40" homemade cast dome

[purplehaze]

Started my 40" cast homebrew pizza oven and it has been a lot more work than I anticipated. Got many of the ideas from this forum.

[gastagg]

Purplehaze, got pics? I have been wondering if anyone has ever done a homemade cast oven...

[UtahBeehiver]

There have been several cast ovens, mikku, iron pony and others

[purplehaze]

I am surprised that this thread surfaced, I had given up after several attempts to post it along with some questions. Yes I do have a few I will post them shortly.

[purplehaze]

Since this is the thread that people responded to I erased the content from the other two. I didnt realize that a moderator had to approve my earlier threads and thought it was my error. I am adding the content from the others to this one.



I started my 40? homemade castable pizza oven at the end of July. I poured the rebar reinforced base slab, dry stacked the block and filled every other void with rebar and cement. The wife had the idea of reducing the wood storage area so as not to create a home for critters to hide. I reduced the wood storage area by making a second storage area at the rear of the oven. The front storage area was to have a cast arch and the rear would be supported with angle iron. I then poured a 4 inch thick pad with rebar to support the oven. I thought that the final height of the oven was going to be too short for me so I poured a 5? thick perlite layer, added two 1? layers of calcium silicate board before laying down the oven floor brick. The height seems perfect.



I found some free Styrofoam 12?x18? blocks on craigslist, glued them up and carved out my 40?x16? form. I just used a handsaw and an orbital sander and eye it. I ran into a snag with the oven opening. Initially I cut a flat area for a 19? wide opening. Most ovens it appears that the vent seems to take up some of the internal ovens real-estate. I don?t know if this takes away from the ovens performance or not. Anyway I second guessed myself, glued the section back on and added and a bump out for the entrance. Due to the round shape of the oven the ends of the 19? wide opening are 5? thick while the 10? top of the entrance is a little over 2.5?.



To make the form easier to remove after the oven is cast I cut the form into six pieces so that they can be removed from the entrance. I should not have done this because now the form does not fit together well making it necessary to tape and fill uneven sections. I then built the exterior forms using scrap wood, it held up fine. I used 3:1:1:1, SS melt extract fibers and polypropylene fibers. I had briefly considered using a cement mixer for this but I am glad I didn?t.

[purplehaze]

Here are some pics of more progress.


Needed to add some height to the oven so I opted for a 5" perlite/cement pad.

Two 1" layers of calcium Silicate board. Do not get this stuff wet it goes from a medium density board to soft sponge.


The finished interior mold, its not pretty but it will work. Filled in any gaps with expanding foam insulation.

[david s]

Nice work. Did the styrofoam come away ok? Have you got pics of the finished casting?

[joeykramer]

looks good purplehaze--- what do you plan on doing to build up the floating slab to the floor of oven? you'll have about 7 inches to fill. Im in the same boat and cant decide how to finish it

[purplehaze]

Pulling the mold out was a pain, the cement held on to the tape that I applied to the outside of the mold. Newspaper or saran wrap probably would have been a better option. There did end up being some voids in the casting nothing too bad. I considered filling them but I was not sure if the repair would hold.

[purplehaze]

joeykramer, I have not decided how to fill in around the oven base. I like the way others have built a house around the oven but the wife wants to retain the igloo shape. I may have to just cover it in stucco before winter and weigh my options in the spring.

I did finally pour my vent transition today.

[joeykramer]

bravo man, thats pretty cool to see those last set of pictures. what ingredients did you use for the cast?

[purplehaze]

Joeykramer, I got the recipe for the refractory mix from this site. I used a 2 gallon pail for measurement and added 3 pails of sharp sand, one of Portland cement, one of lime and one of clay.

I mixed the ingredients dry, added one bag (4 oz?) of polypropylene fibers and mixed again. On the back of the polypropylene bag the instructions read, add one bag per 94 pounds of cement. I added water so that it was close to the consistency of peanut butter. The first two loads I added 2 lbs of Stainless needles, that seemed a bit light so on the three remaining loads I added 3 lbs of the needles.

[david s]

Re filling voids in the casting It maybe too late, but this is the method I use. Take some of the dry mix and sift out the course aggregate. In your case if your sand is fine then just halve the sand quantity so you have a rich mix. You don't want any course aggregate for this operation. Mix the stuff up to peanut butter consistency and work it hard into any voids. I use a butter knife for this so you can force the mix in hard and polish its surface. It is essential that the casting be still a little damp. Not wet but also not dry. I find usually 24 hrs after casting is a good time for this operation. Your casting, made with Portland cement and lime will take much longer to cure than calcium aluminate castable so you should cover it and hold in the moisture for a min of a week.

[purplehaze]

Thanks for the info and comments guys.

davids, I didn't want to attempt filling the interior voids in case they did not adhere, no one wants crunchy food. The exterior ones are going to be covered up anyway. I just poured the vent trans so if there are any voids I will attempt this.

[david s]

With an inner and outer mould, correct fluidity and vibration you shouldn't get any voids, but they're pretty hard to eliminate entirely.