Here’s a little video showing the construction of a super-insulated restaurant oven. The “basket” design seems to be a pretty inexpensive and effective way to insulate — not necessary for every oven, but for ones that really get regular use, I think it’s worth it… It’s a pretty big oven, too, so I opted for hand-made mud bricks instead of mud over a sand-form. For more details about the technique (including brick-making, as well as photos of how well the insulation protects the bamboo), there’s an extensive post and pix about the Gathering Together Farm Oven, which was similarly (re)built. — Kiko
I have just read your excellent book ‘Build Your Own Earth Oven’ and I can’t wait to get building. Although we live in an 450 year old cottage which has a clome (bread) oven built into the left side of our inglenook fireplace, it can’t be used as it contravenes our house insurance. Hence the purchase of your book. My question is that we have a number of spare blocks of clay lump, removed from the wall of a later addition, which would make an ideal clay mix for an earth oven, but it contains straw to give the blocks strength….can we use this?
Hi, Viv (Bruce?), thanks for writing. Yup, you can re-use your old block. It might be worth straining out some of the straw if there’s a lot of it (too much straw will reduce thermal mass and conductivity). Easy to do if you break up the dry block and drop it into buckets full of water. Give it some time to slake (here’s a video on on clay prep that might help). The straw should either float to the top, or be relatively easy to catch on a mixer blade with any kind of forked tool. Then you’ll need to let the clay/sand settle. When the water’s clear, you can pour it off, and perhaps spread it to dry a bit if necessary…. Of course, all advice-from-a-distance is purely theoretical, and may require adaptation depending on the makeup of your block. Good luck. (If you take out that clome oven, send pix!)
Kiko, many thanks for your prompt reply to my question regarding our clay lump blocks. As you probably guessed this is my wife’s e-mail address. I’ll take some pic’s of our clome oven and forward them on to you later on.
Bruce
Hi mr. Denzer, i would like to thank you for the excelent info about making a Cob oven from your book.
I have some question’s that if you don’t mind i woold like to ask.
The angle cut’s to the door bricks that make’s the smoke go to the chemney easy’er how does the door close?Ther must be an empty space at the point.
I’m going to start making a new oven with adobe bricks and i would like to ask for some guidence.
1)If i fire the oven for a long time will the adobe bricks go red as a tranformation to red clay bricks?Is this ok or not?
2)What is the recipe for the bricks?
I have found an old brick factory that has a leftover soil that has 98% clay on it.
Do i have to add sand to archive some kind of a sand to clay ratio or is it ok to use pure clay?
Sorry for the poor Engish i’m trying my best!
Regards Dimitris.
Hi, Dimitris, the door has a flange that fits over the cut brick. This photo might help:
as for your other questions:
1. yes, the bricks will go red, and yes, it’s normal
2. brick recipe will vary in more ways than I can really explain here, and more ways than I really know to explain completely! I recommend you try some different mixes and fire them (in another oven or in a fireplace or wood-fired appliance) and determine for yourself how much they shrink, how hard they are, and how you think they’ll hold up. That said, I’ve been making mixes with roughly half clay and half fine sand (w/fines — that is, particles that vary in size from dust to fine sand — important for making good strong bricks). The sand is especially important for building w/unfired bricks, as pure clay bricks will shrink a lot more when fired, and that could cause structural problems — that is, if all the bricks shrank enough, the dimensions of the entire dome would shrink and probably move — who knows, if it shrank enough, it could collapse…
Isn’t skrinkage a moister problem?
I mean that if the bricks are completly dry before making the oven is it possible to skrink more after the firing up?
As for the sand…here in Greece we only have a mine gravel sand without mentioning how fine it is.
I think i will make the test’s on the half demolished oven i have got(front arch and floor is missing, don’t ask me how 😉
Is it possible to use the oven as a kiln for the bricks?
I know for sure that is can reach 500 Celsius because i have a thermometre that is rated top’s 500 C.
no, clay also shrinks when you fire it, sometimes it can shrink a LOT.
mined gravel sand can be fine and often has lots of “fines” or small particles. In fact, sometimes the stuff they screen out to throw away is perfect. Worth testing.
yes, you can use the oven as a kiln, but you won’t be able to do a lot of bricks at a time because you need a lot of space for the fire.
One more thing.
Is the shape of the perimeter of the oven a big issue?Is an oval shaped perimeter better or worst from an circular?
Thank you Mr Denzer for your help, you’re really an inspiration!