven)
Loved the honesty, amazing video
I appreciate that!
Great presentation,you really educated many views on this subject.👍
Glad you think so!
Question, I built a giant wood fired brick bbq (before seeing your video). It’s all build with similar size bricks burnt with 3 holes that are filled with mortar. It also has 4 inch concrete counter and then more of the brick that goes all the way into the chimney. Inside the bigger size oven opening I layered fire yellow bricks, on the concrete counter and inside oven and only about 4 feet high (inside oven). That brick is about 5 inches fat. Do you think I’m safe?
Hi GOran, what you don't mention is any kind of insulation materials to protect the concrete counter (concrete doesn't survive much past 350C). The bricks with the three holes in them will definitely fail over time, and possible quite rapidly as they are an extruded brick
@@TheFireBrickCo I understand that it will deteriorate in time, but with once a month use I don't think it will be that problematic. Heart of the BBQ has a 5 inches (12.5cm) fat fire bricks, both sitting on top of concrete counter and inside and around about 3-4 (90-120cm) feet high plus the chimney all brick. Opening is quite big, cook box interior is 4 ft (120cm)wide and 2-3 ft (60-90cm) deep and its quite high. Enough place for heat to disperse. I don't thing my counter will ever reach 350C.
Love the test rig ..... well done 👍
It was SO much fun to build. Definitely want to play around with more of that kind of thing when we get some more time...
Well,thank you very much.iv just built an oven in my garage with 100 year old glazed brick and youv really set my mind at ease that they’re not going to explode .🙏🫶✌️🏴
Excellent! Happy to help :)
Great Video, Very informative!
Glad it was helpful!
I wonder if you may have been too kind on the bricks by testing only a thin sliver, which will heat up very quickly but fairly uniformly. A whole brick exposed to rapid temperature cycling on just one surface would presumably see greater stresses from differential expansion of surface and interior, leading to more spalling of the surface. Did you also test whole bricks? (Great video!)
That is a good point right there Tim - We haven't done further testing at this stage but I think you are likely spot on - a full brick would be stone cold in the center while the hot face has reached 300C, leading to much greater thermal stresses. Id say we would actually get bits of brick popping off if we tried it in the test furnace!
What about the actual slab the pizza sits on what do you recommend. I've seen guys just use a patio stone which seems suspect to me... Unless there's mesh through it?
We use fire brick tiles for the floor of the pizza oven if that's what you're referring to?
Are the fire bricks frost resistant?
Good question - the bricks themselves are (as in, a single brick by itself), but when mortared together as a structure you want to avoid them freezing while waterlogged as the subsequent freeze-thaw expansion/contraction cycle will cause significant cracking in the mortar joints as the bricks move relative to each other.
Excellent. This was very helpful for me to make the right decisions for my design of an oven I am going to build. Btw, lol, I like the sounds in this video.
Ha! Thanks David!
Awesome video! Really helpful for my upcoming project. Thanks!
Glad it was helpful!
Excellent Presentation. About a question I didn't know I needed an answer to.
Hahaha, glad to hear it was helpful!
@@TheFireBrickCo Does it also apply to terracotta tiles.
I suspect Yes.
Thinking about a Pearlcrete Pizza Oven on top of an insulated j hook rocket stove.
excellent experiment sir,
Thank you! Cheers!
Straight forward, to the point and honest. Very few can pull this off. Thanks, my friend.
Thank you, I'll put on my list to watch it again.
Thanks!
Nice Demo Mate. I have a Wood fire BBQ (for a better word) which I built from ordinary bricks I had laying around. Its been in service for over 5 years but it only gets used 3 times a year as I have a Normal gas BBQ.
I had never thought about a house Fire place.I guess they do last a while. I can recall some old Pubs with fires every night. Blood Fire heats up the whole Pub!
Thanks Covis!
Thank you for the information my Friend
You're welcome!
Thank you so much for your time and expertise to educate us on this.... really appreciate your efforts.
Thanks
Thanks Amit!
Hi there, I was wondering if you guys stock fire bricks suitable for building a DIY forge? I'm a local in melbourne myself! Thanks
We do, but in these crazy days we aren't able to ship them out or have customers visit! Sighs.
very important informational video !!! thank you very very much.
You're very welcome! Glad you got something out of it!
That was an eye opener!
Thanks Peter!
great video! love the amount of nerd in this! you've sold yourself some fire bricks (metaphorically speaking)!
Haha thankyou!
How about using adobe or compressed earth blocks?
Adobe, clay or 'cobb' materials can be quite heat resistant, but they have issues of their own. My conversations with people who are big fans of cobb ovens have all reinforced my understanding that they just don't last very long. They're incredibly cheap to build, but they tend to fall apart fairly quickly. They also really don't like getting wet, at all, as the clay never reaches temperatures high enough for it to become a ceramic material. It's a good question though, I might have to dust off the Rig and do some more testing!
Thumbs up for all your videos!
So, you are using bricks with 38% alumina; if I use bricks with 30% alumina will it be ok? What are the pros and cons with more alumina?
It would be nice if you could test bricks with different alumina 30% 40% 50% 60% alumina.
Good question! There's a bunch of good info out there to be found on the differences between different alumina content in fire clay bricks, but to give you the very basic answer - the higher the alumina content, the higher the temperature that the brick can withstand. This comes at a cost to their ability to withstand thermal shock though, and they get much more expensive as you go higher. In a Wood Fired Oven environment a 30% alumina brick will likely be fine, but the lower alumina bricks also tend to be of low quality in their production process.
So, you ran your test through 240 cycles. And as you mention, in fireplaces the spalling is in the hottest areas, not on the surface of all the bricks. I'm assuming this would be the same in a pizza/bread oven - so in the dome directly above the fire and the floor directly below it. Less spalling (maybe) in and above the actual cooking area. My concern has always been about the comments saying "regular" bricks will explode. You say that's not gonna happen. If I fired it up a few times per month, regular bricks seem like they ought to last a good while before I have to worry about getting brick dust and bits into my food! Thank you so much for this video!
No worries! Just take you firings very slowly - don't use our Fire and Forget method that's for sure!
Really thank you for such a quality content with experment.
Thank you!
do you deliver to the UK.
We sure do Chris - check out Kennedy Fire Ltd, they may still have some in stock
Firebricks, or bricks that's been harden by fire, got it
. . . What about the binding of the bricks when making an oven? Do I use cement? Or mortar? Or something that's specialized in heat resistant and thermal shock?
Hmmm not quite - technically almost all bricks are 'hardened by fire' - a fire brick is made with a very different type of clay to most building bricks. You would need to use refractory mortar to lay the bricks for a wood fired oven - check out our building series for more info