Wednesday, September 17, 2008

Earth Oven Insulation

I know that many earth oven builders have been using a mixture of sawdust with clay slip for insulation, and I have been one of them. A few days ago I made of a mixture of 6 parts sawdust to 1 part Portland cement, added a little water and formed a tight ball. I did this again, but this time I used 6 parts Perlite to 1 part Portland cement.

After both samples had hardened, I subjected them both to oven heat. As you can see by the photos, the one made with Perlite was untouched by the heat, but the one made with sawdust had completely disintegrated. Maybe the sawdust has some insulation value even in a disintegrated state. I don't know. Even if the sawdust had held up, Perlite still has about twice the insulation value.

Sawdust is free, but you have to buy Perlite. It's your decision to make.

For lots more information about bread and earth oven construction:

Here's an email I just from received from Kiko Denzer, who probably knows more than anyone about earth oven construction.

Hand Print Press

Hey, Stu,

Interesting that the perlite held together w/cement. I would have expected both of them to crumble. My understanding is that cement starts to break down over 700F. And with perlite, there’s really no need to use cement at all, unless you’re building an Alan Scott style oven and need the strength. Otherwise, the addition of cement only reduces insulation value.

The practical test for the sawdust clay mix is to get enough clay into it that when the sawdust is burnt out, you’re left w/a foam that’s high enough in clay to maintain it’s form (and when needed, i.e., for under the hearth, to support weight). Obvioustly, it’s not the sawdust that’s providing the insulation — it’s the clay, in which the burning of the sawdust has created voids. It’s a cheap/easy way to manufacture your own insulating firebrick — but it does help to do some tests. Or, to err on the side of too much clay. Or, under the hearth, to use empty glass bottles for structural support.

I have also had success using a mix of clay AND portland with sawdust — that way, you get the quick setting of the cement, and the lasting power of the clay. Tho if you need such a combo of traits, it’s cheaper and nice to use plaster of paris (gypsum plaster).

-- Kiko Denzer

Hand Print Press • POB 576 • Blodgett OR 97326 • 541-438-4300
"What we learn to do, we learn by doing" – Aristotle

Tuesday, September 16, 2008

Clay Oven in Hampshire, England

Simon Brookes enjoys a pint at his local

Man and dog work together

Simon's finished oven

For detailed construction information, go to Simon's website:

Monday, September 15, 2008

Mom's Birthday Present

"...yesterday we built our oven. It has a lot of layers and took us all day but it worked!..."

"...This one holds heat better than I would have thought. It is still warm in the mornings. The first fire we got the temp up more than 900 degrees which is not good but it was our first fire. The front of the oven, just behind the opening, stays about 500 degrees as long as we have fire in back and then cools to about 400 and we do most of the cooking then. Last night after 3 hours it was still 350 degrees right there..."

"The reason we did not insulate more is that the oven is not where we want the oven to be forever. You might be able to see the grape vines behind the oven. That is where the final oven will be. We have to move the grapes to a trellis behind the house, then dig a deep footing and then build the final dream oven.
Our Oven Layers:
1. 3 rows of cement block with brick and stone pieces stuffed in every hole
2. A solid layer of cement block
3. cheap salvaged brick with holes but we put the holes inside
4. a layer of fire brick but we did not like it and so we did not use it for the floor but we used it for insulation
5. a layer of nice fire brick that we bought and this is the floor of the oven
6. then we used metal pieces that are for fire places brick and we used those to hold up the roof
7. we just stacked up all the salvaged fire brick we could find and then we put more old brick on the outside of that
8. we used up all the fire brick for the roof"

" Last night we baked Ciabatta (bread), pizza, salmon and vegetables. Tonight we cooked eggplants with garlic and tomato, more Ciabatta, s'mores, caramalized peaches and more vegetables. The oven was my for our Mom's birthday and she was very excited..."

"Our Mom loves the oven, neighbors came to see it and we are happy with it as a temporary oven. One neighbor who came to see it spent $2,600. to buy a cement looking shell dome from a place in California, then they have spent $1,000 for stone and they have worked on their oven for 4 months now and it still is not finished! We only spent about $175.00 for cement block and new fire bricks since we salvaged the rest and our oven was working the first day!
We think that is funny