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40" in Hobart, Australia - Materials and design queries

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  • 40" in Hobart, Australia - Materials and design queries

    I'm thinking about building a 40" Pompeii oven in Hobart, Tasmania, Australia. These forums and the FB guide are a great resource for a first time builder!

    I have a few queries on materials and design that I was hoping folks might have some thoughts on. For context, I hope that the oven will retain sufficient heat to allow bread baking on the second day.

    Fire bricks are incredibly expensive here, the cheapest I've found are $6.95AUD per brick (Tasmania is an island, so due to shipping even more expensive than mainland Australia). That price is pretty much a show stopper for me. Alternatively, we have an open fireplace in the house built in the late 1960s that we plan on removing. What are the thoughts on re-using these clay bricks? They are quite solid, dark red in colour and there doesn't seem to have been much/any damage to the ones in the fireplace that have been exposed to fire in the past.

    Next, insulating from the hearth. I can readily obtain vermiculite and have made/used vermacrete in the past. How big is the advantage of using Calcium Silicate board instead? I think it would set me back about $200AUD. If I went to the extent of using the board I think I'd still include a layer of vermacrete as vermiculite is one thing that's actually readily available!

    I can visualise most of the construction process, but have noted a few people talking about hinged doors -- is this worth the effort? Do I even need a insulated door to be able to bake bread the next day? Or would a simple aluminium or stainless steel door with a stand suffice?

    To be able to bake bread the next day should I consider including extra thermal mass (e.g. turning bricks on the floor on their side)?

    Lastly, a bit of a silly question from a pizza oven newbie -- how messy does the floor in front of the oven get (from soot, ashes etc.)? I'm thinking of paving this area in light coloured pavers... Is that a bad idea?

    Thanks in advance!

  • #2
    Plenty of folk have reported success using solid reds although Many are not suitable for ovens or fireplaces, but if your fireplace bricks have stood up ok then they should be ok for the dome, You should however use firebricks for the floor. I've seen plenty of old fireplaces in Victoria with badly spalled solid red floor bricks
    40" is a fairly large family oven and will use a fair amount of fuel. So, unless you are planning to bake for the village or for local markets, a smaller oven may be a better option as it's less costly to build, uses less fuel and is therefore far easier to refire.

    Cal sil board is a superior insulator than a 5:1 vermicrete, but you can simply make it 1/3 thicker to get the same result. The vermicrete needs to be well dried out which takes weeks not days, whilst the cal sil is already dry. There's a big difference in cost.

    Regarding extended baking time, that is dependant on the amount of thermal mass you have, which comes back to oven size and wall and floor thickness. If the walls and floor are really thick they will take longer to heat up and require more fuel to do so. My little oven has 2" walls but is really only suitable for one batch of bread. Most brick ovens are around 4" (half a brick) and that is a good compromise. Some dedicated bakers ovens are 8" (double brick) thick, ditto the floors.

    Almost every kiln I've had experience with has died because of the door. Steel expanding faster than surrounding refractory and therefore expanding faster, corrosion and cracked refractory are all problems when mixing steel with refractory. All hinged doors or gates drop, a pretty universal rule. A door that sits against a rebate in the oven mouth is the most common and best solution IMHO and a couple of thousand years of Italian history would also agree. Most oven manufacturers do not provide an insulated door, but it does improve heat retention enormously. Both mild steel, stainless and aluminium are highly conductive.

    Messy: that depends how often you clean out the oven. I only remove ash around every third or fourth use and mine is right on the edge of a wooden deck. I have only one burn mark in the deck after nine years, but recommend folk put down some aluminium checkerplate if in a similar situation. (Can't take my own advice). Maybe paint your pavers with a sealer to make any cleaning easier.
    Kindled with zeal and fired with passion.