The Igloo is a traditional Italian and Mediterranean pizza oven style that follows the basics lines of the oven dome and chimney -- thus the Igloo shape.
There are two ways of finishing the Igloo shape, either of which can be done by building professionals and home owners. With the first approach, you form the Igloo shape using 1" wire mesh, while in the second you use a combination of 1/4" steel rod and a finer wire net to shape the Igloo.
Both approaches are used widely, and which you choose depends on the availability of materials and personal preference. The 1' wire mesh approach may be easier to install, while the 1/4' steel rod and fine net approach may give you the ability to more accurately shape your oven.
The Technique Overview
As an overview, you wrap your oven and chimney with the insulating blanket, then build a wire frame to the oven shape you want, allowing for 4"-6" of insulating concrete between the blanket insulation and the wire. Fill the gap between the wire net and the oven with a vermiculite-based insulating concrete, which is held in place by the wire frame.
Cover the entire structure with a 1/2"-3/4" undercoat of of stucco, followed by a finish stucco coat to the style you prefer. Finally, seal the entire oven with a weather-proof finish coat or paint.
Using 1" galvanized wire mesh, mold the wire around the oven to the desire shape. The mesh serves two purposes: it holds your insulating concrete in place while it dries, and it provides the form and structure for oven's Igloo shape.
The form your wire forms does not have to be exact, you will have the opportunity to shape your curves with the stucco layer.
Alternatively, you can use a combination of 1/4" steel rod and stucco netting. Drill holes into your hearth every 12", then set the rod and bend to shape. Cover the rod with wire mesh.
Make an insulating concrete mixture of 6 parts vermiculite:1 part portland cement, then cover the oven by filling the space between the insulation and the wire net. The concrete will help hold the vermiculite in place while it dries, without reducing its insulating value by an appreciable amount.
The key to making vermiculite concrete is to work the vermiculite and Portland cement together when they are dry, to where the cement coats the vermiculite beads -- before you add water. Add enough water to make a mix similar to oatmeal, and layer in on the oven, so that it is held in place by the wire frame.
Cover the wire mesh with an external rough concrete stucco mixture, building the material into the final Igloo shape. When it is slightly cured, but still pliable, use a large sponge to smooth out your trowel marks, ridges and low spots to create a smooth finish. Allow this layer to dry.
Cover the rough stucco mixture with a think coat of finish stucco to the color and texture that you want. Finish can range from fully smooth, to sand-size grains, to larger grains. You can put color in the final stucco coat, or paint the Igloo later. Your final coats must be a sealing coat, to keep water from seeping into our oven.
Proceed to Curing Your Oven.
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