Intro: Vermikulite Dome Garden Pizza Oven
Love the taste of Neapolitan pizza? You can now make it yourself at home! However, you will need one thing, besides the obvious foodstuff ingredients ... a wood fired high temperature pizza oven! You might be thinking "expensive" ... but it's not if you build it yourself using the method presented here.
Step 1: Required Items
1. 75cm or larger gym ball
2. 45cm diameter round plastic flower pot tray
3. around 120mm diameter foam pipe insulation (the thicker the better and length around 2.5m)
1. 3x25kg pure cement mix (I actually used about 10 bags but decided to build up the oven to create an 'organic' hill which will blend into the landscape)
2. Medium size vermikulite 100-120L bag
3. A bag, or two, or three ... or a dozen of medium size grain keramsite / ceramsite / leca expanded clay or whatever they call it in your part of the world- here again, I have used 4 bags to build up the structure on top of the oven dome.
4. 5-10m x0,5m roll of fine chickenwire mesh for reinforcement
5. 20-25 fire bricks for the oven floor (the thicker the better as they will provide better heat accumulation/retention)
6. 125mm or similar chimney chute ring - totally optional - I originally was thinking of using this to insert a steel pipe for the chimney, but later decided to build this up from keramsite/cement mix.
Step 2: Base
The base is built using "sloppy masonry" ... using some leftover road tiles/ bricks etc. built on top of an existing hill, to get the pizza oven floor at least at waist level.
The top layer of this structure was then covered with a few cm layer of cement (1:5) and keramsite mix to provide good heat insulation and to even out the surface for the fire brick layer.
After the cement hardened, this was then lined with fire bricks to provide the oven floor.
... But beforehand, the unfinished base was used to support the gym ball during the dome construction, as detailed in the next step.
Step 3: Dome Template
To create the template for the dome, wrap the gym ball with plastic shrink wrap ("Saran wrap") to avoid later cleanup problems. Then use some tape to attach the flower pot tray at the planned opening. Now run a piece of string through the foam pipe insulation tube and wrap it around the middle of the ball to create the bottom support ring. After tightly tying the string you can prop up the ball using some bricks etc., so that it won't move around, when later applying the concrete/vermiculite mix.
Step 4: Dome Build-up
Start building up the dome, working from the bottom - up, applying patches of vermiculite/cement mix with your hands (be sure to wear rubber gloves, as cement is caustic)
For the dome you can use anything from a 1:5 to 1:12 cement to vermiculite mix. The earlier giving less insulation in favor of easier application of the mix, the later giving better insulation but much more difficult to work with. I have used 1:5 but added a bit too much water ending up with a runny mixture, therefore as you can see in the picture I had to use plastic wrap, to hold it in place during the build-up process. I decided that this ratio will be sufficient, as in our case the general plan is to build up a second thicker layer of keramsite/cement mix, to create an 'organic' structure which will blend in with our planned rockery garden.
Step 5: Embedding of the Dome on the Foundation
After the dome hardens (24h) you can remove it from the gym ball, make a ring of fresh vermiculite/cement mix on the base structure and sit the dome on top of it, to achieve a good seal.
To make the front part, cut the flower pot tray in half, brace the two pieces with some pieces of wood and then wrap this with thick cardboard and shrink wrap (unfortunately I didn't take a picture of this, but you can see it in the movie).
Place this at the dome opening, slightly sliding inwards and place the chimney chute ring on top, to guide as the chimney outlet.
Similar to the dome, build up the vermiculite/cement mix on this part, overlapping onto the dome.
After this hardens you should apply the chicken wire mesh to the whole construction and cover it with another layer of vermiculite/cement mix.
Step 6: Finishing Up
You can now remove the front end support template and if you are eager to try out your dome, you can do a very small test fire of some papers (I burned up the cardboard from the support template), however don't be tempted to try getting a full blown fire going at this time, as your dome will need to cure for some weeks, so that it doesn't crack from the moisture trapped in the concrete.
To finish up, you can apply a layer of insulation rockwool etc. on the dome and cover it with another layer of concrete, or as we ultimately plan to do here, continue building up a "hill" which will be sitting in our rockery garden, using a cement/ceramsite mix.