The One-Ton Oven: Temporary Site

On June 29th, 2002, Roger du Pont and Kataryna Dragonsweaver, with no small amount of assistance from passers-by, constructed a brick oven for the baking of bread and other sundries. It was built on the Quad War site with the gracious permission of the owners of that land, HE Alfheim der Wundersman and HE Adeline.

I estimate the oven, in total, masses at least one full ton.

This website is a temporary holding place for the photographs I've scanned so far; it will be replaced (hopefully soon) by a complete report on the construction of the oven.

Here I am standing on the foundation of the oven. You can build these things flat on the ground if you like, but it's a lot easier on the bakers if you can raise them a bit. This foundation is two levels of cinder blocks, so about a foot tall, and six feet long by five feet wide. It looked a bit too big when I was constructing it, but now that I see it with the oven on it, I wouldn't want it any smaller. It's full of dirt that has been compacted by walking on it. The walls are relatively stable, but it probably wouldn't hurt to put some concrete down into the cinder blocks to stabilize things. We roughly leveled the dirt out so that the floor of the oven went on fairly level.

In the foreground you see the pile of bricks that was to become our oven.

Laying the floor bricks went fairly smoothly (I've some pictures of that, too, but they're fairly boring, and a schematic diagram of the construction would probably be more useful.) Then I got to the arches. The rest of the oven can, but probably shouldn't, be built with only two people. The arches, however, really need at least one person per arch brick (so, four,) and a few more are certainly handy. This part really needs a diagram, but, basically, the arch bricks are rounded such that eight of them form a circle with an inner diameter of 24" (twenty-four inches.) They're usually stacked horizontally to make a round firepit on the ground. However, when I saw them at Home Depot, I knew that they'd be great as vertical arches for this oven.

There's one catch, of course. The bricks are designed to be interlocking, so one end has a V-notch, and the other end has a pointy bit to lock into that notch. The problem is that the end of the arch that sits on the pointy bit is horribly unstable. Compounding the problem is that the floor of the oven is 24" wide, so the arch is a few inches wider than it should be, which is why the centerline gap at the bottom edge of the arch is starting to open up. The base of the arch is probably at about 27" or so in diameter; that's about as far as I could push it while keeping some structural integrity.

This is a close-up of how we solved the pointy-brick instability problem. The point rests in a saddle, with bricks on either side of it, holding the shoulders of the point. It seems pretty obvious now that that's the way to handle it, but at the time it was a major breakthrough. The other end of the arch with the notched-brick end was stable enough once the arch was completed.

I'd always heard this about arches, but never really understood it until building this: arches don't fall down. That is to say, they don't fail (typically) by the top falling in. They fail when the sides blow outwards. The grey bricks holding the red brick in this photo are holding it in, in a manner somewhat reminiscent of the flying buttress.

The oven is complete! Well, almost. It would probably be entirely useable at this point, but there's gaps between some of the bricks big enough to put your hand through (especially around the chimney and the door, where the two curved walls don't meet very well.) So your oven would have some terrible cold spots, which wouldn't be good at all. The little 'porch' of firebrick at the front is just to make it a bit easier to insert and remove loaves, and gives the door some place to sit.

That funny horn-shaped structure above the door bears some comment. I'd set up the two bricks on either side of the door, and was trying to figure out how to put some bricks across the top (the lintel) of the door. It's too wide to be bridged by a single brick. Many designs just put a steel bar across this and stack bricks on that.

A passing gentleman suggested that we create an inverted arch, as shown. The bricks rest against each other, making it quite stable. There's a bit of wire around it anyway; now that it's fired, I don't believe it's actually bearing any load, and we plan to cut it off. So, even though the horns look decorative, they are in fact a well-designed, functional bit of work.

The oven looks 'ribbed' because the arches alternate which side gets the pointy bit and the buttress. For various reasons, this meant that one side of the arch was closer to the edge of the floor than the other, so it undulates a bit. I'm not expecting it to pose any sort of problem; ideally, it would have been designed to avoid this, though.

One will notice that there is a chimney rising from the back wall of the oven. Some oven designs have chimneys, some do not. I felt, partially due to the size of this one, that a chimney would be beneficial in getting enough air into the fire for a nice burn. Once the fire is burnt out, it can be blocked off with a handy brick or some such.

