Dogloo pizza oven form

[bobdyce]

I originally found this site from a google search on "dogloo pizza oven". To my surprise the idea HAD been discussed, but it seems that nobody has done it.

We are planning to build an oven this spring. The dogloo method seems like a very inexpensive and simple way to make a very complex shaped form. After all...it's virtually the same shape and you can find one on craigslist for 30 bucks.

I previously hijacked another thread with some questions, theories and proposed Methodologies. I figured it was time to start a new thread devoted to my fixation to cast my oven from a dogloo form!

Okay, enough with the words! It's time for Bob's picture-theory:

Step 1. Remove the bottom 3rd from the dogloo. It's too tall - we just want the top.

Step 2. Cut the Dogloo into 3 pieces - these will be used to cast the negative space.

[bobdyce]

Re: Dogloo pizza oven form

Okay - the "more-complicated shapes for the form are done.

Step 3. Now I could bend thin wood (poplar?) and make circular forms for each dogloo piece.

[bobdyce]

Re: Dogloo pizza oven form

Step 4. Pour cement, cure and pop the dogloo and outter wooden forms off.

Step 5. Roll into place and stack the 3 cast cement pieces.

[bobdyce]

Re: Dogloo pizza oven form

This brings me to the "grey areas" of my method:

What materials to use?
Cement, wood for forms? Structurial re-inforcement / rebar/needles?
How much might this beastie weigh?
Could it even be rolled and lifted into place?
How thick to make the walls?
how much space above the top of the dome?
Should I morter the three chunks together, or let gravity be the seal?
Is this method totally retarded?

Thanks for any feedback you might have - this forum has been a huge inspiration for me and I would love to do something new to add to the pizza oven builders knowldege base.

Bob

[jwnorris]

Re: Dogloo pizza oven form

<snip> How thick to make the walls?

The walls should be at least 2" thick, plus the insulation layer on the exterior.

<snip> Should I mortar the three chunks together, or let gravity be the seal? <snip>

Using the FB Casa series as the inspiration, gravity should do the trick. FB says not to mortar the sections together but to place a bead of refractory mortar over the joints approximately 2" thick and 4" wide.

Hope this helps.

J W

[christo]

Re: Dogloo pizza oven form

What about leaving the form in one piece, digging a hole in the ground (or big pile of sand) the shape of the outer skin and pouring it as one piece? You could pour spacers out of refractory ahead of time and use those as moulded in spacers between the dogloo and the hole to keep wall thickness consistent.

I have no experience or knowledge of casting refractory materials - only refractory insulation... just adding my 2 cents. I may have told you complete rubbish...

christo

[bobdyce]

Re: Dogloo pizza oven form

Thats an interesting idea.

The logic behind the 3 pieces came out of advice from edschmidt.
The 3 segments allow the oven to expand/contract without cracking. The top part of the dome will heat first and get the hottest, while the temp will gradually decrease down the dome walls to the floor. this way, internal metal re-enforcement might not me necessary.

This makes me think that maybe I don't need mortar at all...maybe just a thin layer of sand to act as a flexible, insulating seal in-between layers.

[phoenixzorn]

Re: Dogloo pizza oven form

If I'm not mistaken, you'd probably not want to use plain old cement for the forms... I'd say refractory concrete would be your best choice.

Of course, like christo's, this suggestion may also be complete rubbish. =)

[RTflorida]

Re: Dogloo pizza oven form

I'm certainly not an expert, but everything I've read on the forum and been told by a local refractory supplier points towards CASTABLE refractory, not just refractory mortar/cement. There is a big difference in the two, the castable has something in the mix to minimize cracking and add strength. The stainless steel needles I believe would be a good addition to the mix for strength. Do not use rebar or wire mesh, the diffeneces in expansion rates between the steel and cement is too great and could actually cause more cracking than using nothing at all.

RT

[dmun]

Re: Dogloo pizza oven form

I like Ed's method of making the external mold out of an earthen form - I think your stacked method with cylindrical external moulds will leave you with thin and thick areas of your dome, and it won't heat uniformly. There was a recent discussion of a plain concrete dome. Why not do a test cast of one in portland / sand / gravel and see if it's manageable and if it works. You won't waste a lot of ruinously expensive castible refractory if it breaks turning over, and if it doesn't hold up after a few firings, you could bust it up and use it as rubble fill in your stand block voids. More workable than an earthen form would be a wet sand one in a kiddie pool, which you should be able to find on craigslist like your dogloo. Another advantage of the upside-down method is that you could leave the dogloo intact, and put it back up on craigslist when you were done with it.

[mine]

Re: Dogloo pizza oven form

Call Hi-Temp Inc. in Portland and talk to Jeff about the castable refractory. 1 800 325 2492. From him I learned that there are different densities of this stuff.

I used Greenlite 45L, a lightweight insulating formulation to make a curved brick lining for the firebox on my offset smoker. Added stainless needles for x-tra strength.The 1/4 thick brick lining lowered the external temp of my 1/4 thick steel firebox by ~ 200? F.

The stuff you want will be in the 140-150 lb/cu ft. or higher, much more dense than the Greenlite.

[edschmidt]

Re: Dogloo pizza oven form

I dont think there would be any problem just stacking the sections with no mortar. I am a little concerned about the different thicknesses inside the dome. Something I theorized and executed (then lost interest in) for forming a perfect sphere as an outer form (or inner for that matter) is to purchase a Biggens (love that name) ball. The largest has a max size of 52" but stays perfectly round for anything above 30. What I did was to inflate it to 36" and fiberglass 1/2 of the exterior of the bal.. Now inflate to between 40, and 44 in and again fiberglass the exterior. Each one should use approx. 1 gallon of resin ($30) and I have gotten really good deals on fiberglass cloth scrap on e-bay. If the dogloo is close to round you could do this for the exterior form, just cut in 3 sections to match the dogloo inner forms.

Hope this helps, and bear in mind these are all just suggestions, nobody is saying your idea wont work.

Eddie

[John Fahle]

Re: Dogloo pizza oven form

Dogloos come in different sizes. If you could find one that is 4" larger in diameter, and 2" taller (although height is adjustable, I guess, since you're cutting off the bottom anyway) you could just put one inside the other as the form. You would of course have to shore up the outer form to give it enough strength to hold all that refmix, assuming you cast it upside down. Or, you cast it right side up, fill the inner dome with sand for strength, then place the outer dome over it, with the very top cut off for pouring. I'd think you'd want to use a very wet mixture to minimize the chance of air pockets. And make the hole big enough to fit a curved prod into, for stirring. When it's set, you just lift off the outer form, then lift off the dome. Alternatively, if you poured it onto your already built floor, you could just lift off the outer form, dig out the sand through the door, and then start slashing away at the inner form with a utility knife. Cut it up and take it out in pieces.

[John Fahle]

Re: Dogloo pizza oven form

For that matter, you could just use the dogloo for the outer form, and use sand covered in wet newspaper as the inner form. Just dig out the sand once it's set.

[TDVT]

Re: Dogloo pizza oven form

To those who have used it, what is the mixed consistency of the castable refractory?

Is it so thin as to require an inner & outer form?

Just wondering.