Cast your own

[dmun]

Hi, Welcome. You are welcome to ask questions, and share your ideas and plans.

People use lots of different things for forms. Sand is traditional. A lot of folks here have used ribs made of wood or insulating foam. This is the first i've herd of a newspaper form. Should work, although it would be an awful lot of wet newspaper to get rid of.

Quite a few builders build their domes without any forms at all, or just imprompu ones for the last few courses. This is possible with a refractory mortar that sets up within a few minutes of when you place the brick. This method requires a little skill, but it makes it easier to clean the visible joints on the inside of the dome.

Keeping the dome moist for the week it takes to cure is not difficult. A layer of burlap and an occasional spray with the hose is all it takes.

[Acoma]

DMUN, if you are building during the winter within a tent and the temps are in the 40-50 range, I would think you can skip the burla and occasional spray? What you say makes sense if it is in the 70+ temps where curing can occur to fast, don't you think?

[dmun]

Originally Posted by Acoma

If you are building during the winter within a tent and the temps are in the 40-50 range, I would think you can skip the burlap and occasional spray?

Yes, you're right. everything's cold and damp in this climate this time of year. Just thinking about working with masonry this time of year makes my hands hurt. Be careful if your temperatures approach freezing at night, this can seriously weaken your mortar.

[bobdyce]

I hope somebody goes for the dogloo cast - I had the same thought, googled it and found this forum. This seems to be the only place it has even been considered, and nobody has actually done it. I play to build an oven this spring, and since my outer design doesn't involve brick and the ovens insides are not really seen...the dogloo cast seems like a great idea.

[dmun]

Hi, Bobdyce, and welcome. The problem with the cast oven is the expense of the castable refractory and the stainless reinforcing needles, which are expensive specialty products, compared with firebricks which are relatively cheap. The only problem with the dogloo is how to get it out when your oven is done.

By the way, nobody's dome exterior is visible, no matter how elegantly constructed. You need many inches of insulation under and over the oven to make it practical to fire.

[bobdyce]

What if you split the form into 5 or 6 sections.

It seems like you could get a used dogloo on craigslist for 40 bucks, cut it into pieces, then re-assemble it with large foam-core pieces in the seams. This way, when it drys, you have a few big chunks of cement that you can slide apart to remove the dogloo, and morter back together.

I don;t know if what i am trying to explain makes sense - I can mock it up in 3D and post an image.

Bob

[bobdyce]

Break it into sections, similar to the ones you can buy:

Like this

Can you just add a wire mesh and rebar to strengthen the concrete? or does it have to be the stainless steel needles?

[edschmidt]

I paid $20 per 50# bag of 3000 deg castable, as far as the stainless needles are concerned... The refractory specialist I talked to (who sells the stuff) told me there is a debate concerning stainless steel needles. One school of thought is that with needles the oven will still crack, but the needles will stop the cracks from expanding. The other reasons that because the steel expands at a different rate from the masonary it is actually causing the cracks. So I avoided them all together on my oven. I would recommend casting the oven in sections but not in the traditional manner. I would cast the top as a cap (it will heat up first) and the lower 1/2 as a sepperate unit. Most cast ovens I see have the sections from the bottom to the top from 1 piece which I think is prone to cracking.
good luck

[bobdyce]

Ed,
That is a great idea. This way, gravity would hold the sections tight to each other. I'll cut the un-needed bottom section off the dogloo... too make the dogloo form the exact shape I need to cast. Then cut this upper form into 3 pieces...laterally. Build a cylindrical form with a diameter approx 6 inches larger than the base of the dogloo with same height as the 3 dogloo pieces. I could cast the 3 large cement pieces one at a time...reusing the cylindrical form. I imagine 3-4 strong guys would have no problem lifting and stacking the 3 peices into place. From the outside it would look like 3 large cylindrical blocks stacked - with a negative dome shape inside.

bob

[TDVT]

I'm kind of on the same page as you guys. I found this in another thread, don't know if you've seen it or not.



I thought it was a pretty cool, low-tech design.

I'm thinking about casting my own dome using a foam mold. By my calculations, it would take about 3 bags of refractory material to cast a 30" dome, 2" thick.
In the same thread that I found this. there was a bit of information about Mizzou castable (there are several mixes) that had the same thermal characteristics as fire brick.

Seems like a good route for a trailer-mounted oven.

I'll try to find that thread & post a link.