new adobe oven plan - pls comment

[h&t]

Hi all,

I plan to build small adobe oven to try the whole WFO thing :-)
It's mostly for pizza, may be some bread, occasional use.

Please comment/critique my current plan.

1. dry stack 4 pillars out of cement blocks on the ground, no foundation. If the
oven moves and cracks a bit - no big deal, it's temporary.

2. Construct form out of 2x4 (go 2x6?) wood with plywood bottom. Pour 1:6 cement
to vermiculite into it. I suspect I might need some re-bar and a thin layer
(1"?) of regular concrete at the bottom to strengthen it up? I don't know what's
the strength of vermiculite/cement mix..?
Should I go with thicker base?

3. Dry lay 2.5" fire bricks flat for the hearth.

4. Mound sand for the shape, cover with paper

5. Mix Hawthorne 50 clay 1:3 with sand (I can get either masonry or concrete
sand).

6. Shape the round dome

24" internal diameter
14" int height
12" wide door
9" door height
4" thick walls

Should I consider chimney?

7. cut the door, dry the walls (wait few days?), take out the sand, make fire,
bake pizza :-)

8. Optional - insulate by 3-4" of 6:1 vermiculite/cement mix?



Thanks

[h&t]

ok, makes sense. I mentioned in step 2, I probably need reinforced concrete as a base...

How hard would it be to stick a chunk of 4" duct pipe in as a chimney...
Is it worth it..?

[thijsatteiltje]

Hi,

sounds all good. Do you happen to have a copy of Kiko Denzer's book?
that is the perfect manual for an earth oven.


I just finished the dome of my earth oven this weekend, and your plans look very similar to what I did.

(ignore the rocket stove that is underneath the oven, that is just one of the quirky things i wanted to try out. It could be usefull to pre-heat the dome and chimney i guess but I don't think it will be able to heat up all the mass. The oven is just to big.)

I would recommend a chimney. If it was only to not burn you face and have black soot all over the front of the oven.

good luck

matt

good luck

[h&t]

Thanks. I read the book, but don't have it handy now.
Where should I place the chimney and what materials to use for it?

very nice over in the pics, how big is it?
What did you use to plaster the top white?
Nice view - where is it? Oh I see NZ :-)

Thanks again

[thijsatteiltje]

Well, technically, my chimney is not in the right spot. That is because I was also debating until the last moment if I should put one in.

See my discussion about it here: http://www.fornobravo.com/forum/f9/h...int-17638.html (Height of Chimney intake point)

Ideally, the chimney should be inside the door arch, at 63% of the inner dome height.
In my case, with a brick arch, that meant a more complex construction of the arch to accommodate the flue opening, which I did not feel comfortable with at the time.
Looking back now it would not have been so hard.

If you make the door arch from cob (straw and clay) you have a lot more freedom of course. To get an actually updraft the chimney needs to be a certain height (at least 3 feet i believe, but check the forum) and it should heat up quickly. So either stainless steel (don't use galvanized pipe, it will give off nasty fumes) or some sort of insulated cob/clay/straw/sawdust mix. but making a 3 foot clay chimney might be tricky ;-)

But... as you can see from the last comment on that other discussion, although placing the chimney in the door arch is ideal, placing it just behind the arch will probably work as well.

These are the measurements:

inner diameter: 80cm/31.5"
inner height: 43cm/17"
stem wall: 10cm/4"
door height: 27cm/10.5"
door width: 47cm/18.5"
wall: 8cm/3"

I found this handy calculator:
Dome Calculator | Monolithic

tip: Make at least 1.5 times more clay mix than you calculate. You will need it as lot's is lost in spillage and somehow you always tent to make the walls thicker than you thought.

tip2: cut the shape of the dome out of a thick piece of plywood, you can use it to measure your progress and even very easily 'press' the clay back into shape.

I found that just having the thing have beautiful shape adds so much to the enjoyment of the end result. Also, correct dome shape will be stronger, i understand.

Use a lime and sand plaster for the top. don't use a cement based plaster as the clay will always attract moisture from the air and needs to evaporate this again.

You can get nice cement colours (cheap) to give it a nice colour.
(if you want bright colours, use white plaster sand instead of normal gray sand for the lime mix, otherwise the coulor might come out a bit muddy) (no pun intended)

matt

(p.s. I'm sure they have pretty decent views in Canada? ;-)

[thijsatteiltje]

Originally Posted by h&t

ok, makes sense. I mentioned in step 2, I probably need reinforced concrete as a base...

How hard would it be to stick a chunk of 4" duct pipe in as a chimney...
Is it worth it..?

For me it is, but realise that with a 4" pipe you will still have some smoke coming out of the doorway.

But, even if this is a temporary/first pancake trial, think of how much you would learn from putting in the chimney. That would be invaluable for a next/bigger/better project.

I just place mine on top of the brick arch and attached it with screws to the brick. If you are only going to have a cob arch you could do some cut-ins around the bottom and fold those horizontal so the clay has something to cling to.

(duct pipe is prob zinc or galvanised (or is that the same?), not recommended for high heat)

matt

[h&t]

Matt, thank again for all the help. Or should I say bedankt? :-)

I think I need brick arch and a chimney. Why do these projects always get more complicated than one envisions..?

[h&t]

thanks, that's useful

[h&t]

the oven is finished, first pizza cooked today

[h&t]