Long weekend in Sydney and time to make some progress. First step was to rough out the shape of the oven, igloo-esque seemed to work best. The fire cement ran low and I skimped on this - which has caused some problems. This outline needs to be well cemented-in as the sand mould and working the clay in puts pressure on the sides and a few of the bricks became loose - not so much a problem if your oven is going to be static. A real problem for mobility though!
I built a mould for the door, allowing a lip or the door piece to fit in snugly - this was about 450 wide and 250 high. I weighted this down and then packed the oven space with filler (a few left over Hebel bricks and timber off-cuts). Then the sand mould was created and the flue roughly positioned. This flue is a double-skinned gas flue - it has an stainless interior and galvanised exterior. It’s actually a spacer on to which fits a much longer piece, again something I thought would suit the portability.
Then came the fun bit. My boys helped me mix a 2:1 sand clay mix. We cut the bristles off an old paintbush in order to get some natural fibre into the dry mix and then added a few trowels worth of cement. The whole mix squidged up really quickly when water was sparingly added into a very satisfying (and as it turns out, very throwable, mixture - as my 4 year old discovered). It took about an hour to get 3 layers on the oven with a constant supply of cunningly fashioned patties. The door area took quite a bit of shaping and cajoling, its fun stuff to work with.
I left out the builder mix called for in the plan I’m following (see part 1). The clay I settled for is called ball clay and comes in 25KG bags costing $30 each - I bought three and have used less than one so far.
A few hours later and the clay started to harden up - it had cracked in two places - expected and easily remedied with more mix. One of these was on the door lip and I decided to lose the option for a tightly fitting door in favour of a more rounded opening (not sure I’m going to need a door as we’ll be cooking mainly pizza). Plus It’s so easy to work with I can aways add this later.
Also, in hindsight I think I should have created a bit more height in the outline, now that the sand has been removed I feel the space looks a bit on the tight side - but we’ll see. More pics to come.