The floor of the oven. The total baking surface is about 24" x 36", or two feet by three feet. That's a lot of loaves of bread, or pizzas, or whatever. It felt like a nice size to build, although I'm not entirely sure how it'll be to work with. Much smaller and I think the economies of scale are just working against you -- I don't think it'd actually get any easier to build. Much larger and I can see it being difficult to assemble, fire, and reach the loaves way in the back of the oven.

The floor is tiled with a double layer of fire brick, which may not be required, but is probably a good idea. This sort of oven works by building a big fire inside of it, letting the fire burn down to nothing, removing all the ashes, and then letting the residual heat of the bricks bake your bread through the magic of blackbody radiation. So don't burn anything in your oven that you won't want in your food later.

I don't have many pictures of the next stage, since I was covered in clay. However, in short, it consisted of mixing up some clay, and then applying it to the oven. This took us a while -- a couple more people at this stage would have helped a lot too. We finished around midnight, but we'd started around noon, so I suspect it could probably be done as a dawn-to-dusk job, especially with a few more people.

The site is blessed with some very nice natural clay. With the exception of the occasional twig, it's commercial quality. So it was nice stuff to work with. I estimate that we started with a volume of dry clay equal, approximately, to the volume of the oven itself. Then we mixed in about 25 gallons of water or so (the area has been extremely dry all summer.) Then we started putting the clay onto the oven. A short throwing motion seemed to work very well.

I skipped a step. Prior to applying the clay, we put a single layer of chickenwire over the bricks. Possibly not necessary, but I think it may have helped stabilize the clay, and it's cheap. I believe the clay is about an inch thick in most places over the oven.

The next morning, we started a big fire in it. It got hot. Really hot. I've no doubt that with a decent bellows that it could do duty as a kiln or a forge. The purpose of this fire is to fire the clay into a hard shell around the oven. At its peak, the water-soaked stick I was using to poke the fire back into the oven was bursting into flame as soon as I put it into the oven.

A word to the wise: don't just sit in front of the oven on a hot summer day like an idiot, like I did. You'll get heat stroke, like I did. You could even die from it, which I didn't, but only due to the kindness of passers-by. So be careful, and try to not leave anyone alone tending the oven for too long.

This is what the oven looked like after the firing. Although it looks like smoke damage, this particular type of clay just happens to turn black when it's completely fired (a high iron content, probably.) The clay cracked and crazed rather severely, but I didn't notice it leaking any smoke (possibly because it just went up the chimney instead.) It'll likely get a few more layers of clay, and possibly a layer of sod, before it's done.

We just used some extra bricks as a door, which seemed to work quite well, actually. When the fire was well underway, we mostly closed up the door, and just left it. This is theoretically a fire hazard, but really, it's such a well-contained flame that I can't imagine it posing much of a threat; it's almost certainly safer than those Tiki Torch things. Don't leave a stack of wood beside it, though; the surface of the oven got hot enough that you wouldn't want to touch it.

The oven after firing, from the side. You'll notice the cinder blocks are already starting to look a bit worse for wear; some manner of reinforcement may be in order. The oven itself, though, seemed quite solid. I wouldn't necessarily want to stand on it, but my hunch is that someone (or a number of someones) could stand on it without adverse results. But I'd rather not tempt fate.

A close-up of the crazed surface of the fired clay. As a sense of scale, that big wide black crack near the bottom of the photo is about as wide as my hand, as I recall. Since the clay turns black when it fires completely, I'm inclined to think that the black area around this crack indicates a heat leak. It could stand some more clay packed into it. Although, really, because this oven is so massive, and thus has a huge thermal inertia, I'm not exceptionally worried about the possibility of losing hot air to a few cracks. I'm more concerned that the frost may get in there this winter and try to destroy it.

All in all, it was a great project. It took two dedicated people and the occasional help of a few more people about a full day to complete it. The cost of raw materials came to about CDN$300, or so. If you hired a commercial outfit to build one of these things in your backyard, you would easily be paying thousands of dollars. It's not particularly difficult, but it was very rewarding.

My thanks go out to Kataryna Dragonsweaver -- I wouldn't have been able to do it without her -- and everyone else who assisted or offered kind words of encouragement.

Last updated: 5 July 2002