Gym Ball Pizza Oven (WIP)

You may have seen these around (1,2, etc..). This is my take on it and anything that could have been done better.

  • The biggest gym ball I could find locally was 70cm.
  • The Formply was from a former project.
  • Perlite from Bunnings. I found later that I could have saved money by going to an aquaponics specialist. I bought 4 of them. 5x 25L bags would have been better.
  • Coreflute sheet.

The 2 sheets of Formply where screwed together to form a larger surface. The 2 circles where engraved with a nail in a piece of wood that had the other end screwed into the middle, then rotated. The gym ball was over inflated to make sure it didn’t move, then covered in Cling-wrap. I would seek alternatives to Cling-wrap, I had a heck of a time trying to get it off the concrete when it dried.

The form work for the “entry tunnel” was stappled to moulded Coreflute sheet.

First layer was 1/5 ratio of cement to perlite – I found it very dry and contained too many holes to be structurally sound.

A week later, chicken wire was wrapped around it, and then a second layer of 1/4 cement to perlite was added. I also added more water. While firmly patting the second layer down the first layer had cracks appear.

A week or two later the second layer had dried enough to help reinforce the first layer

You can see the difference in the concrete layers. The outer layer was far better. The shell was turned upside down and place in a hammock. The cook chamber had a thin layer of mortar render to fill the larger cracks and smooth it out.

The shell was then traced to provide the dimensions for the base. Wrapped the MDF sheet in a thin plastic sheet. Nailed long nails around the outline and put long strips of Coreflute onto the nails. The painters tape was used to close any rips in the sheet.

I had intended to pour about an inch of cement and perlite concrete, then add chicken wire, then another half inch. I ended up pouring about an 3/4 inch then the chicken wire wouldn’t stay under the concrete, so I gave up and added a little more. Put the numbered bricks on top, aligning them with the marks on the MDF. Then added more concrete around the edges until it was level with the top of the fire bricks.

  • The thin plastic drop sheet was as equally annoying as the cling-wrap to remove. Mostly removed with a wire brush.
  • The painters tape is now pretty much embedded into the concrete.
  • I shouldn’t have left the base on the blocks to dry and should have used a large flat surface. The base dried slightly warped, and doesn’t sit flat on the stand.
  • I’m not entirely sure the thickness will be sufficient to maintain strength and insulate the frame against the heat.

The stand was made from 40x40x3mm square tubing. I over estimated the required height (1040mm) and cut the legs to just passed the bottom support ring. The castor screw plates were welded on (100x100x5mm). The frame was rock solid and offered no flexing with the base and myself on it.

Put mortar around the base where the top would go, placed top shell on the base and added more mortar to the join as needed.

This is the result after rendered the outside and lightly brushing the loose dirt off as it slowly dried.

I’ll need to wait at least a week for it to dry properly before testing it and then another week before using it.

UPDATE: First test resulted in long but thin hair line cracks mostly. There were 2 that look concerning and will be monitored over time.

UPDATE #2: I tried 3 actual pizza’s, they looked great but the middle of the bases weren’t cooked properly so they had to be finished in the inside oven.

I thought this metal stand might make a difference to better cook the last of the 3. It was added too late and it made no difference.

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